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

[Richard Smith]

                                               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.
> >
> >>
> >>
> >> _______________________________________________
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> >> 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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