[Bug c++/127097] [modules] Alternate include of a header unit reads stdin

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127097

--- Comment #1 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:e1c8dac7ca8dde4d99776685dee43e05cd3ea6d2

commit r17-3819-ge1c8dac7ca8dde4d99776685dee43e05cd3ea6d2
Author: Alexey Klimkin <alexey.klimkin@intel.com>
Date:   Tue Aug 25 20:36:48 2026 -0700

    libcpp: Use -1 for closed header-unit fd [PR c++/127097]

    _cpp_find_header_unit closes the source descriptor after resolving a
    header unit, but records zero instead of the established -1 sentinel.
    A later textual include through an alternate pathname therefore skips
    reopening the source and reads stdin.  Descriptor zero is also a valid
    result from open when stdin was previously closed.

    Close every valid descriptor and restore -1.  Add a module regression
    that imports a header unit and includes the same file through an
    alternate spelling.

    Assisted-by: Claude Opus 5 (Anthropic)

    libcpp/
            PR c++/127097
            * files.cc (_cpp_find_header_unit): Close descriptor zero and set
            the closed descriptor sentinel to -1.

    gcc/testsuite/
            PR c++/127097
            * g++.dg/modules/pragma-once-hu-1_a.H: New test.
            * g++.dg/modules/pragma-once-hu-1_b.C: New test.

    Signed-off-by: Alexey Klimkin <alexey.klimkin@intel.com>