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

[Alp Toker]

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.

>
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