faisalv added inline comments.
================
Comment at: lib/Sema/SemaTemplate.cpp:7735
+ ActOnDocumentableDecl(NewDecl);
+ CurContext->addDecl(NewDecl);
+ return NewDecl;
----------------
changyu wrote:
> faisalv wrote:
> > Why not use 'PushOnScopeChains' onto the enclosing scope?
> > Something along these lines:
> > assert(S->isTemplateParamScope() && S->getParent() &&
> > !S->getParent()->isTemplateParamScope() && "...");
> > PushOnScopeChains(NewDecl, S->getParent(),/*AddToContext*/true);
> The condition
> ```
> S->isTemplateParamScope()
> ```
> fails in this case
> ```
> template<concept T> concept D1 = true; // expected-error {{expected template
> parameter}}
> ```
>
> `ParseTemplateDeclarationOrSpecialization` calls `ParseTemplateParameters`
> which eventually calls `ParseNonTypeTemplateParameter`.
> `ParseNonTypeTemplateParameter` prints the diag and fails but does not cause
> `ParseTemplateParameters` to fail (I'm not sure why).
> `ParseTemplateDeclarationOrSpecialization` proceeds to parse the concept
> definition, and we get this
>
> ```
> /home/changyu/test.cpp:1:10: error: expected template parameter
> template<concept T> concept D1 = true; // expected-error {{expected template
> parameter}}
> ^
> clang: /home/changyu/git/llvm/tools/clang/lib/Sema/SemaTemplate.cpp:7747:
> clang::Decl* clang::Sema::ActOnConceptDefinition(clang::Scope*,
> clang::MultiTemplateParamsArg, clang::IdentifierInfo*, clang::SourceLocation,
> clang::Expr*): Assertion `S->isTemplateParamScope() && "Not in template param
> scope?"' failed.
> ```
>
> What should we do?
I think this occurs because our template parameter list is incorrectly
perceived as empty - i.e. once the error occurs - to continue processing errors
clang assumes this case is an explicit-specialization and replaces the template
parameter scope with the outer scope. I think the thing to do here - which
might also address the case where folks actually write 'template<> concept' is
to actually check if template-parameter-list is empty - and emit a diagnostic
about concepts can not be explicit specializations or some such ...
On a somewhat related note - i think the logic for signaling, handling and
propagating failures of parsing the template parameter list might be a little
broken (fixing which, might avoid triggering the assertion in template<concept>
but not template<>). I might submit a patch to fix that error handling-issue
separately - but either way I think we should handle the
explicit-specialization error?
Thoughts?
https://reviews.llvm.org/D40381
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