Correct error recovery when missing 'class' in a template template parameter.

The diagnostic message correctly informs the user that they have omitted the
'class' keyword, but neither suggests this insertion as a fixit, nor attempts
to recover as if they had provided the keyword.

This fixes the recovery, adds the fixit, and adds a separate diagnostic and
corresponding replacement fixit for cases where the user wrote 'struct' or
'typename' instead of 'class' (suggested by Richard Smith as a possible common
mistake).

I'm not sure the diagnostic message for either the original or new cases feel
very Clang-esque, so I'm open to suggestions there. The fixit hints make it
fairly easy to see what's required, though.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@153887 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang/Basic/DiagnosticParseKinds.td b/include/clang/Basic/DiagnosticParseKinds.td
index 35acec5..b3a0ebd 100644
--- a/include/clang/Basic/DiagnosticParseKinds.td
+++ b/include/clang/Basic/DiagnosticParseKinds.td
@@ -480,6 +480,7 @@
 def err_expected_comma_greater : Error<
   "expected ',' or '>' in template-parameter-list">;
 def err_expected_class_before : Error<"expected 'class' before '%0'">;
+def err_expected_class_instead : Error<"expected 'class' instead of '%0'">;
 def err_template_spec_syntax_non_template : Error<
   "identifier followed by '<' indicates a class template specialization but "
   "%0 %select{does not refer to a template|refers to a function "
diff --git a/lib/Parse/ParseTemplate.cpp b/lib/Parse/ParseTemplate.cpp
index 305f07b..4745193 100644
--- a/lib/Parse/ParseTemplate.cpp
+++ b/lib/Parse/ParseTemplate.cpp
@@ -540,12 +540,17 @@
 
   // Generate a meaningful error if the user forgot to put class before the
   // identifier, comma, or greater.
-  if (!Tok.is(tok::kw_class)) {
-    Diag(Tok.getLocation(), diag::err_expected_class_before)
-      << PP.getSpelling(Tok);
-    return 0;
-  }
-  ConsumeToken();
+  if (Tok.is(tok::kw_typename) || Tok.is(tok::kw_struct)) {
+    Diag(Tok.getLocation(), diag::err_expected_class_instead)
+      << PP.getSpelling(Tok)
+      << FixItHint::CreateReplacement(Tok.getLocation(), "class");
+    ConsumeToken();
+  } else if (!Tok.is(tok::kw_class))
+      Diag(Tok.getLocation(), diag::err_expected_class_before)
+        << PP.getSpelling(Tok)
+        << FixItHint::CreateInsertion(Tok.getLocation(), "class ");
+  else 
+    ConsumeToken();
 
   // Parse the ellipsis, if given.
   SourceLocation EllipsisLoc;
diff --git a/test/FixIt/fixit.cpp b/test/FixIt/fixit.cpp
index 9ed4f3b..c881c63 100644
--- a/test/FixIt/fixit.cpp
+++ b/test/FixIt/fixit.cpp
@@ -199,3 +199,8 @@
   expected-error {{missing 'typename' prior to dependent}}
   return Mystery<T>::get();
 }
+
+template<template<typename> Foo, // expected-error {{expected 'class' before 'Foo'}}
+         template<typename> typename Bar, // expected-error {{expected 'class' instead of 'typename'}}
+         template<typename> struct Baz> // expected-error {{expected 'class' instead of 'struct'}}
+void func();
diff --git a/test/Parser/cxx-template-decl.cpp b/test/Parser/cxx-template-decl.cpp
index 4717dbb..72f2d7d 100644
--- a/test/Parser/cxx-template-decl.cpp
+++ b/test/Parser/cxx-template-decl.cpp
@@ -11,10 +11,8 @@
 // expected-warning {{declaration does not declare anything}}
 template <template X> struct Err1; // expected-error {{expected '<' after 'template'}} \
 // expected-error{{extraneous}}
-template <template <typename> > struct Err2;       // expected-error {{expected 'class' before '>'}} \
-// expected-error{{extraneous}}
-template <template <typename> Foo> struct Err3;    // expected-error {{expected 'class' before 'Foo'}} \
-// expected-error{{extraneous}}
+template <template <typename> > struct Err2;       // expected-error {{expected 'class' before '>'}}
+template <template <typename> Foo> struct Err3;    // expected-error {{expected 'class' before 'Foo'}}
 
 // Template function declarations
 template <typename T> void foo();