From c4450437ec91334d81a28084c4cf637cfdd8bbcb Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aaron@aaronballman.com>
Date: Sat, 7 Sep 2019 20:14:09 +0000
Subject: [PATCH] Fixes an assertion while instantiating a template with an
 incomplete typo-corrected type.

Fixes PR35682. When a template in instantiated with an incomplete typo corrected type an assertion can trigger if the -ferror-limit is used to reduce the number of errors.

Patch by Mark de Wever.

llvm-svn: 371320
---
 clang/lib/Sema/SemaTemplate.cpp                    |  8 ++-
 ...tiate-incomplete-typo-suggested-error-limit.cpp | 60 ++++++++++++++++++++++
 2 files changed, 66 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/SemaTemplate/instantiate-incomplete-typo-suggested-error-limit.cpp

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index d7a1d9e..001e433 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -735,9 +735,13 @@ Sema::BuildDependentDeclRefExpr(const CXXScopeSpec &SS,
                                 SourceLocation TemplateKWLoc,
                                 const DeclarationNameInfo &NameInfo,
                                 const TemplateArgumentListInfo *TemplateArgs) {
+  // DependentScopeDeclRefExpr::Create requires a valid QualifierLoc
+  NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
+  if (!QualifierLoc)
+    return ExprError();
+
   return DependentScopeDeclRefExpr::Create(
-      Context, SS.getWithLocInContext(Context), TemplateKWLoc, NameInfo,
-      TemplateArgs);
+      Context, QualifierLoc, TemplateKWLoc, NameInfo, TemplateArgs);
 }
 
 
diff --git a/clang/test/SemaTemplate/instantiate-incomplete-typo-suggested-error-limit.cpp b/clang/test/SemaTemplate/instantiate-incomplete-typo-suggested-error-limit.cpp
new file mode 100644
index 0000000..7f02b45
--- /dev/null
+++ b/clang/test/SemaTemplate/instantiate-incomplete-typo-suggested-error-limit.cpp
@@ -0,0 +1,60 @@
+// RUN: not %clang -fsyntax-only -std=c++11 -ferror-limit=1 %s 2>&1 | FileCheck %s
+
+// Test case for PR35682.
+// The issue be caused by the typo correction that changes String to the
+// incomplete type string. The example is based on the std::pair code and
+// reduced to a minimal test case. When using std::pair the issue can only be
+// reproduced when using the -stdlib=libc++ compiler option.
+
+template <class T> class allocator;
+
+template <class charT> struct char_traits;
+
+template <class CharT, class Traits = char_traits<CharT>,
+          class Allocator = allocator<CharT>>
+class basic_string;
+typedef basic_string<char, char_traits<char>, allocator<char>> string;
+
+template <bool, class Tp = void> struct enable_if {};
+template <class Tp> struct enable_if<true, Tp> { typedef Tp type; };
+
+template <class Tp, Tp v> struct integral_constant {
+  static constexpr const Tp value = v;
+  typedef Tp value_type;
+  typedef integral_constant type;
+
+  constexpr operator value_type() const noexcept { return value; }
+  constexpr value_type operator()() const noexcept { return value; }
+};
+
+template <class Tp, Tp v> constexpr const Tp integral_constant<Tp, v>::value;
+
+using true_type = integral_constant<bool, true>;
+using false_type = integral_constant<bool, false>;
+
+template <class Tp, class Up> struct is_same : public false_type {};
+template <class Tp> struct is_same<Tp, Tp> : public true_type {};
+
+template <class T> struct single {
+  typedef T first_type;
+
+  T first;
+
+  struct CheckArgs {
+    template <class U1> static constexpr bool enable_implicit() {
+      return is_same<first_type, U1>::value;
+    }
+  };
+
+  template <class U1,
+            typename enable_if<CheckArgs::template enable_implicit<U1>(),
+                               bool>::type = false>
+  single(U1 &&u1);
+};
+
+using SetKeyType = String;
+single<SetKeyType> v;
+
+// CHECK: error: unknown type name 'String'; did you mean 'string'?
+// CHECK: fatal error: too many errors emitted, stopping now [-ferror-limit=]
+// CHECK-NOT: Assertion{{.*}}failed
-- 
2.7.4