[Bug c++/123667] [14 Regression] ICE in finish_decltype_type when using decltype on a structured binding inside a generic lambda since r14-9258

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123667

--- Comment #8 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-14 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:36849881f44079e013c3f1f46d1e0fdc111553fc

commit r14-12396-g36849881f44079e013c3f1f46d1e0fdc111553fc
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Jan 24 10:36:45 2026 +0100

    c++: Fix ICE on decltype on non-local structured binding inside of a
template [PR123667]

    The following testcases ICE when decltype (x) appears in a template
    where x is a tuple based structured binding from outside of that template
    (one testcase shows the sb in a function and template is a lambda within
    that function, the other shows namespace scope sb referenced from a
    template).
    What I wrote in the comment there is true only for structured bindings
    within the current template function, in that case that structured binding
    indeed has to have DECL_VALUE_EXPR and lookup_decomp_type might return
    NULL or might not and depending on that we should choose if it is
    a tuple based structured binding and return its type or if we should
    return unlowered type of expr.
    But if decltype in a template refers to a structured binding elsewhere,
    it could have been finalized already and determined to be tuple based
    structured binding, so DECL_HAVE_VALUE_EXPR_P can be false in that case.
    In that case, if ptds.saved would be false, we'd just always
    return lookup_decomp_type.  So, for this case the patch allows
    that case in the assert and asserts lookup_decomp_type returned non-NULL.

    2026-01-24  Jakub Jelinek  <jakub@redhat.com>

            PR c++/123667
            * semantics.cc (finish_decltype_type): Allow a structured binding
            for ptds.saved to have DECL_HAS_VALUE_EXPR_P cleared, if it is
            not within current_function_decl, but in that case assert that
            lookup_decomp_type succeeded.

            * g++.dg/cpp1z/decomp66.C: New test.
            * g++.dg/cpp1z/decomp67.C: New test.

    (cherry picked from commit 34a47a8b14e2a74d35a65ccc2bd2a166106b9b96)