From 1ed7bfbd4b52795baa6a6a11e7c59d991fb500ef Mon Sep 17 00:00:00 2001
From: Nikola Smiljanic <popizdeh@gmail.com>
Date: Sun, 24 Aug 2014 23:28:47 +0000
Subject: [PATCH] PR20716 - Crash when recovering from type in known dependent
 base.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@216352 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/clang/AST/DeclTemplate.h              |  2 +-
 lib/Sema/SemaDecl.cpp                         |  5 ++++-
 .../ms-lookup-template-base-classes.cpp       | 20 +++++++++++++++++++
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/include/clang/AST/DeclTemplate.h b/include/clang/AST/DeclTemplate.h
index 980a06e35b..7c0da8ff0c 100644
--- a/include/clang/AST/DeclTemplate.h
+++ b/include/clang/AST/DeclTemplate.h
@@ -236,7 +236,7 @@ protected:
       TemplateParams(nullptr) {}
 
   // Construct a template decl with the given name and parameters.
-  // Used when there is not templated element (tt-params, alias?).
+  // Used when there is not templated element (tt-params).
   TemplateDecl(Kind DK, DeclContext *DC, SourceLocation L,
                DeclarationName Name, TemplateParameterList *Params)
     : NamedDecl(DK, DC, L, Name), TemplatedDecl(nullptr),
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 0244d4c4a3..5293188214 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -152,7 +152,10 @@ static ParsedType recoverFromTypeInKnownDependentBase(Sema &S,
     auto *TD = TST->getTemplateName().getAsTemplateDecl();
     if (!TD)
       continue;
-    auto *BasePrimaryTemplate = cast<CXXRecordDecl>(TD->getTemplatedDecl());
+    auto *BasePrimaryTemplate =
+        dyn_cast_or_null<CXXRecordDecl>(TD->getTemplatedDecl());
+    if (!BasePrimaryTemplate)
+      continue;
     // FIXME: Allow lookup into non-dependent bases of dependent bases, possibly
     // by calling or integrating with the main LookupQualifiedName mechanism.
     for (NamedDecl *ND : BasePrimaryTemplate->lookup(&II)) {
diff --git a/test/SemaTemplate/ms-lookup-template-base-classes.cpp b/test/SemaTemplate/ms-lookup-template-base-classes.cpp
index 4bdb97bbbd..979782f1cb 100644
--- a/test/SemaTemplate/ms-lookup-template-base-classes.cpp
+++ b/test/SemaTemplate/ms-lookup-template-base-classes.cpp
@@ -470,3 +470,23 @@ void f() {
   UndefVar.method(); // expected-error {{use of undeclared identifier 'UndefVar'}}
 }
 }
+
+namespace PR20716 {
+template <template <typename T> class A>
+struct B : A<int>
+{
+  XXX x; // expected-error {{unknown type name}}
+};
+
+template <typename T>
+struct C {};
+
+template <typename T>
+using D = C<T>;
+
+template <typename T>
+struct E : D<T>
+{
+  XXX x; // expected-error {{unknown type name}}
+};
+}
-- 
2.40.0