[Bug c++/122915] [16 Regression] ICE in module_state::write_using_directives

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122915

--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Nathaniel Shead <nshead@gcc.gnu.org>:

https://gcc.gnu.org/g:6a83030557ccceef5c12e8b45d6bcd5ba274232b

commit r16-5811-g6a83030557ccceef5c12e8b45d6bcd5ba274232b
Author: Nathaniel Shead <nathanieloshead@gmail.com>
Date:   Mon Dec 1 23:32:40 2025 +1100

    c++/modules: Fix ICE when writing imported using-directive [PR122915]

    The crash in the PR is caused because we are attempting to write a
    using-directive that we never made a dep for.  This should only happen
    for imported using-directives, where if we never opened the relevant
    namespace in the module purview we don't think there's anything
    interesting to discover and so never walk it.

    There's actually no reason we need to emit imported using-directives at
    all, however, unless they came from a partition, because importers will
    be able to get that directive directly from the originating module if it
    was going to be visible anyway.  And we will always walk and create a
    dependency (marked !import_p) for partition decls.  So this patch fixes
    the ICE by just skipping such cases.

    To help validate this the patch also starts setting DECL_MODULE_IMPORT_P
    correctly for using-directives.

            PR c++/122915

    gcc/cp/ChangeLog:

            * module.cc (module_state::write_using_directives): Don't emit
            imported using-directives.
            (module_state::read_using_directives): Rename
            add_using_namespace to add_imported_using_namespace.
            * name-lookup.cc (add_using_namespace): Handle imported
            using-directives.
            (add_imported_using_namespace): Rename to match new
            functionality.
            * name-lookup.h (add_using_namespace): Rename to...
            (add_imported_using_namespace): ...this.

    gcc/testsuite/ChangeLog:

            * g++.dg/modules/namespace-16_a.C: New test.
            * g++.dg/modules/namespace-16_b.C: New test.
            * g++.dg/modules/namespace-16_c.C: New test.
            * g++.dg/modules/namespace-16_d.C: New test.

    Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
    Reviewed-by: Jason Merrill <jason@redhat.com>