Make source location lightweight

Fixes #24

So far the code has used a representation for source locations that is heavy-weight, but typical of research or hobby compilers: a `struct` type containing a line number and a (heap-allocated) string.
This is actually very convenient for debugging, but it means that any data structure that might contain a source location needs careful memory management (because of those strings) and has a tendency to bloat.

The new represnetation is that a source location is just a pointer-sized integer.
In the simplest mental model, you can think of this as just counting every byte of source text that is passed in, and using those to name locations.

Finding the path and line number that corresponds to a location involves a lookup step, but we can arrange to store all the files in an array sorted by their start locations, and do a binary search.
Finding line numbers inside a file is similarly fast (one you pay a one-time cost to build an array of starting offsets for lines).

More advanced compilers like clang actually go further and create a unique range of source locations to represent a file each time it gets included, so that they can track the include stack and reproduce it in diagnostic messages.
I'm not doing anything that clever here.

23 files changed, 1027 insertions, 380 deletions

diff --git a/source/core/slang-string.cpp b/source/core/slang-string.cpp
index 459396f69..9bc9e3a54 100644
--- a/source/core/slang-string.cpp
+++ b/source/core/slang-string.cpp
@@ -51,6 +51,12 @@ namespace Slang
         , endIndex(0)
     {}
 
+    StringSlice::StringSlice(String const& str)
+        : representation(str.buffer)
+        , beginIndex(0)
+        , endIndex(str.Length())
+    {}
+
     StringSlice::StringSlice(String const& str, UInt beginIndex, UInt endIndex)
         : representation(str.buffer)
         , beginIndex(beginIndex)
diff --git a/source/core/slang-string.h b/source/core/slang-string.h
index 552afe833..98fd51a07 100644
--- a/source/core/slang-string.h
+++ b/source/core/slang-string.h
@@ -155,6 +155,8 @@ namespace Slang
     public:
         StringSlice();
 
+        StringSlice(String const& str);
+
         StringSlice(String const& str, UInt beginIndex, UInt endIndex);
 
         UInt getLength() const
diff --git a/source/slang/compiler.cpp b/source/slang/compiler.cpp
index 60f111d83..55b79c00e 100644
--- a/source/slang/compiler.cpp
+++ b/source/slang/compiler.cpp
@@ -196,7 +196,7 @@ namespace Slang
         HMODULE d3dCompiler =  LoadLibraryA(libraryName);
         if (!d3dCompiler)
         {
-            request->mSink.diagnose(CodePosition(), Diagnostics::failedToLoadDynamicLibrary, libraryName);
+            request->mSink.diagnose(SourceLoc(), Diagnostics::failedToLoadDynamicLibrary, libraryName);
         }
         return d3dCompiler;
     }
@@ -373,7 +373,7 @@ namespace Slang
         HMODULE glslCompiler =  LoadLibraryA(libraryName);
         if (!glslCompiler)
         {
-            request->mSink.diagnose(CodePosition(), Diagnostics::failedToLoadDynamicLibrary, libraryName);
+            request->mSink.diagnose(SourceLoc(), Diagnostics::failedToLoadDynamicLibrary, libraryName);
         }
         return glslCompiler;
     }
@@ -611,7 +611,7 @@ namespace Slang
         if (count != 1)
         {
             compileRequest->mSink.diagnose(
-                CodePosition(),
+                SourceLoc(),
                 Diagnostics::cannotWriteOutputFile,
                 path);
         }
@@ -630,7 +630,7 @@ namespace Slang
         if (!file)
         {
             compileRequest->mSink.diagnose(
-                CodePosition(),
+                SourceLoc(),
                 Diagnostics::cannotWriteOutputFile,
                 path);
             return;
diff --git a/source/slang/compiler.h b/source/slang/compiler.h
index fd40a62f6..5a6cb5c19 100644
--- a/source/slang/compiler.h
+++ b/source/slang/compiler.h
@@ -122,17 +122,7 @@ namespace Slang
 //			GLSL,	// pass through GLSL to `glslang` library
     };
 
-    // Represents a single source file (either an on-disk file, or a
-    // "virtual" file passed in as a string)
-    class SourceFile : public RefObject
-    {
-    public:
-        // The file path for a real file, or the nominal path for a virtual file
-        String path;
-
-        // The actual contents of the file
-        String content;
-    };
+    class SourceFile;
 
     // A single translation unit requested to be compiled.
     //
@@ -228,6 +218,10 @@ namespace Slang
         // Are we being driven by the command-line `slangc`, and should act accordingly?
         bool isCommandLineCompile = false;
 
+        // Source manager to help track files loaded
+        SourceManager sourceManagerStorage;
+        SourceManager* sourceManager;
+
         // Output stuff
         DiagnosticSink mSink;
         String mDiagnosticOutput;
@@ -250,12 +244,9 @@ namespace Slang
         Dictionary<String, RefPtr<ModuleDecl>> mapNameToLoadedModules;
 
 
-        CompileRequest(Session* session)
-            : mSession(session)
-        {}
+        CompileRequest(Session* session);
 
-        ~CompileRequest()
-        {}
+        ~CompileRequest();
 
         void parseTranslationUnit(
             TranslationUnitRequest* translationUnit);
@@ -267,6 +258,10 @@ namespace Slang
 
         int addTranslationUnit(SourceLanguage language, String const& name);
 
+        void addTranslationUnitSourceFile(
+            int             translationUnitIndex,
+            SourceFile*     sourceFile);
+
         void addTranslationUnitSourceString(
             int             translationUnitIndex,
             String const&   path,
@@ -285,7 +280,7 @@ namespace Slang
             String const&       name,
             String const&       path,
             String const&       source,
-            CodePosition const& loc);
+            SourceLoc const& loc);
 
         void handlePoundImport(
             String const&       path,
@@ -293,7 +288,18 @@ namespace Slang
 
         RefPtr<ModuleDecl> findOrImportModule(
             String const&       name,
-            CodePosition const& loc);
+            SourceLoc const& loc);
+
+        SourceManager* getSourceManager()
+        {
+            return sourceManager;
+        }
+
+        void setSourceManager(SourceManager* sm)
+        {
+            sourceManager = sm;
+            mSink.sourceManager = sm;
+        }
     };
 
     void generateOutput(
@@ -324,6 +330,9 @@ namespace Slang
 
         List<RefPtr<ModuleDecl>> loadedModuleCode;
 
+        SourceManager   builtinSourceManager;
+
+        SourceManager* getBuiltinSourceManager() { return &builtinSourceManager; }
 
         //
 
diff --git a/source/slang/diagnostics.cpp b/source/slang/diagnostics.cpp
index e0b959a81..eb6a818d3 100644
--- a/source/slang/diagnostics.cpp
+++ b/source/slang/diagnostics.cpp
@@ -1,7 +1,8 @@
-// Diagnostics.cpp
-#include "Diagnostics.h"
+// diagnostics.cpp
+#include "diagnostics.h"
 
-#include "Syntax.h"
+#include "compiler.h"
+#include "syntax.h"
 
 #include <assert.h>
 
@@ -67,17 +68,17 @@ void printDiagnosticArg(StringBuilder& sb, Token const& token)
     sb << token.Content;
 }
 
-CodePosition const& getDiagnosticPos(SyntaxNode const* syntax)
+SourceLoc const& getDiagnosticPos(SyntaxNode const* syntax)
 {
     return syntax->Position;
 }
 
-CodePosition const& getDiagnosticPos(Token const& token)
+SourceLoc const& getDiagnosticPos(Token const& token)
 {
     return token.Position;
 }
 
-CodePosition const& getDiagnosticPos(TypeExp const& typeExp)
+SourceLoc const& getDiagnosticPos(TypeExp const& typeExp)
 {
     return typeExp.exp->Position;
 }
@@ -140,12 +141,18 @@ static void formatDiagnosticMessage(StringBuilder& sb, char const* format, int a
 }
 
 static void formatDiagnostic(
+    DiagnosticSink*     sink,
     StringBuilder&      sb,
     Diagnostic const&   diagnostic)
 {
-    sb << diagnostic.Position.FileName;
+    auto sourceManager = sink->sourceManager;
+
+    auto expandedLoc = sourceManager->expandSourceLoc(diagnostic.Position);
+    auto humaneLoc = sourceManager->getHumaneLoc(expandedLoc);
+
+    sb << humaneLoc.getPath();
     sb << "(";
-    sb << diagnostic.Position.Line;
+    sb << humaneLoc.line;
     sb << "): ";
     sb << getSeverityName(diagnostic.severity);
     sb << " ";
@@ -155,7 +162,7 @@ static void formatDiagnostic(
     sb << "\n";
 }
 
-void DiagnosticSink::diagnoseImpl(CodePosition const& pos, DiagnosticInfo const& info, int argCount, DiagnosticArg const* const* args)
+void DiagnosticSink::diagnoseImpl(SourceLoc const& pos, DiagnosticInfo const& info, int argCount, DiagnosticArg const* const* args)
 {
     StringBuilder sb;
     formatDiagnosticMessage(sb, info.messageFormat, argCount, args);
@@ -176,7 +183,7 @@ void DiagnosticSink::diagnoseImpl(CodePosition const& pos, DiagnosticInfo const&
     {
         // If so, pass the error string along to them
         StringBuilder messageBuilder;
-        formatDiagnostic(messageBuilder, diagnostic);
+        formatDiagnostic(this, messageBuilder, diagnostic);
 
         callback(messageBuilder.ProduceString().begin(), callbackUserData);
     }
@@ -184,7 +191,7 @@ void DiagnosticSink::diagnoseImpl(CodePosition const& pos, DiagnosticInfo const&
     {
         // If the user doesn't have a callback, then just
         // collect our diagnostic messages into a buffer
-        formatDiagnostic(outputBuffer, diagnostic);
+        formatDiagnostic(this, outputBuffer, diagnostic);
     }
 
     if (diagnostic.severity >= Severity::Fatal)
diff --git a/source/slang/diagnostics.h b/source/slang/diagnostics.h
index 6ea677b38..e22320d3d 100644
--- a/source/slang/diagnostics.h
+++ b/source/slang/diagnostics.h
@@ -46,7 +46,7 @@ namespace Slang
     {
     public:
         String Message;
-        CodePosition Position;
+        SourceLoc Position;
         int ErrorID;
         Severity severity;
 
@@ -57,7 +57,7 @@ namespace Slang
         Diagnostic(
             const String & msg,
             int id,
-            const CodePosition & pos,
+            const SourceLoc & pos,
             Severity severity)
             : severity(severity)
         {
@@ -93,16 +93,16 @@ namespace Slang
         printDiagnosticArg(sb, ptr.Ptr());
     }
 
-    inline CodePosition const& getDiagnosticPos(CodePosition const& pos) { return pos;  }
+    inline SourceLoc const& getDiagnosticPos(SourceLoc const& pos) { return pos;  }
 
     class SyntaxNode;
     class ShaderClosure;
-    CodePosition const& getDiagnosticPos(SyntaxNode const* syntax);
-    CodePosition const& getDiagnosticPos(Token const& token);
-    CodePosition const& getDiagnosticPos(TypeExp const& typeExp);
+    SourceLoc const& getDiagnosticPos(SyntaxNode const* syntax);
+    SourceLoc const& getDiagnosticPos(Token const& token);
+    SourceLoc const& getDiagnosticPos(TypeExp const& typeExp);
 
     template<typename T>
-    CodePosition getDiagnosticPos(RefPtr<T> const& ptr)
+    SourceLoc getDiagnosticPos(RefPtr<T> const& ptr)
     {
         return getDiagnosticPos(ptr.Ptr());
     }
@@ -128,6 +128,9 @@ namespace Slang
     class DiagnosticSink
     {
     public:
+        // The source manager to use when mapping source locations to file+line info
+        SourceManager*  sourceManager;
+
         StringBuilder outputBuffer;
 //            List<Diagnostic> diagnostics;
         int errorCount = 0;
@@ -136,43 +139,43 @@ namespace Slang
         void*                   callbackUserData    = nullptr;
 
 /*
-        void Error(int id, const String & msg, const CodePosition & pos)
+        void Error(int id, const String & msg, const SourceLoc & pos)
         {
             diagnostics.Add(Diagnostic(msg, id, pos, Severity::Error));
             errorCount++;
         }
 
-        void Warning(int id, const String & msg, const CodePosition & pos)
+        void Warning(int id, const String & msg, const SourceLoc & pos)
         {
             diagnostics.Add(Diagnostic(msg, id, pos, Severity::Warning));
         }
 */
         int GetErrorCount() { return errorCount; }
 
-        void diagnoseDispatch(CodePosition const& pos, DiagnosticInfo const& info)
+        void diagnoseDispatch(SourceLoc const& pos, DiagnosticInfo const& info)
         {
             diagnoseImpl(pos, info, 0, NULL);
         }
 
-        void diagnoseDispatch(CodePosition const& pos, DiagnosticInfo const& info, DiagnosticArg const& arg0)
+        void diagnoseDispatch(SourceLoc const& pos, DiagnosticInfo const& info, DiagnosticArg const& arg0)
         {
             DiagnosticArg const* args[] = { &arg0 };
             diagnoseImpl(pos, info, 1, args);
         }
 
-        void diagnoseDispatch(CodePosition const& pos, DiagnosticInfo const& info, DiagnosticArg const& arg0, DiagnosticArg const& arg1)
+        void diagnoseDispatch(SourceLoc const& pos, DiagnosticInfo const& info, DiagnosticArg const& arg0, DiagnosticArg const& arg1)
         {
             DiagnosticArg const* args[] = { &arg0, &arg1 };
             diagnoseImpl(pos, info, 2, args);
         }
 
-        void diagnoseDispatch(CodePosition const& pos, DiagnosticInfo const& info, DiagnosticArg const& arg0, DiagnosticArg const& arg1, DiagnosticArg const& arg2)
+        void diagnoseDispatch(SourceLoc const& pos, DiagnosticInfo const& info, DiagnosticArg const& arg0, DiagnosticArg const& arg1, DiagnosticArg const& arg2)
         {
             DiagnosticArg const* args[] = { &arg0, &arg1, &arg2 };
             diagnoseImpl(pos, info, 3, args);
         }
 
-        void diagnoseDispatch(CodePosition const& pos, DiagnosticInfo const& info, DiagnosticArg const& arg0, DiagnosticArg const& arg1, DiagnosticArg const& arg2, DiagnosticArg const& arg3)
+        void diagnoseDispatch(SourceLoc const& pos, DiagnosticInfo const& info, DiagnosticArg const& arg0, DiagnosticArg const& arg1, DiagnosticArg const& arg2, DiagnosticArg const& arg3)
         {
             DiagnosticArg const* args[] = { &arg0, &arg1, &arg2, &arg3 };
             diagnoseImpl(pos, info, 4, args);
@@ -184,7 +187,7 @@ namespace Slang
             diagnoseDispatch(getDiagnosticPos(pos), info, args...);
         }
 
-        void diagnoseImpl(CodePosition const& pos, DiagnosticInfo const& info, int argCount, DiagnosticArg const* const* args);
+        void diagnoseImpl(SourceLoc const& pos, DiagnosticInfo const& info, int argCount, DiagnosticArg const* const* args);
 
         // Add a diagnostic with raw text
         // (used when we get errors from a downstream compiler)
@@ -202,9 +205,9 @@ namespace Slang
 
 #ifdef _DEBUG
 #define SLANG_INTERNAL_ERROR(sink, pos) \
-    (sink)->diagnose(Slang::CodePosition(__LINE__, 0, 0, __FILE__), Slang::Diagnostics::internalCompilerError)
+    (sink)->diagnose(Slang::SourceLoc(__LINE__, 0, 0, __FILE__), Slang::Diagnostics::internalCompilerError)
 #define SLANG_UNIMPLEMENTED(sink, pos, what) \
-    (sink)->diagnose(Slang::CodePosition(__LINE__, 0, 0, __FILE__), Slang::Diagnostics::unimplemented, what)
+    (sink)->diagnose(Slang::SourceLoc(__LINE__, 0, 0, __FILE__), Slang::Diagnostics::unimplemented, what)
 
 #else
 #define SLANG_INTERNAL_ERROR(sink, pos) \
diff --git a/source/slang/emit.cpp b/source/slang/emit.cpp
index 72632260f..2a5f40787 100644
--- a/source/slang/emit.cpp
+++ b/source/slang/emit.cpp
@@ -58,8 +58,8 @@ struct SharedEmitContext
     StringBuilder sb;
 
     // Current source position for tracking purposes...
-    CodePosition loc;
-    CodePosition nextSourceLocation;
+    HumaneSourceLoc loc;
+    HumaneSourceLoc nextSourceLocation;
     bool needToUpdateSourceLocation;
 
     // For GLSL output, we can't emit traidtional `#line` directives
@@ -344,7 +344,7 @@ struct EDeclarator
 
     // Used for `Flavor::Name`
     String name;
-    CodePosition loc;
+    SourceLoc loc;
 
     // Used for `Flavor::Array`
     IntVal* elementCount;
@@ -407,7 +407,7 @@ struct EmitVisitor
         // Update our logical position
         // TODO(tfoley): Need to make "corelib" not use `int` for pointer-sized things...
         auto len = int(textEnd - textBegin);
-        context->shared->loc.Col += len;
+        context->shared->loc.column += len;
     }
 
     void Emit(char const* textBegin, char const* textEnd)
@@ -431,8 +431,8 @@ struct EmitVisitor
                 // At the end of a line, we need to update our tracking
                 // information on code positions
                 emitTextSpan(spanBegin, spanEnd);
-                context->shared->loc.Line++;
-                context->shared->loc.Col = 1;
+                context->shared->loc.line++;
+                context->shared->loc.column = 1;
 
                 // Start a new span for emit purposes
                 spanBegin = spanEnd;
@@ -452,7 +452,7 @@ struct EmitVisitor
 
     void emitName(
         String const&       inName,
-        CodePosition const& loc)
+        SourceLoc const& loc)
     {
         String name = inName;
 
@@ -467,7 +467,7 @@ struct EmitVisitor
 
     void emitName(String const& name)
     {
-        emitName(name, CodePosition());
+        emitName(name, SourceLoc());
     }
 
     void Emit(IntegerLiteralValue value)
@@ -504,12 +504,12 @@ struct EmitVisitor
     // Emit a `#line` directive to the output.
     // Doesn't udpate state of source-location tracking.
     void emitLineDirective(
-        CodePosition const& sourceLocation)
+        HumaneSourceLoc const& sourceLocation)
     {
         emitRawText("\n#line ");
 
         char buffer[16];
-        sprintf(buffer, "%d", sourceLocation.Line);
+        sprintf(buffer, "%d", sourceLocation.line);
         emitRawText(buffer);
 
         emitRawText(" ");
@@ -547,7 +547,7 @@ struct EmitVisitor
 
         if(shouldUseGLSLStyleLineDirective)
         {
-            auto path = sourceLocation.FileName;
+            auto path = sourceLocation.getPath();
 
             // GLSL doesn't support the traditional form of a `#line` directive without
             // an extension. Rather than depend on that extension we will output
@@ -578,7 +578,7 @@ struct EmitVisitor
             // in a module that tracks source files.
 
             emitRawText("\"");
-            for(auto c : sourceLocation.FileName)
+            for(auto c : sourceLocation.getPath())
             {
                 char charBuffer[] = { c, 0 };
                 switch(c)
@@ -607,17 +607,18 @@ struct EmitVisitor
     // ensure that source location tracking information
     // is correct based on the directive we just output.
     void emitLineDirectiveAndUpdateSourceLocation(
-        CodePosition const& sourceLocation)
+        HumaneSourceLoc const& sourceLocation)
     {
         emitLineDirective(sourceLocation);
-    
-        context->shared->loc.FileName = sourceLocation.FileName;
-        context->shared->loc.Line = sourceLocation.Line;
-        context->shared->loc.Col = 1;
+
+        HumaneSourceLoc newLoc = sourceLocation;
+        newLoc.column = 1;
+
+        context->shared->loc = newLoc;
     }
 
     void emitLineDirectiveIfNeeded(
-        CodePosition const& sourceLocation)
+        HumaneSourceLoc const& sourceLocation)
     {
         // Don't do any of this work if the user has requested that we
         // not emit line directives.
@@ -626,31 +627,31 @@ struct EmitVisitor
             return;
 
         // Ignore invalid source locations
-        if(sourceLocation.Line <= 0)
+        if(sourceLocation.line <= 0)
             return;
 
         // If we are currently emitting code at a source location with
         // a differnet file or line, *or* if the source location is
         // somehow later on the line than what we want to emit,
         // then we need to emit a new `#line` directive.
-        if(sourceLocation.FileName != context->shared->loc.FileName
-            || sourceLocation.Line != context->shared->loc.Line
-            || sourceLocation.Col < context->shared->loc.Col)
+        if(sourceLocation.path != context->shared->loc.path
+            || sourceLocation.line != context->shared->loc.line
+            || sourceLocation.column < context->shared->loc.column)
         {
             // Special case: if we are in the same file, and within a small number
             // of lines of the target location, then go ahead and output newlines
             // to get us caught up.
             enum { kSmallLineCount = 3 };
-            auto lineDiff = sourceLocation.Line - context->shared->loc.Line;
-            if(sourceLocation.FileName == context->shared->loc.FileName
-                && sourceLocation.Line > context->shared->loc.Line
+            auto lineDiff = sourceLocation.line - context->shared->loc.line;
+            if(sourceLocation.path == context->shared->loc.path
+                && sourceLocation.line > context->shared->loc.line
                 && lineDiff <= kSmallLineCount)
             {
                 for(int ii = 0; ii < lineDiff; ++ii )
                 {
                     Emit("\n");
                 }
-                SLANG_RELEASE_ASSERT(sourceLocation.Line == context->shared->loc.Line);
+                SLANG_RELEASE_ASSERT(sourceLocation.line == context->shared->loc.line);
             }
             else
             {
@@ -666,28 +667,39 @@ struct EmitVisitor
         // came in as spaces or tabs, so there is necessarily going to be
         // coupling between how the downstream compiler counts columns,
         // and how we do.
-        if(sourceLocation.Col > context->shared->loc.Col)
+        if(sourceLocation.column > context->shared->loc.column)
         {
-            int delta = sourceLocation.Col - context->shared->loc.Col;
+            int delta = sourceLocation.column - context->shared->loc.column;
             for( int ii = 0; ii < delta; ++ii )
             {
                 emitRawText(" ");
             }
-            context->shared->loc.Col = sourceLocation.Col;
+            context->shared->loc.column = sourceLocation.column;
         }
     }
 
     void advanceToSourceLocation(
-        CodePosition const& sourceLocation)
+        HumaneSourceLoc const& sourceLocation)
     {
         // Skip invalid locations
-        if(sourceLocation.Line <= 0)
+        if(sourceLocation.line <= 0)
             return;
 
         context->shared->needToUpdateSourceLocation = true;
         context->shared->nextSourceLocation = sourceLocation;
     }
 
+    SourceManager* getSourceManager()
+    {
+        return context->shared->entryPoint->compileRequest->getSourceManager();
+    }
+
+    void advanceToSourceLocation(
+        SourceLoc const& sourceLocation)
+    {
+        advanceToSourceLocation(getSourceManager()->getHumaneLoc(sourceLocation));
+    }
+
     void flushSourceLocationChange()
     {
         if(!context->shared->needToUpdateSourceLocation)
@@ -707,9 +719,8 @@ struct EmitVisitor
         if (mode == LineDirectiveMode::None)
             return;
 
-
         if ((mode == LineDirectiveMode::None)
-            || token.Position.FileName.Length() == 0)
+            || !token.Position.isValid())
         {
             // If we don't have the original position info, or we are in the
             // mode where the user didn't want line directives, we need to play
@@ -755,7 +766,7 @@ struct EmitVisitor
         }
         else
         {
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unknown type of integer constant value");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unknown type of integer constant value");
         }
     }
 
@@ -787,7 +798,7 @@ struct EmitVisitor
             break;
 
         default:
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unknown declarator flavor");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unknown declarator flavor");
             break;
         }
     }
@@ -808,7 +819,7 @@ struct EmitVisitor
             case BaseType::Bool:	Emit("b");		break;
             case BaseType::Double:	Emit("d");		break;
             default:
-                SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled GLSL type prefix");
+                SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled GLSL type prefix");
                 break;
             }
         }
@@ -822,7 +833,7 @@ struct EmitVisitor
         }
         else
         {
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled GLSL type prefix");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled GLSL type prefix");
         }
     }
 
@@ -851,7 +862,7 @@ struct EmitVisitor
             break;
 
         default:
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled resource access mode");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled resource access mode");
             break;
         }
 
@@ -863,7 +874,7 @@ struct EmitVisitor
         case TextureType::ShapeCube:	Emit("TextureCube");	break;
         case TextureType::ShapeBuffer:  Emit("Buffer");         break;
         default:
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled resource shape");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled resource shape");
             break;
         }
 
@@ -895,7 +906,7 @@ struct EmitVisitor
         case TextureType::ShapeCube:	Emit("Cube");	break;
         case TextureType::ShapeBuffer:	Emit("Buffer");	break;
         default:
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled resource shape");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled resource shape");
             break;
         }
 
@@ -941,7 +952,7 @@ struct EmitVisitor
             break;
 
         default:
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled code generation target");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled code generation target");
             break;
         }
     }
@@ -956,7 +967,7 @@ struct EmitVisitor
             break;
 
         default:
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "this target should see combined texture-sampler types");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "this target should see combined texture-sampler types");
             break;
         }
     }
@@ -975,7 +986,7 @@ struct EmitVisitor
             break;
 
         default:
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "this target should see GLSL image types");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "this target should see GLSL image types");
             break;
         }
     }
@@ -1026,7 +1037,7 @@ struct EmitVisitor
         case BaseType::Bool:	Emit("bool");		break;
         case BaseType::Double:	Emit("double");		break;
         default:
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled scalar type");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled scalar type");
             break;
         }
 
@@ -1058,7 +1069,7 @@ struct EmitVisitor
             break;
 
         default:
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled code generation target");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled code generation target");
             break;
         }
 
@@ -1096,7 +1107,7 @@ struct EmitVisitor
             break;
 
         default:
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled code generation target");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled code generation target");
             break;
         }
 
@@ -1136,7 +1147,7 @@ struct EmitVisitor
             case SamplerStateType::Flavor::SamplerState:			Emit("SamplerState");			break;
             case SamplerStateType::Flavor::SamplerComparisonState:	Emit("SamplerComparisonState");	break;
             default:
-                SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled sampler state flavor");
+                SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled sampler state flavor");
                 break;
             }
             break;
@@ -1147,7 +1158,7 @@ struct EmitVisitor
             case SamplerStateType::Flavor::SamplerState:			Emit("sampler");		break;
             case SamplerStateType::Flavor::SamplerComparisonState:	Emit("samplerShadow");	break;
             default:
-                SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled sampler state flavor");
+                SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled sampler state flavor");
                 break;
             }
             break;
@@ -1187,9 +1198,9 @@ struct EmitVisitor
 
     void EmitType(
         RefPtr<Type>  type,
-        CodePosition const&     typeLoc,
+        SourceLoc const&     typeLoc,
         String const&           name,
-        CodePosition const&     nameLoc)
+        SourceLoc const&     nameLoc)
     {
         advanceToSourceLocation(typeLoc);
 
@@ -1203,7 +1214,7 @@ struct EmitVisitor
 
     void EmitType(RefPtr<Type> type, Token const& nameToken)
     {
-        EmitType(type, CodePosition(), nameToken.Content, nameToken.Position);
+        EmitType(type, SourceLoc(), nameToken.Content, nameToken.Position);
     }
 
     void EmitType(RefPtr<Type> type)
@@ -1232,13 +1243,13 @@ struct EmitVisitor
         }
     }
 
-    void EmitType(TypeExp const& typeExp, String const& name, CodePosition const& nameLoc)
+    void EmitType(TypeExp const& typeExp, String const& name, SourceLoc const& nameLoc)
     {
         if (!typeExp.type || typeExp.type->As<ErrorType>())
         {
             if (!typeExp.exp)
             {
-                SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unresolved type expression should have expression part");
+                SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unresolved type expression should have expression part");
             }
 
             EDeclarator nameDeclarator;
@@ -1251,7 +1262,7 @@ struct EmitVisitor
         else
         {
             EmitType(typeExp.type,
-                typeExp.exp ? typeExp.exp->Position : CodePosition(),
+                typeExp.exp ? typeExp.exp->Position : SourceLoc(),
                 name, nameLoc);
         }
     }
@@ -1263,7 +1274,7 @@ struct EmitVisitor
 
     void EmitType(TypeExp const& typeExp, String const& name)
     {
-        EmitType(typeExp, name, CodePosition());
+        EmitType(typeExp, name, SourceLoc());
     }
 
     void emitTypeExp(TypeExp const& typeExp)
@@ -1463,7 +1474,7 @@ struct EmitVisitor
         switch(context->shared->target)
         {
         default:
-            SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled code generation target");
+            SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled code generation target");
             return false;
 
         case CodeGenTarget::GLSL: return targetName == "glsl";
@@ -3203,7 +3214,7 @@ struct EmitVisitor
                 Emit("s");
                 break;
             default:
-                SLANG_DIAGNOSE_UNEXPECTED(getSink(), CodePosition(), "unhandled HLSL register type");
+                SLANG_DIAGNOSE_UNEXPECTED(getSink(), SourceLoc(), "unhandled HLSL register type");
                 break;
             }
             Emit(info.index);
diff --git a/source/slang/lexer.cpp b/source/slang/lexer.cpp
index 84b34c9a9..fe01878d1 100644
--- a/source/slang/lexer.cpp
+++ b/source/slang/lexer.cpp
@@ -1,4 +1,12 @@
-#include "Lexer.h"
+// lexer.cpp
+#include "lexer.h"
+
+// This file implements the lexer/scanner, which is responsible for taking a raw stream of
+// input bytes and turning it into semantically useful tokens.
+//
+
+#include "compiler.h"
+#include "source-loc.h"
 
 #include <assert.h>
 
@@ -6,7 +14,7 @@ namespace Slang
 {
     static Token GetEndOfFileToken()
     {
-        return Token(TokenType::EndOfFile, "", 0, 0, 0, "");
+        return Token(TokenType::EndOfFile, "", SourceLoc());
     }
 
     Token* TokenList::begin() const
@@ -52,10 +60,10 @@ namespace Slang
         return mCursor->type;
     }
 
-    CodePosition TokenReader::PeekLoc() const
+    SourceLoc TokenReader::PeekLoc() const
     {
         if (!mCursor)
-            return CodePosition();
+            return SourceLoc();
         SLANG_ASSERT(mCursor);
         return mCursor->Position;
     }
@@ -75,18 +83,22 @@ namespace Slang
 
     // Lexer
 
-    Lexer::Lexer(
-        String const&   path,
-        String const&   content,
-        DiagnosticSink* sink)
-        : path(path)
-        , content(content)
-        , sink(sink)
+    void Lexer::initialize(
+        SourceFile*     inSourceFile,
+        DiagnosticSink* inSink)
     {
+        sourceFile = inSourceFile;
+        sink = inSink;
+
+        auto content = inSourceFile->content;
+
+        begin   = content.begin();
         cursor  = content.begin();
         end     = content.end();
 
-        loc = CodePosition(1, 1, 0, path);
+        spellingStartLoc = inSourceFile->sourceRange.begin;
+        presumedStartLoc = spellingStartLoc;
+
         tokenFlags = TokenFlag::AtStartOfLine | TokenFlag::AfterWhitespace;
         lexerFlags = 0;
     }
@@ -142,9 +154,6 @@ namespace Slang
         {
             advanceRaw(lexer);
         }
-
-        lexer->loc.Line++;
-        lexer->loc.Col = 1;
     }
 
     // Look ahead one code point, dealing with complications like
@@ -224,12 +233,7 @@ namespace Slang
 
             // TODO: Need to handle non-ASCII code points.
 
-            // Default case is to advance by one location
-            // and return the raw byte we saw.
-
-            lexer->loc.Col++;
-            lexer->loc.Pos++;
-
+            // Default case is to return the raw byte we saw.
             return c;
         }
     }
@@ -323,6 +327,27 @@ namespace Slang
         }
     }
 
+    static SourceLoc getSourceLoc(Lexer* lexer)
+    {
+        return lexer->presumedStartLoc + (lexer->cursor - lexer->begin);
+    }
+
+    // Begin overriding the reported locations of tokens,
+    // based on a `#line` directives
+    void Lexer::startOverridingSourceLocations(
+        SourceLoc loc)
+    {
+        if(loc.isValid())
+        {
+            presumedStartLoc = loc;
+        }
+    }
+
+    void Lexer::stopOverridingSourceLocations()
+    {
+        presumedStartLoc = spellingStartLoc;
+    }
+
     static void lexDigits(Lexer* lexer, int base)
     {
         for(;;)
@@ -355,7 +380,7 @@ namespace Slang
             if(digitVal >= base)
             {
                 char buffer[] = { (char) c, 0 };
-                lexer->sink->diagnose(lexer->loc, Diagnostics::invalidDigitForBase, buffer, base);
+                lexer->sink->diagnose(getSourceLoc(lexer), Diagnostics::invalidDigitForBase, buffer, base);
             }
 
             advance(lexer);
@@ -695,11 +720,11 @@ namespace Slang
             switch(c)
             {
             case kEOF:
-                lexer->sink->diagnose(lexer->loc, Diagnostics::endOfFileInLiteral);
+                lexer->sink->diagnose(getSourceLoc(lexer), Diagnostics::endOfFileInLiteral);
                 return;
 
             case '\n': case '\r':
-                lexer->sink->diagnose(lexer->loc, Diagnostics::newlineInLiteral);
+                lexer->sink->diagnose(getSourceLoc(lexer), Diagnostics::newlineInLiteral);
                 return;
 
             case '\\':
@@ -952,7 +977,7 @@ namespace Slang
 
         case '0':
             {
-                auto loc = lexer->loc;
+                auto loc = getSourceLoc(lexer);
                 advance(lexer);
                 switch(peek(lexer))
                 {
@@ -1170,7 +1195,7 @@ namespace Slang
             // If none of the above cases matched, then we have an
             // unexpected/invalid character.
 
-            auto loc = lexer->loc;
+            auto loc = getSourceLoc(lexer);
             auto sink = lexer->sink;
             int c = advance(lexer);
             if(c >= 0x20 && c <=  0x7E)
@@ -1194,7 +1219,7 @@ namespace Slang
         for(;;)
         {
             Token token;
-            token.Position = loc;
+            token.Position = getSourceLoc(this);
 
             char const* textBegin = cursor;
 
@@ -1314,7 +1339,7 @@ namespace Slang
     TokenList Lexer::Parse(const String & fileName, const String & str, DiagnosticSink * sink)
     {
         TokenList tokenList;
-        tokenList.mTokens = TokenizeText(fileName, str, [&](TokenizeErrorType errType, CodePosition pos)
+        tokenList.mTokens = TokenizeText(fileName, str, [&](TokenizeErrorType errType, SourceLoc pos)
         {
             auto curChar = str[pos.Pos];
             switch (errType)
diff --git a/source/slang/lexer.h b/source/slang/lexer.h
index 71b2e85b1..9bb4d34aa 100644
--- a/source/slang/lexer.h
+++ b/source/slang/lexer.h
@@ -47,7 +47,7 @@ namespace Slang
         bool IsAtEnd() const { return mCursor == mEnd; }
         Token PeekToken() const;
         TokenType PeekTokenType() const;
-        CodePosition PeekLoc() const;
+        SourceLoc PeekLoc() const;
 
         Token AdvanceToken();
 
@@ -66,9 +66,8 @@ namespace Slang
 
     struct Lexer
     {
-        Lexer(
-            String const&   path,
-            String const&   content,
+        void initialize(
+            SourceFile*     sourceFile,
             DiagnosticSink* sink);
 
         ~Lexer();
@@ -77,13 +76,30 @@ namespace Slang
 
         TokenList lexAllTokens();
 
-        String          path;
-        String          content;
+        // Begin overriding the reported locations of tokens,
+        // based on a `#line` directives
+        void startOverridingSourceLocations(SourceLoc loc);
+
+        // Stop overriding source locations, and go back
+        // to reporting source locations in the original file
+        void stopOverridingSourceLocations();
+
+        SourceFile*     sourceFile;
         DiagnosticSink* sink;
 
         char const*     cursor;
+
+        char const*     begin;
         char const*     end;
-        CodePosition    loc;
+
+        // The starting source location for the code as written,
+        // which cannot be overridden.
+        SourceLoc       spellingStartLoc;
+
+        // The nominal starting location for the file, taking
+        // any active `#line` directive into account.
+        SourceLoc       presumedStartLoc;
+
         TokenFlags      tokenFlags;
         LexerFlags      lexerFlags;
     };
diff --git a/source/slang/lower.cpp b/source/slang/lower.cpp
index 611180415..e253abca6 100644
--- a/source/slang/lower.cpp
+++ b/source/slang/lower.cpp
@@ -318,7 +318,7 @@ class PseudoVarDecl : public RefObject
 {
 public:
     Token Name;
-    CodePosition Position;
+    SourceLoc Position;
     TypeExp type;
 };
 
@@ -339,7 +339,7 @@ public:
 class PseudoExpr : public RefObject
 {
 public:
-    CodePosition Position;
+    SourceLoc Position;
     QualType type;
 };
 
@@ -384,7 +384,7 @@ public:
     List<Element>   elements;
 };
 
-static CodePosition getPosition(LoweredExpr const& expr)
+static SourceLoc getPosition(LoweredExpr const& expr)
 {
     switch (expr.getFlavor())
     {
@@ -393,7 +393,7 @@ static CodePosition getPosition(LoweredExpr const& expr)
     case LoweredExpr::Flavor::VaryingTuple: return expr.getVaryingTupleExpr()->Position;
     default:
         SLANG_UNREACHABLE("all cases handled");
-        return CodePosition();
+        return SourceLoc();
     }
 }
 
@@ -804,7 +804,7 @@ struct LoweringVisitor
     }
 
     RefPtr<Expr> createSimpleVarRef(
-        CodePosition const& loc,
+        SourceLoc const& loc,
         VarDeclBase*        decl)
     {
         RefPtr<VarExpr> result = new VarExpr();
@@ -816,7 +816,7 @@ struct LoweringVisitor
     }
 
     LoweredExpr createVarRef(
-        CodePosition const& loc,
+        SourceLoc const& loc,
         LoweredDecl const&  decl)
     {
         switch (decl.getFlavor())
@@ -838,7 +838,7 @@ struct LoweringVisitor
 
 
     LoweredExpr createTupleRef(
-        CodePosition const&     loc,
+        SourceLoc const&     loc,
         TupleVarDecl*           decl)
     {
         RefPtr<TupleExpr> result = new TupleExpr();
@@ -868,7 +868,7 @@ struct LoweringVisitor
     }
 
     LoweredExpr createVaryingTupleRef(
-        CodePosition const&     /*loc*/,
+        SourceLoc const&     /*loc*/,
         VaryingTupleVarDecl*    decl)
     {
         return decl->expr;
diff --git a/source/slang/options.cpp b/source/slang/options.cpp
index 49f33f58d..a360695f2 100644
--- a/source/slang/options.cpp
+++ b/source/slang/options.cpp
@@ -596,7 +596,7 @@ struct OptionsParser
             else if (rawOutputPaths.Count() > rawEntryPoints.Count())
             {
                 requestImpl->mSink.diagnose(
-                    CodePosition(),
+                    SourceLoc(),
                     Diagnostics::tooManyOutputPathsSpecified,
                     rawOutputPaths.Count(),
                     rawEntryPoints.Count());
@@ -611,7 +611,7 @@ struct OptionsParser
                     if (entryPoint.outputPathIndex < 0)
                     {
                         requestImpl->mSink.diagnose(
-                            CodePosition(),
+                            SourceLoc(),
                             Diagnostics::noOutputPathSpecifiedForEntryPoint,
                             entryPoint.name);
 
@@ -639,7 +639,7 @@ struct OptionsParser
                             // This file didn't imply a target, and that
                             // needs to be an error:
                             requestImpl->mSink.diagnose(
-                                CodePosition(),
+                                SourceLoc(),
                                 Diagnostics::cannotDeduceOutputFormatFromPath,
                                 rawOutputPath.path);
 
@@ -669,7 +669,7 @@ struct OptionsParser
                                 // This file didn't imply a target, and that
                                 // needs to be an error:
                                 requestImpl->mSink.diagnose(
-                                    CodePosition(),
+                                    SourceLoc(),
                                     Diagnostics::outputPathsImplyDifferentFormats,
                                     rawOutputPaths[0].path,
                                     rawOutputPath.path);
diff --git a/source/slang/parser.cpp b/source/slang/parser.cpp
index 41a4411d2..cc6a0dd6f 100644
--- a/source/slang/parser.cpp
+++ b/source/slang/parser.cpp
@@ -41,7 +41,6 @@ namespace Slang
 
         TokenReader tokenReader;
         DiagnosticSink * sink;
-        String fileName;
         int genericDepth = 0;
 
         // Have we seen any `import` declarations? If so, we need
@@ -73,11 +72,9 @@ namespace Slang
         Parser(
             TokenSpan const& _tokens,
             DiagnosticSink * sink,
-            String _fileName,
             RefPtr<Scope> const& outerScope)
             : tokenReader(_tokens)
             , sink(sink)
-            , fileName(_fileName)
             , outerScope(outerScope)
         {}
 
@@ -614,7 +611,7 @@ namespace Slang
         RefPtr<Modifier>* modifierLink = &modifiers.first;
         for (;;)
         {
-            CodePosition loc = parser->tokenReader.PeekLoc();
+            SourceLoc loc = parser->tokenReader.PeekLoc();
 
             if (0) {}
 
@@ -1003,7 +1000,7 @@ namespace Slang
     struct PointerDeclarator : Declarator
     {
         // location of the `*` token
-        CodePosition starLoc;
+        SourceLoc starLoc;
 
         RefPtr<Declarator>				inner;
     };
@@ -1014,7 +1011,7 @@ namespace Slang
         RefPtr<Declarator>				inner;
 
         // location of the `[` token
-        CodePosition openBracketLoc;
+        SourceLoc openBracketLoc;
 
         // The expression that yields the element count, or NULL
         RefPtr<Expr>	elementCountExpr;
@@ -1377,7 +1374,7 @@ namespace Slang
     // Either a single declaration, or a group of them
     struct DeclGroupBuilder
     {
-        CodePosition        startPosition;
+        SourceLoc        startPosition;
         RefPtr<Decl>        decl;
         RefPtr<DeclGroup>   group;
 
@@ -1546,7 +1543,7 @@ namespace Slang
         Parser*         parser,
         ContainerDecl*  containerDecl)
     {
-        CodePosition startPosition = parser->tokenReader.PeekLoc();
+        SourceLoc startPosition = parser->tokenReader.PeekLoc();
 
         auto typeSpec = parseTypeSpec(parser);
 
@@ -1780,7 +1777,7 @@ namespace Slang
         // We first look at the declaration keywrod to determine
         // the type of buffer to declare:
         String bufferWrapperTypeName;
-        CodePosition bufferWrapperTypeNamePos = parser->tokenReader.PeekLoc();
+        SourceLoc bufferWrapperTypeNamePos = parser->tokenReader.PeekLoc();
         if (AdvanceIf(parser, "cbuffer"))
         {
             bufferWrapperTypeName = "ConstantBuffer";
@@ -1914,7 +1911,7 @@ namespace Slang
         // will see through it to the members inside.
 
 
-        CodePosition pos = parser->tokenReader.PeekLoc();
+        SourceLoc pos = parser->tokenReader.PeekLoc();
 
         // The initial name before the `{` is only supposed
         // to be made visible to reflection
@@ -2446,7 +2443,7 @@ namespace Slang
         }
 
         PushScope(program);
-        program->Position = CodePosition(0, 0, 0, fileName);
+        program->Position = tokenReader.PeekLoc();
         ParseDeclBody(this, program, TokenType::EndOfFile);
         PopScope();
 
@@ -3853,10 +3850,9 @@ namespace Slang
         TranslationUnitRequest*         translationUnit,
         TokenSpan const&                tokens,
         DiagnosticSink*                 sink,
-        String const&                   fileName,
         RefPtr<Scope> const&            outerScope)
     {
-        Parser parser(tokens, sink, fileName, outerScope);
+        Parser parser(tokens, sink, outerScope);
 
         parser.translationUnit = translationUnit;
 
diff --git a/source/slang/parser.h b/source/slang/parser.h
index 8dfef4c12..41a82602a 100644
--- a/source/slang/parser.h
+++ b/source/slang/parser.h
@@ -12,7 +12,6 @@ namespace Slang
         TranslationUnitRequest*         translationUnit,
         TokenSpan const&                tokens,
         DiagnosticSink*                 sink,
-        String const&                   fileName,
         RefPtr<Scope> const&            outerScope);
 ;
 }
diff --git a/source/slang/preprocessor.cpp b/source/slang/preprocessor.cpp
index 53f0c4774..9c9a340ae 100644
--- a/source/slang/preprocessor.cpp
+++ b/source/slang/preprocessor.cpp
@@ -60,45 +60,61 @@ struct PreprocessorEnvironment
 // In general, input streams can be nested, so we have to keep a conceptual
 // stack of input.
 
+struct PrimaryInputStream;
+
 // A stream of input tokens to be consumed
 struct PreprocessorInputStream
 {
+    // The primary input stream that is the parent to this one,
+    // or NULL if this stream is itself a primary stream.
+    PrimaryInputStream*             primaryStream;
+
     // The next input stream up the stack, if any.
     PreprocessorInputStream*        parent;
 
-    // The deepest preprocessor conditional active for this stream.
-    PreprocessorConditional*        conditional;
-
     // Environment to use when looking up macros
     PreprocessorEnvironment*        environment;
 
-    // Reader for pre-tokenized input
-    TokenReader                     tokenReader;
+    // Destructor is virtual so that we can clean up
+    // after concrete subtypes.
+    virtual ~PreprocessorInputStream() = default;
+};
 
-    // If we are clobbering source locations with `#line`, then
-    // the state is tracked here:
+// A "primary" input stream represents the top-level context of a file
+// being parsed, and tracks things like preprocessor conditional state
+struct PrimaryInputStream : PreprocessorInputStream
+{
+    // The next *primary* input stream up the stack
+    PrimaryInputStream*             parentPrimaryInputStream;
 
-    // Are we overriding source locations?
-    bool                            isOverridingSourceLoc;
+    // The deepest preprocessor conditional active for this stream.
+    PreprocessorConditional*        conditional;
 
-    // What is the file name we are overriding to?
-    String                          overrideFileName;
+    // The lexer state that will provide input
+    Lexer lexer;
 
-    // What is the relative offset to apply to any line numbers?
-    int                             overrideLineOffset;
+    // One token of lookahead
+    Token token;
+};
 
-    // Destructor is virtual so that we can clean up
-    // after concrete subtypes.
-    virtual ~PreprocessorInputStream() = default;
+// A "secondary" input stream represents code that is being expanded
+// into the current scope, but which had already been tokenized before.
+//
+struct PretokenizedInputStream : PreprocessorInputStream
+{
+    // Reader for pre-tokenized input
+    TokenReader                     tokenReader;
 };
 
-struct SourceTextInputStream : PreprocessorInputStream
+// A pre-tokenized input stream that will only be used once, and which
+// therefore owns the memory for its tokens.
+struct SimpleTokenInputStream : PretokenizedInputStream
 {
-    // The pre-tokenized input
-    TokenList           lexedTokens;
+    // A list of raw tokens that will provide input
+    TokenList lexedTokens;
 };
 
-struct MacroExpansion : PreprocessorInputStream
+struct MacroExpansion : PretokenizedInputStream
 {
     // The macro we will expand
     PreprocessorMacro*  macro;
@@ -204,39 +220,55 @@ static void DestroyMacro(Preprocessor* preprocessor, PreprocessorMacro* macro);
 //
 
 // Create a fresh input stream
-static void  InitializeInputStream(Preprocessor* preprocessor, PreprocessorInputStream* inputStream)
+static void  initializeInputStream(Preprocessor* preprocessor, PreprocessorInputStream* inputStream)
 {
     inputStream->parent = NULL;
-    inputStream->conditional = NULL;
     inputStream->environment = &preprocessor->globalEnv;
 }
 
+static void initializePrimaryInputStream(Preprocessor* preprocessor, PrimaryInputStream* inputStream)
+{
+    initializeInputStream(preprocessor, inputStream);
+    inputStream->primaryStream = inputStream;
+    inputStream->conditional = NULL;
+}
+
 // Destroy an input stream
-static void DestroyInputStream(Preprocessor* /*preprocessor*/, PreprocessorInputStream* inputStream)
+static void destroyInputStream(Preprocessor* /*preprocessor*/, PreprocessorInputStream* inputStream)
 {
     delete inputStream;
 }
 
 // Create an input stream to represent a pre-tokenized input file.
 // TODO(tfoley): pre-tokenizing files isn't going to work in the long run.
-static PreprocessorInputStream* CreateInputStreamForSource(Preprocessor* preprocessor, String const& source, String const& fileName)
+static PreprocessorInputStream* CreateInputStreamForSource(
+    Preprocessor*   preprocessor,
+    SourceFile*     sourceFile)
 {
-    SourceTextInputStream* inputStream = new SourceTextInputStream();
-    InitializeInputStream(preprocessor, inputStream);
+    PrimaryInputStream* inputStream = new PrimaryInputStream();
+    initializePrimaryInputStream(preprocessor, inputStream);
 
-    // Use existing `Lexer` to generate a token stream.
-    Lexer lexer(fileName, source, GetSink(preprocessor));
-    inputStream->lexedTokens = lexer.lexAllTokens();
-    inputStream->tokenReader = TokenReader(inputStream->lexedTokens);
+    // initialize the embedded lexer so that it can generate a token stream
+    inputStream->lexer.initialize(sourceFile, GetSink(preprocessor));
+    inputStream->token = inputStream->lexer.lexToken();
 
     return inputStream;
 }
 
+static PrimaryInputStream* asPrimaryInputStream(PreprocessorInputStream* inputStream)
+{
+    auto primaryStream = inputStream->primaryStream;
+    if(primaryStream == inputStream)
+        return primaryStream;
+    return nullptr;
+}
 
 
 static void PushInputStream(Preprocessor* preprocessor, PreprocessorInputStream* inputStream)
 {
     inputStream->parent = preprocessor->inputStream;
+    if(!asPrimaryInputStream(inputStream))
+        inputStream->primaryStream = preprocessor->inputStream->primaryStream;
     preprocessor->inputStream = inputStream;
 }
 
@@ -244,52 +276,69 @@ static void PushInputStream(Preprocessor* preprocessor, PreprocessorInputStream*
 // Performs some validation and then destroys the input stream if required.
 static void EndInputStream(Preprocessor* preprocessor, PreprocessorInputStream* inputStream)
 {
-    // If there are any conditionals that weren't completed, then it is an error
-    if (inputStream->conditional)
+    if(auto primaryStream = asPrimaryInputStream(inputStream))
     {
-        PreprocessorConditional* conditional = inputStream->conditional;
+        // If there are any conditionals that weren't completed, then it is an error
+        if (primaryStream->conditional)
+        {
+            PreprocessorConditional* conditional = primaryStream->conditional;
 
-        GetSink(preprocessor)->diagnose(conditional->ifToken.Position, Diagnostics::endOfFileInPreprocessorConditional);
+            GetSink(preprocessor)->diagnose(conditional->ifToken.Position, Diagnostics::endOfFileInPreprocessorConditional);
 
-        while (conditional)
-        {
-            PreprocessorConditional* parent = conditional->parent;
-            DestroyConditional(conditional);
-            conditional = parent;
+            while (conditional)
+            {
+                PreprocessorConditional* parent = conditional->parent;
+                DestroyConditional(conditional);
+                conditional = parent;
+            }
         }
     }
 
-    DestroyInputStream(preprocessor, inputStream);
-}
-
-// Potentially clobber source location information based on `#line`
-static Token PossiblyOverrideSourceLoc(PreprocessorInputStream* inputStream, Token const& token)
-{
-    Token result = token;
-    if( inputStream->isOverridingSourceLoc )
-    {
-        result.Position.FileName = inputStream->overrideFileName;
-        result.Position.Line += inputStream->overrideLineOffset;
-    }
-    return result;
+    destroyInputStream(preprocessor, inputStream);
 }
 
 // Consume one token from an input stream
 static Token AdvanceRawToken(PreprocessorInputStream* inputStream)
 {
-    return PossiblyOverrideSourceLoc(inputStream, inputStream->tokenReader.AdvanceToken());
+    if( auto primaryStream = asPrimaryInputStream(inputStream) )
+    {
+        auto result = primaryStream->token;
+        primaryStream->token = primaryStream->lexer.lexToken();
+        return result;
+    }
+    else
+    {
+        PretokenizedInputStream* pretokenized = (PretokenizedInputStream*) inputStream;
+        return pretokenized->tokenReader.AdvanceToken();
+    }
 }
 
 // Peek one token from an input stream
 static Token PeekRawToken(PreprocessorInputStream* inputStream)
 {
-    return PossiblyOverrideSourceLoc(inputStream, inputStream->tokenReader.PeekToken());
+    if( auto primaryStream = asPrimaryInputStream(inputStream) )
+    {
+        return primaryStream->token;
+    }
+    else
+    {
+        PretokenizedInputStream* pretokenized = (PretokenizedInputStream*) inputStream;
+        return pretokenized->tokenReader.PeekToken();
+    }
 }
 
 // Peek one token type from an input stream
 static TokenType PeekRawTokenType(PreprocessorInputStream* inputStream)
 {
-    return inputStream->tokenReader.PeekTokenType();
+    if( auto primaryStream = asPrimaryInputStream(inputStream) )
+    {
+        return primaryStream->token.type;
+    }
+    else
+    {
+        PretokenizedInputStream* pretokenized = (PretokenizedInputStream*) inputStream;
+        return pretokenized->tokenReader.PeekTokenType();
+    }
 }
 
 
@@ -355,55 +404,8 @@ static Token PeekRawToken(Preprocessor* preprocessor)
     }
 }
 
-// Without advancing preprocessor state, look *two* raw tokens ahead
-// (This is only needed in order to determine when we are possibly
-// expanding a function-style macro)
-TokenType PeekSecondRawTokenType(Preprocessor* preprocessor)
-{
-    // We need to find the strema that `advanceRawToken` would read from.
-    PreprocessorInputStream* inputStream = preprocessor->inputStream;
-    int count = 1;
-    for (;;)
-    {
-        if (!inputStream)
-        {
-            // No more input streams left to read
-            return TokenType::EndOfFile;
-        }
-
-        // The top-most input stream may be at its end, so
-        // look one entry up the stack (don't actually pop
-        // here, since we are just peeking)
-
-        TokenReader reader = inputStream->tokenReader;
-        if (reader.PeekTokenType() == TokenType::EndOfFile)
-        {
-            inputStream = inputStream->parent;
-            continue;
-        }
-
-        if (count)
-        {
-            count--;
-
-            // Note: we are advancing our temporary
-            // copy of the token reader
-            reader.AdvanceToken();
-            if (reader.PeekTokenType() == TokenType::EndOfFile)
-            {
-                inputStream = inputStream->parent;
-                continue;
-            }
-        }
-
-        // Everything worked, so peek a token from the top-most stream
-        return reader.PeekTokenType();
-    }
-}
-
-
 // Get the location of the current (raw) token
-static CodePosition PeekLoc(Preprocessor* preprocessor)
+static SourceLoc PeekLoc(Preprocessor* preprocessor)
 {
     return PeekRawToken(preprocessor).Position;
 }
@@ -471,7 +473,7 @@ static PreprocessorEnvironment* GetCurrentEnvironment(Preprocessor* preprocessor
 
         // If the current input stream is at its end, then
         // fall back to its parent stream.
-        if (inputStream->tokenReader.PeekTokenType() == TokenType::EndOfFile)
+        if (PeekRawTokenType(inputStream) == TokenType::EndOfFile)
         {
             inputStream = inputStream->parent;
             continue;
@@ -528,7 +530,11 @@ static void InitializeMacroExpansion(
     MacroExpansion*     expansion,
     PreprocessorMacro*  macro)
 {
-    InitializeInputStream(preprocessor, expansion);
+    initializeInputStream(preprocessor, expansion);
+
+    expansion->parent = preprocessor->inputStream;
+    expansion->primaryStream = preprocessor->inputStream->primaryStream;
+
     expansion->environment = macro->environment;
     expansion->macro = macro;
     expansion->tokenReader = TokenReader(macro->tokens);
@@ -550,6 +556,26 @@ static void AddEndOfStreamToken(
     macro->tokens.mTokens.Add(token);
 }
 
+static SimpleTokenInputStream* createSimpleInputStream(
+    Preprocessor*   preprocessor,
+    Token const&    token)
+{
+    SimpleTokenInputStream* inputStream = new SimpleTokenInputStream();
+    initializeInputStream(preprocessor, inputStream);
+
+    inputStream->lexedTokens.mTokens.Add(token);
+
+    Token eofToken;
+    eofToken.type = TokenType::EndOfFile;
+    eofToken.Position = token.Position;
+    eofToken.flags = TokenFlag::AfterWhitespace | TokenFlag::AtStartOfLine;
+    inputStream->lexedTokens.mTokens.Add(eofToken);
+ 
+    inputStream->tokenReader = TokenReader(inputStream->lexedTokens);
+
+    return inputStream;
+}
+
 // Check whether the current token on the given input stream should be
 // treated as a macro invocation, and if so set up state for expanding
 // that macro.
@@ -561,7 +587,7 @@ static void MaybeBeginMacroExpansion(
     for (;;)
     {
         // Look at the next token ahead of us
-        Token const& token = PeekRawToken(preprocessor);
+        Token token = PeekRawToken(preprocessor);
 
         // Not an identifier? Can't be a macro.
         if (token.type != TokenType::Identifier)
@@ -585,12 +611,29 @@ static void MaybeBeginMacroExpansion(
         // requires more lookahead than we usually have/need
         if (macro->flavor == PreprocessorMacroFlavor::FunctionLike)
         {
-            if(PeekSecondRawTokenType(preprocessor) != TokenType::LParent)
-                return;
-
-            // Consume the token that triggered macro expansion
+            // Consume the token that (possibly) triggered macro expansion
             AdvanceRawToken(preprocessor);
 
+            // Look at the next token, and see if it is an opening `(`
+            // that indicates we should actually expand a macro.
+            if(PeekRawTokenType(preprocessor) != TokenType::LParent)
+            {
+                // In this case, we are in a bit of a mess, because we have
+                // consumed the token that named the macro, but we need to
+                // make sure that token (and not whatever came after it)
+                // gets returned to the user.
+                //
+                // To work around this we will construct a short-lived input
+                // stream just to handle that one token, and also set
+                // a flag on the token to keep us from doing this logic again.
+
+                token.flags |= TokenFlag::SuppressMacroExpansion;
+
+                SimpleTokenInputStream* simpleStream = createSimpleInputStream(preprocessor, token);
+                PushInputStream(preprocessor, simpleStream);
+                return;
+            }
+
             // Consume the opening `(`
             Token leftParen = AdvanceRawToken(preprocessor);
 
@@ -762,8 +805,22 @@ top:
         }
 
         // Now re-lex the input
-        PreprocessorInputStream* inputStream = CreateInputStreamForSource(preprocessor, sb.ProduceString(), "token paste");
-        if (inputStream->tokenReader.GetCount() != 1)
+
+        // We create a dummy file to represent the token-paste operation
+        SourceFile* sourceFile = preprocessor->getCompileRequest()->getSourceManager()->allocateSourceFile("token paste", sb.ProduceString());
+
+        Lexer lexer;
+        lexer.initialize(sourceFile, GetSink(preprocessor));
+
+        SimpleTokenInputStream* inputStream = new SimpleTokenInputStream();
+        initializeInputStream(preprocessor, inputStream);
+
+        inputStream->lexedTokens = lexer.lexAllTokens();
+        inputStream->tokenReader = TokenReader(inputStream->lexedTokens);
+
+        // We expect the reuslt of lexing to be two tokens: one for the actual value,
+        // and one for the end-of-input marker.
+        if (inputStream->tokenReader.GetCount() != 2)
         {
             // We expect a token paste to produce a single token
             // TODO(tfoley): emit a diagnostic here
@@ -839,7 +896,7 @@ inline String const& GetDirectiveName(PreprocessorDirectiveContext* context)
 }
 
 // Get the location of the directive being parsed.
-inline CodePosition const& GetDirectiveLoc(PreprocessorDirectiveContext* context)
+inline SourceLoc const& GetDirectiveLoc(PreprocessorDirectiveContext* context)
 {
     return context->directiveToken.Position;
 }
@@ -851,7 +908,7 @@ static inline DiagnosticSink* GetSink(PreprocessorDirectiveContext* context)
 }
 
 // Wrapper to get a "current" location when parsing a directive
-static CodePosition PeekLoc(PreprocessorDirectiveContext* context)
+static SourceLoc PeekLoc(PreprocessorDirectiveContext* context)
 {
     return PeekLoc(context->preprocessor);
 }
@@ -970,8 +1027,11 @@ static bool IsSkipping(Preprocessor* preprocessor)
     PreprocessorInputStream* inputStream = preprocessor->inputStream;
     if (!inputStream) return false;
 
+    PrimaryInputStream* primaryStream = inputStream->primaryStream;
+    if(!primaryStream) return false;
+
     // If we are not inside a preprocessor conditional, then don't skip
-    PreprocessorConditional* conditional = inputStream->conditional;
+    PreprocessorConditional* conditional = primaryStream->conditional;
     if (!conditional) return false;
 
     // skip tokens unless the conditional is inside its `true` case
@@ -1032,8 +1092,9 @@ static void beginConditional(
     conditional->state = state;
 
     // Push conditional onto the stack
-    conditional->parent = inputStream->conditional;
-    inputStream->conditional = conditional;
+    auto primaryStream = inputStream->primaryStream;
+    conditional->parent = primaryStream->conditional;
+    primaryStream->conditional = conditional;
 }
 
 // Start a preprocessor conditional, with an initial enable/disable state.
@@ -1348,7 +1409,7 @@ static void HandleElseDirective(PreprocessorDirectiveContext* context)
     SLANG_ASSERT(inputStream);
 
     // if we aren't inside a conditional, then error
-    PreprocessorConditional* conditional = inputStream->conditional;
+    PreprocessorConditional* conditional = inputStream->primaryStream->conditional;
     if (!conditional)
     {
         GetSink(context)->diagnose(GetDirectiveLoc(context), Diagnostics::directiveWithoutIf, GetDirectiveName(context));
@@ -1402,7 +1463,7 @@ static void HandleElifDirective(PreprocessorDirectiveContext* context)
     PreprocessorExpressionValue value = ParseAndEvaluateExpression(context);
 
     // if we aren't inside a conditional, then error
-    PreprocessorConditional* conditional = inputStream->conditional;
+    PreprocessorConditional* conditional = inputStream->primaryStream->conditional;
     if (!conditional)
     {
         GetSink(context)->diagnose(GetDirectiveLoc(context), Diagnostics::directiveWithoutIf, GetDirectiveName(context));
@@ -1440,14 +1501,14 @@ static void HandleEndIfDirective(PreprocessorDirectiveContext* context)
     SLANG_ASSERT(inputStream);
 
     // if we aren't inside a conditional, then error
-    PreprocessorConditional* conditional = inputStream->conditional;
+    PreprocessorConditional* conditional = inputStream->primaryStream->conditional;
     if (!conditional)
     {
         GetSink(context)->diagnose(GetDirectiveLoc(context), Diagnostics::directiveWithoutIf, GetDirectiveName(context));
         return;
     }
 
-    inputStream->conditional = conditional->parent;
+    inputStream->primaryStream->conditional = conditional->parent;
     DestroyConditional(conditional);
 }
 
@@ -1492,8 +1553,9 @@ static void HandleIncludeDirective(PreprocessorDirectiveContext* context)
 
     String path = getFileNameTokenValue(pathToken);
 
-    // TODO(tfoley): make this robust in presence of `#line`
-    String pathIncludedFrom = GetDirectiveLoc(context).FileName;
+    auto directiveLoc = GetDirectiveLoc(context);
+    auto expandedDirectiveLoc = context->preprocessor->translationUnit->compileRequest->getSourceManager()->expandSourceLoc(directiveLoc);
+    String pathIncludedFrom = expandedDirectiveLoc.getSpellingPath();
     String foundPath;
     String foundSource;
 
@@ -1524,7 +1586,10 @@ static void HandleIncludeDirective(PreprocessorDirectiveContext* context)
 
     // Push the new file onto our stack of input streams
     // TODO(tfoley): check if we have made our include stack too deep
-    PreprocessorInputStream* inputStream = CreateInputStreamForSource(context->preprocessor, foundSource, foundPath);
+
+    SourceFile* sourceFile = context->preprocessor->getCompileRequest()->getSourceManager()->allocateSourceFile(foundPath, foundSource);
+
+    PreprocessorInputStream* inputStream = CreateInputStreamForSource(context->preprocessor, sourceFile);
     inputStream->parent = context->preprocessor->inputStream;
     context->preprocessor->inputStream = inputStream;
 }
@@ -1654,18 +1719,26 @@ static void HandleErrorDirective(PreprocessorDirectiveContext* context)
 // Handle a `#line` directive
 static void HandleLineDirective(PreprocessorDirectiveContext* context)
 {
+    auto inputStream = context->preprocessor->inputStream;
+
     int line = 0;
+
+    // `#line <integer-literal> ...`
     if (PeekTokenType(context) == TokenType::IntegerLiteral)
     {
         line = StringToInt(AdvanceToken(context).Content);
     }
-    else if (PeekTokenType(context) == TokenType::Identifier
-        && PeekToken(context).Content == "default")
+    // `#line`
+    // `#line default`
+    else if (
+        PeekTokenType(context) == TokenType::EndOfDirective
+        || (PeekTokenType(context) == TokenType::Identifier
+            && PeekToken(context).Content == "default"))
     {
         AdvanceToken(context);
 
         // Stop overiding soure locations.
-        context->preprocessor->inputStream->isOverridingSourceLoc = false;
+        inputStream->primaryStream->lexer.stopOverridingSourceLocations();
         return;
     }
     else
@@ -1678,16 +1751,19 @@ static void HandleLineDirective(PreprocessorDirectiveContext* context)
         return;
     }
 
-    CodePosition directiveLoc = GetDirectiveLoc(context);
+    SourceLoc directiveLoc = GetDirectiveLoc(context);
+
+    auto sourceManager = context->preprocessor->translationUnit->compileRequest->getSourceManager();
+    auto expandedDirectiveLoc = sourceManager->expandSourceLoc(directiveLoc);
 
     String file;
     if (PeekTokenType(context) == TokenType::EndOfDirective)
     {
-        file = directiveLoc.FileName;
+        file = expandedDirectiveLoc.getPath();
     }
     else if (PeekTokenType(context) == TokenType::StringLiteral)
     {
-        file = AdvanceToken(context).Content;
+        file = getStringLiteralTokenValue(AdvanceToken(context));
     }
     else if (PeekTokenType(context) == TokenType::IntegerLiteral)
     {
@@ -1701,11 +1777,9 @@ static void HandleLineDirective(PreprocessorDirectiveContext* context)
         return;
     }
 
-    PreprocessorInputStream* inputStream = context->preprocessor->inputStream;
+    SourceLoc newLoc = sourceManager->allocateSourceFileForLineDirective(expandedDirectiveLoc, file, line);
 
-    inputStream->isOverridingSourceLoc = true;
-    inputStream->overrideFileName = file;
-    inputStream->overrideLineOffset = line - (directiveLoc.Line + 1);
+    inputStream->primaryStream->lexer.startOverridingSourceLocations(newLoc);
 }
 
 // Handle a `#pragma` directive
@@ -2005,10 +2079,14 @@ static void DefineMacro(
     String fileName = "command line";
     PreprocessorMacro* macro = CreateMacro(preprocessor);
 
+    SourceFile* keyFile = preprocessor->translationUnit->compileRequest->getSourceManager()->allocateSourceFile(fileName, key);
+    SourceFile* valueFile = preprocessor->translationUnit->compileRequest->getSourceManager()->allocateSourceFile(fileName, value);
+
     // Use existing `Lexer` to generate a token stream.
-    Lexer lexer(fileName, value, GetSink(preprocessor));
+    Lexer lexer;
+    lexer.initialize(valueFile, GetSink(preprocessor));
     macro->tokens = lexer.lexAllTokens();
-    macro->nameToken = Token(TokenType::Identifier, key, 0, 0, 0, fileName);
+    macro->nameToken = Token(TokenType::Identifier, key, keyFile->sourceRange.begin);
 
     PreprocessorMacro* oldMacro = NULL;
     if (preprocessor->globalEnv.macros.TryGetValue(key, oldMacro))
@@ -2039,8 +2117,7 @@ static TokenList ReadAllTokens(
 }
 
 TokenList preprocessSource(
-    String const&               source,
-    String const&               fileName,
+    SourceFile*                 file,
     DiagnosticSink*             sink,
     IncludeHandler*             includeHandler,
     Dictionary<String, String>  defines,
@@ -2057,7 +2134,7 @@ TokenList preprocessSource(
     }
 
     // create an initial input stream based on the provided buffer
-    preprocessor.inputStream = CreateInputStreamForSource(&preprocessor, source, fileName);
+    preprocessor.inputStream = CreateInputStreamForSource(&preprocessor, file);
 
     TokenList tokens = ReadAllTokens(&preprocessor);
 
@@ -2097,8 +2174,9 @@ static void HandleImportDirective(PreprocessorDirectiveContext* context)
 
     String path = getFileNameTokenValue(pathToken);
 
-    // TODO(tfoley): make this robust in presence of `#line`
-    String pathIncludedFrom = GetDirectiveLoc(context).FileName;
+    auto directiveLoc = GetDirectiveLoc(context);
+    auto expandedDirectiveLoc = context->preprocessor->translationUnit->compileRequest->getSourceManager()->expandSourceLoc(directiveLoc);
+    String pathIncludedFrom = expandedDirectiveLoc.getSpellingPath();
     String foundPath;
     String foundSource;
 
@@ -2162,7 +2240,8 @@ static void HandleImportDirective(PreprocessorDirectiveContext* context)
             PreprocessorInputStream* savedStream = preprocessor->inputStream;
 
             // Create an input stream for reading from the imported file
-            PreprocessorInputStream* subInputStream = CreateInputStreamForSource(preprocessor, foundSource, foundPath);
+            SourceFile* sourceFile = context->preprocessor->getCompileRequest()->getSourceManager()->allocateSourceFile(foundPath, foundSource);
+            PreprocessorInputStream* subInputStream = CreateInputStreamForSource(preprocessor, sourceFile);
 
             // Now preprocess that stream
             preprocessor->inputStream = subInputStream;
@@ -2180,24 +2259,18 @@ static void HandleImportDirective(PreprocessorDirectiveContext* context)
  
     // Now create a dummy token stream to represent the import request,
     // so that it can be manifest in the user's program
-    SourceTextInputStream* inputStream = new SourceTextInputStream();
- 
+
     Token token;
     token.type = TokenType::PoundImport;
     token.Position = GetDirectiveLoc(context);
     token.flags = 0;
     token.Content = foundPath;
- 
-    inputStream->lexedTokens.mTokens.Add(token);
- 
-    token.type = TokenType::EndOfFile;
-    token.flags = TokenFlag::AfterWhitespace | TokenFlag::AtStartOfLine;
-    inputStream->lexedTokens.mTokens.Add(token);
- 
-    inputStream->tokenReader = TokenReader(inputStream->lexedTokens);
- 
-    inputStream->parent = context->preprocessor->inputStream;
-    context->preprocessor->inputStream = inputStream;
+
+    SimpleTokenInputStream* inputStream = createSimpleInputStream(
+        context->preprocessor,
+        token);
+
+    PushInputStream(context->preprocessor, inputStream);
 }
 
 
diff --git a/source/slang/preprocessor.h b/source/slang/preprocessor.h
index 008707ffb..64591ef03 100644
--- a/source/slang/preprocessor.h
+++ b/source/slang/preprocessor.h
@@ -31,8 +31,7 @@ struct IncludeHandler
 
 // Take a string of source code and preprocess it into a list of tokens.
 TokenList preprocessSource(
-    String const&               source,
-    String const&               fileName,
+    SourceFile*                 file,
     DiagnosticSink*             sink,
     IncludeHandler*             includeHandler,
     Dictionary<String, String>  defines,
diff --git a/source/slang/slang.cpp b/source/slang/slang.cpp
index 0dcbf44ea..e66884923 100644
--- a/source/slang/slang.cpp
+++ b/source/slang/slang.cpp
@@ -20,6 +20,9 @@ namespace Slang {
 
 Session::Session()
 {
+    // Make sure our source manager is initialized
+    builtinSourceManager.initialize(nullptr);
+
     // Initialize representations of some very basic types:
     initializeTypes();
 
@@ -82,6 +85,16 @@ struct IncludeHandlerImpl : IncludeHandler
     }
 };
 
+CompileRequest::CompileRequest(Session* session)
+    : mSession(session)
+{
+    setSourceManager(&sourceManagerStorage);
+
+    sourceManager->initialize(session->getBuiltinSourceManager());
+}
+
+CompileRequest::~CompileRequest()
+{}
 
 void CompileRequest::parseTranslationUnit(
     TranslationUnitRequest* translationUnit)
@@ -117,12 +130,8 @@ void CompileRequest::parseTranslationUnit(
 
     for (auto sourceFile : translationUnit->sourceFiles)
     {
-        auto sourceFilePath = sourceFile->path;
-        String source = sourceFile->content;
-
         auto tokens = preprocessSource(
-            source,
-            sourceFilePath,
+            sourceFile,
             &mSink,
             &includeHandler,
             combinedPreprocessorDefinitions,
@@ -132,7 +141,6 @@ void CompileRequest::parseTranslationUnit(
             translationUnit,
             tokens,
             &mSink,
-            sourceFilePath,
             languageScope);
     }
 }
@@ -297,16 +305,21 @@ int CompileRequest::addTranslationUnit(SourceLanguage language, String const&)
     return (int) result;
 }
 
+void CompileRequest::addTranslationUnitSourceFile(
+    int             translationUnitIndex,
+    SourceFile*     sourceFile)
+{
+    translationUnits[translationUnitIndex]->sourceFiles.Add(sourceFile);
+}
+
 void CompileRequest::addTranslationUnitSourceString(
     int             translationUnitIndex,
     String const&   path,
     String const&   source)
 {
-    RefPtr<SourceFile> sourceFile = new SourceFile();
-    sourceFile->path = path;
-    sourceFile->content = source;
+    RefPtr<SourceFile> sourceFile = getSourceManager()->allocateSourceFile(path, source);
 
-    translationUnits[translationUnitIndex]->sourceFiles.Add(sourceFile);
+    addTranslationUnitSourceFile(translationUnitIndex, sourceFile);
 }
 
 void CompileRequest::addTranslationUnitSourceFile(
@@ -322,7 +335,7 @@ void CompileRequest::addTranslationUnitSourceFile(
     {
         // Emit a diagnostic!
         mSink.diagnose(
-            CodePosition(0, 0, 0, path),
+            SourceLoc(),
             Diagnostics::cannotOpenFile,
             path);
         return;
@@ -359,7 +372,7 @@ RefPtr<ModuleDecl> CompileRequest::loadModule(
     String const&       name,
     String const&       path,
     String const&       source,
-    CodePosition const&)
+    SourceLoc const&)
 {
     RefPtr<TranslationUnitRequest> translationUnit = new TranslationUnitRequest();
     translationUnit->compileRequest = this;
@@ -370,9 +383,7 @@ RefPtr<ModuleDecl> CompileRequest::loadModule(
     //
     // TODO: decide which options, if any, should be inherited.
 
-    RefPtr<SourceFile> sourceFile = new SourceFile();
-    sourceFile->path = path;
-    sourceFile->content = source;
+    RefPtr<SourceFile> sourceFile = getSourceManager()->allocateSourceFile(path, source);
 
     translationUnit->sourceFiles.Add(sourceFile);
 
@@ -413,7 +424,6 @@ void CompileRequest::handlePoundImport(
         translationUnit.Ptr(),
         tokens,
         &mSink,
-        path,
         languageScope);
 
     // TODO: handle errors
@@ -438,7 +448,7 @@ void CompileRequest::handlePoundImport(
 
 RefPtr<ModuleDecl> CompileRequest::findOrImportModule(
     String const&       name,
-    CodePosition const& loc)
+    SourceLoc const& loc)
 {
     // Have we already loaded a module matching this name?
     // If so, return it.
@@ -470,7 +480,9 @@ RefPtr<ModuleDecl> CompileRequest::findOrImportModule(
     IncludeHandlerImpl includeHandler;
     includeHandler.request = this;
 
-    String pathIncludedFrom = loc.FileName;
+    auto expandedLoc = getSourceManager()->expandSourceLoc(loc);
+
+    String pathIncludedFrom = expandedLoc.getSpellingPath();
 
     String foundPath;
     String foundSource;
@@ -508,7 +520,7 @@ RefPtr<ModuleDecl> CompileRequest::findOrImportModule(
 RefPtr<ModuleDecl> findOrImportModule(
     CompileRequest*     request,
     String const&       name,
-    CodePosition const& loc)
+    SourceLoc const& loc)
 {
     return request->findOrImportModule(name, loc);
 }
@@ -519,9 +531,12 @@ void Session::addBuiltinSource(
     String const&           source)
 {
     RefPtr<CompileRequest> compileRequest = new CompileRequest(this);
+    compileRequest->setSourceManager(getBuiltinSourceManager());
 
     auto translationUnitIndex = compileRequest->addTranslationUnit(SourceLanguage::Slang, path);
 
+    RefPtr<SourceFile> sourceFile = builtinSourceManager.allocateSourceFile(path, source);
+
     compileRequest->addTranslationUnitSourceString(
         translationUnitIndex,
         path,
@@ -818,7 +833,7 @@ SLANG_API int spCompile(
     }
     catch (...)
     {
-        req->mSink.diagnose(Slang::CodePosition(), Slang::Diagnostics::compilationAborted);
+        req->mSink.diagnose(Slang::SourceLoc(), Slang::Diagnostics::compilationAborted);
         return 1;
     }
 }
diff --git a/source/slang/slang.vcxproj b/source/slang/slang.vcxproj
index 4a1e75bc3..7da5c39d6 100644
--- a/source/slang/slang.vcxproj
+++ b/source/slang/slang.vcxproj
@@ -213,6 +213,7 @@
     <ClCompile Include="reflection.cpp" />
     <ClCompile Include="slang-stdlib.cpp" />
     <ClCompile Include="slang.cpp" />
+    <ClCompile Include="source-loc.cpp" />
     <ClCompile Include="syntax.cpp" />
     <ClCompile Include="token.cpp" />
     <ClCompile Include="type-layout.cpp" />
diff --git a/source/slang/slang.vcxproj.filters b/source/slang/slang.vcxproj.filters
index c43cd9dbb..2241dc67c 100644
--- a/source/slang/slang.vcxproj.filters
+++ b/source/slang/slang.vcxproj.filters
@@ -56,5 +56,6 @@
     <ClCompile Include="type-layout.cpp" />
     <ClCompile Include="options.cpp" />
     <ClCompile Include="lower.cpp" />
+    <ClCompile Include="source-loc.cpp" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/source/slang/source-loc.cpp b/source/slang/source-loc.cpp
new file mode 100644
index 000000000..cea8441e6
--- /dev/null
+++ b/source/slang/source-loc.cpp
@@ -0,0 +1,332 @@
+// source-loc.cpp
+#include "source-loc.h"
+
+namespace Slang {
+
+String ExpandedSourceLoc::getPath() const
+{
+    if(!sourceManager)
+        return String();
+
+    return sourceManager->sourceFiles[entryIndex].path;
+}
+
+String ExpandedSourceLoc::getSpellingPath() const
+{
+    if(!sourceManager)
+        return String();
+
+    return sourceManager->sourceFiles[entryIndex].sourceFile->path;
+}
+
+SourceFile* ExpandedSourceLoc::getSourceFile() const
+{
+    if(!sourceManager)
+        return nullptr;
+
+    return sourceManager->sourceFiles[entryIndex].sourceFile;
+}
+
+void SourceManager::initialize(
+    SourceManager*  p)
+{
+    parent = p;
+
+    if( p )
+    {
+        // If we have a parent source manager, then we assume that all code at that level
+        // has already been loaded, and it is safe to start our own source locations
+        // right after those from the parent.
+        //
+        // TODO: more clever allocation in cases where that might not be reasonable
+        startLoc = p->nextLoc;
+    }
+    else
+    {
+        // Location zero is reserved for an invalid location,
+        // so we need to start reserving locations starting at 1.
+        startLoc = SourceLoc::fromRaw(1);
+    }
+
+    nextLoc = startLoc;
+}
+
+SourceRange SourceManager::allocateSourceRange(UInt size)
+{
+    // TODO: consider using atomics here
+
+
+    SourceLoc beginLoc  = nextLoc;
+    SourceLoc endLoc    = beginLoc + size;
+
+    // We need to be able to represent the location that is *at* the end of
+    // the input source, so the next available location for a new file
+    // must be placed one after the end of this one.
+
+    nextLoc = endLoc + 1;
+
+    return SourceRange(beginLoc, endLoc);
+}
+
+SourceFile* SourceManager::allocateSourceFile(
+    String const&   path,
+    String const&   content)
+{
+    UInt size = content.Length();
+
+    SourceRange sourceRange = allocateSourceRange(size);
+
+    SourceFile* sourceFile = new SourceFile();
+    sourceFile->path = path;
+    sourceFile->content = content;
+    sourceFile->sourceRange = sourceRange;
+
+    Entry entry;
+    entry.sourceFile = sourceFile;
+    entry.startLoc = sourceRange.begin;
+    entry.path = path;
+
+    sourceFiles.Add(entry);
+
+    return sourceFile;
+}
+
+SourceLoc SourceManager::allocateSourceFileForLineDirective(
+    SourceLoc const&    directiveLoc,
+    String const&       path,
+    UInt                line)
+{
+    // First, we need to find out what file we are being asked to remap
+    ExpandedSourceLoc expandedDirectiveLoc = expandSourceLoc(getSpellingLoc(directiveLoc));
+    HumaneSourceLoc humaneDirectiveLoc = getHumaneLoc(expandedDirectiveLoc);
+
+    SourceFile* sourceFile = expandedDirectiveLoc.getSourceFile();
+    if(!sourceFile)
+        return SourceLoc();
+
+    // We are going to be wasteful here and allocate a range of source locations
+    // that can cover the entire input file. This will lead to a problem with
+    // memory usage if we ever had a large input file that used many `#line` directives,
+    // since our usage of ranges would be quadratic!
+
+    // Count how many locations we'd need to reserve for a complete clone of the input
+    UInt size = sourceFile->sourceRange.end.getRaw() - sourceFile->sourceRange.begin.getRaw();
+
+    // Allocate a fresh range for our logically remapped file
+    SourceRange sourceRange = allocateSourceRange(size);
+
+    // Now fill in an entry that will point at the original source file,
+    // but use our new range.
+    Entry entry;
+    entry.sourceFile = sourceFile;
+    entry.startLoc = sourceRange.begin;
+    entry.path = path;
+
+    // We also need to make sure that any lookups for line numbers will
+    // get corrected based on this files location.
+    entry.lineAdjust = Int(line) - Int(humaneDirectiveLoc.line + 1);
+
+    sourceFiles.Add(entry);
+
+    return entry.startLoc;
+}
+
+static ExpandedSourceLoc expandSourceLoc(
+    SourceManager*      inSourceManager,
+    SourceLoc const&    loc)
+{
+    SourceManager* sourceManager = inSourceManager;
+
+    ExpandedSourceLoc expanded;
+
+    SourceLoc::RawValue rawValue = loc.getRaw();
+
+    // Invalid location? -> invalid expanded location
+    if(rawValue == 0)
+        return expanded;
+
+    // Past the end of what we can handle? -> invalid
+    if(rawValue >= sourceManager->nextLoc.getRaw())
+        return expanded;
+
+    // Maybe the location came from a parent source manager
+    while( rawValue < sourceManager->startLoc.getRaw()
+        && sourceManager->parent)
+    {
+        sourceManager = sourceManager->parent;
+    }
+
+    SLANG_ASSERT(sourceManager->sourceFiles.Count() > 0);
+
+    UInt lo = 0;
+    UInt hi = sourceManager->sourceFiles.Count();
+
+    while( lo+1 < hi )
+    {
+        UInt mid = lo + (hi - lo) / 2;
+
+        SourceManager::Entry const& midEntry = sourceManager->sourceFiles[mid];
+        SourceLoc::RawValue midValue = midEntry.startLoc.getRaw();
+
+        if( midValue <= rawValue )
+        {
+            // The location we seek is at or after this entry
+            lo = mid;
+        }
+        else
+        {
+            // The location we seek is before this entry
+            hi = mid;
+        }
+    }
+
+    // `lo` should now point at the entry we want
+    UInt entryIndex = lo;
+
+    expanded.setRaw(loc.getRaw());
+    expanded.sourceManager = sourceManager;
+    expanded.entryIndex = entryIndex;
+
+    return expanded;
+
+
+}
+
+ExpandedSourceLoc SourceManager::expandSourceLoc(SourceLoc const& loc)
+{
+    return Slang::expandSourceLoc(this, loc);
+}
+
+HumaneSourceLoc SourceManager::getHumaneLoc(ExpandedSourceLoc const& loc)
+{
+    // First check if this location maps to an actual file.
+    SourceFile* sourceFile = loc.getSourceFile();
+    if(!sourceFile)
+        return HumaneSourceLoc();
+
+    auto& entry = sourceFiles[loc.entryIndex];
+    UInt offset = loc.getRaw() - entry.startLoc.getRaw();
+
+    // We now have a raw input file that we can search for line breaks.
+    // We obviously don't want to do a linear scan over and over, so we will
+    // cache an array of line break locations in the file.
+    auto& lineBreakOffsets = sourceFile->lineBreakOffsets;
+    if( lineBreakOffsets.Count() == 0 )
+    {
+        char const* begin = sourceFile->content.begin();
+        char const* end = sourceFile->content.end();
+
+        char const* cursor = begin;
+
+        // Treat the beginning of the file as a line break
+        lineBreakOffsets.Add(0);
+
+        while( cursor != end )
+        {
+            int c = *cursor++;
+            switch( c )
+            {
+            case '\r': case '\n':
+                {
+                    // When we see a line-break character we need
+                    // to record the line break, but we also need
+                    // to deal with the annoying issue of encodings,
+                    // where a multi-byte sequence might encode
+                    // the line break.
+
+                    int d = *cursor;
+                    if( (c^d) == ('\r' ^ '\n'))
+                        cursor++;
+
+                    lineBreakOffsets.Add(cursor - begin);
+                }
+                break;
+
+            default:
+                break;
+            }
+        }
+
+        // Note taht we do *not* treat the end of the file as a line
+        // break, because otherwise we would report errors like
+        // "end of file inside string literal" with a line number
+        // that points at a line that doesn't exist.
+    }
+
+    // At this point we can assume the `lineBreakOffsets` array has been filled in.
+    // We will use a binary search to find the line index that contains our
+    // chosen offset.
+    UInt lo = 0;
+    UInt hi = lineBreakOffsets.Count();
+
+    while( lo+1 < hi )
+    {
+        UInt mid = lo + (hi - lo)/2;
+
+        UInt midOffset = lineBreakOffsets[mid];
+        if( midOffset <= offset )
+        {
+            lo = mid;
+        }
+        else
+        {
+            hi = mid;
+        }
+    }
+
+    UInt lineIndex = lo;
+    UInt byteIndexInLine = offset - lineBreakOffsets[lineIndex];
+
+    // Apply adjustment to the line number
+    lineIndex = lineIndex + entry.lineAdjust;
+
+    // TODO: we should really translate the byte index in the line
+    // to deal with:
+    //
+    // - Non-ASCII characters, while might consume multiple bytes
+    //
+    // - Tab characters, which should really adjust how we report
+    //   columns (although how are we supposed to know the setting
+    //   that an IDE expects us to use when reporting locations?)
+
+    HumaneSourceLoc humaneLoc;
+    humaneLoc.path = entry.path;
+    humaneLoc.line = lineIndex + 1;
+    humaneLoc.column = byteIndexInLine + 1;
+
+    return humaneLoc;
+}
+
+HumaneSourceLoc SourceManager::getHumaneLoc(SourceLoc const& loc)
+{
+    return getHumaneLoc(expandSourceLoc(loc));
+
+}
+
+SourceLoc SourceManager::getSpellingLoc(ExpandedSourceLoc const& loc)
+{
+    // First check if this location maps to some raw source file,
+    // so that a "spelling" is even possible
+    SourceFile* sourceFile = loc.getSourceFile();
+    if(!sourceFile)
+        return loc;
+
+    // If we mapped to a source file, then the location must represent
+    // some offset from an entry in our array.
+    auto& entry = sourceFiles[loc.entryIndex];
+
+    // We extract the offset of the location from the start of the entry
+    SourceLoc::RawValue offsetFromStart = loc.getRaw() - entry.startLoc.getRaw();
+
+    // And instead apply that offset to the spelling location of the file start
+    SourceLoc result = sourceFile->sourceRange.begin + offsetFromStart;
+
+    return result;
+}
+
+SourceLoc SourceManager::getSpellingLoc(SourceLoc const& loc)
+{
+    return getSpellingLoc(expandSourceLoc(loc));
+}
+
+} // namespace Slang
diff --git a/source/slang/source-loc.h b/source/slang/source-loc.h
index 59f2f10ea..8bb89c645 100644
--- a/source/slang/source-loc.h
+++ b/source/slang/source-loc.h
@@ -6,36 +6,181 @@
 
 namespace Slang {
 
-class CodePosition
+class SourceLoc
 {
 public:
-	int Line = -1, Col = -1, Pos = -1;
-	String FileName;
-	String ToString()
-	{
-		StringBuilder sb(100);
-		sb << FileName;
-		if (Line != -1)
-			sb << "(" << Line << ")";
-		return sb.ProduceString();
-	}
-	CodePosition() = default;
-	CodePosition(int line, int col, int pos, String fileName)
-	{
-		Line = line;
-		Col = col;
-		Pos = pos;
-		this->FileName = fileName;
-	}
-	bool operator < (const CodePosition & pos) const
-	{
-		return FileName < pos.FileName || (FileName == pos.FileName && Line < pos.Line) ||
-			(FileName == pos.FileName && Line == pos.Line && Col < pos.Col);
-	}
-	bool operator == (const CodePosition & pos) const
-	{
-		return FileName == pos.FileName && Line == pos.Line && Col == pos.Col;
-	}
+    typedef UInt RawValue;
+
+private:
+    RawValue raw;
+
+public:
+    SourceLoc()
+        : raw(0)
+    {}
+
+    SourceLoc(
+        SourceLoc const& loc)
+        : raw(loc.raw)
+    {}
+
+    RawValue getRaw() const { return raw; }
+    void setRaw(RawValue value) { raw = value; }
+
+    static SourceLoc fromRaw(RawValue value)
+    {
+        SourceLoc result;
+        result.setRaw(value);
+        return result;
+    }
+
+    bool isValid() const
+    {
+        return raw != 0;
+    }
+};
+
+inline SourceLoc operator+(SourceLoc loc, Int offset)
+{
+    return SourceLoc::fromRaw(loc.getRaw() + UInt(offset));
+}
+
+// A range of locations in the input source
+struct SourceRange
+{
+    SourceRange()
+    {}
+
+    SourceRange(SourceLoc loc)
+        : begin(loc)
+        , end(loc)
+    {}
+
+    SourceRange(SourceLoc begin, SourceLoc end)
+        : begin(begin)
+        , end(end)
+    {}
+
+    SourceLoc begin;
+    SourceLoc end;
+};
+
+// A logical or phyiscal storage object for a range of input code
+// that has logically contiguous source locations.
+class SourceFile : public RefObject
+{
+public:
+    // The logical file path to report for locations inside this span.
+    String path;
+
+    // The actual contents of the file.
+    String content;
+
+    // The range of source locations that the span covers
+    SourceRange sourceRange;
+
+    // In order to speed up lookup of line number information,
+    // we will cache the starting offset of each line break in
+    // the input file:
+    List<UInt> lineBreakOffsets;
+};
+
+struct SourceManager;
+
+// A source location in a format a human might like to see
+struct HumaneSourceLoc
+{
+    String  path;
+    Int     line = 0;
+    Int     column = 0;
+
+    String const& getPath() const { return path; }
+    Int getLine() const { return line; }
+    Int getColumn() const { return column; }
+};
+
+// A source location that has been expanded with the info
+// needed to reconstruct a "humane" location if needed.
+struct ExpandedSourceLoc : public SourceLoc
+{
+    // The source manager that owns this location
+    SourceManager*  sourceManager = nullptr;
+
+    // The entry index that is used to understand the location
+    UInt            entryIndex = 0;
+
+    // Get the nominal path for this location
+    String getPath() const;
+
+    // Get the actual file path where this location appears
+    String getSpellingPath() const;
+
+    // Get the original source file that holds this location
+    SourceFile* getSourceFile() const;
+};
+
+
+
+struct SourceManager
+{
+    // Initialize a source manager, with an optional parent
+    void initialize(
+        SourceManager*  parent);
+
+    SourceRange allocateSourceRange(UInt size);
+
+    SourceFile* allocateSourceFile(
+        String const&   path,
+        String const&   content);
+
+    SourceLoc allocateSourceFileForLineDirective(
+        SourceLoc const&    directiveLoc,
+        String const&       path,
+        UInt                line);
+
+    // Expand a source location to include more explicit info
+    ExpandedSourceLoc expandSourceLoc(SourceLoc const& loc);
+
+    // Get a "humane" version of a source location
+    HumaneSourceLoc getHumaneLoc(ExpandedSourceLoc const& loc);
+    HumaneSourceLoc getHumaneLoc(SourceLoc const& loc);
+
+
+    // Get the source location that represents the spelling location corresponding to a location.
+    SourceLoc getSpellingLoc(ExpandedSourceLoc const& loc);
+    SourceLoc getSpellingLoc(SourceLoc const& loc);
+
+    // The first location available to this source manager
+    // (may not be the first location of all, because we might
+    // have a parent source manager)
+    SourceLoc startLoc;
+
+    // The "parent" source manager that owns locations ahead of `startLoc`
+    SourceManager* parent = nullptr;
+
+    // The location to be used by the next source file to be loaded
+    SourceLoc nextLoc;
+
+    // Each entry represents some contiguous span of locations that
+    // all map to the same logical file.
+    struct Entry
+    {
+        // Where does this entry begin?
+        SourceLoc        startLoc;
+
+        // The soure file that represents the actual data
+        RefPtr<SourceFile>  sourceFile;
+
+        // What is the presumed path for this entry
+        String path;
+
+        // Adjustment to apply to source line numbers when printing presumed locations
+        Int lineAdjust = 0;
+    };
+
+    // An array of soure files we have loaded, ordered by
+    // increasing starting location
+    List<Entry> sourceFiles;
 };
 
 
diff --git a/source/slang/syntax-base-defs.h b/source/slang/syntax-base-defs.h
index d76607106..711c4425b 100644
--- a/source/slang/syntax-base-defs.h
+++ b/source/slang/syntax-base-defs.h
@@ -9,7 +9,7 @@
 ABSTRACT_SYNTAX_CLASS(SyntaxNodeBase, RefObject)
 
     // The primary source location associated with this AST node
-    FIELD(CodePosition, Position)
+    FIELD(SourceLoc, Position)
 
     RAW(
     // Allow dynamic casting with a convenient syntax
diff --git a/source/slang/syntax-visitors.h b/source/slang/syntax-visitors.h
index f2c080a57..0780bab2a 100644
--- a/source/slang/syntax-visitors.h
+++ b/source/slang/syntax-visitors.h
@@ -26,7 +26,7 @@ namespace Slang
     RefPtr<ModuleDecl> findOrImportModule(
         CompileRequest*     request,
         String const&       name,
-        CodePosition const& loc);
+        SourceLoc const& loc);
 }
 
 #endif
\ No newline at end of file
diff --git a/source/slang/token.h b/source/slang/token.h
index f29f2b4c6..306d4a2f2 100644
--- a/source/slang/token.h
+++ b/source/slang/token.h
@@ -18,8 +18,9 @@ char const* TokenTypeToString(TokenType type);
 
 enum TokenFlag : unsigned int
 {
-    AtStartOfLine   = 1 << 0,
-    AfterWhitespace = 1 << 1,
+    AtStartOfLine           = 1 << 0,
+    AfterWhitespace         = 1 << 1,
+    SuppressMacroExpansion  = 1 << 2,
 };
 typedef unsigned int TokenFlags;
 
@@ -28,15 +29,21 @@ class Token
 public:
 	TokenType type = TokenType::Unknown;
 	String Content;
-	CodePosition Position;
+	SourceLoc Position;
     TokenFlags flags = 0;
+
 	Token() = default;
-	Token(TokenType type, const String & content, int line, int col, int pos, String fileName, TokenFlags flags = 0)
+
+    Token(
+        TokenType type,
+        const String & content,
+        SourceLoc loc,
+        TokenFlags flags = 0)
         : flags(flags)
 	{
 		type = type;
 		Content = content;
-		Position = CodePosition(line, col, pos, fileName);
+        Position = loc;
 	}
 };