Language Server improvements. (#2269)

* Language Server improvements.
- Improve parser robustness around `attribute_syntax`.
- Exclude instance members in a static query.
- Coloring accessors
- Improved signature help cursor range check.

* Add expected test result.

* Language server: support configuring predefined macros.

* Fix constructor highlighting.

* Improving performance by supporting incremental text change notifications.

* Fix UTF16 positions and highlighting of constructor calls.

* Add completion suggestions for HLSL semantics.

* Fix tests.

* Fix: don't skip static variables in a static query.

* Include literal init expr value in hover text.

* Fix scenarios where completion failed to trigger.

* Fixing language server protocol field initializations.

Co-authored-by: Yong He <yhe@nvidia.com>

39 files changed, 1846 insertions, 686 deletions

diff --git a/build/visual-studio/slang/slang.vcxproj b/build/visual-studio/slang/slang.vcxproj
index a2ba8be7a..a19dfd1d2 100644
--- a/build/visual-studio/slang/slang.vcxproj
+++ b/build/visual-studio/slang/slang.vcxproj
@@ -407,7 +407,7 @@ IF EXIST ..\..\..\external\slang-binaries\bin\windows-aarch64\slang-glslang.dll\
     <ClInclude Include="..\..\..\source\slang\slang-ir-wrap-structured-buffers.h" />

     <ClInclude Include="..\..\..\source\slang\slang-ir.h" />

     <ClInclude Include="..\..\..\source\slang\slang-language-server-ast-lookup.h" />

-    <ClInclude Include="..\..\..\source\slang\slang-language-server-collect-member.h" />

+    <ClInclude Include="..\..\..\source\slang\slang-language-server-completion.h" />

     <ClInclude Include="..\..\..\source\slang\slang-language-server-semantic-tokens.h" />

     <ClInclude Include="..\..\..\source\slang\slang-language-server.h" />

     <ClInclude Include="..\..\..\source\slang\slang-legalize-types.h" />

@@ -556,7 +556,7 @@ IF EXIST ..\..\..\external\slang-binaries\bin\windows-aarch64\slang-glslang.dll\
     <ClCompile Include="..\..\..\source\slang\slang-ir-wrap-structured-buffers.cpp" />

     <ClCompile Include="..\..\..\source\slang\slang-ir.cpp" />

     <ClCompile Include="..\..\..\source\slang\slang-language-server-ast-lookup.cpp" />

-    <ClCompile Include="..\..\..\source\slang\slang-language-server-collect-member.cpp" />

+    <ClCompile Include="..\..\..\source\slang\slang-language-server-completion.cpp" />

     <ClCompile Include="..\..\..\source\slang\slang-language-server-semantic-tokens.cpp" />

     <ClCompile Include="..\..\..\source\slang\slang-language-server.cpp" />

     <ClCompile Include="..\..\..\source\slang\slang-legalize-types.cpp" />

diff --git a/build/visual-studio/slang/slang.vcxproj.filters b/build/visual-studio/slang/slang.vcxproj.filters
index 9784bfef5..48f9b98ac 100644
--- a/build/visual-studio/slang/slang.vcxproj.filters
+++ b/build/visual-studio/slang/slang.vcxproj.filters
@@ -318,7 +318,7 @@
     <ClInclude Include="..\..\..\source\slang\slang-language-server-ast-lookup.h">

       <Filter>Header Files</Filter>

     </ClInclude>

-    <ClInclude Include="..\..\..\source\slang\slang-language-server-collect-member.h">

+    <ClInclude Include="..\..\..\source\slang\slang-language-server-completion.h">

       <Filter>Header Files</Filter>

     </ClInclude>

     <ClInclude Include="..\..\..\source\slang\slang-language-server-semantic-tokens.h">

@@ -761,7 +761,7 @@
     <ClCompile Include="..\..\..\source\slang\slang-language-server-ast-lookup.cpp">

       <Filter>Source Files</Filter>

     </ClCompile>

-    <ClCompile Include="..\..\..\source\slang\slang-language-server-collect-member.cpp">

+    <ClCompile Include="..\..\..\source\slang\slang-language-server-completion.cpp">

       <Filter>Source Files</Filter>

     </ClCompile>

     <ClCompile Include="..\..\..\source\slang\slang-language-server-semantic-tokens.cpp">

diff --git a/source/compiler-core/slang-diagnostic-sink.cpp b/source/compiler-core/slang-diagnostic-sink.cpp
index 0110b16d7..c934157d2 100644
--- a/source/compiler-core/slang-diagnostic-sink.cpp
+++ b/source/compiler-core/slang-diagnostic-sink.cpp
@@ -570,7 +570,7 @@ void DiagnosticSink::diagnoseImpl(DiagnosticInfo const& info, const UnownedStrin
         m_parentSink->diagnoseImpl(info, formattedMessage);
     }
 
-    if (info.severity >= Severity::Fatal)
+    if (getEffectiveMessageSeverity(info) >= Severity::Fatal)
     {
         // TODO: figure out a better policy for aborting compilation
         SLANG_ABORT_COMPILATION("");
diff --git a/source/compiler-core/slang-language-server-protocol.cpp b/source/compiler-core/slang-language-server-protocol.cpp
index 3e8907b9a..713d209dd 100644
--- a/source/compiler-core/slang-language-server-protocol.cpp
+++ b/source/compiler-core/slang-language-server-protocol.cpp
@@ -181,12 +181,35 @@ const StructRttiInfo DidCloseTextDocumentParams::g_rttiInfo = _makeDidCloseTextD
 const UnownedStringSlice DidCloseTextDocumentParams::methodName =
     UnownedStringSlice::fromLiteral("textDocument/didClose");
 
+static const StructRttiInfo _makeWorkspaceFoldersServerCapabilitiesRtti()
+{
+    WorkspaceFoldersServerCapabilities obj;
+    StructRttiBuilder builder(&obj, "LanguageServerProtocol::WorkspaceFoldersServerCapabilities", nullptr);
+    builder.addField("supported", &obj.supported);
+    builder.addField("changeNotifications", &obj.changeNotifications);
+    builder.ignoreUnknownFields();
+    return builder.make();
+}
+const StructRttiInfo WorkspaceFoldersServerCapabilities::g_rttiInfo =
+    _makeWorkspaceFoldersServerCapabilitiesRtti();
+
+static const StructRttiInfo _makeWorkspaceCapabilitiesRtti()
+{
+    WorkspaceCapabilities obj;
+    StructRttiBuilder builder(&obj, "LanguageServerProtocol::WorkspaceCapabilities", nullptr);
+    builder.addField("workspaceFolders", &obj.workspaceFolders);
+    builder.ignoreUnknownFields();
+    return builder.make();
+}
+const StructRttiInfo WorkspaceCapabilities::g_rttiInfo = _makeWorkspaceCapabilitiesRtti();
+
 static const StructRttiInfo _makeServerCapabilitiesRtti()
 {
     ServerCapabilities obj;
     StructRttiBuilder builder(&obj, "LanguageServerProtocol::ServerCapabilities", nullptr);
     builder.addField("positionEncoding", &obj.positionEncoding);
     builder.addField("textDocumentSync", &obj.textDocumentSync);
+    builder.addField("workspace", &obj.workspace);
     builder.addField("hoverProvider", &obj.hoverProvider);
     builder.addField("definitionProvider", &obj.definitionProvider);
     builder.addField("completionProvider", &obj.completionProvider);
@@ -470,6 +493,87 @@ static const StructRttiInfo _makeSignatureHelpRtti()
 }
 const StructRttiInfo SignatureHelp::g_rttiInfo = _makeSignatureHelpRtti();
 
+static const StructRttiInfo _makeDidChangeConfigurationParamsRtti()
+{
+    DidChangeConfigurationParams obj;
+    StructRttiBuilder builder(&obj, "LanguageServerProtocol::DidChangeConfigurationParams", nullptr);
+    builder.addField("settings", &obj.settings, StructRttiInfo::Flag::Optional);
+    builder.ignoreUnknownFields();
+    return builder.make();
+}
+const StructRttiInfo DidChangeConfigurationParams::g_rttiInfo =
+    _makeDidChangeConfigurationParamsRtti();
+const UnownedStringSlice DidChangeConfigurationParams::methodName =
+    UnownedStringSlice::fromLiteral("workspace/didChangeConfiguration");
+
+static const StructRttiInfo _makeConfigurationItemRtti()
+{
+    ConfigurationItem obj;
+    StructRttiBuilder builder(
+        &obj, "LanguageServerProtocol::ConfigurationItem", nullptr);
+    builder.addField("section", &obj.section, StructRttiInfo::Flag::Optional);
+    builder.ignoreUnknownFields();
+    return builder.make();
+}
+const StructRttiInfo ConfigurationItem::g_rttiInfo = _makeConfigurationItemRtti();
+
+static const StructRttiInfo _makeConfigurationParamsRtti()
+{
+    ConfigurationParams obj;
+    StructRttiBuilder builder(
+        &obj, "LanguageServerProtocol::ConfigurationParams", nullptr);
+    builder.addField("items", &obj.items, StructRttiInfo::Flag::Optional);
+    builder.ignoreUnknownFields();
+    return builder.make();
+}
+const StructRttiInfo ConfigurationParams::g_rttiInfo = _makeConfigurationParamsRtti();
+const UnownedStringSlice ConfigurationParams::methodName =
+    UnownedStringSlice::fromLiteral("workspace/configuration");
+
+static const StructRttiInfo _makeRegistrationRtti()
+{
+    Registration obj;
+    StructRttiBuilder builder(&obj, "LanguageServerProtocol::Registration", nullptr);
+    builder.addField("id", &obj.id, StructRttiInfo::Flag::Optional);
+    builder.addField("method", &obj.method, StructRttiInfo::Flag::Optional);
+    builder.ignoreUnknownFields();
+    return builder.make();
+}
+const StructRttiInfo Registration::g_rttiInfo = _makeRegistrationRtti();
+
+static const StructRttiInfo _makeRegistrationParamsRtti()
+{
+    RegistrationParams obj;
+    StructRttiBuilder builder(&obj, "LanguageServerProtocol::RegistrationParams", nullptr);
+    builder.addField("registrations", &obj.registrations, StructRttiInfo::Flag::Optional);
+    builder.ignoreUnknownFields();
+    return builder.make();
+}
+const StructRttiInfo RegistrationParams::g_rttiInfo = _makeRegistrationParamsRtti();
+
+static const StructRttiInfo _makeCancelParamsRtti()
+{
+    CancelParams obj;
+    StructRttiBuilder builder(&obj, "LanguageServerProtocol::CancelParams", nullptr);
+    builder.addField("id", &obj.id, StructRttiInfo::Flag::Optional);
+    builder.ignoreUnknownFields();
+    return builder.make();
+}
+const StructRttiInfo CancelParams::g_rttiInfo = _makeCancelParamsRtti();
+
+static const StructRttiInfo _makeLogMessageParamsRtti()
+{
+    LogMessageParams obj;
+    StructRttiBuilder builder(&obj, "LanguageServerProtocol::LogMessageParams", nullptr);
+    builder.addField("type", &obj.type, StructRttiInfo::Flag::Optional);
+    builder.addField("message", &obj.message, StructRttiInfo::Flag::Optional);
+    builder.ignoreUnknownFields();
+    return builder.make();
+}
+const StructRttiInfo LogMessageParams::g_rttiInfo = _makeLogMessageParamsRtti();
+const UnownedStringSlice LogMessageParams::methodName =
+    UnownedStringSlice::fromLiteral("window/logMessage");
+
 } // namespace LanguageServerProtocol
 
 }
diff --git a/source/compiler-core/slang-language-server-protocol.h b/source/compiler-core/slang-language-server-protocol.h
index e1ac47beb..11446bd0b 100644
--- a/source/compiler-core/slang-language-server-protocol.h
+++ b/source/compiler-core/slang-language-server-protocol.h
@@ -205,6 +205,33 @@ struct DidCloseTextDocumentParams
     static const UnownedStringSlice methodName;
 };
 
+struct WorkspaceFoldersServerCapabilities
+{
+    /**
+     * The server has support for workspace folders
+     */
+    bool supported = false;
+
+    /**
+     * Whether the server wants to receive workspace folder
+     * change notifications.
+     *
+     * If a string is provided, the string is treated as an ID
+     * under which the notification is registered on the client
+     * side. The ID can be used to unregister for these events
+     * using the `client/unregisterCapability` request.
+     */
+    bool changeNotifications = false;
+
+    static const StructRttiInfo g_rttiInfo;
+};
+
+struct WorkspaceCapabilities
+{
+    WorkspaceFoldersServerCapabilities workspaceFolders;
+    static const StructRttiInfo g_rttiInfo;
+};
+
 struct ServerCapabilities
 {
     String positionEncoding;
@@ -214,6 +241,7 @@ struct ServerCapabilities
     CompletionOptions completionProvider;
     SemanticTokensOptions semanticTokensProvider;
     SignatureHelpOptions signatureHelpProvider;
+    WorkspaceCapabilities workspace;
     static const StructRttiInfo g_rttiInfo;
 };
 
@@ -245,11 +273,13 @@ struct InitializeResult
     static const StructRttiInfo g_rttiInfo;
 };
 
-struct ShutdownParams {
+struct ShutdownParams
+{
     static const UnownedStringSlice methodName;
 };
 
-struct ExitParams {
+struct ExitParams
+{
     static const UnownedStringSlice methodName;
 };
 
@@ -630,5 +660,85 @@ struct SignatureHelp
 };
 
 
+struct DidChangeConfigurationParams
+{
+    /**
+     * The actual changed settings
+     */
+    JSONValue settings = JSONValue::makeInvalid();
+
+    static const StructRttiInfo g_rttiInfo;
+
+    static const UnownedStringSlice methodName;
+};
+
+struct ConfigurationItem
+{
+    /**
+     * The configuration section asked for.
+     */
+    String section;
+
+    static const StructRttiInfo g_rttiInfo;
+};
+
+struct ConfigurationParams
+{
+    List<ConfigurationItem> items;
+
+    static const StructRttiInfo g_rttiInfo;
+
+    static const UnownedStringSlice methodName;
+};
+
+struct Registration
+{
+    /**
+    * The id used to register the request. The id can be used to deregister
+    * the request again.
+    */
+    String id;
+
+    /**
+    * The method / capability to register for.
+    */
+    String method;
+
+    static const StructRttiInfo g_rttiInfo;
+};
+
+struct RegistrationParams
+{
+    List<Registration> registrations;
+
+    static const StructRttiInfo g_rttiInfo;
+};
+
+struct CancelParams
+{
+    /**
+     * The request id to cancel.
+     */
+    int64_t id = 0;
+
+    static const StructRttiInfo g_rttiInfo;
+};
+
+struct LogMessageParams
+{
+    /**
+     * The message type. See {@link MessageType}
+     */
+    int type = 0;
+
+    /**
+     * The actual message
+     */
+    String message;
+
+    static const StructRttiInfo g_rttiInfo;
+    static const UnownedStringSlice methodName;
+};
+
 } // namespace LanguageServerProtocol
 } // namespace Slang
diff --git a/source/slang/slang-ast-decl.h b/source/slang/slang-ast-decl.h
index 433d42d4a..65eaea4f1 100644
--- a/source/slang/slang-ast-decl.h
+++ b/source/slang/slang-ast-decl.h
@@ -16,6 +16,10 @@ class DeclGroup: public DeclBase
     List<Decl*> decls;
 };
 
+class UnresolvedDecl : public Decl
+{
+    SLANG_AST_CLASS(UnresolvedDecl)
+};
 
 // A "container" decl is a parent to other declarations
 class ContainerDecl: public Decl
diff --git a/source/slang/slang-ast-support-types.h b/source/slang/slang-ast-support-types.h
index eb918f0b9..e3dea7df1 100644
--- a/source/slang/slang-ast-support-types.h
+++ b/source/slang/slang-ast-support-types.h
@@ -517,7 +517,10 @@ namespace Slang
             return cf(astBuilder);
         }
 
-        SLANG_FORCE_INLINE bool isSubClassOfImpl(SyntaxClassBase const& super) const { return classInfo->isSubClassOf(*super.classInfo); }
+        SLANG_FORCE_INLINE bool isSubClassOfImpl(SyntaxClassBase const& super) const
+        {
+            return classInfo ? classInfo->isSubClassOf(*super.classInfo) : false;
+        }
 
         ReflectClassInfo const* classInfo = nullptr;
     };
diff --git a/source/slang/slang-check-impl.h b/source/slang/slang-check-impl.h
index 6fddbc453..bc037b0c2 100644
--- a/source/slang/slang-check-impl.h
+++ b/source/slang/slang-check-impl.h
@@ -255,6 +255,12 @@ namespace Slang
             return m_module;
         }
 
+        bool isInLanguageServer()
+        {
+            if (m_linkage)
+                return m_linkage->isInLanguageServer();
+            return false;
+        }
             /// Get the list of extension declarations that appear to apply to `decl` in this context
         List<ExtensionDecl*> const& getCandidateExtensionsForTypeDecl(AggTypeDecl* decl);
 
@@ -1685,12 +1691,13 @@ namespace Slang
         // deal with this cases here, even if they are no-ops.
         //
 
-    #define CASE(NAME)                                  \
-        Expr* visit##NAME(NAME* expr)            \
-        {                                               \
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), expr,  \
-                "should not appear in input syntax");   \
-            return expr;                                \
+    #define CASE(NAME)                                                                           \
+        Expr* visit##NAME(NAME* expr)                                                            \
+        {                                                                                        \
+            if (!getShared()->isInLanguageServer())                                              \
+                SLANG_DIAGNOSE_UNEXPECTED(getSink(), expr, "should not appear in input syntax"); \
+            expr->type = m_astBuilder->getErrorType();                                           \
+            return expr;                                                                         \
         }
 
         CASE(DerefExpr)
diff --git a/source/slang/slang-check-modifier.cpp b/source/slang/slang-check-modifier.cpp
index 176609106..429479a38 100644
--- a/source/slang/slang-check-modifier.cpp
+++ b/source/slang/slang-check-modifier.cpp
@@ -594,7 +594,7 @@ namespace Slang
             return uncheckedAttr;
         }
 
-        if(!attrDecl->syntaxClass.isSubClassOf<Attribute>())
+        if (!attrDecl->syntaxClass.isSubClassOf<Attribute>())
         {
             SLANG_DIAGNOSE_UNEXPECTED(getSink(), attrDecl, "attribute declaration does not reference an attribute class");
             return uncheckedAttr;
diff --git a/source/slang/slang-compiler.h b/source/slang/slang-compiler.h
index 148b0205b..280bdf688 100755
--- a/source/slang/slang-compiler.h
+++ b/source/slang/slang-compiler.h
@@ -1671,6 +1671,14 @@ namespace Slang
         /// lookup additional loaded modules.
     typedef Dictionary<Name*, Module*> LoadedModuleDictionary;
 
+    class Linkage;
+    class IModuleCache
+    {
+    public:
+        virtual RefPtr<Module> tryLoadModule(Linkage* linkage, String filePath) = 0;
+        virtual void storeModule(Linkage* linkage, String filePath, RefPtr<Module> module) = 0;
+    };
+
         /// A context for loading and re-using code modules.
     class Linkage : public RefObject, public slang::ISession
     {
@@ -1791,6 +1799,8 @@ namespace Slang
 
         TypeCheckingCache* m_typeCheckingCache = nullptr;
 
+        void setModuleCache(IModuleCache* cache) { m_moduleCache = cache; }
+
         // Modules that have been dynamically loaded via `import`
         //
         // This is a list of unique modules loaded, in the order they were encountered.
@@ -1925,7 +1935,7 @@ namespace Slang
 
         RefPtr<Session> m_retainedSession;
 
-
+        IModuleCache* m_moduleCache = nullptr;
 
             /// Tracks state of modules currently being loaded.
             ///
diff --git a/source/slang/slang-language-server-ast-lookup.cpp b/source/slang/slang-language-server-ast-lookup.cpp
index 768c8ef2d..3a35e699b 100644
--- a/source/slang/slang-language-server-ast-lookup.cpp
+++ b/source/slang/slang-language-server-ast-lookup.cpp
@@ -1,23 +1,12 @@
 #include "slang-language-server-ast-lookup.h"
 #include "slang-visitor.h"
+#include "slang-workspace-version.h"
 
 namespace Slang
 {
-struct Loc
-{
-    Int line;
-    Int col;
-    bool operator<(const Loc& other)
-    {
-        return line < other.line || line == other.line && col < other.col;
-    }
-    bool operator<=(const Loc& other)
-    {
-        return line < other.line || line == other.line && col <= other.col;
-    }
-};
 struct ASTLookupContext
 {
+    DocumentVersion* doc;
     SourceManager* sourceManager;
     List<SyntaxNode*> nodePath;
     ASTLookupType findType;
@@ -29,12 +18,18 @@ struct ASTLookupContext
 
     Loc getLoc(SourceLoc loc, String* outFileName)
     {
-        auto humaneLoc = sourceManager->getHumaneLoc(loc, SourceLocType::Actual);
-        if (outFileName)
-            *outFileName = humaneLoc.pathInfo.foundPath;
-        return Loc{humaneLoc.line, humaneLoc.column};
+        return Loc::fromSourceLoc(sourceManager, loc, outFileName);
     }
 };
+
+Loc Loc::fromSourceLoc(SourceManager* manager, SourceLoc loc, String* outFileName)
+{
+    auto humaneLoc = manager->getHumaneLoc(loc, SourceLocType::Actual);
+    if (outFileName)
+        *outFileName = humaneLoc.pathInfo.foundPath;
+    return Loc{humaneLoc.line, humaneLoc.column};
+}
+
 struct PushNode
 {
     ASTLookupContext* context;
@@ -46,12 +41,21 @@ struct PushNode
     ~PushNode() { if (context) context->nodePath.removeLast(); }
 };
 
-static Index _getDeclNameLength(Name* name)
+static Index _getDeclNameLength(Name* name, Decl* optionalDecl = nullptr)
 {
     if (!name)
         return 0;
     if (name->text.startsWith("$"))
+    {
+        if (auto ctorDecl = as<ConstructorDecl>(optionalDecl))
+        {
+            if (ctorDecl->parentDecl && optionalDecl->parentDecl->getName())
+            {
+                return optionalDecl->parentDecl->getName()->text.getLength();
+            }
+        }
         return 0;
+    }
     // HACK: our __subscript functions currently have a name "operator[]".
     // Since this isn't the name that actually appears in user's code,
     // we need to shorten its reported length to 1 for now.
@@ -168,17 +172,31 @@ public:
 
     bool visitVarExpr(VarExpr* expr)
     {
-        if (expr->name && expr->declRef.getDecl() &&
-            _isLocInRange(context, expr->loc, _getDeclNameLength(expr->name)))
+        if (expr->name && expr->declRef.getDecl())
         {
             if (expr->declRef.getDecl()->hasModifier<ImplicitConversionModifier>())
                 return false;
-            ASTLookupResult result;
-            result.path = context->nodePath;
-            result.path.add(expr);
-            context->results.add(result);
-            return true;
+            Int declLength = 0;
+            if (auto ctorDecl = as<ConstructorDecl>(expr->declRef.getDecl()))
+            {
+                auto humaneLoc = context->sourceManager->getHumaneLoc(expr->loc, SourceLocType::Actual);
+                declLength = context->doc->getTokenLength(humaneLoc.line, humaneLoc.column);
+            }
+            else
+            {
+                declLength = _getDeclNameLength(expr->name, expr->declRef.getDecl());
+            }
+            if (_isLocInRange(
+                    context, expr->loc, declLength))
+            {
+                ASTLookupResult result;
+                result.path = context->nodePath;
+                result.path.add(expr);
+                context->results.add(result);
+                return true;
+            }
         }
+        
         return dispatchIfNotNull(expr->originalExpr);
     }
 
@@ -524,6 +542,21 @@ bool _findAstNodeImpl(ASTLookupContext& context, SyntaxNode* node)
             if (visitor.dispatchIfNotNull(typedefDecl->type.exp))
                 return true;
         }
+        for (auto modifier : decl->modifiers)
+        {
+            if (auto hlslSemantic = as<HLSLSemantic>(modifier))
+            {
+                if (_isLocInRange(
+                        &context, hlslSemantic->loc, hlslSemantic->name.getContentLength()))
+                {
+                    ASTLookupResult result;
+                    result.path = context.nodePath;
+                    result.path.add(hlslSemantic);
+                    context.results.add(result);
+                    return true;
+                }
+            }
+        }
         if (auto container = as<ContainerDecl>(node))
         {
             bool shouldInspectChildren = true;
@@ -550,7 +583,7 @@ bool _findAstNodeImpl(ASTLookupContext& context, SyntaxNode* node)
 }
 
 List<ASTLookupResult> findASTNodesAt(
-    SourceManager* sourceManager, ModuleDecl* moduleDecl, ASTLookupType findType, UnownedStringSlice fileName, Int line, Int col)
+    DocumentVersion* doc, SourceManager* sourceManager, ModuleDecl* moduleDecl, ASTLookupType findType, UnownedStringSlice fileName, Int line, Int col)
 {
     ASTLookupContext context;
     context.sourceManager = sourceManager;
@@ -559,6 +592,7 @@ List<ASTLookupResult> findASTNodesAt(
     context.cursorLoc = Loc{line, col};
     context.findType = findType;
     context.sourceFileName = fileName;
+    context.doc = doc;
     _findAstNodeImpl(context, moduleDecl);
     return context.results;
 }
diff --git a/source/slang/slang-language-server-ast-lookup.h b/source/slang/slang-language-server-ast-lookup.h
index 9fad5e8bd..93e94a869 100644
--- a/source/slang/slang-language-server-ast-lookup.h
+++ b/source/slang/slang-language-server-ast-lookup.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "slang-ast-all.h"
+#include "slang-workspace-version.h"
 
 namespace Slang
 {
@@ -13,7 +14,23 @@ enum class ASTLookupType
     Decl,
     Invoke,
 };
+
+struct Loc
+{
+    Int line;
+    Int col;
+    bool operator<(const Loc& other)
+    {
+        return line < other.line || line == other.line && col < other.col;
+    }
+    bool operator<=(const Loc& other)
+    {
+        return line < other.line || line == other.line && col <= other.col;
+    }
+    static Loc fromSourceLoc(SourceManager* manager, SourceLoc loc, String* outFileName = nullptr);
+};
 List<ASTLookupResult> findASTNodesAt(
+    DocumentVersion* doc,
     SourceManager* sourceManager,
     ModuleDecl* moduleDecl,
     ASTLookupType findType,
diff --git a/source/slang/slang-language-server-collect-member.cpp b/source/slang/slang-language-server-collect-member.cpp
deleted file mode 100644
index 73539b9d9..000000000
--- a/source/slang/slang-language-server-collect-member.cpp
+++ /dev/null
@@ -1,156 +0,0 @@
-// slang-language-server-collect-member.cpp
-
-// This file implements the logic to collect all members from a parsed type.]
-// The flow is mostly the same as `lookupMemberInType`, but instead of looking for a specific name,
-// we collect all members we see.
-
-#include "slang-language-server-collect-member.h"
-
-namespace Slang
-{
-void collectMembersInType(MemberCollectingContext* context, Type* type)
-{
-    if (auto pointerLikeType = as<PointerLikeType>(type))
-    {
-        collectMembersInType(context, pointerLikeType->elementType);
-        return;
-    }
-
-    if (auto declRefType = as<DeclRefType>(type))
-    {
-        auto declRef = declRefType->declRef;
-
-        collectMembersInTypeDeclImpl(
-            context,
-            declRef);
-    }
-    else if (auto nsType = as<NamespaceType>(type))
-    {
-        auto declRef = nsType->declRef;
-
-        collectMembersInTypeDeclImpl(context, declRef);
-    }
-    else if (auto extractExistentialType = as<ExtractExistentialType>(type))
-    {
-        // We want lookup to be performed on the underlying interface type of the existential,
-        // but we need to have a this-type substitution applied to ensure that the result of
-        // lookup will have a comparable substitution applied (allowing things like associated
-        // types, etc. used in the signature of a method to resolve correctly).
-        //
-        auto interfaceDeclRef = extractExistentialType->getSpecializedInterfaceDeclRef();
-        collectMembersInTypeDeclImpl(context, interfaceDeclRef);
-    }
-    else if (auto thisType = as<ThisType>(type))
-    {
-        auto interfaceType = DeclRefType::create(context->astBuilder, thisType->interfaceDeclRef);
-        collectMembersInType(context, interfaceType);
-    }
-    else if (auto andType = as<AndType>(type))
-    {
-        auto leftType = andType->left;
-        auto rightType = andType->right;
-        collectMembersInType(context, leftType);
-        collectMembersInType(context, rightType);
-    }
-}
-
-void collectMembersInTypeDeclImpl(
-    MemberCollectingContext* context,
-    DeclRef<Decl> declRef)
-{
-    if (declRef.getDecl()->checkState.getState() < DeclCheckState::ReadyForLookup)
-        return;
-
-    if (auto genericTypeParamDeclRef = declRef.as<GenericTypeParamDecl>())
-    {
-        // If the type we are doing lookup in is a generic type parameter,
-        // then the members it provides can only be discovered by looking
-        // at the constraints that are placed on that type.
-        auto genericDeclRef = genericTypeParamDeclRef.getParent().as<GenericDecl>();
-        assert(genericDeclRef);
-
-        for (auto constraintDeclRef : getMembersOfType<GenericTypeConstraintDecl>(genericDeclRef))
-        {
-            if (constraintDeclRef.decl->checkState.getState() < DeclCheckState::ReadyForLookup)
-            {
-                continue;
-            }
-
-            collectMembersInType(
-                context,
-                getSup(context->astBuilder, constraintDeclRef));
-        }
-    }
-    else if (declRef.as<AssocTypeDecl>() || declRef.as<GlobalGenericParamDecl>())
-    {
-        for (auto constraintDeclRef :
-             getMembersOfType<TypeConstraintDecl>(declRef.as<ContainerDecl>()))
-        {
-            if (constraintDeclRef.decl->checkState.getState() < DeclCheckState::ReadyForLookup)
-            {
-                continue;
-            }
-            collectMembersInType(context, getSup(context->astBuilder, constraintDeclRef));
-        }
-    }
-    else if (auto namespaceDecl = declRef.as<NamespaceDecl>())
-    {
-        for (auto member : namespaceDecl.getDecl()->members)
-        {
-            if (member->getName())
-            {
-                context->members.add(member);
-            }
-        }
-    }
-    else if (auto aggTypeDeclBaseRef = declRef.as<AggTypeDeclBase>())
-    {
-        // In this case we are peforming lookup in the context of an aggregate
-        // type or an `extension`, so the first thing to do is to look for
-        // matching members declared directly in the body of the type/`extension`.
-        //
-        for (auto member : aggTypeDeclBaseRef.getDecl()->members)
-        {
-            if (member->getName())
-            {
-                context->members.add(member);
-            }
-        }
-        
-        if (auto aggTypeDeclRef = aggTypeDeclBaseRef.as<AggTypeDecl>())
-        {
-            auto extensions =
-                context->semanticsContext.getCandidateExtensionsForTypeDecl(aggTypeDeclRef);
-            for (auto extDecl : extensions)
-            {
-                // TODO: check if the extension can be applied before including its members.
-                // TODO: eventually we need to insert a breadcrumb here so that
-                // the constructed result can somehow indicate that a member
-                // was found through an extension.
-                //
-                collectMembersInTypeDeclImpl(
-                    context,
-                    DeclRef<Decl>(extDecl, nullptr));
-            }
-        }
-
-        // For both aggregate types and their `extension`s, we want lookup to follow
-        // through the declared inheritance relationships on each declaration.
-        //
-        for (auto inheritanceDeclRef : getMembersOfType<InheritanceDecl>(aggTypeDeclBaseRef))
-        {
-            // Some things that are syntactically `InheritanceDecl`s don't actually
-            // represent a subtype/supertype relationship, and thus we shouldn't
-            // include members from the base type when doing lookup in the
-            // derived type.
-            //
-            if (inheritanceDeclRef.getDecl()->hasModifier<IgnoreForLookupModifier>())
-                continue;
-
-            collectMembersInType(
-                context, getSup(context->astBuilder, inheritanceDeclRef));
-        }
-    }
-}
-
-} // namespace Slang
diff --git a/source/slang/slang-language-server-collect-member.h b/source/slang/slang-language-server-collect-member.h
deleted file mode 100644
index bb48c4d5b..000000000
--- a/source/slang/slang-language-server-collect-member.h
+++ /dev/null
@@ -1,25 +0,0 @@
-// slang-language-server-collect-member.h
-#pragma once
-
-#include "slang-ast-all.h"
-#include "slang-syntax.h"
-#include "slang-check-impl.h"
-
-namespace Slang
-{
-
-struct MemberCollectingContext
-{
-    ASTBuilder* astBuilder;
-    List<Decl*> members;
-    SharedSemanticsContext semanticsContext;
-    MemberCollectingContext(Linkage* linkage, Module* module, DiagnosticSink* sink)
-        : semanticsContext(linkage, module, sink)
-    {}
-};
-
-void collectMembersInTypeDeclImpl(MemberCollectingContext* context, DeclRef<Decl> declRef);
-
-void collectMembersInType(MemberCollectingContext* context, Type* type);
-
-} // namespace Slang
diff --git a/source/slang/slang-language-server-completion.cpp b/source/slang/slang-language-server-completion.cpp
new file mode 100644
index 000000000..c47e951fb
--- /dev/null
+++ b/source/slang/slang-language-server-completion.cpp
@@ -0,0 +1,472 @@
+// slang-language-server-completion.cpp
+
+#include "slang-language-server-completion.h"
+#include "slang-language-server-ast-lookup.h"
+#include "slang-language-server.h"
+
+#include "slang-ast-all.h"
+#include "slang-syntax.h"
+#include "slang-check-impl.h"
+
+namespace Slang
+{
+
+static bool _isIdentifierChar(char ch)
+{
+    return ch >= '0' && ch <= '9' || ch >= 'a' && ch <= 'z' || ch >= 'A' && ch <= 'Z' || ch == '_';
+}
+
+static bool _isWhitespaceChar(char ch) { return ch == ' ' || ch == '\r' || ch == '\n' || ch == '\t'; }
+
+static const char* hlslSemanticNames[] = {
+    "register",
+    "packoffset",
+    "read",
+    "write",
+    "SV_ClipDistance",
+    "SV_CullDistance",
+    "SV_Coverage",
+    "SV_Depth",
+    "SV_DepthGreaterEqual",
+    "SV_DepthLessEqual",
+    "SV_DispatchThreadID",
+    "SV_DomainLocation",
+    "SV_GroupID",
+    "SV_GroupIndex",
+    "SV_GroupThreadID",
+    "SV_GSInstanceID",
+    "SV_InnerCoverage",
+    "SV_InsideTessFactor",
+    "SV_InstanceID",
+    "SV_IsFrontFace",
+    "SV_OutputControlPointID",
+    "SV_Position",
+    "SV_PrimitiveID",
+    "SV_RenderTargetArrayIndex",
+    "SV_SampleIndex",
+    "SV_StencilRef",
+    "SV_Target",
+    "SV_TessFactor",
+    "SV_VertexID",
+    "SV_ViewportArrayIndex",
+    "SV_ShadingRate",
+};
+
+SlangResult CompletionContext::tryCompleteHLSLSemantic()
+{
+    auto findResult = findASTNodesAt(
+        doc,
+        version->linkage->getSourceManager(),
+        parsedModule->getModuleDecl(),
+        ASTLookupType::Decl,
+        canonicalPath,
+        line,
+        col);
+    if (findResult.getCount() == 1 && findResult[0].path.getCount() != 0)
+    {
+        if (auto semantic = as<HLSLSemantic>(findResult[0].path.getLast()))
+        {
+            List<LanguageServerProtocol::CompletionItem> items;
+            for (auto name : hlslSemanticNames)
+            {
+                LanguageServerProtocol::CompletionItem item;
+                item.label = name;
+                item.kind = LanguageServerProtocol::kCompletionItemKindKeyword;
+                for (auto ch : getCommitChars())
+                    item.commitCharacters.add(ch);
+                items.add(item);
+            }
+            server->m_connection->sendResult(&items, responseId);
+            return SLANG_OK;
+        }
+    }
+    return SLANG_FAIL;
+}
+
+SlangResult CompletionContext::tryCompleteMember()
+{
+    // Scan backward until we locate a '.' or ':'.
+    if (cursorOffset > 0)
+        cursorOffset--;
+    while (cursorOffset > 0 && _isWhitespaceChar(doc->getText()[cursorOffset]))
+    {
+        cursorOffset--;
+    }
+    while (cursorOffset > 0 && _isIdentifierChar(doc->getText()[cursorOffset]))
+    {
+        cursorOffset--;
+    }
+    while (cursorOffset > 0 && _isWhitespaceChar(doc->getText()[cursorOffset]))
+    {
+        cursorOffset--;
+    }
+    if (cursorOffset > 0 && doc->getText()[cursorOffset] == ':')
+        cursorOffset--;
+    if (cursorOffset <= 0 ||
+        (doc->getText()[cursorOffset] != '.' && doc->getText()[cursorOffset] != ':'))
+    {
+        return SLANG_FAIL;
+    }
+    doc->offsetToLineCol(cursorOffset, line, col);
+    auto findResult = findASTNodesAt(
+        doc,
+        version->linkage->getSourceManager(),
+        parsedModule->getModuleDecl(),
+        ASTLookupType::Decl,
+        canonicalPath,
+        line,
+        col);
+    if (findResult.getCount() != 1)
+    {
+        return SLANG_FAIL;
+    }
+    if (findResult[0].path.getCount() == 0)
+    {
+        return SLANG_FAIL;
+    }
+    Expr* baseExpr = nullptr;
+    if (auto memberExpr = as<MemberExpr>(findResult[0].path.getLast()))
+    {
+        baseExpr = memberExpr->baseExpression;
+    }
+    else if (auto staticMemberExpr = as<StaticMemberExpr>(findResult[0].path.getLast()))
+    {
+        baseExpr = staticMemberExpr->baseExpression;
+    }
+    else if (auto swizzleExpr = as<SwizzleExpr>(findResult[0].path.getLast()))
+    {
+        baseExpr = swizzleExpr->base;
+    }
+    else if (auto matSwizzleExpr = as<MatrixSwizzleExpr>(findResult[0].path.getLast()))
+    {
+        baseExpr = matSwizzleExpr->base;
+    }
+    if (!baseExpr || !baseExpr->type.type ||
+        baseExpr->type.type->equals(version->linkage->getASTBuilder()->getErrorType()))
+    {
+        return SLANG_FAIL;
+    }
+
+    List<LanguageServerProtocol::CompletionItem> items = collectMembers(baseExpr);
+    server->m_connection->sendResult(&items, responseId);
+    return SLANG_OK;
+}
+
+// The following collectMember* functions implement the logic to collect all members from a parsed type.]
+// The flow is mostly the same as `lookupMemberInType`, but instead of looking for a specific name,
+// we collect all members we see.
+
+struct MemberCollectingContext
+{
+    ASTBuilder* astBuilder;
+    List<Decl*> members;
+    bool includeInstanceMembers = true;
+    SharedSemanticsContext semanticsContext;
+    MemberCollectingContext(Linkage* linkage, Module* module, DiagnosticSink* sink)
+        : semanticsContext(linkage, module, sink)
+    {}
+};
+
+void collectMembersInTypeDeclImpl(MemberCollectingContext* context, DeclRef<Decl> declRef);
+
+void collectMembersInType(MemberCollectingContext* context, Type* type);
+
+void collectMembersInType(MemberCollectingContext* context, Type* type)
+{
+    if (auto pointerLikeType = as<PointerLikeType>(type))
+    {
+        collectMembersInType(context, pointerLikeType->elementType);
+        return;
+    }
+
+    if (auto declRefType = as<DeclRefType>(type))
+    {
+        auto declRef = declRefType->declRef;
+
+        collectMembersInTypeDeclImpl(
+            context,
+            declRef);
+    }
+    else if (auto nsType = as<NamespaceType>(type))
+    {
+        auto declRef = nsType->declRef;
+
+        collectMembersInTypeDeclImpl(context, declRef);
+    }
+    else if (auto extractExistentialType = as<ExtractExistentialType>(type))
+    {
+        // We want lookup to be performed on the underlying interface type of the existential,
+        // but we need to have a this-type substitution applied to ensure that the result of
+        // lookup will have a comparable substitution applied (allowing things like associated
+        // types, etc. used in the signature of a method to resolve correctly).
+        //
+        auto interfaceDeclRef = extractExistentialType->getSpecializedInterfaceDeclRef();
+        collectMembersInTypeDeclImpl(context, interfaceDeclRef);
+    }
+    else if (auto thisType = as<ThisType>(type))
+    {
+        auto interfaceType = DeclRefType::create(context->astBuilder, thisType->interfaceDeclRef);
+        collectMembersInType(context, interfaceType);
+    }
+    else if (auto andType = as<AndType>(type))
+    {
+        auto leftType = andType->left;
+        auto rightType = andType->right;
+        collectMembersInType(context, leftType);
+        collectMembersInType(context, rightType);
+    }
+}
+
+void collectMembersInTypeDeclImpl(
+    MemberCollectingContext* context,
+    DeclRef<Decl> declRef)
+{
+    if (declRef.getDecl()->checkState.getState() < DeclCheckState::ReadyForLookup)
+        return;
+
+    if (auto genericTypeParamDeclRef = declRef.as<GenericTypeParamDecl>())
+    {
+        // If the type we are doing lookup in is a generic type parameter,
+        // then the members it provides can only be discovered by looking
+        // at the constraints that are placed on that type.
+        auto genericDeclRef = genericTypeParamDeclRef.getParent().as<GenericDecl>();
+        assert(genericDeclRef);
+
+        for (auto constraintDeclRef : getMembersOfType<GenericTypeConstraintDecl>(genericDeclRef))
+        {
+            if (constraintDeclRef.decl->checkState.getState() < DeclCheckState::ReadyForLookup)
+            {
+                continue;
+            }
+
+            collectMembersInType(
+                context,
+                getSup(context->astBuilder, constraintDeclRef));
+        }
+    }
+    else if (declRef.as<AssocTypeDecl>() || declRef.as<GlobalGenericParamDecl>())
+    {
+        for (auto constraintDeclRef :
+             getMembersOfType<TypeConstraintDecl>(declRef.as<ContainerDecl>()))
+        {
+            if (constraintDeclRef.decl->checkState.getState() < DeclCheckState::ReadyForLookup)
+            {
+                continue;
+            }
+            collectMembersInType(context, getSup(context->astBuilder, constraintDeclRef));
+        }
+    }
+    else if (auto namespaceDecl = declRef.as<NamespaceDecl>())
+    {
+        for (auto member : namespaceDecl.getDecl()->members)
+        {
+            if (member->getName())
+            {
+                context->members.add(member);
+            }
+        }
+    }
+    else if (auto aggTypeDeclBaseRef = declRef.as<AggTypeDeclBase>())
+    {
+        // In this case we are peforming lookup in the context of an aggregate
+        // type or an `extension`, so the first thing to do is to look for
+        // matching members declared directly in the body of the type/`extension`.
+        //
+        for (auto member : aggTypeDeclBaseRef.getDecl()->members)
+        {
+            if (member->getName())
+            {
+                if (!context->includeInstanceMembers)
+                {
+                    // Skip non-static members.
+                    if (as<PropertyDecl>(member))
+                        continue;
+                    if (as<SubscriptDecl>(member))
+                        continue;
+                    if (as<VarDeclBase>(member) || as<FuncDecl>(member))
+                    {
+                        if (!member->findModifier<HLSLStaticModifier>())
+                        {
+                            continue;
+                        }
+                    }
+                }
+                context->members.add(member);
+            }
+        }
+        
+        if (auto aggTypeDeclRef = aggTypeDeclBaseRef.as<AggTypeDecl>())
+        {
+            auto extensions =
+                context->semanticsContext.getCandidateExtensionsForTypeDecl(aggTypeDeclRef);
+            for (auto extDecl : extensions)
+            {
+                // TODO: check if the extension can be applied before including its members.
+                // TODO: eventually we need to insert a breadcrumb here so that
+                // the constructed result can somehow indicate that a member
+                // was found through an extension.
+                //
+                collectMembersInTypeDeclImpl(
+                    context,
+                    DeclRef<Decl>(extDecl, nullptr));
+            }
+        }
+
+        // For both aggregate types and their `extension`s, we want lookup to follow
+        // through the declared inheritance relationships on each declaration.
+        //
+        for (auto inheritanceDeclRef : getMembersOfType<InheritanceDecl>(aggTypeDeclBaseRef))
+        {
+            // Some things that are syntactically `InheritanceDecl`s don't actually
+            // represent a subtype/supertype relationship, and thus we shouldn't
+            // include members from the base type when doing lookup in the
+            // derived type.
+            //
+            if (inheritanceDeclRef.getDecl()->hasModifier<IgnoreForLookupModifier>())
+                continue;
+
+            collectMembersInType(
+                context, getSup(context->astBuilder, inheritanceDeclRef));
+        }
+    }
+}
+
+List<LanguageServerProtocol::CompletionItem> CompletionContext::collectMembers(Expr* baseExpr)
+{
+    List<LanguageServerProtocol::CompletionItem> result;
+    auto linkage = version->linkage;
+    Type* type = baseExpr->type.type;
+    bool isInstance = true;
+    if (auto typeType = as<TypeType>(type))
+    {
+        type = typeType->type;
+        isInstance = false;
+    }
+    version->currentCompletionItems.clear();
+    if (type)
+    {
+        if (isInstance && as<ArithmeticExpressionType>(type))
+        {
+            // Hard code members for vector and matrix types.
+            result.clear();
+            version->currentCompletionItems.clear();
+            int elementCount = 0;
+            Type* elementType = nullptr;
+            const char* memberNames[4] = {"x", "y", "z", "w"};
+            if (auto vectorType = as<VectorExpressionType>(type))
+            {
+                if (auto elementCountVal = as<ConstantIntVal>(vectorType->elementCount))
+                {
+                    elementCount = (int)elementCountVal->value;
+                    elementType = vectorType->elementType;
+                }
+            }
+            else if (auto matrixType = as<MatrixExpressionType>(type))
+            {
+                if (auto elementCountVal = as<ConstantIntVal>(matrixType->getRowCount()))
+                {
+                    elementCount = (int)elementCountVal->value;
+                    elementType = matrixType->getRowType();
+                }
+            }
+            String typeStr;
+            if (elementType)
+                typeStr = elementType->toString();
+            elementCount = Math::Min(elementCount, 4);
+            for (int i = 0; i < elementCount; i++)
+            {
+                LanguageServerProtocol::CompletionItem item;
+                item.data = 0;
+                item.detail = typeStr;
+                item.kind = LanguageServerProtocol::kCompletionItemKindVariable;
+                item.label = memberNames[i];
+                result.add(item);
+            }
+        }
+        else
+        {
+            DiagnosticSink sink;
+            MemberCollectingContext context(linkage, parsedModule, &sink);
+            context.astBuilder = linkage->getASTBuilder();
+            context.includeInstanceMembers = isInstance;
+            collectMembersInType(&context, type);
+            HashSet<String> deduplicateSet;
+            for (auto member : context.members)
+            {
+                LanguageServerProtocol::CompletionItem item;
+                item.label = member->getName()->text;
+                item.kind = 0;
+                if (as<TypeConstraintDecl>(member))
+                {
+                    continue;
+                }
+                if (as<ConstructorDecl>(member))
+                {
+                    continue;
+                }
+                if (as<SubscriptDecl>(member))
+                {
+                    continue;
+                }
+
+                if (item.label.startsWith("$"))
+                    continue;
+                if (!deduplicateSet.Add(item.label))
+                    continue;
+
+                if (as<StructDecl>(member))
+                {
+                    item.kind = LanguageServerProtocol::kCompletionItemKindStruct;
+                }
+                else if (as<ClassDecl>(member))
+                {
+                    item.kind = LanguageServerProtocol::kCompletionItemKindClass;
+                }
+                else if (as<InterfaceDecl>(member))
+                {
+                    item.kind = LanguageServerProtocol::kCompletionItemKindInterface;
+                }
+                else if (as<SimpleTypeDecl>(member))
+                {
+                    item.kind = LanguageServerProtocol::kCompletionItemKindClass;
+                }
+                else if (as<PropertyDecl>(member))
+                {
+                    item.kind = LanguageServerProtocol::kCompletionItemKindProperty;
+                }
+                else if (as<EnumDecl>(member))
+                {
+                    item.kind = LanguageServerProtocol::kCompletionItemKindEnum;
+                }
+                else if (as<VarDeclBase>(member))
+                {
+                    item.kind = LanguageServerProtocol::kCompletionItemKindVariable;
+                }
+                else if (as<EnumCaseDecl>(member))
+                {
+                    item.kind = LanguageServerProtocol::kCompletionItemKindEnumMember;
+                }
+                else if (as<CallableDecl>(member))
+                {
+                    item.kind = LanguageServerProtocol::kCompletionItemKindMethod;
+                }
+                else if (as<AssocTypeDecl>(member))
+                {
+                    item.kind = LanguageServerProtocol::kCompletionItemKindClass;
+                }
+                item.data = String(version->currentCompletionItems.getCount());
+                result.add(item);
+                version->currentCompletionItems.add(member);
+            }
+        }
+
+        for (auto& item : result)
+        {
+            for (auto ch : getCommitChars())
+                item.commitCharacters.add(ch);
+        }
+    }
+    return result;
+}
+
+} // namespace Slang
diff --git a/source/slang/slang-language-server-completion.h b/source/slang/slang-language-server-completion.h
new file mode 100644
index 000000000..73aad6cd1
--- /dev/null
+++ b/source/slang/slang-language-server-completion.h
@@ -0,0 +1,27 @@
+// slang-language-server-completion.h
+#pragma once
+
+#include "slang-workspace-version.h"
+
+namespace Slang
+{
+class LanguageServer;
+
+struct CompletionContext
+{
+    LanguageServer* server;
+    Index cursorOffset;
+    WorkspaceVersion* version;
+    DocumentVersion* doc;
+    Module* parsedModule;
+    JSONValue responseId;
+    UnownedStringSlice canonicalPath;
+    Int line;
+    Int col;
+
+    SlangResult tryCompleteMember();
+    SlangResult tryCompleteHLSLSemantic();
+    List<LanguageServerProtocol::CompletionItem> collectMembers(Expr* baseExpr);
+};
+
+} // namespace Slang
diff --git a/source/slang/slang-language-server-semantic-tokens.cpp b/source/slang/slang-language-server-semantic-tokens.cpp
index 34c40d8fd..806fa69ba 100644
--- a/source/slang/slang-language-server-semantic-tokens.cpp
+++ b/source/slang/slang-language-server-semantic-tokens.cpp
@@ -1,6 +1,7 @@
 #include "slang-language-server-semantic-tokens.h"
 #include "slang-visitor.h"
 #include "slang-ast-support-types.h"
+#include "../core/slang-char-util.h"
 #include <algorithm>
 
 namespace Slang
@@ -412,7 +413,7 @@ void iterateAST(UnownedStringSlice fileName, SourceManager* manager, SyntaxNode*
 }
 
 const char* kSemanticTokenTypes[] = {
-    "type", "enumMember", "variable", "parameter", "function", "property", "namespace"};
+    "type", "enumMember", "variable", "parameter", "function", "property", "namespace", "keyword" };
 
 static_assert(SLANG_COUNT_OF(kSemanticTokenTypes) == (int)SemanticTokenType::NormalText, "kSemanticTokenTypes must match SemanticTokenType");
 
@@ -420,15 +421,15 @@ SemanticToken _createSemanticToken(SourceManager* manager, SourceLoc loc, Name*
 {
     SemanticToken token;
     auto humaneLoc = manager->getHumaneLoc(loc, SourceLocType::Actual);
-    token.line = (int)(humaneLoc.line - 1);
-    token.col = (int)(humaneLoc.column - 1);
+    token.line = (int)(humaneLoc.line);
+    token.col = (int)(humaneLoc.column);
     token.length =
         name ? (int)(name->text.getLength()) : 0;
     token.type = SemanticTokenType::NormalText;
     return token;
 }
 
-List<SemanticToken> getSemanticTokens(Linkage* linkage, Module* module, UnownedStringSlice fileName)
+List<SemanticToken> getSemanticTokens(Linkage* linkage, Module* module, UnownedStringSlice fileName, DocumentVersion* doc)
 {
     auto manager = linkage->getSourceManager();
 
@@ -439,7 +440,6 @@ List<SemanticToken> getSemanticTokens(Linkage* linkage, Module* module, UnownedS
             token.type != SemanticTokenType::NormalText)
             result.add(token);
     };
-
     iterateAST(
         fileName,
         manager,
@@ -465,6 +465,11 @@ List<SemanticToken> getSemanticTokens(Linkage* linkage, Module* module, UnownedS
                             return;
                         token.type = SemanticTokenType::Type;
                     }
+                    else if (as<ConstructorDecl>(target))
+                    {
+                        token.type = SemanticTokenType::Type;
+                        token.length = doc->getTokenLength(token.line, token.col);
+                    }
                     else if (as<SimpleTypeDecl>(target))
                     {
                         token.type = SemanticTokenType::Type;
@@ -479,6 +484,11 @@ List<SemanticToken> getSemanticTokens(Linkage* linkage, Module* module, UnownedS
                     }
                     else if (as<VarDecl>(target))
                     {
+                        if (as<MemberExpr>(declRef->originalExpr) ||
+                            as<StaticMemberExpr>(declRef->originalExpr))
+                        {
+                            return;
+                        }
                         token.type = SemanticTokenType::Variable;
                     }
                     else if (as<FunctionDeclBase>(target))
@@ -503,6 +513,13 @@ List<SemanticToken> getSemanticTokens(Linkage* linkage, Module* module, UnownedS
                 }
 
             }
+            else if (auto accessorDecl = as<AccessorDecl>(node))
+            {
+                SemanticToken token = _createSemanticToken(
+                    manager, accessorDecl->loc, accessorDecl->getName());
+                token.type = SemanticTokenType::Keyword;
+                maybeInsertToken(token);
+            }
             else if (auto typeDecl = as<SimpleTypeDecl>(node))
             {
                 if (typeDecl->getName())
diff --git a/source/slang/slang-language-server-semantic-tokens.h b/source/slang/slang-language-server-semantic-tokens.h
index 925972200..c7cd8b63a 100644
--- a/source/slang/slang-language-server-semantic-tokens.h
+++ b/source/slang/slang-language-server-semantic-tokens.h
@@ -5,12 +5,13 @@
 #include "slang-ast-all.h"
 #include "slang-syntax.h"
 #include "slang-compiler.h"
+#include "slang-workspace-version.h"
 
 namespace Slang
 {
 enum class SemanticTokenType
 {
-    Type, EnumMember, Variable, Parameter, Function, Property, Namespace, NormalText
+    Type, EnumMember, Variable, Parameter, Function, Property, Namespace, Keyword, NormalText
 };
 extern const char* kSemanticTokenTypes[(int)SemanticTokenType::NormalText];
 
@@ -30,7 +31,7 @@ struct SemanticToken
     }
 };
 List<SemanticToken> getSemanticTokens(
-    Linkage* linkage, Module* module, UnownedStringSlice fileName);
+    Linkage* linkage, Module* module, UnownedStringSlice fileName, DocumentVersion* doc);
 List<uint32_t> getEncodedTokens(List<SemanticToken>& tokens);
 
 } // namespace Slang
diff --git a/source/slang/slang-language-server.cpp b/source/slang/slang-language-server.cpp
index d81e7dd8b..9f7329e2c 100644
--- a/source/slang/slang-language-server.cpp
+++ b/source/slang/slang-language-server.cpp
@@ -12,61 +12,29 @@
 #include "../core/slang-secure-crt.h"
 #include "../core/slang-range.h"
 #include "../../slang-com-helper.h"
+#include "../compiler-core/slang-json-native.h"
 #include "../compiler-core/slang-json-rpc-connection.h"
 #include "../compiler-core/slang-language-server-protocol.h"
 #include "slang-language-server.h"
 #include "slang-workspace-version.h"
 #include "slang-language-server-ast-lookup.h"
-#include "slang-language-server-collect-member.h"
+#include "slang-language-server-completion.h"
 #include "slang-language-server-semantic-tokens.h"
 #include "slang-ast-print.h"
 #include "slang-doc-markdown-writer.h"
+#include "../../tools/platform/performance-counter.h"
 
 namespace Slang
 {
 using namespace LanguageServerProtocol;
 
-class LanguageServer
+ArrayView<const char*> getCommitChars()
 {
-public:
-    RefPtr<JSONRPCConnection> m_connection;
-    ComPtr<slang::IGlobalSession> m_session;
-    RefPtr<Workspace> m_workspace;
-    Dictionary<String, String> m_lastPublishedDiagnostics;
-    time_t m_lastDiagnosticUpdateTime = 0;
-
-    bool m_quit = false;
-    List<LanguageServerProtocol::WorkspaceFolder> m_workspaceFolders;
-
-    SlangResult init(const LanguageServerProtocol::InitializeParams& args);
-    SlangResult execute();
-    void update();
-    SlangResult didOpenTextDocument(const LanguageServerProtocol::DidOpenTextDocumentParams& args);
-    SlangResult didCloseTextDocument(
-        const LanguageServerProtocol::DidCloseTextDocumentParams& args);
-    SlangResult didChangeTextDocument(
-        const LanguageServerProtocol::DidChangeTextDocumentParams& args);
-    SlangResult hover(const LanguageServerProtocol::HoverParams& args, const JSONValue& responseId);
-    SlangResult gotoDefinition(const LanguageServerProtocol::DefinitionParams& args, const JSONValue& responseId);
-    SlangResult completion(
-        const LanguageServerProtocol::CompletionParams& args, const JSONValue& responseId);
-    SlangResult completionResolve(
-        const LanguageServerProtocol::CompletionItem& args, const JSONValue& responseId);
-    SlangResult semanticTokens(
-        const LanguageServerProtocol::SemanticTokensParams& args, const JSONValue& responseId);
-    SlangResult signatureHelp(
-        const LanguageServerProtocol::SignatureHelpParams& args, const JSONValue& responseId);
-
-    List<LanguageServerProtocol::CompletionItem> collectMembers(
-        WorkspaceVersion* wsVersion, Module* module, Expr* baseExpr);
-
-private:
-    SlangResult _executeSingle();
-    slang::IGlobalSession* getOrCreateGlobalSession();
-    void resetDiagnosticUpdateTime();
-    void publishDiagnostics();
-};
-
+    static const char* _commitCharsArray[] = {",", ".", ";", ":", "(", ")", "[", "]",
+                                              "<", ">", "{", "}", "*", "&", "^", "%",
+                                              "!", "-", "=", "+", "|", "/", "?", " "};
+    return makeArrayView(_commitCharsArray, SLANG_COUNT_OF(_commitCharsArray));
+}
 
 SlangResult LanguageServer::init(const InitializeParams& args)
 {
@@ -105,14 +73,8 @@ String uriToCanonicalPath(const String& uri)
     return canonnicalPath;
 }
 
-SlangResult LanguageServer::_executeSingle()
+SlangResult LanguageServer::parseNextMessage()
 {
-    // If we don't have a message, we can quit for now
-    if (!m_connection->hasMessage())
-    {
-        return SLANG_OK;
-    }
-
     const JSONRPCMessageType msgType = m_connection->getMessageType();
 
     switch (msgType)
@@ -121,8 +83,6 @@ SlangResult LanguageServer::_executeSingle()
         {
             JSONRPCCall call;
             SLANG_RETURN_ON_FAIL(m_connection->getRPCOrSendError(&call));
-
-            // Do different things
             if (call.method == ExitParams::methodName)
             {
                 m_quit = true;
@@ -143,15 +103,14 @@ SlangResult LanguageServer::_executeSingle()
                 InitializeResult result;
                 result.serverInfo.name = "SlangLanguageServer";
                 result.serverInfo.version = "1.0";
-                result.capabilities.positionEncoding = "utf-8";
+                result.capabilities.positionEncoding = "utf-16";
                 result.capabilities.textDocumentSync.openClose = true;
-                result.capabilities.textDocumentSync.change = (int)TextDocumentSyncKind::Full;
+                result.capabilities.textDocumentSync.change = (int)TextDocumentSyncKind::Incremental;
+                result.capabilities.workspace.workspaceFolders.supported = true;
+                result.capabilities.workspace.workspaceFolders.changeNotifications = false;
                 result.capabilities.hoverProvider = true;
                 result.capabilities.definitionProvider = true;
-                const char* commitChars[] = {",", ".", ";", ":", "(", ")", "[", "]",
-                                             "<", ">", "{", "}", "*", "&", "^", "%",
-                                             "!", "-", "=", "+", "|", "/", "?"};
-                for (auto ch : commitChars)
+                for (auto ch : getCommitChars())
                     result.capabilities.completionProvider.allCommitCharacters.add(ch);
                 result.capabilities.completionProvider.triggerCharacters.add(".");
                 result.capabilities.completionProvider.triggerCharacters.add(":");
@@ -166,84 +125,49 @@ SlangResult LanguageServer::_executeSingle()
                 m_connection->sendResult(&result, call.id);
                 return SLANG_OK;
             }
-            else if (call.method == DidOpenTextDocumentParams::methodName)
-            {
-                DidOpenTextDocumentParams args;
-                SLANG_RETURN_ON_FAIL(
-                    m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
-                return didOpenTextDocument(args);
-            }
-            else if (call.method == DidCloseTextDocumentParams::methodName)
-            {
-                DidCloseTextDocumentParams args;
-                SLANG_RETURN_ON_FAIL(
-                    m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
-                return didCloseTextDocument(args);
-            }
-            else if (call.method == DidChangeTextDocumentParams::methodName)
-            {
-                DidChangeTextDocumentParams args;
-                SLANG_RETURN_ON_FAIL(
-                    m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
-                return didChangeTextDocument(args);
-            }
-            else if (call.method == HoverParams::methodName)
-            {
-                HoverParams args;
-                SLANG_RETURN_ON_FAIL(
-                    m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
-                return hover(args, call.id);
-            }
-            else if (call.method == DefinitionParams::methodName)
-            {
-                DefinitionParams args;
-                SLANG_RETURN_ON_FAIL(
-                    m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
-                return gotoDefinition(args, call.id);
-            }
-            else if (call.method == CompletionParams::methodName)
-            {
-                CompletionParams args;
-                SLANG_RETURN_ON_FAIL(
-                    m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
-                return completion(args, call.id);
-            }
-            else if (call.method == SemanticTokensParams::methodName)
-            {
-                SemanticTokensParams args;
-                SLANG_RETURN_ON_FAIL(
-                    m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
-                return semanticTokens(args, call.id);
-            }
-            else if (call.method == SignatureHelpParams::methodName)
-            {
-                SignatureHelpParams args;
-                SLANG_RETURN_ON_FAIL(
-                    m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
-                return signatureHelp(args, call.id);
-            }
-            else if (call.method == "completionItem/resolve")
-            {
-                CompletionItem args;
-                SLANG_RETURN_ON_FAIL(
-                    m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
-                return completionResolve(args, call.id);
-                
-            }
             else if (call.method == "initialized")
             {
+                sendConfigRequest();
+                registerCapability("workspace/didChangeConfiguration");
+                m_initialized = true;
                 return SLANG_OK;
             }
-            else if (call.method.startsWith("$/"))
+            else
             {
-                // Ignore.
+                queueJSONCall(call);
                 return SLANG_OK;
             }
-            else
+
+        }
+    case JSONRPCMessageType::Result:
+        {
+            JSONResultResponse response;
+            SLANG_RETURN_ON_FAIL(m_connection->getRPCOrSendError(&response));
+            auto responseId = (int)m_connection->getContainer()->asInteger(response.id);
+            switch (responseId)
             {
-                return m_connection->sendError(JSONRPC::ErrorCode::MethodNotFound, call.id);
+            case kConfigResponseId:
+                if (response.result.getKind() == JSONValue::Kind::Array)
+                {
+                    auto arr = m_connection->getContainer()->getArray(response.result);
+                    if (arr.getCount() > 0)
+                    {
+                        updatePredefinedMacros(arr[0]);
+                    }
+                }
+                break;
             }
+            return SLANG_OK;
         }
+    case JSONRPCMessageType::Error:
+        {
+#if 0 // Enable for debug only
+            JSONRPCErrorResponse error;
+            SLANG_RETURN_ON_FAIL(m_connection->getRPCOrSendError(&error));
+#endif
+            return SLANG_OK;
+        }
+        break;
     default:
         {
             return m_connection->sendError(
@@ -268,6 +192,14 @@ String getDeclSignatureString(DeclRef<Decl> declRef, ASTBuilder* astBuilder)
             ASTPrinter::OptionFlag::ParamNames | ASTPrinter::OptionFlag::NoInternalKeywords |
                 ASTPrinter::OptionFlag::SimplifiedBuiltinType);
         printer.addDeclSignature(declRef);
+        if (auto varDecl = as<VarDeclBase>(declRef.getDecl()))
+        {
+            auto& sb = printer.getStringBuilder();
+            if (auto litExpr = as<LiteralExpr>(varDecl->initExpr))
+            {
+                sb << " = " << litExpr->token.getContent();
+            }
+        }
         return printer.getString();
     }
     return "unknown";
@@ -332,6 +264,15 @@ SlangResult LanguageServer::hover(
     const LanguageServerProtocol::HoverParams& args, const JSONValue& responseId)
 {
     String canonicalPath = uriToCanonicalPath(args.textDocument.uri);
+    RefPtr<DocumentVersion> doc;
+    if (!m_workspace->openedDocuments.TryGetValue(canonicalPath, doc))
+    {
+        m_connection->sendResult(NullResponse::get(), responseId);
+        return SLANG_OK;
+    }
+    Index line, col;
+    doc->zeroBasedUTF16LocToOneBasedUTF8Loc(args.position.line, args.position.character, line, col);
+
     auto version = m_workspace->getCurrentVersion();
     Module* parsedModule = version->getOrLoadModule(canonicalPath);
     if (!parsedModule)
@@ -340,12 +281,13 @@ SlangResult LanguageServer::hover(
         return SLANG_OK;
     }
     auto findResult = findASTNodesAt(
+        doc.Ptr(),
         version->linkage->getSourceManager(),
         parsedModule->getModuleDecl(),
         ASTLookupType::Decl,
         canonicalPath.getUnownedSlice(),
-        args.position.line + 1,
-        args.position.character + 1);
+        line,
+        col);
     if (findResult.getCount() == 0 || findResult[0].path.getCount() == 0)
     {
         m_connection->sendResult(NullResponse::get(), responseId);
@@ -375,10 +317,18 @@ SlangResult LanguageServer::hover(
             hover.range.start.line = int(nodeHumaneLoc.line - 1);
             hover.range.end.line = int(nodeHumaneLoc.line - 1);
             hover.range.start.character = int(nodeHumaneLoc.column - 1);
-            if (declRef.getName())
+            auto name = declRef.getName();
+            if (auto ctorDecl = declRef.as<ConstructorDecl>())
+            {
+                auto parent = ctorDecl.getDecl()->parentDecl;
+                if (parent)
+                {
+                    name = parent->getName();
+                }
+            }
+            if (name)
             {
-                hover.range.end.character =
-                    int(nodeHumaneLoc.column + declRef.getName()->text.getLength() - 1);
+                hover.range.end.character = int(nodeHumaneLoc.column + name->text.getLength() - 1);
             }
         }
     };
@@ -413,6 +363,15 @@ SlangResult LanguageServer::gotoDefinition(
     const LanguageServerProtocol::DefinitionParams& args, const JSONValue& responseId)
 {
     String canonicalPath = uriToCanonicalPath(args.textDocument.uri);
+    RefPtr<DocumentVersion> doc;
+    if (!m_workspace->openedDocuments.TryGetValue(canonicalPath, doc))
+    {
+        m_connection->sendResult(NullResponse::get(), responseId);
+        return SLANG_OK;
+    }
+    Index line, col;
+    doc->zeroBasedUTF16LocToOneBasedUTF8Loc(args.position.line, args.position.character, line, col);
+
     auto version = m_workspace->getCurrentVersion();
     Module* parsedModule = version->getOrLoadModule(canonicalPath);
     if (!parsedModule)
@@ -421,12 +380,13 @@ SlangResult LanguageServer::gotoDefinition(
         return SLANG_OK;
     }
     auto findResult = findASTNodesAt(
+        doc.Ptr(),
         version->linkage->getSourceManager(),
         parsedModule->getModuleDecl(),
         ASTLookupType::Decl,
         canonicalPath.getUnownedSlice(),
-        args.position.line + 1,
-        args.position.character + 1);
+        line,
+        col);
     if (findResult.getCount() == 0 || findResult[0].path.getCount() == 0)
     {
         m_connection->sendResult(NullResponse::get(), responseId);
@@ -444,7 +404,9 @@ SlangResult LanguageServer::gotoDefinition(
         if (declRefExpr->declRef.getDecl())
         {
             auto location = version->linkage->getSourceManager()->getHumaneLoc(
-                declRefExpr->declRef.getNameLoc(), SourceLocType::Actual);
+                    declRefExpr->declRef.getNameLoc().isValid() ? declRefExpr->declRef.getNameLoc()
+                                                                : declRefExpr->declRef.getLoc(),
+                    SourceLocType::Actual);
             auto name = declRefExpr->declRef.getName();
             locations.add(LocationResult{location, name ? (int)name->text.getLength() : 0});
         }
@@ -485,28 +447,22 @@ SlangResult LanguageServer::gotoDefinition(
         for (auto loc : locations)
         {
             Location result;
-            result.uri = URI::fromLocalFilePath(loc.loc.pathInfo.foundPath.getUnownedSlice()).uri;
-            result.range.start.line = int(loc.loc.line - 1);
-            result.range.start.character = int(loc.loc.column - 1);
-            result.range.end = result.range.start;
-            result.range.end.character += loc.length;
-            results.add(result);
+            if (File::exists(loc.loc.pathInfo.foundPath))
+            {
+                result.uri =
+                    URI::fromLocalFilePath(loc.loc.pathInfo.foundPath.getUnownedSlice()).uri;
+                result.range.start.line = int(loc.loc.line - 1);
+                result.range.start.character = int(loc.loc.column - 1);
+                result.range.end = result.range.start;
+                result.range.end.character += loc.length;
+                results.add(result);
+            }
         }
         m_connection->sendResult(&results, responseId);
         return SLANG_OK;
     }
 }
 
-bool _isIdentifierChar(char ch)
-{
-    return ch >= '0' && ch <= '9' || ch >= 'a' && ch <= 'z' || ch >= 'A' && ch <= 'Z' || ch == '_';
-}
-
-bool _isWhitespaceChar(char ch)
-{
-    return ch == ' ' || ch == '\r' || ch == '\n' || ch == '\t';
-}
-
 SlangResult LanguageServer::completion(
     const LanguageServerProtocol::CompletionParams& args, const JSONValue& responseId)
 {
@@ -518,39 +474,16 @@ SlangResult LanguageServer::completion(
         m_connection->sendResult(NullResponse::get(), responseId);
         return SLANG_OK;
     }
-    
-    auto cursorOffset = doc->getOffset(args.position.line + 1, args.position.character + 1);
+    Index utf8Line, utf8Col;
+    doc->zeroBasedUTF16LocToOneBasedUTF8Loc(
+        args.position.line, args.position.character, utf8Line, utf8Col);
+    auto cursorOffset = doc->getOffset(utf8Line, utf8Col);
     if (cursorOffset == -1 || doc->getText().getLength() == 0)
     {
         m_connection->sendResult(NullResponse::get(), responseId);
         return SLANG_OK;
     }
-    // Scan backward until we locate a '.' or ':'.
-    if (cursorOffset == doc->getText().getLength())
-        cursorOffset--;
-    while (cursorOffset > 0 && _isWhitespaceChar(doc->getText()[cursorOffset]))
-    {
-        cursorOffset--;
-    }
-    while (cursorOffset > 0 && _isIdentifierChar(doc->getText()[cursorOffset]))
-    {
-        cursorOffset--;
-    }
-    while (cursorOffset > 0 && _isWhitespaceChar(doc->getText()[cursorOffset]))
-    {
-        cursorOffset--;
-    }
-    if (cursorOffset > 0 && doc->getText()[cursorOffset] == ':')
-        cursorOffset--;
-    if (cursorOffset <= 0 ||
-        (doc->getText()[cursorOffset] != '.' && doc->getText()[cursorOffset] != ':'))
-    {
-        m_connection->sendResult(NullResponse::get(), responseId);
-        return SLANG_OK;
-    }
-    Index line = 0;
-    Index col = 0;
-    doc->offsetToLineCol(cursorOffset, line, col);
+    
     auto version = m_workspace->getCurrentVersion();
     Module* parsedModule = version->getOrLoadModule(canonicalPath);
     if (!parsedModule)
@@ -558,48 +491,26 @@ SlangResult LanguageServer::completion(
         m_connection->sendResult(NullResponse::get(), responseId);
         return SLANG_OK;
     }
-    auto findResult = findASTNodesAt(
-        version->linkage->getSourceManager(),
-        parsedModule->getModuleDecl(),
-        ASTLookupType::Decl,
-        canonicalPath.getUnownedSlice(),
-        line,
-        col);
-    if (findResult.getCount() != 1)
+
+    CompletionContext context;
+    context.server = this;
+    context.cursorOffset = cursorOffset;
+    context.version = version;
+    context.doc = doc.Ptr();
+    context.parsedModule = parsedModule;
+    context.responseId = responseId;
+    context.canonicalPath = canonicalPath.getUnownedSlice();
+    context.line = utf8Line;
+    context.col = utf8Col;
+    if (SLANG_SUCCEEDED(context.tryCompleteMember()))
     {
-        m_connection->sendResult(NullResponse::get(), responseId);
         return SLANG_OK;
     }
-    if (findResult[0].path.getCount() == 0)
+    if (SLANG_SUCCEEDED(context.tryCompleteHLSLSemantic()))
     {
-        m_connection->sendResult(NullResponse::get(), responseId);
         return SLANG_OK;
     }
-    Expr* baseExpr = nullptr;
-    if (auto memberExpr = as<MemberExpr>(findResult[0].path.getLast()))
-    {
-        baseExpr = memberExpr->baseExpression;
-    }
-    else if (auto staticMemberExpr = as<StaticMemberExpr>(findResult[0].path.getLast()))
-    {
-        baseExpr = staticMemberExpr->baseExpression;
-    }
-    else if (auto swizzleExpr = as<SwizzleExpr>(findResult[0].path.getLast()))
-    {
-        baseExpr = swizzleExpr->base;
-    }
-    else if (auto matSwizzleExpr = as<MatrixSwizzleExpr>(findResult[0].path.getLast()))
-    {
-        baseExpr = matSwizzleExpr->base;
-    }
-    if (!baseExpr || !baseExpr->type.type || baseExpr->type.type->equals(version->linkage->getASTBuilder()->getErrorType()))
-    {
-        m_connection->sendResult(NullResponse::get(), responseId);
-        return SLANG_OK;
-    }
-
-    List<LanguageServerProtocol::CompletionItem> items = collectMembers(version, parsedModule, baseExpr);
-    m_connection->sendResult(&items, responseId);
+    m_connection->sendResult(NullResponse::get(), responseId);
     return SLANG_OK;
 }
 
@@ -628,6 +539,13 @@ SlangResult LanguageServer::semanticTokens(
 {
     String canonicalPath = uriToCanonicalPath(args.textDocument.uri);
 
+    RefPtr<DocumentVersion> doc;
+    if (!m_workspace->openedDocuments.TryGetValue(canonicalPath, doc))
+    {
+        m_connection->sendResult(NullResponse::get(), responseId);
+        return SLANG_OK;
+    }
+
     auto version = m_workspace->getCurrentVersion();
     Module* parsedModule = version->getOrLoadModule(canonicalPath);
     if (!parsedModule)
@@ -636,7 +554,18 @@ SlangResult LanguageServer::semanticTokens(
         return SLANG_OK;
     }
 
-    auto tokens = getSemanticTokens(version->linkage, parsedModule, canonicalPath.getUnownedSlice());
+    auto tokens = getSemanticTokens(version->linkage, parsedModule, canonicalPath.getUnownedSlice(), doc.Ptr());
+    for (auto& token : tokens)
+    {
+        Index line, col;
+        doc->oneBasedUTF8LocToZeroBasedUTF16Loc(token.line, token.col, line, col);
+        Index lineEnd, colEnd;
+        doc->oneBasedUTF8LocToZeroBasedUTF16Loc(
+            token.line, token.col + token.length, lineEnd, colEnd);
+        token.line = (int)line;
+        token.col = (int)col;
+        token.length = (int)(colEnd - col);
+    }
     SemanticTokens response;
     response.resultId = "";
     response.data = getEncodedTokens(tokens);
@@ -648,6 +577,14 @@ SlangResult LanguageServer::signatureHelp(
     const LanguageServerProtocol::SignatureHelpParams& args, const JSONValue& responseId)
 {
     String canonicalPath = uriToCanonicalPath(args.textDocument.uri);
+    RefPtr<DocumentVersion> doc;
+    if (!m_workspace->openedDocuments.TryGetValue(canonicalPath, doc))
+    {
+        m_connection->sendResult(NullResponse::get(), responseId);
+        return SLANG_OK;
+    }
+    Index line, col;
+    doc->zeroBasedUTF16LocToOneBasedUTF8Loc(args.position.line, args.position.character, line, col);
 
     auto version = m_workspace->getCurrentVersion();
     Module* parsedModule = version->getOrLoadModule(canonicalPath);
@@ -658,12 +595,13 @@ SlangResult LanguageServer::signatureHelp(
     }
 
     auto findResult = findASTNodesAt(
+        doc.Ptr(),
         version->linkage->getSourceManager(),
         parsedModule->getModuleDecl(),
         ASTLookupType::Invoke,
         canonicalPath.getUnownedSlice(),
-        args.position.line + 1,
-        args.position.character + 1);
+        line,
+        col);
 
     if (findResult.getCount() == 0)
     {
@@ -673,6 +611,7 @@ SlangResult LanguageServer::signatureHelp(
 
     AppExprBase* appExpr = nullptr;
     auto& declPath = findResult[0].path;
+    Loc currentLoc = {args.position.line + 1, args.position.character + 1};
     for (Index i = declPath.getCount() - 1; i >= 0; i--)
     {
         if (auto expr = as<AppExprBase>(declPath[i]))
@@ -681,8 +620,14 @@ SlangResult LanguageServer::signatureHelp(
             // This allows us to skip the invoke expr nodes for operators/implcit casts.
             if (expr->argumentDelimeterLocs.getCount())
             {
-                appExpr = expr;
-                break;
+                auto start = Loc::fromSourceLoc(version->linkage->getSourceManager(), expr->argumentDelimeterLocs.getFirst());
+                auto end = Loc::fromSourceLoc(
+                    version->linkage->getSourceManager(), expr->argumentDelimeterLocs.getLast());
+                if (start < currentLoc && currentLoc <= end)
+                {
+                    appExpr = expr;
+                    break;
+                }
             }
         }
     }
@@ -746,7 +691,18 @@ SlangResult LanguageServer::signatureHelp(
     };
     if (auto declRefExpr = as<DeclRefExpr>(funcExpr))
     {
-        addDeclRef(declRefExpr->declRef);
+        if (auto aggDecl = as<AggTypeDecl>(declRefExpr->declRef.getDecl()))
+        {
+            // Look for initializers
+            for (auto member : aggDecl->getMembersOfType<ConstructorDecl>())
+            {
+                addDeclRef(DeclRef<Decl>(member, declRefExpr->declRef.substitutions));
+            }
+        }
+        else
+        {
+            addDeclRef(declRefExpr->declRef);
+        }
     }
     else if (auto overloadedExpr = as<OverloadedExpr>(funcExpr))
     {
@@ -773,171 +729,6 @@ SlangResult LanguageServer::signatureHelp(
     return SLANG_OK;
 }
 
-
-List<LanguageServerProtocol::CompletionItem> LanguageServer::collectMembers(WorkspaceVersion* version, Module* module, Expr* baseExpr)
-{
-    List<LanguageServerProtocol::CompletionItem> result;
-    auto linkage = version->linkage;
-    Type* type = baseExpr->type.type;
-    if (auto typeType = as<TypeType>(type))
-    {
-        type = typeType->type;
-    }
-    version->currentCompletionItems.clear();
-    if (type)
-    {
-        if (as<ArithmeticExpressionType>(type))
-        {
-            // Hard code members for vector and matrix types.
-            result.clear();
-            version->currentCompletionItems.clear();
-            int elementCount = 0;
-            Type* elementType = nullptr;
-            const char* memberNames[4] = {"x", "y", "z", "w"};
-            if (auto vectorType = as<VectorExpressionType>(type))
-            {
-                if (auto elementCountVal = as<ConstantIntVal>(vectorType->elementCount))
-                {
-                    elementCount = (int)elementCountVal->value;
-                    elementType = vectorType->elementType;
-                }
-            }
-            else if (auto matrixType = as<MatrixExpressionType>(type))
-            {
-                if (auto elementCountVal = as<ConstantIntVal>(matrixType->getRowCount()))
-                {
-                    elementCount = (int)elementCountVal->value;
-                    elementType = matrixType->getRowType();
-                }
-            }
-            String typeStr;
-            if (elementType)
-                typeStr = elementType->toString();
-            for (int i = 0; i < elementCount; i++)
-            {
-                CompletionItem item;
-                item.data = 0;
-                item.detail = typeStr;
-                item.kind = LanguageServerProtocol::kCompletionItemKindVariable;
-                item.label = memberNames[i];
-                result.add(item);
-            }
-        }
-        else
-        {
-            DiagnosticSink sink;
-            MemberCollectingContext context(linkage, module, &sink);
-            context.astBuilder = linkage->getASTBuilder();
-            collectMembersInType(&context, type);
-            HashSet<String> deduplicateSet;
-            for (auto member : context.members)
-            {
-                CompletionItem item;
-                item.label = member->getName()->text;
-                item.kind = 0;
-                if (as<TypeConstraintDecl>(member))
-                {
-                    continue;
-                }
-                if (as<ConstructorDecl>(member))
-                {
-                    continue;
-                }
-                if (as<SubscriptDecl>(member))
-                {
-                    continue;
-                }
-
-                if (item.label.startsWith("$"))
-                    continue;
-                if (!deduplicateSet.Add(item.label))
-                    continue;
-
-                if (as<StructDecl>(member))
-                {
-                    item.kind = LanguageServerProtocol::kCompletionItemKindStruct;
-                }
-                else if (as<ClassDecl>(member))
-                {
-                    item.kind = LanguageServerProtocol::kCompletionItemKindClass;
-                }
-                else if (as<InterfaceDecl>(member))
-                {
-                    item.kind = LanguageServerProtocol::kCompletionItemKindInterface;
-                }
-                else if (as<SimpleTypeDecl>(member))
-                {
-                    item.kind = LanguageServerProtocol::kCompletionItemKindClass;
-                }
-                else if (as<PropertyDecl>(member))
-                {
-                    item.kind = LanguageServerProtocol::kCompletionItemKindProperty;
-                }
-                else if (as<EnumDecl>(member))
-                {
-                    item.kind = LanguageServerProtocol::kCompletionItemKindEnum;
-                }
-                else if (as<VarDeclBase>(member))
-                {
-                    item.kind = LanguageServerProtocol::kCompletionItemKindVariable;
-                }
-                else if (as<EnumCaseDecl>(member))
-                {
-                    item.kind = LanguageServerProtocol::kCompletionItemKindEnumMember;
-                }
-                else if (as<CallableDecl>(member))
-                {
-                    item.kind = LanguageServerProtocol::kCompletionItemKindMethod;
-                }
-                else if (as<AssocTypeDecl>(member))
-                {
-                    item.kind = LanguageServerProtocol::kCompletionItemKindClass;
-                }
-                item.data = String(version->currentCompletionItems.getCount());
-                result.add(item);
-                version->currentCompletionItems.add(member);
-            }
-        }
-
-        for (auto& item : result)
-        {
-            switch (item.kind)
-            {
-            case LanguageServerProtocol::kCompletionItemKindMethod:
-                item.commitCharacters.add("(");
-                item.commitCharacters.add("[");
-                item.commitCharacters.add(" ");
-                break;
-            default:
-                item.commitCharacters.add("(");
-                item.commitCharacters.add(")");
-                item.commitCharacters.add(".");
-                item.commitCharacters.add(";");
-                item.commitCharacters.add(":");
-                item.commitCharacters.add(",");
-                item.commitCharacters.add("<");
-                item.commitCharacters.add(">");
-                item.commitCharacters.add("[");
-                item.commitCharacters.add("]");
-                item.commitCharacters.add("{");
-                item.commitCharacters.add("}");
-                item.commitCharacters.add("-");
-                item.commitCharacters.add("*");
-                item.commitCharacters.add("/");
-                item.commitCharacters.add("%");
-                item.commitCharacters.add("+");
-                item.commitCharacters.add("=");
-                item.commitCharacters.add("&");
-                item.commitCharacters.add("|");
-                item.commitCharacters.add("!");
-                item.commitCharacters.add(" ");
-                break;
-            }
-        }
-    }
-    return result;
-}
-
 void LanguageServer::publishDiagnostics()
 {
     time_t timeNow = 0;
@@ -982,28 +773,236 @@ void LanguageServer::publishDiagnostics()
     }
 }
 
+void LanguageServer::updatePredefinedMacros(const JSONValue& macros)
+{
+    if (macros.isValid())
+    {
+        auto container = m_connection->getContainer();
+        JSONToNativeConverter converter(container, m_connection->getSink());
+        List<String> predefinedMacros;
+        if (SLANG_SUCCEEDED(converter.convert(macros, &predefinedMacros)))
+        {
+            if (m_workspace->updatePredefinedMacros(predefinedMacros))
+            {
+                m_connection->sendCall(
+                    UnownedStringSlice("workspace/semanticTokens/refresh"), JSONValue::makeInt(0));
+            }
+        }
+    }
+}
+
+void LanguageServer::sendConfigRequest()
+{
+    ConfigurationParams args;
+    ConfigurationItem item;
+    item.section = "slang.predefinedMacros";
+    args.items.add(item);
+    m_connection->sendCall(
+        ConfigurationParams::methodName, &args, JSONValue::makeInt(kConfigResponseId));
+}
+
+void LanguageServer::registerCapability(const char* methodName)
+{
+    RegistrationParams args;
+    Registration reg;
+    reg.method = methodName;
+    reg.id = reg.method;
+    args.registrations.add(reg);
+    m_connection->sendCall(
+        UnownedStringSlice("client/registerCapability"), &args, JSONValue::makeInt(999));
+}
+
+void LanguageServer::logMessage(int type, String message)
+{
+    LanguageServerProtocol::LogMessageParams args;
+    args.type = type;
+    args.message = message;
+    m_connection->sendCall(LanguageServerProtocol::LogMessageParams::methodName, &args);
+}
+
+SlangResult LanguageServer::queueJSONCall(JSONRPCCall call)
+{
+    Command cmd;
+    cmd.id = PersistentJSONValue(call.id, m_connection->getContainer());
+    cmd.method = call.method;
+    if (call.method == DidOpenTextDocumentParams::methodName)
+    {
+        DidOpenTextDocumentParams args;
+        SLANG_RETURN_ON_FAIL(m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
+        cmd.openDocArgs = args;
+    }
+    else if (call.method == DidCloseTextDocumentParams::methodName)
+    {
+        DidCloseTextDocumentParams args;
+        SLANG_RETURN_ON_FAIL(m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
+        cmd.closeDocArgs = args;
+    }
+    else if (call.method == DidChangeTextDocumentParams::methodName)
+    {
+        DidChangeTextDocumentParams args;
+        SLANG_RETURN_ON_FAIL(m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
+        cmd.changeDocArgs = args;
+    }
+    else if (call.method == HoverParams::methodName)
+    {
+        HoverParams args;
+        SLANG_RETURN_ON_FAIL(m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
+        cmd.hoverArgs = args;
+    }
+    else if (call.method == DefinitionParams::methodName)
+    {
+        DefinitionParams args;
+        SLANG_RETURN_ON_FAIL(m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
+        cmd.definitionArgs = args;
+    }
+    else if (call.method == CompletionParams::methodName)
+    {
+        CompletionParams args;
+        SLANG_RETURN_ON_FAIL(m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
+        cmd.completionArgs = args;
+    }
+    else if (call.method == SemanticTokensParams::methodName)
+    {
+        SemanticTokensParams args;
+        SLANG_RETURN_ON_FAIL(m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
+        cmd.semanticTokenArgs = args;
+    }
+    else if (call.method == SignatureHelpParams::methodName)
+    {
+        SignatureHelpParams args;
+        SLANG_RETURN_ON_FAIL(m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
+        cmd.signatureHelpArgs = args;
+    }
+    else if (call.method == "completionItem/resolve")
+    {
+        CompletionItem args;
+        SLANG_RETURN_ON_FAIL(m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
+        cmd.completionResolveArgs = args;
+    }
+    else if (call.method == DidChangeConfigurationParams::methodName)
+    {
+        DidChangeConfigurationParams args;
+        SLANG_RETURN_ON_FAIL(m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
+        // We need to process it now instead of sending to queue.
+        // This is because there is reference to JSONValue that is only available here.
+        return didChangeConfiguration(args);
+    }
+    else if (call.method == "$/cancelRequest")
+    {
+        CancelParams args;
+        SLANG_RETURN_ON_FAIL(m_connection->toNativeArgsOrSendError(call.params, &args, call.id));
+        cmd.cancelArgs = args;
+    }
+    commands.add(_Move(cmd));
+    return SLANG_OK;
+}
+
+SlangResult LanguageServer::runCommand(Command& call)
+{
+    // Do different things
+    if (call.method == DidOpenTextDocumentParams::methodName)
+    {
+        return didOpenTextDocument(call.openDocArgs.get());
+    }
+    else if (call.method == DidCloseTextDocumentParams::methodName)
+    {
+        return didCloseTextDocument(call.closeDocArgs.get());
+    }
+    else if (call.method == DidChangeTextDocumentParams::methodName)
+    {
+        return didChangeTextDocument(call.changeDocArgs.get());
+    }
+    else if (call.method == HoverParams::methodName)
+    {
+        return hover(call.hoverArgs.get(), call.id);
+    }
+    else if (call.method == DefinitionParams::methodName)
+    {
+        return gotoDefinition(call.definitionArgs.get(), call.id);
+    }
+    else if (call.method == CompletionParams::methodName)
+    {
+        return completion(call.completionArgs.get(), call.id);
+    }
+    else if (call.method == SemanticTokensParams::methodName)
+    {
+        return semanticTokens(call.semanticTokenArgs.get(), call.id);
+    }
+    else if (call.method == SignatureHelpParams::methodName)
+    {
+        return signatureHelp(call.signatureHelpArgs.get(), call.id);
+    }
+    else if (call.method == "completionItem/resolve")
+    {
+        return completionResolve(call.completionResolveArgs.get(), call.id);
+    }
+    else if (call.method == DidChangeConfigurationParams::methodName)
+    {
+        return didChangeConfiguration(call.changeConfigArgs.get());
+    }
+    else if (call.method.startsWith("$/"))
+    {
+        // Ignore.
+        return SLANG_OK;
+    }
+    else
+    {
+        return m_connection->sendError(JSONRPC::ErrorCode::MethodNotFound, call.id);
+    }
+}
+
+void LanguageServer::processCommands()
+{
+    HashSet<int64_t> canceledIDs;
+    for (auto& cmd : commands)
+    {
+        if (cmd.method == "$/cancelRequest")
+        {
+            auto id = cmd.cancelArgs.get().id;
+            if (id > 0)
+            {
+                canceledIDs.Add(id);
+            }
+        }
+    }
+    const int kErrorRequestCanceled = -32800;
+    for (auto& cmd : commands)
+    {
+        if (cmd.id.getKind() == JSONValue::Kind::Integer && canceledIDs.Contains(cmd.id.asInteger()))
+        {
+            m_connection->sendError((JSONRPC::ErrorCode)kErrorRequestCanceled, cmd.id);
+        }
+        else
+        {
+            runCommand(cmd);
+        }
+    }
+}
+
 SlangResult LanguageServer::didCloseTextDocument(const DidCloseTextDocumentParams& args)
 {
     String canonicalPath = uriToCanonicalPath(args.textDocument.uri);
-    m_workspace->openedDocuments.Remove(canonicalPath);
-    m_workspace->invalidate();
+    m_workspace->closeDoc(canonicalPath);
     resetDiagnosticUpdateTime();
     return SLANG_OK;
 }
 SlangResult LanguageServer::didChangeTextDocument(const DidChangeTextDocumentParams& args)
 {
     String canonicalPath = uriToCanonicalPath(args.textDocument.uri);
-
-    RefPtr<DocumentVersion> doc;
-    if (m_workspace->openedDocuments.TryGetValue(canonicalPath, doc))
-    {
-        doc->setText(args.contentChanges[0].text.getUnownedSlice());
-    }
-    m_workspace->invalidate();
+    for (auto change : args.contentChanges)
+        m_workspace->changeDoc(canonicalPath, change.range, change.text);
     resetDiagnosticUpdateTime();
     return SLANG_OK;
 }
 
+SlangResult LanguageServer::didChangeConfiguration(
+    const LanguageServerProtocol::DidChangeConfigurationParams& args)
+{
+    SLANG_UNUSED(args);
+    sendConfigRequest();
+    return SLANG_OK;
+}
+
 void LanguageServer::update()
 {
     if (!m_workspace)
@@ -1013,24 +1012,38 @@ void LanguageServer::update()
 
 SlangResult LanguageServer::execute()
 {
-
     m_connection = new JSONRPCConnection();
     m_connection->initWithStdStreams();
     
     while (m_connection->isActive() && !m_quit)
     {
         // Consume all messages first.
+        commands.clear();
+        auto start = platform::PerformanceCounter::now();
         while (true)
         {
             m_connection->tryReadMessage();
             if (!m_connection->hasMessage())
                 break;
-            const SlangResult res = _executeSingle();
-
+            parseNextMessage();
         }
-
+        auto parseTime = platform::PerformanceCounter::getElapsedTimeInSeconds(start);
+        auto parseEnd = platform::PerformanceCounter::now();
+        processCommands();
         // Now we can use this time to reparse user's code, report diagnostics, etc.
         update();
+        auto workTime = platform::PerformanceCounter::getElapsedTimeInSeconds(parseEnd);
+
+        if (commands.getCount() > 0 && m_initialized)
+        {
+            StringBuilder msgBuilder;
+            msgBuilder << "Server processed " << commands.getCount() << " commands, parsed in "
+                       << String(int(parseTime * 1000)) << "ms, executed in "
+                       << String(int(workTime * 1000)) << "ms";
+            logMessage(3, msgBuilder.ProduceString());
+        }
+
+        std::this_thread::sleep_for(std::chrono::milliseconds(10));
     }
 
     return SLANG_OK;
diff --git a/source/slang/slang-language-server.h b/source/slang/slang-language-server.h
index e3abfb2e5..f9ba2ddfc 100644
--- a/source/slang/slang-language-server.h
+++ b/source/slang/slang-language-server.h
@@ -1,8 +1,124 @@
 #pragma once
 
 #include "../../slang.h"
+#include "../compiler-core/slang-json-rpc.h"
+#include "../compiler-core/slang-json-rpc-connection.h"
+
+#include "slang-workspace-version.h"
 
 namespace Slang
 {
+ArrayView<const char*> getCommitChars();
+
+struct Command
+{
+    PersistentJSONValue id;
+    String method;
+
+    template <typename T> struct Optional
+    {
+    public:
+        T* value = nullptr;
+        bool isValid() { return value != nullptr; }
+        T& operator=(const T& val)
+        {
+            delete value;
+            value = new T(val);
+            return *value;
+        }
+        T& operator=(Optional&& other)
+        {
+            if (other.isValid())
+                *this = (other.get());
+            other.value = nullptr;
+            return *value;
+        }
+        T& get()
+        {
+            SLANG_ASSERT(isValid());
+            return *value;
+        }
+        Optional() = default;
+        Optional(const Optional& other)
+        {
+            if (other.isValid())
+                *this = (other.get());
+        }
+        Optional(Optional&& other)
+        {
+            if (other.isValid())
+                *this = (other.get());
+            other.value = nullptr;
+        }
+
+        ~Optional() { delete value; }
+    };
+
+    Optional<LanguageServerProtocol::CompletionParams> completionArgs;
+    Optional<LanguageServerProtocol::CompletionItem> completionResolveArgs;
+    Optional<LanguageServerProtocol::DidChangeConfigurationParams> changeConfigArgs;
+    Optional<LanguageServerProtocol::SignatureHelpParams> signatureHelpArgs;
+    Optional<LanguageServerProtocol::DefinitionParams> definitionArgs;
+    Optional<LanguageServerProtocol::SemanticTokensParams> semanticTokenArgs;
+    Optional<LanguageServerProtocol::HoverParams> hoverArgs;
+    Optional<LanguageServerProtocol::DidOpenTextDocumentParams> openDocArgs;
+    Optional<LanguageServerProtocol::DidChangeTextDocumentParams> changeDocArgs;
+    Optional<LanguageServerProtocol::DidCloseTextDocumentParams> closeDocArgs;
+    Optional<LanguageServerProtocol::CancelParams> cancelArgs;
+};
+
+class LanguageServer
+{
+private:
+    static const int kConfigResponseId = 0x1213;
+
+public:
+    bool m_initialized = false;
+    RefPtr<JSONRPCConnection> m_connection;
+    ComPtr<slang::IGlobalSession> m_session;
+    RefPtr<Workspace> m_workspace;
+    Dictionary<String, String> m_lastPublishedDiagnostics;
+    time_t m_lastDiagnosticUpdateTime = 0;
+    bool m_quit = false;
+    List<LanguageServerProtocol::WorkspaceFolder> m_workspaceFolders;
+
+    SlangResult init(const LanguageServerProtocol::InitializeParams& args);
+    SlangResult execute();
+    void update();
+    SlangResult didOpenTextDocument(const LanguageServerProtocol::DidOpenTextDocumentParams& args);
+    SlangResult didCloseTextDocument(
+        const LanguageServerProtocol::DidCloseTextDocumentParams& args);
+    SlangResult didChangeTextDocument(
+        const LanguageServerProtocol::DidChangeTextDocumentParams& args);
+    SlangResult didChangeConfiguration(
+        const LanguageServerProtocol::DidChangeConfigurationParams& args);
+    SlangResult hover(const LanguageServerProtocol::HoverParams& args, const JSONValue& responseId);
+    SlangResult gotoDefinition(
+        const LanguageServerProtocol::DefinitionParams& args, const JSONValue& responseId);
+    SlangResult completion(
+        const LanguageServerProtocol::CompletionParams& args, const JSONValue& responseId);
+    SlangResult completionResolve(
+        const LanguageServerProtocol::CompletionItem& args, const JSONValue& responseId);
+    SlangResult semanticTokens(
+        const LanguageServerProtocol::SemanticTokensParams& args, const JSONValue& responseId);
+    SlangResult signatureHelp(
+        const LanguageServerProtocol::SignatureHelpParams& args, const JSONValue& responseId);
+
+private:
+    SlangResult parseNextMessage();
+    slang::IGlobalSession* getOrCreateGlobalSession();
+    void resetDiagnosticUpdateTime();
+    void publishDiagnostics();
+    void updatePredefinedMacros(const JSONValue& macros);
+    void sendConfigRequest();
+    void registerCapability(const char* methodName);
+    void logMessage(int type, String message);
+
+    List<Command> commands;
+    SlangResult queueJSONCall(JSONRPCCall call);
+    SlangResult runCommand(Command& cmd);
+    void processCommands();
+};
+
 SLANG_API SlangResult runLanguageServer();
 } // namespace Slang
diff --git a/source/slang/slang-mangled-lexer.cpp b/source/slang/slang-mangled-lexer.cpp
index 32a8fa741..4920cfce3 100644
--- a/source/slang/slang-mangled-lexer.cpp
+++ b/source/slang/slang-mangled-lexer.cpp
@@ -158,8 +158,14 @@ UnownedStringSlice MangledLexer::readSimpleName()
     }
 }
 
-UnownedStringSlice MangledLexer::readRawStringSegment()
+String MangledLexer::readRawStringSegment()
 {
+    bool escapeMode = false;
+    if (peekChar() == 'R')
+    {
+        escapeMode = true;
+        nextChar();
+    }
     // Read the length part
     UInt count = readCount();
     if (count > UInt(m_end - m_cursor))
@@ -170,9 +176,52 @@ UnownedStringSlice MangledLexer::readRawStringSegment()
 
     auto result = UnownedStringSlice(m_cursor, m_cursor + count);
     m_cursor += count;
+    if (escapeMode)
+        return unescapeString(result);
     return result;
 }
 
+String MangledLexer::unescapeString(UnownedStringSlice str)
+{
+    StringBuilder sb;
+    Index cursor = 0;
+    while (cursor < str.getLength())
+    {
+        auto ch = str[cursor];
+        auto nextCh = 0;
+        if (cursor + 1 < str.getLength())
+        {
+            nextCh = str[cursor + 1];
+        }
+        if (ch == '_' && nextCh == 'u')
+        {
+            sb.appendChar('_');
+            cursor += 2;
+        }
+        else if (ch == '_')
+        {
+            cursor++;
+            Int charValue = 0;
+            while (cursor < str.getLength())
+            {
+                auto current = str[cursor];
+                if (current == 'x')
+                    break;
+                charValue = charValue * 16 + CharUtil::getHexDigitValue(current);
+                cursor++;
+            }
+            sb.appendChar((char)charValue);
+            cursor++;
+        }
+        else
+        {
+            sb.appendChar(ch);
+            cursor++;
+        }
+    }
+    return sb.ProduceString();
+}
+
 UInt MangledLexer::readParamCount()
 {
     _expect("p");
@@ -183,25 +232,24 @@ UInt MangledLexer::readParamCount()
 
 /* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! MangledNameParser !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! */
 
-/* static */SlangResult MangledNameParser::parseModuleName(const UnownedStringSlice& in, UnownedStringSlice& outModuleName)
+/* static */SlangResult MangledNameParser::parseModuleName(const UnownedStringSlice& in, String& outModuleName)
 {
     MangledLexer lexer(in);
-
     {
         switch (lexer.peekChar())
         {
-            case 'T':
-            case 'G':
-            case 'V':
-            {
-                lexer.nextChar();
-                break;
-            }
-            default: break;
+        case 'T':
+        case 'G':
+        case 'V':
+        {
+            lexer.nextChar();
+            break;
+        }
+        default: break;
         }
     }
 
-    UnownedStringSlice name = lexer.readRawStringSegment();
+    auto name = lexer.readRawStringSegment();
     if (name.getLength() == 0)
     {
         return SLANG_FAIL;
diff --git a/source/slang/slang-mangled-lexer.h b/source/slang/slang-mangled-lexer.h
index 7d096e45e..c9d051259 100644
--- a/source/slang/slang-mangled-lexer.h
+++ b/source/slang/slang-mangled-lexer.h
@@ -24,7 +24,7 @@ public:
 
     SLANG_INLINE void readSimpleIntVal();
 
-    UnownedStringSlice readRawStringSegment();
+    String readRawStringSegment();
 
     void readNamedType();
 
@@ -47,7 +47,8 @@ public:
         // Returns the current character and moves to next character.
     char nextChar() { return *m_cursor++; }
 
-    
+    static String unescapeString(UnownedStringSlice str);
+
         /// Ctor
     SLANG_FORCE_INLINE MangledLexer(const UnownedStringSlice& slice);
 
@@ -126,7 +127,7 @@ SLANG_INLINE void MangledLexer::_expect(char c)
 struct MangledNameParser
 {
         /// Tries to extract the module name from this mangled name. 
-    static SlangResult parseModuleName(const UnownedStringSlice& in, UnownedStringSlice& outModuleName);
+    static SlangResult parseModuleName(const UnownedStringSlice& in, String& outModuleName);
 };
 
 }
diff --git a/source/slang/slang-parser.cpp b/source/slang/slang-parser.cpp
index b2179c1af..38317009d 100644
--- a/source/slang/slang-parser.cpp
+++ b/source/slang/slang-parser.cpp
@@ -3105,7 +3105,11 @@ namespace Slang
     static NodeBase* parseConstructorDecl(Parser* parser, void* /*userData*/)
     {
         ConstructorDecl* decl = parser->astBuilder->create<ConstructorDecl>();
-        parser->FillPosition(decl);
+
+        // Note: we leave the source location of this decl as invalid, to
+        // trigger the fallback logic that fills in the location of the
+        // `__init` keyword later.
+
         parser->PushScope(decl);
 
         // TODO: we need to make sure that all initializers have
@@ -3132,6 +3136,7 @@ namespace Slang
 
         AccessorDecl* decl = nullptr;
         auto loc = peekToken(parser).loc;
+        auto name = peekToken(parser).getName();
         if( AdvanceIf(parser, "get") )
         {
             decl = parser->astBuilder->create<GetterDecl>();
@@ -3150,6 +3155,8 @@ namespace Slang
             return nullptr;
         }
         decl->loc = loc;
+        decl->nameAndLoc.name = name;
+        decl->nameAndLoc.loc = loc;
 
         _addModifiers(decl, modifiers);
 
diff --git a/source/slang/slang-serialize-container.cpp b/source/slang/slang-serialize-container.cpp
index 344b4aa02..09aea6c8b 100644
--- a/source/slang/slang-serialize-container.cpp
+++ b/source/slang/slang-serialize-container.cpp
@@ -350,7 +350,7 @@ static List<ExtensionDecl*>& _getCandidateExtensionList(
         {
             auto startChunk = chunk;
 
-            RefPtr<ASTBuilder> astBuilder;
+            RefPtr<ASTBuilder> astBuilder = options.astBuilder;
             NodeBase* astRootNode = nullptr;
             RefPtr<IRModule> irModule;
 
@@ -385,8 +385,10 @@ static List<ExtensionDecl*>& _getCandidateExtensionList(
 
                     StringBuilder buf;
                     buf << "tu" << out.modules.getCount();
-
-                    astBuilder = new ASTBuilder(options.sharedASTBuilder, buf.ProduceString());
+                    if (!astBuilder)
+                    {
+                        astBuilder = new ASTBuilder(options.sharedASTBuilder, buf.ProduceString());
+                    }
 
                     DefaultSerialObjectFactory objectFactory(astBuilder);
 
@@ -419,7 +421,7 @@ static List<ExtensionDecl*>& _getCandidateExtensionList(
                             {
                                 UnownedStringSlice mangledName = reader.getStringSlice(SerialIndex(i));
 
-                                UnownedStringSlice moduleName;
+                                String moduleName;
                                 SLANG_RETURN_ON_FAIL(MangledNameParser::parseModuleName(mangledName, moduleName));
 
                                 // If we already have looked up this module and it has the same name just use what we have
@@ -457,8 +459,11 @@ static List<ExtensionDecl*>& _getCandidateExtensionList(
                                         options.sink->diagnose(SourceLoc::fromRaw(0), Diagnostics::unableToFindSymbolInModule, mangledName, moduleName);
                                     }
 
-                                    // If didn't find the export then we are done
-                                    return SLANG_FAIL;
+                                    // If didn't find the export then we create an UnresolvedDecl node to represent the error.
+                                    auto unresolved = astBuilder->create<UnresolvedDecl>();
+                                    unresolved->nameAndLoc.name =
+                                        options.linkage->getNamePool()->getName(mangledName);
+                                    nodeBase = unresolved;
                                 }
 
                                 // set the result
diff --git a/source/slang/slang-serialize-container.h b/source/slang/slang-serialize-container.h
index 5368f62e6..9ee0625bf 100644
--- a/source/slang/slang-serialize-container.h
+++ b/source/slang/slang-serialize-container.h
@@ -89,6 +89,7 @@ struct SerialContainerUtil
         SourceManager* sourceManager = nullptr;
         NamePool* namePool = nullptr;
         SharedASTBuilder* sharedASTBuilder = nullptr;
+        ASTBuilder* astBuilder = nullptr; // Optional. If not provided will create one in SerialContainerData.
         Linkage* linkage = nullptr;
         DiagnosticSink* sink = nullptr;
     };
diff --git a/source/slang/slang-serialize-factory.cpp b/source/slang/slang-serialize-factory.cpp
index a6b7e0ba8..351742e60 100644
--- a/source/slang/slang-serialize-factory.cpp
+++ b/source/slang/slang-serialize-factory.cpp
@@ -75,14 +75,12 @@ SerialIndex ModuleSerialFilter::writePointer(SerialWriter* writer, const NodeBas
     if (Decl* decl = as<Decl>(ptr))
     {
         ModuleDecl* moduleDecl = findModuleForDecl(decl);
-        SLANG_ASSERT(moduleDecl);
         if (moduleDecl && moduleDecl != m_moduleDecl)
         {
             ASTBuilder* astBuilder = m_moduleDecl->module->getASTBuilder();
 
             // It's a reference to a declaration in another module, so first get the symbol name. 
             String mangledName = getMangledName(astBuilder, decl);
-
             // Add as an import symbol
             return writer->addImportSymbol(mangledName);
         }
@@ -110,6 +108,8 @@ SerialIndex ModuleSerialFilter::writePointer(SerialWriter* writer, const NodeBas
     //
     // For now we just ignore all stmts
 
+    // TODO(yong): We should by default serialize everything. The logic to skip bodies need to be
+    // behind a option flag.
     if (Stmt* stmt = as<Stmt>(ptr))
     {
         //
diff --git a/source/slang/slang-serialize-source-loc.cpp b/source/slang/slang-serialize-source-loc.cpp
index 331ca96ae..35473a1be 100644
--- a/source/slang/slang-serialize-source-loc.cpp
+++ b/source/slang/slang-serialize-source-loc.cpp
@@ -286,13 +286,13 @@ SlangResult SerialSourceLocReader::read(const SerialSourceLocData* serialData, S
                 const auto& lineInfo = lineInfos[lineInfoIndex];
 
                 const uint32_t offset = lineInfo.m_lineStartOffset;
-                SLANG_ASSERT(offset > 0);
                 const int finishIndex = int(lineInfo.m_lineIndex);
 
                 SLANG_ASSERT(finishIndex < numLines);
 
                 for (; lineIndex < finishIndex; ++lineIndex)
                 {
+                    SLANG_ASSERT(offset > 0);
                     lineBreakOffsets[lineIndex] = offset - 1;
                 }
                 lineBreakOffsets[lineIndex] = offset;
diff --git a/source/slang/slang-workspace-version.cpp b/source/slang/slang-workspace-version.cpp
index 1e92c31ca..d93be86b7 100644
--- a/source/slang/slang-workspace-version.cpp
+++ b/source/slang/slang-workspace-version.cpp
@@ -2,6 +2,7 @@
 #include "../core/slang-io.h"
 #include "../core/slang-file-system.h"
 #include "../compiler-core/slang-lexer.h"
+#include "slang-serialize-container.h"
 
 namespace Slang
 {
@@ -32,10 +33,75 @@ DocumentVersion* Workspace::openDoc(String path, String text)
     doc->setURI(URI::fromLocalFilePath(path.getUnownedSlice()));
     openedDocuments[path] = doc;
     searchPaths.Add(Path::getParentDirectory(path));
+    moduleCache.invalidate(path);
     invalidate();
     return doc.Ptr();
 }
 
+void Workspace::changeDoc(const String& path, LanguageServerProtocol::Range range, const String& text)
+{
+    RefPtr<DocumentVersion> doc;
+    if (openedDocuments.TryGetValue(path, doc))
+    {
+        Index line, col;
+        doc->zeroBasedUTF16LocToOneBasedUTF8Loc(range.start.line, range.start.character, line, col);
+        auto startOffset = doc->getOffset(line, col);
+        doc->zeroBasedUTF16LocToOneBasedUTF8Loc(range.end.line, range.end.character, line, col);
+        auto endOffset = doc->getOffset(line, col);
+        auto originalText = doc->getText().getUnownedSlice();
+        StringBuilder newText;
+        newText << originalText.head(startOffset) << text << originalText.tail(endOffset);
+        doc->setText(newText.ProduceString());
+    }
+    moduleCache.invalidate(path);
+    invalidate();
+}
+
+void Workspace::closeDoc(const String& path)
+{
+    moduleCache.invalidate(path);
+    openedDocuments.Remove(path);
+    invalidate();
+}
+
+bool Workspace::updatePredefinedMacros(List<String> macros)
+{
+    List<OnwedPreprocessorMacroDefinition> newDefs;
+    for (auto macro : macros)
+    {
+        auto index = macro.indexOf('=');
+        OnwedPreprocessorMacroDefinition def;
+        def.name = macro.getUnownedSlice().head(index).trim();
+        if (index != -1)
+        {
+            def.value = macro.getUnownedSlice().tail(index + 1).trim();
+        }
+        newDefs.add(def);
+    }
+    
+    bool changed = false;
+    if (newDefs.getCount() != predefinedMacros.getCount())
+        changed = true;
+    else
+    {
+        for (Index i = 0; i < newDefs.getCount(); i++)
+        {
+            if (newDefs[i].name != predefinedMacros[i].name ||
+                newDefs[i].value != predefinedMacros[i].value)
+            {
+                changed = true;
+                break;
+            }
+        }
+    }
+    if (changed)
+    {
+        predefinedMacros = _Move(newDefs);
+        invalidate();
+    }
+    return changed;
+}
+
 void Workspace::init(List<URI> rootDirURI, slang::IGlobalSession* globalSession)
 {
     for (auto uri : rootDirURI)
@@ -73,7 +139,7 @@ void Workspace::init(List<URI> rootDirURI, slang::IGlobalSession* globalSession)
 
 void Workspace::invalidate() { currentVersion = nullptr; }
 
-void parseDiagnostics(Dictionary<String, DocumentDiagnostics>& diagnostics, String compilerOutput)
+void WorkspaceVersion::parseDiagnostics(String compilerOutput)
 {
     List<UnownedStringSlice> lines;
     StringUtil::calcLines(compilerOutput.getUnownedSlice(), lines);
@@ -95,12 +161,12 @@ void parseDiagnostics(Dictionary<String, DocumentDiagnostics>& diagnostics, Stri
         int lineLoc = StringUtil::parseIntAndAdvancePos(line, pos);
         if (lineLoc == 0)
             lineLoc = 1;
-        diagnostic.range.end.line = diagnostic.range.start.line = lineLoc - 1;
+        diagnostic.range.end.line = diagnostic.range.start.line = lineLoc;
         pos++;
         int colLoc = StringUtil::parseIntAndAdvancePos(line, pos);
         if (colLoc == 0)
             colLoc = 1;
-        diagnostic.range.end.character = diagnostic.range.start.character = colLoc - 1;
+        diagnostic.range.end.character = diagnostic.range.start.character = colLoc;
         if (pos >= line.getLength())
             continue;
         line = line.tail(colonIndex + 3);
@@ -133,7 +199,31 @@ void parseDiagnostics(Dictionary<String, DocumentDiagnostics>& diagnostics, Stri
             auto tokenLength = StringUtil::parseIntAndAdvancePos(line, pos);
             diagnostic.range.end.character += tokenLength;
         }
+
+        if (auto doc = workspace->openedDocuments.TryGetValue(fileName))
+        {
+            // If the file is open, translate to UTF16 positions using the document.
+            Index lineUTF16, colUTF16;
+            doc->Ptr()->oneBasedUTF8LocToZeroBasedUTF16Loc(
+                diagnostic.range.start.line, diagnostic.range.start.character, lineUTF16, colUTF16);
+            diagnostic.range.start.line = (int)lineUTF16;
+            diagnostic.range.start.character = (int)colUTF16;
+            doc->Ptr()->oneBasedUTF8LocToZeroBasedUTF16Loc(
+                diagnostic.range.end.line, diagnostic.range.end.character, lineUTF16, colUTF16);
+            diagnostic.range.end.line = (int)lineUTF16;
+            diagnostic.range.end.character = (int)colUTF16;
+        }
+        else
+        {
+            // Otherwise, just return an 0-based position.
+            diagnostic.range.start.line--;
+            diagnostic.range.start.character--;
+            diagnostic.range.end.line--;
+            diagnostic.range.end.character--;
+        }
         diagnosticList.messages.Add(diagnostic);
+        if (diagnosticList.messages.Count() >= 1000)
+            break;
     }
 }
 
@@ -148,17 +238,33 @@ RefPtr<WorkspaceVersion> Workspace::createWorkspaceVersion()
     slang::TargetDesc targetDesc = {};
     targetDesc.profile = slangGlobalSession->findProfile("sm_6_6");
     desc.targets = &targetDesc;
-
     List<const char*> searchPathsRaw;
-    
     for (auto path : searchPaths)
         searchPathsRaw.add(path.getBuffer());
     desc.searchPaths = searchPathsRaw.getBuffer();
     desc.searchPathCount = searchPathsRaw.getCount();
 
+    desc.preprocessorMacroCount = predefinedMacros.getCount();
+    List<slang::PreprocessorMacroDesc> macroDescs;
+    for (auto& macro : predefinedMacros)
+    {
+        slang::PreprocessorMacroDesc macroDesc;
+        macroDesc.name = macro.name.getBuffer();
+        macroDesc.value = macro.value.getBuffer();
+        macroDescs.add(macroDesc);
+    }
+    desc.preprocessorMacros = macroDescs.getBuffer();
+
     ComPtr<slang::ISession> session;
     slangGlobalSession->createSession(desc, session.writeRef());
     version->linkage = static_cast<Linkage*>(session.get());
+    // TODO(yong): module cache does improves performance by 30%. However there are some issues
+    // that prevents the deserialization to resolve the imported decls from the correct module.
+    // This doesn't lead to crash, but may cause problems. We can enable this when the issues
+    // are fixed.
+#if 0
+    version->linkage->setModuleCache(&moduleCache);
+#endif
     return version;
 }
 
@@ -194,14 +300,79 @@ void* Workspace::getInterface(const Guid& uuid)
 void DocumentVersion::setText(const String& newText)
 {
     text = newText;
-    lineBreaks.clear();
-    for (Index i = 0; i < newText.getLength(); i++)
+    StringUtil::calcLines(text.getUnownedSlice(), lines);
+    utf16CharStarts.clear();
+}
+ArrayView<Index> DocumentVersion::getUTF16Boundaries(Index line)
+{
+    if (!utf16CharStarts.getCount())
+    {
+        for (auto slice : lines)
+        {
+            List<Index> bounds;
+            Index index = 0;
+            while (index < slice.getLength())
+            {
+                auto startIndex = index;
+                const Char32 codePoint = getUnicodePointFromUTF8(
+                    [&]() -> Byte
+                    {
+                        if (index < slice.getLength())
+                            return slice[index++];
+                        else
+                            return '\0';
+                    });
+                if (!codePoint)
+                    break;
+                Char16 buffer[2];
+                int count = encodeUnicodePointToUTF16Reversed(codePoint, buffer);
+                for (int i = 0; i < count; i++)
+                    bounds.add(startIndex);
+            }
+            bounds.add(slice.getLength());
+            utf16CharStarts.add(_Move(bounds));
+        }
+    }
+    return line >= 1 && line <= utf16CharStarts.getCount() ? utf16CharStarts[line - 1].getArrayView()
+                                                           : ArrayView<Index>();
+}
+
+void DocumentVersion::oneBasedUTF8LocToZeroBasedUTF16Loc(
+    Index inLine, Index inCol, Index& outLine, Index& outCol)
+{
+    Index rsLine = inLine - 1;
+    auto line = lines[rsLine];
+    auto bounds = getUTF16Boundaries(inLine);
+    outLine = rsLine;
+    outCol = std::lower_bound(bounds.begin(), bounds.end(), inCol - 1) - bounds.begin();
+}
+
+void DocumentVersion::zeroBasedUTF16LocToOneBasedUTF8Loc(
+    Index inLine, Index inCol, Index& outLine, Index& outCol)
+{
+    outLine = inLine + 1;
+    auto bounds = getUTF16Boundaries(inLine + 1);
+    outCol = inCol >=0 && inCol < bounds.getCount()? bounds[inCol] + 1 : 0;
+}
+
+static bool _isIdentifierChar(char ch)
+{
+    return ch >= 'a' && ch <= 'z' || ch >= 'A' && ch <= 'Z' || ch >= '0' && ch <= '9' || ch == '_';
+}
+
+int DocumentVersion::getTokenLength(Index line, Index col)
+{
+    auto offset = getOffset(line, col);
+    if (offset >= 0)
     {
-        if (newText[i] == '\n')
-            lineBreaks.add(i);
+        Index pos = offset;
+        for (; pos < text.getLength() && _isIdentifierChar(text[pos]); ++pos)
+        {}
+        return (int)(pos - offset);
     }
-    lineBreaks.add(newText.getLength());
+    return 0;
 }
+
 ASTMarkup* WorkspaceVersion::getOrCreateMarkupAST(ModuleDecl* module)
 {
     RefPtr<ASTMarkup> astMarkup;
@@ -209,6 +380,7 @@ ASTMarkup* WorkspaceVersion::getOrCreateMarkupAST(ModuleDecl* module)
         return astMarkup.Ptr();
     DiagnosticSink sink;
     astMarkup = new ASTMarkup();
+    sink.setSourceManager(linkage->getSourceManager());
     ASTMarkupUtil::extract(module, linkage->getSourceManager(), &sink, astMarkup.Ptr());
     markupASTs[module] = astMarkup;
     return astMarkup.Ptr();
@@ -238,7 +410,7 @@ Module* WorkspaceVersion::getOrLoadModule(String path)
     if (diagnosticBlob)
     {
         auto diagnosticString = String((const char*)diagnosticBlob->getBufferPointer());
-        parseDiagnostics(diagnostics, diagnosticString);
+        parseDiagnostics(diagnosticString);
         auto docDiagnostic = diagnostics.TryGetValue(path);
         if (docDiagnostic)
             docDiagnostic->originalOutput = diagnosticString;
@@ -246,4 +418,63 @@ Module* WorkspaceVersion::getOrLoadModule(String path)
     return static_cast<Module*>(parsedModule);
 }
 
+RefPtr<Module> SerializedModuleCache::tryLoadModule(
+    Linkage* linkage, String filePath)
+{
+    Path::getCanonical(filePath, filePath);
+    if (List<uint8_t>* rawData = serializedModules.TryGetValue(filePath))
+    {
+        RefPtr<MemoryStreamBase> memStream =
+            new MemoryStreamBase(FileAccess::Read, rawData->getBuffer(), rawData->getCount());
+        RiffContainer riffContainer;
+        RiffUtil::read(memStream.Ptr(), riffContainer);
+        SerialContainerData outData;
+        SerialContainerUtil::ReadOptions options;
+        options.linkage = linkage;
+        options.namePool = linkage->getNamePool();
+        options.session = linkage->getSessionImpl();
+        options.sharedASTBuilder = linkage->getASTBuilder()->getSharedASTBuilder();
+        options.astBuilder = linkage->getASTBuilder();
+        DiagnosticSink sink(linkage->getSourceManager(), Lexer::sourceLocationLexer);
+        options.sink = &sink;
+        options.sourceManager = linkage->getSourceManager();
+        SLANG_RETURN_NULL_ON_FAIL(SerialContainerUtil::read(&riffContainer, options, outData));
+        if (outData.modules.getCount() == 1)
+        {
+            RefPtr<Module> module = new Module(linkage, linkage->getASTBuilder());
+            auto moduleDecl = as<ModuleDecl>(outData.modules[0].astRootNode);
+            if (moduleDecl)
+            {
+                moduleDecl->module = module.Ptr();
+                module->setModuleDecl(moduleDecl);
+                return module;
+            }
+        }
+    }
+    return nullptr;
+}
+
+void SerializedModuleCache::storeModule(
+    Linkage* linkage, String filePath, RefPtr<Module> module)
+{
+    Path::getCanonical(filePath, filePath);
+    RiffContainer container;
+    SerialContainerUtil::WriteOptions options;
+    options.sourceManager = linkage->getSourceManager();
+    options.compressionType = SerialCompressionType::None;
+    options.optionFlags = SerialOptionFlag::SourceLocation | SerialOptionFlag::ASTModule;
+    SerialContainerData data;
+    SerialContainerData::Module moduleData;
+    moduleData.astBuilder = linkage->getASTBuilder();
+    moduleData.astRootNode = module->getModuleDecl();
+    moduleData.irModule = nullptr;
+    data.modules.add(moduleData);
+    SerialContainerUtil::write(data, options, &container);
+    RefPtr<OwnedMemoryStream> memStream = new OwnedMemoryStream(FileAccess::Write);
+    RiffUtil::write(&container, memStream);
+    List<uint8_t> rawData;
+    memStream->swapContents(rawData);
+    serializedModules[filePath] = _Move(rawData);
+}
+
 } // namespace Slang
diff --git a/source/slang/slang-workspace-version.h b/source/slang/slang-workspace-version.h
index 2aa2619f1..ee4d51896 100644
--- a/source/slang/slang-workspace-version.h
+++ b/source/slang/slang-workspace-version.h
@@ -18,7 +18,8 @@ namespace Slang
     private:
         URI uri;
         String text;
-        List<Int> lineBreaks;
+        List<UnownedStringSlice> lines;
+        List<List<Index>> utf16CharStarts;
     public:
         void setURI(URI newURI)
         {
@@ -27,43 +28,65 @@ namespace Slang
         URI getURI() { return uri; }
         const String& getText() { return text; }
         void setText(const String& newText);
+
+        ArrayView<Index> getUTF16Boundaries(Index line);
+
+        void oneBasedUTF8LocToZeroBasedUTF16Loc(
+            Index inLine, Index inCol, Index& outLine, Index& outCol);
+        void zeroBasedUTF16LocToOneBasedUTF8Loc(
+            Index inLine, Index inCol, Index& outLine, Index& outCol);
+
+        // Get starting offset of line.
+        Index getLineStart(UnownedStringSlice line) { return line.begin() - text.begin(); }
+
+        // Get offset from 1-based, utf-8 encoding location.
         Index getOffset(Index lineIndex, Index colIndex)
         {
             if(lineIndex < 0) return -1;
-            if (lineIndex - 1 >= lineBreaks.getCount())
+            if (lineIndex - 1 >= lines.getCount())
                 return -1;
-            if (lineBreaks.getCount() == 0)
+            if (lines.getCount() == 0)
                 return -1;
 
-            Index lineStart = lineIndex >= 2 ? lineBreaks[lineIndex - 2] : 0;
+            Index lineStart = lineIndex >= 1 ? getLineStart(lines[lineIndex - 1]) : 0;
             return lineStart + colIndex - 1;
         }
+
+        // Get 1-based, utf-8 encoding location from offset.
         void offsetToLineCol(Index offset, Index& line, Index& col)
         {
-            auto firstGreater = std::upper_bound(lineBreaks.begin(), lineBreaks.end(), offset);
-            line = Index(firstGreater - lineBreaks.begin() + 1);
-            if (firstGreater == lineBreaks.begin())
+            auto firstGreater = std::upper_bound(
+                lines.begin(),
+                lines.end(),
+                offset,
+                [this](Index first, UnownedStringSlice second)
+                { return first < getLineStart(second); });
+            line = Index(firstGreater - lines.begin());
+            if (firstGreater == lines.begin())
             {
                 col = offset + 1;
             }
             else
             {
-                col = Index(offset - *(firstGreater - 1));
+                col = Index(offset - getLineStart(lines[line-1])) + 1;
             }
         }
+
+        // Get line from 1-based index.
         UnownedStringSlice getLine(Index lineIndex)
         {
             if (lineIndex < 0)
                 return UnownedStringSlice();
-            if (lineIndex - 1 >= lineBreaks.getCount())
+            if (lineIndex - 1 >= lines.getCount())
                 return UnownedStringSlice();
-            if (lineBreaks.getCount() == 0)
+            if (lines.getCount() == 0)
                 return UnownedStringSlice();
 
-            Int lineStart = lineIndex >= 2 ? lineBreaks[lineIndex - 2] : 0;
-            Int lineEnd = lineBreaks[lineIndex - 1];
-            return text.getUnownedSlice().subString(lineStart, lineEnd);
+            return lineIndex > 0 ? lines[lineIndex - 1] : UnownedStringSlice();
         }
+
+        // Get length of an identifier token starting at the specified position.
+        int getTokenLength(Index line, Index col);
     };
 
     struct DocumentDiagnostics
@@ -72,11 +95,25 @@ namespace Slang
         String originalOutput;
     };
 
+    
+    class SerializedModuleCache
+        : public RefObject
+        , public IModuleCache
+    {
+    public:
+        Dictionary<String, List<uint8_t>> serializedModules;
+
+        void invalidate(const String& path) { serializedModules.Remove(path); }
+        virtual RefPtr<Module> tryLoadModule(Linkage* linkage, String filePath) override;
+        virtual void storeModule(Linkage* linkage, String filePath, RefPtr<Module> module) override;
+    };
+
     class WorkspaceVersion : public RefObject
     {
     private:
         Dictionary<String, Module*> modules;
         Dictionary<ModuleDecl*, RefPtr<ASTMarkup>> markupASTs;
+        void parseDiagnostics(String compilerOutput);
     public:
         Workspace* workspace;
         RefPtr<Linkage> linkage;
@@ -86,7 +123,12 @@ namespace Slang
 
         Module* getOrLoadModule(String path);
     };
-    
+
+    struct OnwedPreprocessorMacroDefinition
+    {
+        String name;
+        String value;
+    };
     class Workspace
         : public ISlangFileSystem
         , public ComObject
@@ -97,10 +139,18 @@ namespace Slang
     public:
         List<String> rootDirectories;
         OrderedHashSet<String> searchPaths;
+        List<OnwedPreprocessorMacroDefinition> predefinedMacros;
+        SerializedModuleCache moduleCache;
 
         slang::IGlobalSession* slangGlobalSession;
         Dictionary<String, RefPtr<DocumentVersion>> openedDocuments;
         DocumentVersion* openDoc(String path, String text);
+        void changeDoc(const String& path, LanguageServerProtocol::Range range, const String& text);
+        void closeDoc(const String& path);
+
+        // Update predefined macro settings. Returns true if the new settings are different from existing ones.
+        bool updatePredefinedMacros(List<String> predefinedMacros);
+
         void init(List<URI> rootDirURI, slang::IGlobalSession* globalSession);
         void invalidate();
         WorkspaceVersion* getCurrentVersion();
diff --git a/source/slang/slang.cpp b/source/slang/slang.cpp
index 7602096d4..02b1efedf 100644
--- a/source/slang/slang.cpp
+++ b/source/slang/slang.cpp
@@ -2611,6 +2611,11 @@ void Linkage::loadParsedModule(
         }
     }
     loadedModulesList.add(loadedModule);
+
+    if (m_moduleCache)
+    {
+        m_moduleCache->storeModule(this, pathInfo.foundPath, loadedModule);
+    }
 }
 
 Module* Linkage::loadModule(String const& name)
@@ -2794,6 +2799,19 @@ RefPtr<Module> Linkage::findOrImportModule(
     if (mapPathToLoadedModule.TryGetValue(filePathInfo.getMostUniqueIdentity(), loadedModule))
         return loadedModule;
 
+    // Is this module in user provided cache?
+    // (yong): module cache is intended to speed up language server reparsing.
+    // currently it is *not* enabled in language server.
+    if (m_moduleCache)
+    {
+        loadedModule = m_moduleCache->tryLoadModule(this, filePathInfo.foundPath);
+        if (loadedModule)
+        {
+            mapPathToLoadedModule[filePathInfo.getMostUniqueIdentity()] = loadedModule;
+            return loadedModule;
+        }
+    }
+
     // Try to load it
     ComPtr<ISlangBlob> fileContents;
     if(SLANG_FAILED(includeSystem.loadFile(filePathInfo, fileContents)))
@@ -2945,9 +2963,7 @@ static bool _canExportDeclSymbol(ASTNodeType type)
 {
     switch (type)
     {
-        case ASTNodeType::ModuleDecl:
         case ASTNodeType::EmptyDecl:
-        case ASTNodeType::NamespaceDecl:
         {
             return false;
         }
diff --git a/tests/language-server/member-completion-broken-syntax.slang b/tests/language-server/member-completion-broken-syntax.slang
new file mode 100644
index 000000000..948f4b31e
--- /dev/null
+++ b/tests/language-server/member-completion-broken-syntax.slang
@@ -0,0 +1,13 @@
+//TEST:LANG_SERVER:
+//COMPLETE:11,26
+struct MyType
+{
+    int getSum() { return 0; }
+}
+
+void m()
+{
+    MyType t;
+    if ((t.getSum() || t.)
+    for()
+}
diff --git a/tests/language-server/member-completion-broken-syntax.slang.expected.txt b/tests/language-server/member-completion-broken-syntax.slang.expected.txt
new file mode 100644
index 000000000..5faa1d323
--- /dev/null
+++ b/tests/language-server/member-completion-broken-syntax.slang.expected.txt
@@ -0,0 +1,3 @@
+--------
+getSum: 2  ,.;:()[]<>{}*&^%!-=+|/? 
+
diff --git a/tests/language-server/member-completion-if-condition.slang b/tests/language-server/member-completion-if-condition.slang
new file mode 100644
index 000000000..172bd0e8a
--- /dev/null
+++ b/tests/language-server/member-completion-if-condition.slang
@@ -0,0 +1,12 @@
+//TEST:LANG_SERVER:
+//COMPLETE:11,11
+struct MyType
+{
+    int getSum() { return 0; }
+}
+
+void m()
+{
+    MyType t;
+    if (t.)
+}
diff --git a/tests/language-server/member-completion-if-condition.slang.expected.txt b/tests/language-server/member-completion-if-condition.slang.expected.txt
new file mode 100644
index 000000000..5faa1d323
--- /dev/null
+++ b/tests/language-server/member-completion-if-condition.slang.expected.txt
@@ -0,0 +1,3 @@
+--------
+getSum: 2  ,.;:()[]<>{}*&^%!-=+|/? 
+
diff --git a/tests/language-server/robustness-5.slang b/tests/language-server/robustness-5.slang
new file mode 100644
index 000000000..a2d54b398
--- /dev/null
+++ b/tests/language-server/robustness-5.slang
@@ -0,0 +1,13 @@
+//TEST:LANG_SERVER:
+//
+//Broken syntax
+//HOVER:9,11
+
+__attributeTarget(StructDecl)
+attribute_syntax [MyAttribute(name:String)];
+[MyAttribute]
+struct MyStruct
+{
+    int a = 5;
+    
+}
\ No newline at end of file
diff --git a/tests/language-server/robustness-5.slang.expected.txt b/tests/language-server/robustness-5.slang.expected.txt
new file mode 100644
index 000000000..dd2c29b31
--- /dev/null
+++ b/tests/language-server/robustness-5.slang.expected.txt
@@ -0,0 +1,3 @@
+--------
+null
+
diff --git a/tests/language-server/smoke.slang.expected.txt b/tests/language-server/smoke.slang.expected.txt
index 5f0bd3915..aa0a2cd56 100644
--- a/tests/language-server/smoke.slang.expected.txt
+++ b/tests/language-server/smoke.slang.expected.txt
@@ -1,7 +1,7 @@
 --------
-first: 6  ().;:,<>[]{}-*/%+=&|! 
-second: 6  ().;:,<>[]{}-*/%+=&|! 
-getSum: 2  ([ 
+first: 6  ,.;:()[]<>{}*&^%!-=+|/? 
+second: 6  ,.;:()[]<>{}*&^%!-=+|/? 
+getSum: 2  ,.;:()[]<>{}*&^%!-=+|/? 
 --------
 range: 24,26 - 24,31
 content:
diff --git a/tests/language-server/vector-member.slang.expected.txt b/tests/language-server/vector-member.slang.expected.txt
index d93d9183f..4082a026c 100644
--- a/tests/language-server/vector-member.slang.expected.txt
+++ b/tests/language-server/vector-member.slang.expected.txt
@@ -1,6 +1,6 @@
 --------
-x: 6 float ().;:,<>[]{}-*/%+=&|! 
-y: 6 float ().;:,<>[]{}-*/%+=&|! 
-z: 6 float ().;:,<>[]{}-*/%+=&|! 
-w: 6 float ().;:,<>[]{}-*/%+=&|! 
+x: 6 float ,.;:()[]<>{}*&^%!-=+|/? 
+y: 6 float ,.;:()[]<>{}*&^%!-=+|/? 
+z: 6 float ,.;:()[]<>{}*&^%!-=+|/? 
+w: 6 float ,.;:()[]<>{}*&^%!-=+|/? 
 
diff --git a/tools/slang-test/slang-test-main.cpp b/tools/slang-test/slang-test-main.cpp
index 753ae5569..f80521707 100644
--- a/tools/slang-test/slang-test-main.cpp
+++ b/tools/slang-test/slang-test-main.cpp
@@ -1386,7 +1386,7 @@ TestResult runLanguageServerTest(TestContext* context, TestInput& input)
     auto waitForNonDiagnosticResponse = [&]() -> SlangResult
     {
         repeat:
-        if (SLANG_FAILED(connection->waitForResult(10000)))
+        if (SLANG_FAILED(connection->waitForResult(-1)))
             return SLANG_FAIL;
         if (connection->getMessageType() == JSONRPCMessageType::Call)
         {