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

Tue Aug 11 15:46:49 PDT 2015

On Tue, Aug 11, 2015 at 3:35 PM, Nathan Wilson <nwilson20 at gmail.com> wrote:

>
>
> 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.
>

Is there any reason to duplicate this rather than reusing the same
diagnostic?

> 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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