[Bug c++/126783] [16/17 Regression] [modules] ICE when a GMF variable is later defined inline

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126783

--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-16 branch has been updated by Patrick Palka
<[email protected]>:

https://gcc.gnu.org/g:61f16b5960e4a53d7ac5881f4db74ccfb7cb6df7

commit r16-9532-g61f16b5960e4a53d7ac5881f4db74ccfb7cb6df7
Author: Patrick Palka <[email protected]>
Date:   Thu Aug 13 18:07:25 2026 -0400

    c++/modules: ICE with GMF variable later defined inline [PR126783]

    Here transfer_defining_module (added in r16-5213) assumes that if
    a redeclaration has DECL_LANG_SPECIFIC allocated, then so must the
    original declaration, but this isn't true for q below.  Instead we
    should call retrofit_lang_decl to allocate DECL_LANG_SPECIFIC as
    needed; other parts of duplicate_decls do the same.

            PR c++/126783

    gcc/cp/ChangeLog:

            * module.cc (transfer_defining_module): Call retrofit_lang_decl
            instead of assuming the old declaration already has
            DECL_LANG_SPECIFIC allocated.

    gcc/testsuite/ChangeLog:

            * g++.dg/modules/gmf-6.C: New test.

    Reviewed-by: Jason Merrill <[email protected]>
    (cherry picked from commit a03b3ab4b0a6a446fe9a1d7e6e82967a8dd3edcf)