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

Tue Aug 11 14:54:28 PDT 2015

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?

> 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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