[PATCH] PR16909: Diagnose missing 'typename' on dependent template

[Ben Langmuir]

> On Feb 18, 2015, at 7:45 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> 
> On Wed, Feb 18, 2015 at 5:20 PM, Ben Langmuir <blangmuir at apple.com <mailto:blangmuir at apple.com>> wrote:
> 
>> On Feb 18, 2015, at 5:09 PM, Richard Smith <richard at metafoo.co.uk <mailto:richard at metafoo.co.uk>> wrote:
>> 
>> Makes sense to me. I'm not too unhappy about the class.qual p2 case; it's not ideal, but the new diagnostic explains one way to fix the problem, which is in some sense an improvement, and it only arises if the user makes several errors all at once. A FIXME in the test would be nice, though.
> 
> Okay.
> 
>> 
>> Should we also diagnose the missing 'template' keyword? (I'd note that http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1710 <http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1710> removes the need for that keyword here, but isn't fully baked yet).
> 
> Yeah it’s probably better to not have the user recompile just to get the second error.
> 
>> 
>> More generally, should we rebuild the whole nested name specifier as a dependent specifier, rather than just the last component?
> 
> My goal was to match what was produced if you put in the typename and template keywords.  I’m willing to admit I might have got it wrong - it’s been a while since I traced through it.  I’ll take a look.
> 
> I agree that's what we should be doing. My concern is what happens if you have:
> 
>   template<typename T> X<T>::Y<T>::Z<T> f();
> 
> It looks like you'll only rebuild the X<T>::Y<T>::Z to be a dependent template name, and the X<T>::Y will be treated as a non-dependent name as a member of the primary X<T> template.

Okay, makes sense.  I should also add a test case like that.

>  
> Thanks for the review,
> 
> Ben
> 
>> 
>> On Mon, Jan 26, 2015 at 9:08 AM, Ben Langmuir <blangmuir at apple.com <mailto:blangmuir at apple.com>> wrote:
>> This patch diagnoses a missing ‘typename’ keyword on nested template types like A<T>::B<U>, to fix llvm.org/pr16909 <http://llvm.org/pr16909>. In addition to fixing an accepts-invalid, in C++11 such types would cause assertion failures and/or invalid LLVM IR when used with ‘auto’.
>> 
>> I’m not 100% sure if the changes to test/CXX/basic/basic.lookup/basic.lookup.qual/class.qual/p2.cpp are desirable, or if we should suppress the missing ‘typename’ diagnostic when we’re already recovering on X<T>::X<T>.  I’m open to suggestions :-)
>> 
>> Ben
>> 
>> 
>> 
>> 
> 
> 

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