[PATCH] [RFC] PR20146 - Cannot return void with qualifiers
Richard Smith
richard at metafoo.co.uk
Mon Aug 4 15:55:25 PDT 2014
Thanks, this patch looks nice. One comment and one tiny nit:
@@ -2043,10 +2043,21 @@
static void diagnoseIgnoredFunctionQualifiers(Sema &S, QualType RetTy,
Declarator &D,
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 in C (allowed in C++).
+ if (!S.getLangOpts().CPlusPlus &&
+ RetTy->isVoidType() && RetTy.getCVRQualifiers()) {
+ diagnoseIgnoredQualifiers(S, diag::ext_func_returning_qualified_void,
+ RetTy.getCVRQualifiers(),
D.getIdentifierLoc());
+ return;
This looks like you're diagnosing (and potentially rejecting) cv-qualified
void on all function types. To my reading, C's 6.9.1/3 only applies to
function definitions. For whatever reason, this appears to be valid:
const void f(); // no definition
const void (*p)() = NULL;
I think we should still warn on such cases, but probably shouldn't reject
them in -pedantic-errors mode.
[Such a function also can't be called. See also https://gcc.gnu.org/PR35210;
we fail to reject such constructs.]
unsigned AtomicQual = RetTy->isAtomicType() ? DeclSpec::TQ_atomic :
0;
- diagnoseIgnoredQualifiers(S, RetTy.getCVRQualifiers() | AtomicQual,
- D.getIdentifierLoc());
+ diagnoseIgnoredQualifiers(S, diag::warn_qual_return_type,
Too much indentation here.
On Mon, Aug 4, 2014 at 9:52 AM, Zach Davis <zdavkeos at gmail.com> wrote:
> { including cfe-commits }
>
> Thanks for the word-smithing, and for forcing me to do it the right
> way by taking advantage of Sema::
> diagnoseIgnoredQualifiers...
>
> - Changed the wording of the warning
> - Parameterized Sema::diagnoseIgnoredQualifiers so we can use our new
> diagnostic text
>
> On Wed, Jul 16, 2014 at 5:35 PM, Richard Smith <richard at metafoo.co.uk>
> wrote:
> > It's a little confusing to put "X cannot have Y" in an ExtWarn; we
> usually
> > phrase such things as "X has Y" or "ISO C does not allow X to have Y" to
> > make it clear that we may be allowing this despite the standard saying
> > otherwise. Also, the trailing %0 in the diagnostic text doesn't seem to
> fit
> > into the sentence very well. Suggestion:
> >
> > ISO C does not allow %0 qualifier%plural{1:|:s} on void return type
> >
> > ... and use Sema::diagnoseIgnoredQualifiers to produce a diagnostic with
> the
> > relevant qualifiers listed.
> >
> > Other than the diagnostic wording, this looks good to me, thanks.
> >
> > On Thu, Jul 10, 2014 at 7:57 AM, Zach Davis <zdavkeos at gmail.com> wrote:
> >>
> >> 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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