Instantiate incomplete class used in template method.

If a class is absent from instantiation and is incomplete, instantiate it as
an incomplete class thus avoiding compiler crash.

This change fixes PR18653.

Differential Revision: http://reviews.llvm.org/D8281

llvm-svn: 236426

2 files changed, 13 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 62b506276e6..18747825537 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -2788,6 +2788,11 @@ LocalInstantiationScope::findInstantiationOf(const Decl *D) {
       isa<TemplateTemplateParmDecl>(D))
     return nullptr;
 
+  // Tag type may be referenced prior to definition, in this case it does not
+  // have instantiation yet.
+  if (isa<TagDecl>(D))
+    return nullptr;
+
   // If we didn't find the decl, then we either have a sema bug, or we have a
   // forward reference to a label declaration.  Return null to indicate that
   // we have an uninstantiated label.
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 8f2e95a6152..41245d9b3fd 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -4434,6 +4434,14 @@ NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
     if (D->isInvalidDecl())
       return nullptr;
 
+    // Tag type may be referenced prior to definition, in this case it must be
+    // instantiated now.
+    if (const TagDecl *TD = dyn_cast<TagDecl>(D)) {
+      Decl *Inst = SubstDecl(D, CurContext, TemplateArgs);
+      CurrentInstantiationScope->InstantiatedLocal(D, Inst);
+      return cast<TypeDecl>(Inst);
+    }
+
     // If we didn't find the decl, then we must have a label decl that hasn't
     // been found yet.  Lazily instantiate it and return it now.
     assert(isa<LabelDecl>(D));