Improve parser recovery when we encounter a dependent template name

that is missing the 'template' keyword, e.g., 

  t->getAs<T>()

where getAs is a member of an unknown specialization. C++ requires
that we treat "getAs" as a value, but that would fail to parse since T
is the name of a type. We would then fail at the '>', since a type
cannot be followed by a '>'.

This is a very common error for C++ programmers to make, especially
since GCC occasionally allows it when it shouldn't (as does Visual
C++). So, when we are in this case, we use tentative parsing to see if
the tokens starting at "<" can only be parsed as a template argument
list. If so, we produce a diagnostic with a fix-it that states that
the 'template' keyword is needed:

test/SemaTemplate/dependent-template-recover.cpp:5:8: error: 'template' keyword
      is required to treat 'getAs' as a dependent template name
    t->getAs<T>();
       ^
       template 

This is just a start of this patch; I'd like to apply the same
approach to everywhere that a template-id with dependent template name
can be parsed.

llvm-svn: 104406

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
index bfcb6e7ee76..37475d23fe0 100644
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -980,10 +980,11 @@ bool Parser::TryAnnotateTypeOrScopeToken(bool EnteringContext) {
       TemplateTy Template;
       UnqualifiedId TemplateName;
       TemplateName.setIdentifier(Tok.getIdentifierInfo(), Tok.getLocation());
+      bool MemberOfUnknownSpecialization;
       if (TemplateNameKind TNK
             = Actions.isTemplateName(CurScope, SS, TemplateName, 
                                      /*ObjectType=*/0, EnteringContext,
-                                     Template)) {
+                                     Template, MemberOfUnknownSpecialization)) {
         // Consume the identifier.
         ConsumeToken();
         if (AnnotateTemplateIdToken(Template, TNK, &SS, TemplateName)) {