Re: [PATCH] c++: Implement -Wdangling-reference [PR106393]

[Jason Merrill <jason@redhat.com>]

On 10/25/22 09:14, Marek Polacek wrote:
> On Tue, Oct 25, 2022 at 12:34:50PM +0100, Jonathan Wakely wrote:
>> On Mon, 24 Oct 2022 at 18:30, Jason Merrill wrote:
>>>
>>> On 10/21/22 19:28, Marek Polacek wrote:
>>>> When testing a previous version of the patch, there were many FAILs in
>>>> libstdc++'s 22_locale/; all of them because the warning triggered on
>>>>
>>>>     const test_type& obj = std::use_facet<test_type>(std::locale());
>>>>
>>>> but this code looks valid -- std::use_facet doesn't return a reference
>>>> to its parameter.  Therefore I added code to suppress the warning when
>>>> the call is std::use_facet.  Now 22_locale/* pass even with the warning
>>>> on.  We could exclude more std:: functions like this if desirable.
>>>
>>> Instead of adding special cases in the compiler, let's disable the
>>> warning around the definition of use_facet (and adjust the compiler as
>>> needed so that avoids the warning).
>>
>> I assume you mean using #pragma here. If we disable it around the
>> definition of use_facet, will that disable it for callers of
>> use_facet, or only within the definition of use_facet itself?
> 
> Right, a #pragma will not help, it would only disable the warning
> within the definition of use_facet itself.

That's why I mentioned adjusting the compiler, i.e. check 
warning_enabled_at (DECL_SOURCE_LOCATION (fn)

Jason