[Bug c++/116418] [12/13/14/15 Regression] statement expressions as initializer for decltype auto breaks in templates with optimization turned on and debug info turned on due to gstatement-frontiers

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116418

--- Comment #9 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:12bdcc3d7970860b9d66ed4dea203bde8fd68d4d

commit r15-3611-g12bdcc3d7970860b9d66ed4dea203bde8fd68d4d
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Sep 12 12:45:03 2024 -0400

    c++: decltype(auto) deduction of statement-expression [PR116418]

    r8-7538 for PR84968 made strip_typedefs_expr diagnose STATEMENT_LIST
    so that we reject statement-expressions in noexcept-specifiers to
    match our behavior in template arguments (which the parser diagnoses
    directly).

    Later r11-7452 made decltype(auto) deduction canonicalize the expression
    (as an implementation detail) which in turn calls strip_typedefs_expr,
    and so ever since we inadvertently reject decltype(auto) deduction of a
    statement-expression.

    This patch just removes the diagnostic in strip_typedefs_expr and instead
    treats statement-expressions similar to lambda-expressions.  The function
    doesn't seem like the right place for such a diagnostic and so it seems
    easier to just accept rather than try to reject them in a suitable place.

            PR c++/116418

    gcc/cp/ChangeLog:

            * tree.cc (strip_typedefs_expr) <case STATEMENT_LIST>: Replace
            this error path with ...
            <case STMT_EXPR>: ... this, returning the original tree.

    gcc/testsuite/ChangeLog:

            * g++.dg/eh/pr84968.C: No longer expect an ahead of time diagnostic
            for the statement-expresssion.  Instantiate the template and expect
            an incomplete type error instead.
            * g++.dg/ext/stmtexpr26.C: New test.

    Reviewed-by: Jason Merrill <jason@redhat.com>