From 4c51174677306561eb4a18bb05b20cd3030d4b74 Mon Sep 17 00:00:00 2001
From: Serge Pavlov <sepavloff@gmail.com>
Date: Mon, 4 May 2015 16:44:39 +0000
Subject: 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
---
 clang/lib/Sema/SemaTemplateInstantiate.cpp     | 5 +++++
 clang/lib/Sema/SemaTemplateInstantiateDecl.cpp | 8 ++++++++
 2 files changed, 13 insertions(+)

(limited to 'clang/lib')

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));
-- 
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