Re: [PATCH] c++/objective-c++; Do not claim feature(modules), it is clang-specific.

On 8/4/26 4:56 AM, Iain Sandoe wrote:
> Tested on x86_64 darwin24 where we now correctly create the std module
> sources and gcms.  OK for trunk and relevant backports? thanks,

OK.
> --- 8< ---
> 
> It appears that we misinterpreted the modules feature and that it is intended
> to signal that the compiler supports "clang modules".  These are a similar
> approach to PCH and tightly coupled to clang AST - so not something that we
> are realistically likely to implement.
> 
> Unfortunately, the macOS SDKs use this feature test to decide on some
> header declaration ordering where it needs to change for clang modules.
> 
> This causes a fail to build the std. module sources on macOS meaning that we
> get an empty std.cc. Our intention should be parity with/without -fmodules.
> 
> The solution is not to claim feature(modules) - C++20 modules are gated on
> __cpp_module and so do not need it.
> 
> gcc/cp/ChangeLog:
> 
> 	* cp-objcp-common.cc: Remove claim to support clang modules.
> 
> Signed-off-by: Iain Sandoe <[email protected]>
> ---
>   gcc/cp/cp-objcp-common.cc | 1 -
>   1 file changed, 1 deletion(-)
> 
> diff --git a/gcc/cp/cp-objcp-common.cc b/gcc/cp/cp-objcp-common.cc
> index 0a67aa8ce14..8c9930bb2f3 100644
> --- a/gcc/cp/cp-objcp-common.cc
> +++ b/gcc/cp/cp-objcp-common.cc
> @@ -148,7 +148,6 @@ static constexpr cp_feature_info cp_feature_table[] =
>     { "cxx_relaxed_constexpr", cxx14 },
>     { "cxx_return_type_deduction", cxx14 },
>     { "cxx_variable_templates", cxx14 },
> -  { "modules", &flag_modules },
>   };
>   
>   /* Register C++ language features for __has_{feature,extension}.  */