Support link time type specialization. (#3604)

12 files changed, 149 insertions, 12 deletions

diff --git a/source/core/slang-list.h b/source/core/slang-list.h
index 250b6dc49..c0fe28937 100644
--- a/source/core/slang-list.h
+++ b/source/core/slang-list.h
@@ -570,7 +570,7 @@ namespace Slang
         }
 
         template<typename T2>
-        int binarySearch(const T2& obj)
+        Index binarySearch(const T2& obj)
         {
             return binarySearch(obj, 
                 [](T & curObj, const T2 & thatObj)->int
diff --git a/source/slang/slang-ast-decl.cpp b/source/slang/slang-ast-decl.cpp
index 9dbd006a0..cd9c43410 100644
--- a/source/slang/slang-ast-decl.cpp
+++ b/source/slang/slang-ast-decl.cpp
@@ -136,4 +136,19 @@ InterfaceDecl* ThisTypeConstraintDecl::getInterfaceDecl()
     return as<InterfaceDecl>(parentDecl->parentDecl);
 }
 
+void AggTypeDecl::addTag(TypeTag tag)
+{
+    typeTags = (TypeTag)((int)tag | (int)tag);
+}
+
+bool AggTypeDecl::hasTag(TypeTag tag)
+{
+    return ((int)typeTags & (int)tag) != 0;
+}
+
+void AggTypeDecl::unionTagsWith(TypeTag other)
+{
+    addTag(other);
+}
+
 } // namespace Slang
diff --git a/source/slang/slang-ast-decl.h b/source/slang/slang-ast-decl.h
index 5d8023eaf..7a4d46947 100644
--- a/source/slang/slang-ast-decl.h
+++ b/source/slang/slang-ast-decl.h
@@ -130,11 +130,24 @@ class ExtensionDecl : public AggTypeDeclBase
     TypeExp targetType;
 };
 
+enum class TypeTag
+{
+    None = 0,
+    Unsized = 1,
+    Incomplete = 2
+};
+
 // Declaration of a type that represents some sort of aggregate
 class AggTypeDecl : public  AggTypeDeclBase
 {
     SLANG_ABSTRACT_AST_CLASS(AggTypeDecl)
 
+    TypeTag typeTags = TypeTag::None;
+
+    void unionTagsWith(TypeTag other);
+    void addTag(TypeTag tag);
+    bool hasTag(TypeTag tag);
+
     FilteredMemberList<VarDecl> getFields()
     {
         return getMembersOfType<VarDecl>();
diff --git a/source/slang/slang-ast-dump.cpp b/source/slang/slang-ast-dump.cpp
index 9c40fb12b..ccd9b9ee7 100644
--- a/source/slang/slang-ast-dump.cpp
+++ b/source/slang/slang-ast-dump.cpp
@@ -343,6 +343,10 @@ struct ASTDumpContext
     {
         m_writer->emit((int)v);
     }
+    void dump(TypeTag tag)
+    {
+        m_writer->emit((int)tag);
+    }
     void dump(const String& string)
     {
         dump(string.getUnownedSlice());
diff --git a/source/slang/slang-ast-support-types.h b/source/slang/slang-ast-support-types.h
index c1984910c..d3529b963 100644
--- a/source/slang/slang-ast-support-types.h
+++ b/source/slang/slang-ast-support-types.h
@@ -1503,6 +1503,9 @@ namespace Slang
         // The type witnessesd by the witness table (a concrete type).
         Type* witnessedType;
 
+        // Whether or not this witness table is an extern declaration.
+        bool isExtern = false;
+
         // Satisfying values of each requirement.
         List<KeyValuePair<Decl*, RequirementWitness>> m_requirements;
 
diff --git a/source/slang/slang-check-conformance.cpp b/source/slang/slang-check-conformance.cpp
index 4376b1135..726572d08 100644
--- a/source/slang/slang-check-conformance.cpp
+++ b/source/slang/slang-check-conformance.cpp
@@ -242,6 +242,59 @@ namespace Slang
         return isSubtype(type, m_astBuilder->getDiffInterfaceType());
     }
 
+    bool SemanticsVisitor::doesTypeHaveTag(Type* type, TypeTag tag)
+    {
+        if (auto arrayType = as<ArrayExpressionType>(type))
+        {
+            return doesTypeHaveTag(arrayType->getElementType(), tag);
+        }
+        if (auto modifiedType = as<ModifiedType>(type))
+        {
+            return doesTypeHaveTag(modifiedType->getBase(), tag);
+        }
+        if (auto declRefType = as<DeclRefType>(type))
+        {
+            if (auto aggTypeDecl = as<AggTypeDecl>(declRefType->getDeclRef()))
+                return aggTypeDecl.getDecl()->hasTag(tag);
+        }
+        return false;
+    }
+
+    TypeTag SemanticsVisitor::getTypeTags(Type* type)
+    {
+        if (auto arrayType = as<ArrayExpressionType>(type))
+        {
+            return getTypeTags(arrayType->getElementType());
+        }
+        if (auto modifiedType = as<ModifiedType>(type))
+        {
+            return getTypeTags(modifiedType->getBase());
+        }
+        if (auto declRefType = as<DeclRefType>(type))
+        {
+            if (auto aggTypeDecl = as<AggTypeDecl>(declRefType->getDeclRef()))
+                return aggTypeDecl.getDecl()->typeTags;
+        }
+        return TypeTag::None;
+    }
+
+
+    Type* SemanticsVisitor::getBufferElementType(Type* type)
+    {
+        if (auto arrType = as<ArrayExpressionType>(type))
+            return getBufferElementType(arrType->getElementType());
+        if (auto modifiedType = as<ModifiedType>(type))
+            return getBufferElementType(modifiedType->getBase());
+        if (auto constantBuffer = as<ConstantBufferType>(type))
+            return constantBuffer->getElementType();
+        if (auto structuredBuffer = as<HLSLStructuredBufferTypeBase>(type))
+            return structuredBuffer->getElementType();
+        if (auto storageBuffer = as<GLSLShaderStorageBufferType>(type))
+            return storageBuffer->getElementType();
+        return nullptr;
+    }
+
+
     SubtypeWitness* SemanticsVisitor::tryGetInterfaceConformanceWitness(
         Type*   type,
         Type*   interfaceType)
diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index 3fb2725e2..dc888ccda 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -302,6 +302,8 @@ namespace Slang
         void visitFunctionDeclBase(FunctionDeclBase* funcDecl);
 
         void visitParamDecl(ParamDecl* paramDecl);
+
+        void visitAggTypeDecl(AggTypeDecl* aggTypeDecl);
     };
 
     template<typename VisitorType>
@@ -1705,6 +1707,15 @@ namespace Slang
             }
         }
 
+        // Propagate type tags.
+        if (auto parentAggTypeDecl = as<AggTypeDecl>(getParentDecl(varDecl)))
+        {
+            if (auto varDeclRefType = as<DeclRefType>(varDecl->type.type))
+            {
+                parentAggTypeDecl->unionTagsWith(getTypeTags(varDecl->type.type));
+            }
+        }
+
         checkVisibility(varDecl);
     }
 
@@ -1722,11 +1733,20 @@ namespace Slang
         {
             addModifier(structDecl, m_astBuilder->create<NVAPIMagicModifier>());
         }
+
+        if (structDecl->hasModifier<ExternModifier>())
+        {
+            structDecl->addTag(TypeTag::Incomplete);
+        }
         checkVisibility(structDecl);
     }
 
     void SemanticsDeclHeaderVisitor::visitClassDecl(ClassDecl* classDecl)
     {
+        if (classDecl->hasModifier<ExternModifier>())
+        {
+            classDecl->addTag(TypeTag::Incomplete);
+        }
         checkVisibility(classDecl);
     }
 
@@ -1812,6 +1832,13 @@ namespace Slang
                 varDecl->initExpr = CompleteOverloadCandidate(overloadContext, *overloadContext.bestCandidate);
             }
         }
+        if (auto elementType = getBufferElementType(varDecl->getType()))
+        {
+            if (doesTypeHaveTag(elementType, TypeTag::Incomplete))
+            {
+                getSink()->diagnose(varDecl->type.exp->loc, Diagnostics::incompleteTypeCannotBeUsedInBuffer, elementType);
+            }
+        }
         maybeRegisterDifferentiableType(getASTBuilder(), varDecl->getType());
     }
 
@@ -4784,6 +4811,9 @@ namespace Slang
         SubtypeWitness*             subIsSuperWitness,
         WitnessTable*               witnessTable)
     {
+        if (witnessTable->isExtern)
+            return true;
+
         if (auto supereclRefType = as<DeclRefType>(superType))
         {
             auto superTypeDeclRef = supereclRefType->getDeclRef();
@@ -4896,6 +4926,7 @@ namespace Slang
             witnessTable = new WitnessTable();
             witnessTable->baseType = superType;
             witnessTable->witnessedType = subType;
+            witnessTable->isExtern = parentDecl->hasModifier<ExternModifier>();
             inheritanceDecl->witnessTable = witnessTable;
         }
 
@@ -5179,6 +5210,7 @@ namespace Slang
         // order) is allowed to declare a base `class` type.
         //
         SLANG_OUTER_SCOPE_CONTEXT_DECL_RAII(this, decl);
+
         Index inheritanceClauseCounter = 0;
         for (auto inheritanceDecl : decl->getMembersOfType<InheritanceDecl>())
         {
@@ -6544,6 +6576,14 @@ namespace Slang
         }
     }
 
+    void SemanticsDeclBodyVisitor::visitAggTypeDecl(AggTypeDecl* aggTypeDecl)
+    {
+        if (aggTypeDecl->hasTag(TypeTag::Incomplete) && aggTypeDecl->hasModifier<HLSLExportModifier>())
+        {
+            getSink()->diagnose(aggTypeDecl->loc, Diagnostics::cannotExportIncompleteType, aggTypeDecl);
+        }
+    }
+
     void SemanticsDeclHeaderVisitor::cloneModifiers(Decl* dest, Decl* src)
     {
         dest->modifiers = src->modifiers;
diff --git a/source/slang/slang-check-impl.h b/source/slang/slang-check-impl.h
index 3af85b73d..ba8e2f4cd 100644
--- a/source/slang/slang-check-impl.h
+++ b/source/slang/slang-check-impl.h
@@ -1957,6 +1957,12 @@ namespace Slang
 
         bool isTypeDifferentiable(Type* type);
 
+        bool doesTypeHaveTag(Type* type, TypeTag tag);
+
+        TypeTag getTypeTags(Type* type);
+
+        Type* getBufferElementType(Type* type);
+
             /// Check whether `subType` is a sub-type of `superTypeDeclRef`,
             /// and return a witness to the sub-type relationship if it holds
             /// (return null otherwise).
diff --git a/source/slang/slang-check-modifier.cpp b/source/slang/slang-check-modifier.cpp
index 9117eb6ec..a4e906ac9 100644
--- a/source/slang/slang-check-modifier.cpp
+++ b/source/slang/slang-check-modifier.cpp
@@ -1109,7 +1109,8 @@ namespace Slang
         case ASTNodeType::HLSLExportModifier:
         case ASTNodeType::ExternCppModifier:
             return as<VarDeclBase>(decl) || as<AggTypeDeclBase>(decl) || as<NamespaceDeclBase>(decl) || as<CallableDecl>(decl)
-                || as<TypeDefDecl>(decl) || as<PropertyDecl>(decl) || as<SyntaxDecl>(decl) || as<AttributeDecl>(decl);
+                || as<TypeDefDecl>(decl) || as<PropertyDecl>(decl) || as<SyntaxDecl>(decl) || as<AttributeDecl>(decl)
+                || as<InheritanceDecl>(decl);
 
         case ASTNodeType::ExportedModifier:
             return as<ImportDecl>(decl);
diff --git a/source/slang/slang-diagnostic-defs.h b/source/slang/slang-diagnostic-defs.h
index ac1f9aff9..722085744 100644
--- a/source/slang/slang-diagnostic-defs.h
+++ b/source/slang/slang-diagnostic-defs.h
@@ -438,6 +438,9 @@ DIAGNOSTIC(31155, Error, customDerivativeNotAllowedForMemberFunctionsOfDifferent
 DIAGNOSTIC(31200, Warning, deprecatedUsage, "$0 has been deprecated: $1")
 DIAGNOSTIC(31201, Error, modifierNotAllowed, "modifier '$0' is not allowed here.")
 DIAGNOSTIC(31202, Error, duplicateModifier, "modifier '$0' is redundant or conflicting with existing modifier '$1'")
+DIAGNOSTIC(31203, Error, cannotExportIncompleteType, "cannot export incomplete type '$0'")
+DIAGNOSTIC(31204, Error, incompleteTypeCannotBeUsedInBuffer, "incomplete type '$0' cannot be used in a buffer")
+
 // Enums
 
 DIAGNOSTIC(32000, Error, invalidEnumTagType,        "invalid tag type for 'enum': '$0'")
diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index 8531e4029..b560bb156 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -657,17 +657,11 @@ bool isFromStdLib(Decl* decl)
 bool isImportedDecl(IRGenContext* context, Decl* decl)
 {
     // If the declaration has the extern attribute then it must be imported
-    // from another module
+    // from another module.
+    // Note that `extern` declarations will have a mangled name that does not
+    // include the module name so the linking step can resolve them correctly.
     //
-    // The [__extern] attribute is a very special case feature (aka "a hack") that allows a symbol to be declared
-    // as if it is part of the current module for AST purposes, but then expects to be imported from another IR module.
-    // For that linkage to work, both the exporting and importing modules must have the same name (which would
-    // usually indicate that they are the same module).
-    //
-    // Note that in practice for matching during linking uses the fully qualified name - including module name.
-    // Thus using extern __attribute isn't useful for symbols that are imported via `import`, only symbols
-    // that notionally come from the same module but are split into separate compilations (as can be done with -module-name)
-    if (decl->findModifier<ExternAttribute>())
+    if (decl->findModifier<ExternAttribute>() || decl->findModifier<ExternModifier>())
     {
         return true;
     }
diff --git a/source/slang/slang-parser.cpp b/source/slang/slang-parser.cpp
index e0ffba53c..b89b93138 100644
--- a/source/slang/slang-parser.cpp
+++ b/source/slang/slang-parser.cpp
@@ -3232,6 +3232,9 @@ namespace Slang
                 inheritanceDecl->base = base;
 
                 AddMember(decl, inheritanceDecl);
+                
+                if (parser->pendingModifiers->hasModifier<ExternModifier>())
+                    addModifier(inheritanceDecl, parser->astBuilder->create<ExternModifier>());
 
             } while (AdvanceIf(parser, TokenType::Comma));
         }
@@ -4730,6 +4733,8 @@ namespace Slang
             // We allow for an inheritance clause on a `struct`
             // so that it can conform to interfaces.
             parseOptionalInheritanceClause(this, rs);
+            if (AdvanceIf(this, TokenType::Semicolon))
+                return rs;
             parseDeclBody(this, rs);
             return rs;
         });