[Bug libstdc++/103086] [11/12 Regression] std::unique_ptr printer gets confused by [[no_unique_address]] in tuple

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103086

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:a634928f5c8a281442ac8f5fb1636aed048ed72c

commit r12-4928-ga634928f5c8a281442ac8f5fb1636aed048ed72c
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Nov 4 22:50:02 2021 +0000

    libstdc++: Fix pretty printing of std::unique_ptr [PR103086]

    Since std::tuple started using [[no_unique_address]] the tuple<T*, D>
    member of std::unique_ptr<T, D> has two _M_head_impl subobjects, in
    different base classes. That means this printer code is ambiguous:

        tuple_head_type = tuple_impl_type.fields()[1].type   # _Head_base
        head_field = tuple_head_type.fields()[0]
        if head_field.name == '_M_head_impl':
            self.pointer = tuple_member['_M_head_impl']

    In older versions of GDB it happened to work by chance, because GDB
    returned the last _M_head_impl member and std::tuple's base classes are
    stored in reverse order, so the last one was the T* element of the
    tuple. Since GDB 11 it returns the first _M_head_impl, which is the
    deleter element.

    The fix is for the printer to stop using an ambiguous field name and
    cast the tuple to the correct base class before accessing the
    _M_head_impl member.

    Instead of fixing this in both UniquePointerPrinter and StdPathPrinter a
    new unique_ptr_get function is defined to do it correctly. That is
    defined in terms of new tuple_get and _tuple_impl_get functions.

    It would be possible to reuse _tuple_impl_get to access each element in
    StdTuplePrinter._iterator.__next__, but that already does the correct
    casting, and wouldn't be much simpler anyway.

    libstdc++-v3/ChangeLog:

            PR libstdc++/103086
            * python/libstdcxx/v6/printers.py (_tuple_impl_get): New helper
            for accessing the tuple element stored in a _Tuple_impl node.
            (tuple_get): New function for accessing a tuple element.
            (unique_ptr_get): New function for accessing a unique_ptr.
            (UniquePointerPrinter, StdPathPrinter): Use unique_ptr_get.
            * python/libstdcxx/v6/xmethods.py (UniquePtrGetWorker): Cast
            tuple to its base class before accessing _M_head_impl.