1 files changed, 24 insertions, 10 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index e2b921bfe78f..051fad04219f 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -13088,9 +13088,10 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
   // C++ [module.import/6] external definitions are not permitted in header
   // units.
   if (getLangOpts().CPlusPlusModules && currentModuleIsHeaderUnit() &&
-      VDecl->isThisDeclarationADefinition() &&
+      !VDecl->isInvalidDecl() && VDecl->isThisDeclarationADefinition() &&
       VDecl->getFormalLinkage() == Linkage::ExternalLinkage &&
-      !VDecl->isInline()) {
+      !VDecl->isInline() && !VDecl->isTemplated() &&
+      !isa<VarTemplateSpecializationDecl>(VDecl)) {
     Diag(VDecl->getLocation(), diag::err_extern_def_in_header_unit);
     VDecl->setInvalidDecl();
   }
@@ -15259,9 +15260,10 @@ Decl *Sema::ActOnStartOfFunctionDef(Scope *FnBodyScope, Decl *D,
   // FIXME: Consider an alternate location for the test where the inlined()
   // state is complete.
   if (getLangOpts().CPlusPlusModules && currentModuleIsHeaderUnit() &&
+      !FD->isInvalidDecl() && !FD->isInlined() &&
+      BodyKind != FnBodyKind::Delete && BodyKind != FnBodyKind::Default &&
       FD->getFormalLinkage() == Linkage::ExternalLinkage &&
-      !FD->isInvalidDecl() && BodyKind != FnBodyKind::Delete &&
-      BodyKind != FnBodyKind::Default && !FD->isInlined()) {
+      !FD->isTemplated() && !FD->isTemplateInstantiation()) {
     assert(FD->isThisDeclarationADefinition());
     Diag(FD->getLocation(), diag::err_extern_def_in_header_unit);
     FD->setInvalidDecl();
@@ -16616,8 +16618,7 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
                bool &IsDependent, SourceLocation ScopedEnumKWLoc,
                bool ScopedEnumUsesClassTag, TypeResult UnderlyingType,
                bool IsTypeSpecifier, bool IsTemplateParamOrArg,
-               OffsetOfKind OOK, UsingShadowDecl *&FoundUsingShadow,
-               SkipBodyInfo *SkipBody) {
+               OffsetOfKind OOK, SkipBodyInfo *SkipBody) {
   // If this is not a definition, it must have a name.
   IdentifierInfo *OrigName = Name;
   assert((Name != nullptr || TUK == TUK_Definition) &&
@@ -17052,7 +17053,6 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
     // redefinition if either context is within the other.
     if (auto *Shadow = dyn_cast<UsingShadowDecl>(DirectPrevDecl)) {
       auto *OldTag = dyn_cast<TagDecl>(PrevDecl);
-      FoundUsingShadow = Shadow;
       if (SS.isEmpty() && TUK != TUK_Reference && TUK != TUK_Friend &&
           isDeclInScope(Shadow, SearchDC, S, isMemberSpecialization) &&
           !(OldTag && isAcceptableTagRedeclContext(
@@ -18871,10 +18871,24 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
     ProcessDeclAttributeList(S, Record, Attrs);
 
     // Check to see if a FieldDecl is a pointer to a function.
-    auto IsFunctionPointer = [&](const Decl *D) {
+    auto IsFunctionPointerOrForwardDecl = [&](const Decl *D) {
       const FieldDecl *FD = dyn_cast<FieldDecl>(D);
-      if (!FD)
+      if (!FD) {
+        // Check whether this is a forward declaration that was inserted by
+        // Clang. This happens when a non-forward declared / defined type is
+        // used, e.g.:
+        //
+        //   struct foo {
+        //     struct bar *(*f)();
+        //     struct bar *(*g)();
+        //   };
+        //
+        // "struct bar" shows up in the decl AST as a "RecordDecl" with an
+        // incomplete definition.
+        if (const auto *TD = dyn_cast<TagDecl>(D))
+          return !TD->isCompleteDefinition();
         return false;
+      }
       QualType FieldType = FD->getType().getDesugaredType(Context);
       if (isa<PointerType>(FieldType)) {
         QualType PointeeType = cast<PointerType>(FieldType)->getPointeeType();
@@ -18888,7 +18902,7 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
     if (!getLangOpts().CPlusPlus &&
         (Record->hasAttr<RandomizeLayoutAttr>() ||
          (!Record->hasAttr<NoRandomizeLayoutAttr>() &&
-          llvm::all_of(Record->decls(), IsFunctionPointer))) &&
+          llvm::all_of(Record->decls(), IsFunctionPointerOrForwardDecl))) &&
         !Record->isUnion() && !getLangOpts().RandstructSeed.empty() &&
         !Record->isRandomized()) {
       SmallVector<Decl *, 32> NewDeclOrdering;