Re: [PATCH v3] c++: Accept elaborated-enum-base with pedwarn

[Alex Coplan <alex.coplan@arm.com>]

On 16/06/2023 09:07, Jason Merrill wrote:
> On 6/16/23 07:58, Alex Coplan wrote:
> > Hi,
> > 
> > This is a v3 patch addressing feedback for:
> > https://gcc.gnu.org/pipermail/gcc-patches/2023-June/621714.html
> > 
> > The only change since the previous version is that the new option is
> > documented in invoke.texi (and the description in c.opt was shortened as
> > requested).
> > 
> > ------
> > 
> > macOS SDK headers using the CF_ENUM macro can expand to invalid C++ code
> > of the form:
> > 
> > typedef enum T : BaseType T;
> > 
> > i.e. an elaborated-type-specifier with an additional enum-base.
> > Upstream LLVM can be made to accept the above construct with
> > -Wno-error=elaborated-enum-base.
> > 
> > This patch adds the -Welaborated-enum-base warning to GCC and adjusts
> > the C++ parser to emit this warning instead of rejecting this code
> > outright.
> > 
> > The macro expansion in the macOS headers occurs in the case that the
> > compiler declares support for enums with underlying type using
> > __has_feature, see
> > https://gcc.gnu.org/pipermail/gcc-patches/2023-May/618450.html
> > 
> > GCC rejecting this construct outright means that GCC fails to bootstrap
> > on Darwin in the case that it (correctly) implements __has_feature and
> > declares support for C++ enums with underlying type.
> > 
> > With this patch, GCC can bootstrap on Darwin in combination with the
> > (WIP) __has_feature patch posted at:
> > https://gcc.gnu.org/pipermail/gcc-patches/2023-May/617878.html
> > 
> > Bootstrapped/regtested on aarch64-linux-gnu and x86_64-apple-darwin.
> > OK for trunk?
> 
> OK, thanks.

Thanks for the reviews, pushed as
g:b106f11dc6adb8df15cc5c268896d314c76ca35f.

> 
> > Thanks,
> > Alex
> > 
> > gcc/c-family/ChangeLog:
> > 
> > 	* c.opt (Welaborated-enum-base): New.
> > 
> > gcc/ChangeLog:
> > 
> > 	* doc/invoke.texi: Document -Welaborated-enum-base.
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	* parser.cc (cp_parser_enum_specifier): Don't reject
> > 	elaborated-type-specifier with enum-base, instead emit new
> > 	Welaborated-enum-base warning.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	* g++.dg/cpp0x/enum40.C: Adjust expected diagnostics.
> > 	* g++.dg/cpp0x/forw_enum6.C: Likewise.
> > 	* g++.dg/cpp0x/elab-enum-base.C: New test.
>