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

1 files changed, 8 insertions, 0 deletions

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));