faisalv added inline comments.
================
Comment at: lib/Parse/ParseTemplate.cpp:181
+ TemplateParameterList *TPL = ParamLists[0];
+ if (TPL->getLAngleLoc().getLocWithOffset(1) == TPL->getRAngleLoc()) {
+ Diag(TPL->getTemplateLoc(),
----------------
changyu wrote:
> There's one problem here.
>
> I added this `if` in attempt to catch the following case (but it's wrong)
> ```
> template<> concept D1 = true; // expected-error {{expected template
> parameter}}
> ```
> The problem is I'm not sure how to differentiate between the above situation
> and the following
> ```
> template<concept T> concept D1 = true; // expected-error {{expected
> template parameter}}
> ```
> Both have an empty template parameter list. The latter case has diagnostic
> printed by `ParseNonTypeTemplateParameter` while the former has not (so we
> try to catch it here).
>
> What should we do?
>
I was thinking that we would just emit a (redundant in the case of a bad
template parameter) message in Sema if the template-parameters are empty that
explicit specializations are not allowed here. while it would be a little
misleading in the invalid template parameter case - to fix this robustly would
require some fine-tuning and correcting some of the
handshaking/error-propagation between the parsing of the template parameters
and the code that calls it, I think. I would vote for not holding up this
patch for that, unless you feel strongly you'd like to fix that behavior - then
we can try and work on that first?
Thoughts?
https://reviews.llvm.org/D40381
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