Allow the parser to recover gracefully if a typename is used to introduce a decltype type.
In Microsoft mode, we emit a warning instead of an error.

This fixes a couple of errors when parsing the MSVC 11 RC headers with clang.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@160613 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Parse/Parser.cpp b/lib/Parse/Parser.cpp
index e95af05..760c7bf 100644
--- a/lib/Parse/Parser.cpp
+++ b/lib/Parse/Parser.cpp
@@ -1334,10 +1334,12 @@
                                        0, /*IsTypename*/true))
       return true;
     if (!SS.isSet()) {
-      if (Tok.is(tok::identifier) || Tok.is(tok::annot_template_id)) {
+      if (Tok.is(tok::identifier) || Tok.is(tok::annot_template_id) ||
+          Tok.is(tok::annot_decltype)) {
         // Attempt to recover by skipping the invalid 'typename'
-        if (!TryAnnotateTypeOrScopeToken(EnteringContext, NeedType) &&
-            Tok.isAnnotation()) {
+        if (Tok.is(tok::annot_decltype) ||
+            (!TryAnnotateTypeOrScopeToken(EnteringContext, NeedType) &&
+            Tok.isAnnotation())) {
           unsigned DiagID = diag::err_expected_qualified_after_typename;
           // MS compatibility: MSVC permits using known types with typename.
           // e.g. "typedef typename T* pointer_type"
diff --git a/test/SemaCXX/MicrosoftCompatibility.cpp b/test/SemaCXX/MicrosoftCompatibility.cpp
index 74d54ef..6a48f36 100644
--- a/test/SemaCXX/MicrosoftCompatibility.cpp
+++ b/test/SemaCXX/MicrosoftCompatibility.cpp
@@ -4,6 +4,8 @@
 typedef unsigned short char16_t;
 typedef unsigned int char32_t;
 
+typename decltype(3) a; // expected-warning {{expected a qualified name after 'typename'}}
+
 namespace ms_conversion_rules {
 
 void f(float a);