[ASTImporter] Handle redecl chain of FunctionTemplateDecls

Summary:
Redecl chains of function templates are not handled well currently. We
want to handle them similarly to functions, i.e. try to keep the
structure of the original AST as much as possible. The aim is to not
squash a prototype with a definition, rather we create both and put them
in a redecl chain.

Reviewers: a_sidorin, shafik, a.sidorin

Subscribers: rnkovacs, dkrupp, Szelethus, gamesh411, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D58494

llvm-svn: 355593

1 files changed, 40 insertions, 16 deletions

diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 3b484f94003..da102988dec 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -4943,15 +4943,15 @@ ASTNodeImporter::VisitTemplateTemplateParmDecl(TemplateTemplateParmDecl *D) {
   return ToD;
 }
 
-// Returns the definition for a (forward) declaration of a ClassTemplateDecl, if
+// Returns the definition for a (forward) declaration of a TemplateDecl, if
 // it has any definition in the redecl chain.
-static ClassTemplateDecl *getDefinition(ClassTemplateDecl *D) {
-  CXXRecordDecl *ToTemplatedDef = D->getTemplatedDecl()->getDefinition();
+template <typename T> static auto getTemplateDefinition(T *D) -> T * {
+  assert(D->getTemplatedDecl() && "Should be called on templates only");
+  auto *ToTemplatedDef = D->getTemplatedDecl()->getDefinition();
   if (!ToTemplatedDef)
     return nullptr;
-  ClassTemplateDecl *TemplateWithDef =
-      ToTemplatedDef->getDescribedClassTemplate();
-  return TemplateWithDef;
+  auto *TemplateWithDef = ToTemplatedDef->getDescribedTemplate();
+  return cast_or_null<T>(TemplateWithDef);
 }
 
 ExpectedDecl ASTNodeImporter::VisitClassTemplateDecl(ClassTemplateDecl *D) {
@@ -4983,7 +4983,8 @@ ExpectedDecl ASTNodeImporter::VisitClassTemplateDecl(ClassTemplateDecl *D) {
       if (FoundTemplate) {
 
         if (IsStructuralMatch(D, FoundTemplate)) {
-          ClassTemplateDecl *TemplateWithDef = getDefinition(FoundTemplate);
+          ClassTemplateDecl *TemplateWithDef =
+              getTemplateDefinition(FoundTemplate);
           if (D->isThisDeclarationADefinition() && TemplateWithDef) {
             return Importer.MapImported(D, TemplateWithDef);
           }
@@ -5046,6 +5047,8 @@ ExpectedDecl ASTNodeImporter::VisitClassTemplateDecl(ClassTemplateDecl *D) {
     // and this time the lookup finds the previous fwd friend class template.
     // In this case we must set up the previous decl for the templated decl.
     if (!ToTemplated->getPreviousDecl()) {
+      assert(FoundByLookup->getTemplatedDecl() &&
+             "Found decl must have its templated decl set");
       CXXRecordDecl *PrevTemplated =
           FoundByLookup->getTemplatedDecl()->getMostRecentDecl();
       if (ToTemplated != PrevTemplated)
@@ -5508,8 +5511,11 @@ ASTNodeImporter::VisitFunctionTemplateDecl(FunctionTemplateDecl *D) {
   if (ToD)
     return ToD;
 
+  const FunctionTemplateDecl *FoundByLookup = nullptr;
+
   // Try to find a function in our own ("to") context with the same name, same
   // type, and in the same context as the function we're importing.
+  // FIXME Split this into a separate function.
   if (!LexicalDC->isFunctionOrMethod()) {
     unsigned IDNS = Decl::IDNS_Ordinary | Decl::IDNS_OrdinaryFriend;
     auto FoundDecls = Importer.findDeclsInToCtx(DC, Name);
@@ -5517,18 +5523,21 @@ ASTNodeImporter::VisitFunctionTemplateDecl(FunctionTemplateDecl *D) {
       if (!FoundDecl->isInIdentifierNamespace(IDNS))
         continue;
 
-      if (auto *FoundFunction =
-          dyn_cast<FunctionTemplateDecl>(FoundDecl)) {
-        if (FoundFunction->hasExternalFormalLinkage() &&
+      if (auto *FoundTemplate = dyn_cast<FunctionTemplateDecl>(FoundDecl)) {
+        if (FoundTemplate->hasExternalFormalLinkage() &&
             D->hasExternalFormalLinkage()) {
-          if (IsStructuralMatch(D, FoundFunction)) {
-            Importer.MapImported(D, FoundFunction);
-            // FIXME: Actually try to merge the body and other attributes.
-            return FoundFunction;
+          if (IsStructuralMatch(D, FoundTemplate)) {
+            FunctionTemplateDecl *TemplateWithDef =
+                getTemplateDefinition(FoundTemplate);
+            if (D->isThisDeclarationADefinition() && TemplateWithDef) {
+              return Importer.MapImported(D, TemplateWithDef);
+            }
+            FoundByLookup = FoundTemplate;
+            break;
           }
+          // TODO: handle conflicting names
         }
       }
-      // TODO: handle conflicting names
     }
   }
 
@@ -5547,10 +5556,25 @@ ASTNodeImporter::VisitFunctionTemplateDecl(FunctionTemplateDecl *D) {
     return ToFunc;
 
   TemplatedFD->setDescribedFunctionTemplate(ToFunc);
+
   ToFunc->setAccess(D->getAccess());
   ToFunc->setLexicalDeclContext(LexicalDC);
-
   LexicalDC->addDeclInternal(ToFunc);
+
+  if (FoundByLookup) {
+    auto *Recent =
+        const_cast<FunctionTemplateDecl *>(FoundByLookup->getMostRecentDecl());
+    if (!TemplatedFD->getPreviousDecl()) {
+      assert(FoundByLookup->getTemplatedDecl() &&
+             "Found decl must have its templated decl set");
+      auto *PrevTemplated =
+          FoundByLookup->getTemplatedDecl()->getMostRecentDecl();
+      if (TemplatedFD != PrevTemplated)
+        TemplatedFD->setPreviousDecl(PrevTemplated);
+    }
+    ToFunc->setPreviousDecl(Recent);
+  }
+
   return ToFunc;
 }