[PATCH] libstdc++: Define P0952 generate_canonical in inline namespace.

[Tomasz Kaminski]

On Wed, Dec 17, 2025 at 1:41 PM Jonathan Wakely <jwakely@redhat.com> wrote:

> On Wed, 17 Dec 2025 at 12:38, Jonathan Wakely <jwakely@redhat.com> wrote:
> >
> > On Wed, 17 Dec 2025 at 10:34, Tomasz Kamiński <tkaminsk@redhat.com>
> wrote:
> > >
> > > Defining the new implementation inside the _V2 inline namespace,
> > > would guaranteed TUs using old definition (GCC-15 or ones defining
> > > _GLIBCXX_USE_OLD_GENERATE_CANONICAL) will observe old behavior
> > > (call old implementation) when linked against TUs using new
> > > implementation.
> > >
> > > This updates random/pr60037-neg.cc to accept static assertion
> > > with a given message on any line number. Preventing need for
> > > constant updates.
> > >
> > > libstdc++-v3/ChangeLog:
> > >
> > >         * include/bits/random.h (generate_canonical)
> > >         [!_GLIBCXX_USE_OLD_GENERATE_CANONICAL]: Define inside
> > >         _V2 inline namespace.
> > >         * include/bits/random.tcc (generate_canonical)
> > >         [!_GLIBCXX_USE_OLD_GENERATE_CANONICAL]: Likewise.
> > >         * testsuite/26_numerics/random/pr60037-neg.cc: Make
> > >         test independed on line of which static assert is placed.
> >
> > "independent of line on which"
>
> FWIW, I used this commit msg in my local commit. The extra text about
> the change to the test might be worth using ... but on the other hand
> it's a lot of words for a tiny change to one test!
>
>    libstdc++: Move new std::generate_canonical to inline namespace
>
>    This ensures that the new definition of std::generate_canonical has a
>    different mangled name from the old one, so that TUs compiled with GCC
>    16 will be sure to use the new definition, even if the linker also sees
>    a symbol instantiated from the old definition. We use the same _V2
>    inline namespace as used elsewhere (std::_V2::condition_variable,
>    std::_V2::__rotate, and std::chrono::_V2::system_clock), and use a macro
>    to add it conditionally so that it's not used for the ABI-unstable
>    gnu-versioned-namespace configuration.
>
This is much nicer description, and will be useful for someone who will
wonder
why _V2 was used, so I would suggest that you post your local change.

>
>    We can simplify the 26_numerics/random/pr60037-neg.cc test to only use
>    one dg-error without a line number, so that it matches any of the three
>    relevant static_assert failures for this test: the one from _Adaptor in
>    <bits/random.h> and the ones from the new and old definitions of
>    std::generate_canonical in <bits/random.tcc>. Without this change, the
>    line number for the dg-error matching the <bits/random.tcc> error epends
>    on the _GLIBCXX_USE_OLD_GENERATE_CANONICAL macro, which is awkward to
>    depend on in the test (because DejaGnu sees all dg-error directives, it
>    doesn't care if they're guarded by #ifdef preprocessor checks).
>


>    libstdc++-v3/ChangeLog:
>
>            * include/bits/random.h [!_GLIBCXX_USE_OLD_GENERATE_CANONICAL]
>            (generate_canonical): Use inline namespace _V2.
>            * include/bits/random.tcc [!_GLIBCXX_USE_OLD_GENERATE_CANONICAL]
>            (generate_canonical): Likewise.
>            * testsuite/26_numerics/random/pr60037-neg.cc: Remove lineno so
>            that one dg-error matches both diagnostics.
>
>
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