[PATCH] [RFC] PR20146 - Cannot return void with qualifiers

[Zach Davis]

Thanks for the suggestions. In this patch:

- The error is now a warning with a "return-qualified-void" group
- The warning only applies to C code
- Re-formatted the code

The warning is currently on by default.


On Tue, Jul 8, 2014 at 7:29 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>                                                unsigned FunctionChunkIndex)
> {
> +
> +  // C99 6.9.1/3: The return type of a function shall be void or
> +  // an object type other than array type.
> +  // A return type of void cannot be qualified.
>
>
> Micro-nit: no blank line at the start of a function body.
>
> This should only apply in C; 'const void' is explicitly a valid return type
> in C++ (see for instance 6.6.3/2, "a function with the return type cv
> void").
>
> Please make this an ExtWarn rather than an error, since GCC accepts it by
> default (and doesn't even diagnose it if it's on a non-definition function
> declaration), and it seems thoroughly harmless.
>
> On Mon, Jul 7, 2014 at 9:22 AM, Zach Davis <zdavkeos at gmail.com> wrote:
>>
>> Thanks for the comments.  I have:
>>
>> - Cleaned up the code
>> - Made the warning an error
>> - Moved the check into diagnoseIgnoredFunctionQualifiers()
>> - Added 3 test cases to test/Sema/function.c
>>
>>
>>
>> On Thu, Jul 3, 2014 at 4:41 PM, Alp Toker <alp at nuanti.com> wrote:
>> >
>> > On 03/07/2014 22:08, Zach Davis wrote:
>> >>
>> >> As reported in bug 20146, a function cannot have a return type of
>> >> 'void' with qualifiers.
>> >>
>> >> Clang does emit a warning that the qualifiers are ignored
>> >> [-Wignored-qualifiers] (off by default), but according to [1] this
>> >> code is non-conforming.
>> >>
>> >> The attached patch makes Clang issue a more specific warning like so:
>> >>
>> >>      test3.c:8:18: warning: return type of void cannot be qualified
>> >> 'volatile void'
>> >>      volatile void baz(void) { return; }
>> >>                    ^
>> >>
>> >> [1]http://www.open-std.org/jtc1/sc22/wg14/docs/rr/dr_113.html
>> >
>> >
>> > It seems fine to make this a hard error instead of a warning for C, and
>> > probably C++ too. Richard?
>> >
>> >>
>> >> 20146_return_qual_void.patch
>> >>
>> >>
>> >> Index: lib/Sema/SemaType.cpp
>> >> ===================================================================
>> >> --- lib/Sema/SemaType.cpp       (revision 212275)
>> >> +++ lib/Sema/SemaType.cpp       (working copy)
>> >> @@ -2741,6 +2741,15 @@
>> >>           D.setInvalidType(true);
>> >>         }
>> >>   +      // C99 6.9.1/3: The return type of a function shall be void or
>> >> +      // an object type other than array type.
>> >> +      // A return type of void cannot be qualified.
>> >> +      if (T->isVoidType() && T.getCVRQualifiers()) {
>> >> +          unsigned diagID = diag::warn_func_returning_qualified_void;
>> >
>> >
>> > Just pass the ID directly to Diag().
>> >
>> >> +          S.Diag(DeclType.Loc, diagID) << T;
>> >> +          D.setInvalidType(true);
>> >> +      }
>> >> +
>> >
>> >
>> > How about placing this check with an early return at the top of
>> > diagnoseIgnoredFunctionQualifiers()?
>> >
>> >>         // Do not allow returning half FP value.
>> >>         // FIXME: This really should be in BuildFunctionType.
>> >>         if (T->isHalfType()) {
>> >> Index: include/clang/Basic/DiagnosticSemaKinds.td
>> >> ===================================================================
>> >> --- include/clang/Basic/DiagnosticSemaKinds.td  (revision 212275)
>> >> +++ include/clang/Basic/DiagnosticSemaKinds.td  (working copy)
>> >> @@ -4160,6 +4160,8 @@
>> >>     def err_func_returning_array_function : Error<
>> >>     "function cannot return %select{array|function}0 type %1">;
>> >> +def warn_func_returning_qualified_void : Warning<
>> >> +  "return type of void cannot be qualified %0">;
>> >
>> >
>> > (Warnings need to have a diagnostic group / -W flag, though it doesn't
>> > matter if you go ahead and make it an error.)
>> >
>> >>   def err_field_declared_as_function : Error<"field %0 declared as a
>> >> function">;
>> >>   def err_field_incomplete : Error<"field has incomplete type %0">;
>> >>   def ext_variable_sized_type_in_struct : ExtWarn<
>> >
>> >
>> > Test case?
>> >
>> > Alp.
>> >
>> >>
>> >>
>> >> _______________________________________________
>> >> cfe-commits mailing list
>> >> cfe-commits at cs.uiuc.edu
>> >> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>> >
>> >
>> > --
>> > http://www.nuanti.com
>> > the browser experts
>> >
>
>
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