[PATCH] D11916: [CONCEPTS] Add diagnostic; invalid tag when concept specified

[Nathan Wilson via cfe-commits]

On Tue, Aug 11, 2015 at 4:54 PM, Richard Smith <richard at metafoo.co.uk>
wrote:

> On Tue, Aug 11, 2015 at 2:46 PM, Nathan Wilson <nwilson20 at gmail.com>
> wrote:
>
>> Okay, I'll make the change.
>>
>> Hmm, do you guys have any suggestions as far as renaming err_concept_decl_non_template?
>> How about err_concept_specifier_non_template?
>>
>
> Maybe err_concept_wrong_decl_kind?
>

I'd be okay with that.

Is okay to have two different tags with the same text?

We'd use err_concept_decl_non_template in HandleDeclarator when we
encounter a non-template when `concept` is specified, and we could use
err_concept_wrong_decl_kind
for the checks in this Patch.


>
>
>> We'd have to keep in mind that err_concept_decl_non_template is also
>> used outside of this check, i.e. `concept bool = true`.
>>
>>
>> On Tue, Aug 11, 2015 at 4:19 PM, Hubert Tong <
>> hubert.reinterpretcast at gmail.com> wrote:
>>
>>> From Aaron's description of the user experience, I think the
>>> err_concept_decl_non_template message text is good (although
>>> err_concept_decl_non_template might need to be renamed).
>>>
>>> -- HT
>>>
>>> On Tue, Aug 11, 2015 at 4:01 PM, Aaron Ballman <aaron.ballman at gmail.com>
>>> wrote:
>>>
>>>> On Tue, Aug 11, 2015 at 3:36 PM, Nathan Wilson <nwilson20 at gmail.com>
>>>> wrote:
>>>> >
>>>> >
>>>> > On Tue, Aug 11, 2015 at 8:54 AM, Aaron Ballman <
>>>> aaron.ballman at gmail.com>
>>>> > wrote:
>>>> >>
>>>> >> On Mon, Aug 10, 2015 at 3:00 PM, Nathan Wilson <nwilson20 at gmail.com>
>>>> >> wrote:
>>>> >> > nwilson created this revision.
>>>> >> > nwilson added reviewers: rsmith, hubert.reinterpretcast,
>>>> fraggamuffin,
>>>> >> > faisalv, aaron.ballman.
>>>> >> > nwilson added a subscriber: cfe-commits.
>>>> >> >
>>>> >> > Adding check to emit diagnostic for invalid tag when concept is
>>>> >> > specified and associated tests.
>>>> >> >
>>>> >> > http://reviews.llvm.org/D11916
>>>> >> >
>>>> >> > Files:
>>>> >> >   include/clang/Basic/DiagnosticSemaKinds.td
>>>> >> >   lib/Sema/SemaDecl.cpp
>>>> >> >   test/SemaCXX/cxx-concept-declaration.cpp
>>>> >> >
>>>> >> > Index: test/SemaCXX/cxx-concept-declaration.cpp
>>>> >> > ===================================================================
>>>> >> > --- test/SemaCXX/cxx-concept-declaration.cpp
>>>> >> > +++ test/SemaCXX/cxx-concept-declaration.cpp
>>>> >> > @@ -23,3 +23,13 @@
>>>> >> >  template<typename T>
>>>> >> >  concept bool D6; // expected-error {{variable concept declaration
>>>> must
>>>> >> > be initialized}}
>>>> >> >
>>>> >> > +// Tag
>>>> >> > +concept class CC1 {}; // expected-error {{class cannot be marked
>>>> >> > concept}}
>>>> >> > +concept struct CS1 {}; // expected-error {{struct cannot be marked
>>>> >> > concept}}
>>>> >> > +concept union CU1 {}; // expected-error {{union cannot be marked
>>>> >> > concept}}
>>>> >> > +concept enum CE1 {}; // expected-error {{enum cannot be marked
>>>> >> > concept}}
>>>> >> > +template <typename T> concept class TCC1 {}; // expected-error
>>>> {{class
>>>> >> > cannot be marked concept}}
>>>> >> > +template <typename T> concept struct TCS1 {}; // expected-error
>>>> >> > {{struct cannot be marked concept}}
>>>> >> > +template <typename T> concept union TCU1 {}; // expected-error
>>>> {{union
>>>> >> > cannot be marked concept}}
>>>> >> > +
>>>> >> > +extern concept bool ExtC; // expected-error {{'concept' can only
>>>> appear
>>>> >> > on the definition of a function template or variable template}}
>>>> >> > Index: lib/Sema/SemaDecl.cpp
>>>> >> > ===================================================================
>>>> >> > --- lib/Sema/SemaDecl.cpp
>>>> >> > +++ lib/Sema/SemaDecl.cpp
>>>> >> > @@ -3662,6 +3662,19 @@
>>>> >> >      return TagD;
>>>> >> >    }
>>>> >> >
>>>> >> > +  if (DS.isConceptSpecified()) {
>>>> >> > +    // C++ Concepts TS [dcl.spec.concept]p1: A concept definition
>>>> >> > refers to
>>>> >> > +    // either a function concept and its definition or a variable
>>>> >> > concept and
>>>> >> > +    // its initializer.
>>>> >> > +    if (Tag)
>>>> >> > +      Diag(DS.getConceptSpecLoc(), diag::err_concept_tag)
>>>> >> > +          << GetDiagnosticTypeSpecifierID(DS.getTypeSpecType());
>>>> >> > +    else
>>>> >> > +      Diag(DS.getConceptSpecLoc(),
>>>> >> > diag::err_concept_decl_non_template);
>>>> >> > +    // Don't emit warnings after this error.
>>>> >> > +    return TagD;
>>>> >> > +  }
>>>> >>
>>>> >> I'm not certain I understand why we need two different diagnostics
>>>> for
>>>> >> this case. I think err_concept_decl_non_template is sufficiently
>>>> clear
>>>> >> for both.
>>>> >>
>>>> >> ~Aaron
>>>> >
>>>> >
>>>> > This was based on how constexpr handles these checks.
>>>> >
>>>> > Perhaps someone can correct me if I'm wrong, but I believe the idea
>>>> is that
>>>> > when the `struct` tag exists, for example, we think the user meant to
>>>> > declare a `struct` and not the start of a `concept` declaration. So,
>>>> the
>>>> > `concept` specifier would be erroneous and we try give a more helpful
>>>> > diagnostic.
>>>>
>>>> It could just be me, but I don't find the new diagnostic particularly
>>>> helpful. "foo cannot be marked concept" tells me why I have an error
>>>> but does not tell me what to do about it. "'concept' can only appear
>>>> on the definition of a function template or variable template" tells
>>>> me what I need to do to not have the error in the first place, as well
>>>> as why I have the error.
>>>>
>>>> However, others may have differing opinions on the subject.
>>>>
>>>> ~Aaron
>>>>
>>>> >
>>>> > I would need to add/fix the test case for this, but I tend to think
>>>> the
>>>> > declaration such as `concept bool;` could be the users intention to
>>>> try to
>>>> > create a `concept` declaration which is where the
>>>> > err_concept_decl_non_template comes in.
>>>> >
>>>> >>
>>>> >>
>>>> >> > +
>>>> >> >    DiagnoseFunctionSpecifiers(DS);
>>>> >> >
>>>> >> >    if (DS.isFriendSpecified()) {
>>>> >> > Index: include/clang/Basic/DiagnosticSemaKinds.td
>>>> >> > ===================================================================
>>>> >> > --- include/clang/Basic/DiagnosticSemaKinds.td
>>>> >> > +++ include/clang/Basic/DiagnosticSemaKinds.td
>>>> >> > @@ -1973,6 +1973,8 @@
>>>> >> >    "function concept declaration must be a definition">;
>>>> >> >  def err_var_concept_not_initialized : Error<
>>>> >> >    "variable concept declaration must be initialized">;
>>>> >> > +def err_concept_tag : Error<
>>>> >> > +  "%select{class|struct|interface|union|enum}0 cannot be marked
>>>> >> > concept">;
>>>> >> >
>>>> >> >  // C++11 char16_t/char32_t
>>>> >> >  def warn_cxx98_compat_unicode_type : Warning<
>>>> >> >
>>>> >> >
>>>> >
>>>> >
>>>>
>>>
>>>
>>
>
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