r188510 - Fix for dependent contexts in alias templates.

[Richard Smith]

On Thu, Aug 15, 2013 at 5:29 PM, Eli Friedman <eli.friedman at gmail.com>wrote:

> On Thu, Aug 15, 2013 at 4:59 PM, Eli Friedman <eli.friedman at gmail.com>wrote:
>
>> Author: efriedma
>> Date: Thu Aug 15 18:59:20 2013
>> New Revision: 188510
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=188510&view=rev
>> Log:
>> Fix for dependent contexts in alias templates.
>>
>> When we are parsing a type for an alias template, we are not entering
>> the context, so we can't look into dependent classes.  Make sure the
>> parser handles this correctly.
>>
>> PR16904.
>>
>> Modified:
>>     cfe/trunk/lib/Parse/ParseDecl.cpp
>>     cfe/trunk/test/SemaTemplate/alias-templates.cpp
>>
>> Modified: cfe/trunk/lib/Parse/ParseDecl.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/ParseDecl.cpp?rev=188510&r1=188509&r2=188510&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Parse/ParseDecl.cpp (original)
>> +++ cfe/trunk/lib/Parse/ParseDecl.cpp Thu Aug 15 18:59:20 2013
>> @@ -2436,7 +2436,7 @@ void Parser::ParseDeclarationSpecifiers(
>>
>>      case tok::coloncolon: // ::foo::bar
>>        // C++ scope specifier.  Annotate and loop, or bail out on error.
>> -      if (TryAnnotateCXXScopeToken(true)) {
>> +      if (TryAnnotateCXXScopeToken(EnteringContext)) {
>>          if (!DS.hasTypeSpecifier())
>>            DS.SetTypeSpecError();
>>          goto DoneWithDeclSpec;
>> @@ -2632,7 +2632,7 @@ void Parser::ParseDeclarationSpecifiers(
>>        // In C++, check to see if this is a scope specifier like
>> foo::bar::, if
>>        // so handle it as such.  This is important for ctor parsing.
>>        if (getLangOpts().CPlusPlus) {
>> -        if (TryAnnotateCXXScopeToken(true)) {
>> +        if (TryAnnotateCXXScopeToken(EnteringContext)) {
>>            if (!DS.hasTypeSpecifier())
>>              DS.SetTypeSpecError();
>>            goto DoneWithDeclSpec;
>>
>>
>
> Ugh... I just spent some more time thinking about this; while this fix
> doesn't break anything as far as I know, it isn't really complete.
>  Consider the following testcase:
>
> template <typename,typename>
>
> struct base {
>
>   template <typename> struct derived;
>
> };
>
> template <typename T, typename U, typename V> base<T, U>::derived<V> foo();
>
> There's a missing typename keyword, but clang fails to detect this.  Any
> suggestions?
>

This looks closely related to PR15554. Perhaps we could introduce an
'unknown' value for EnteringContext (where '<' is known to introduce a
template, but which is otherwise parsed as if we're not entering the
context), and then once we've parsed far enough to know whether we're
entering the context, either transform it to the concrete form or diagnose
missing 'template' keywords.
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