Re: [committed] libstdc++: Fix filesystem::path comparisons for C++23

[Jonathan Wakely <jwakely@redhat.com>]

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On Mon, 14 Jun 2021 at 13:58, Christophe Lyon
<christophe.lyon@linaro.org> wrote:
>
> Hi Jonathan,
>
> On Fri, 11 Jun 2021 at 20:25, Jonathan Wakely via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > In C++23 there is a basic_string_view(Range&&) constructor, which is
> > constrained to take a range (specifically, a contiguous_range). When the
> > filesystem::path comparison operators call lhs.compare(rhs) the overload
> > taking a string_view is considered, which means checking whether path
> > satisfies the range concept. That satisfaction result changes depending
> > whether path::iterator is complete, which is ill-formed; no diagnostic
> > required. To avoid the problem, this change ensures that the overload
> > resolution is performed in a context where path::iterator is complete
> > and the range concept is satisfied. (The result of overload resolution
> > is always that the compare(const path&) overload is the best match, but
> > we still have to consider the compare(basic_string_view<value_type>) one
> > to decide if it even participates in overload resolution).
> >
> > For std::filesystem::path we can't define the comparison operators later
> > in the file, because they are hidden friends, so a new helper is
> > introduced that gets defined when everything else is complete.
> >
> > For std::experimental::filesystem::path we can just move the definitions
> > of the comparison operators later in the file.
> >
> > Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
> >
> > libstdc++-v3/ChangeLog:
> >
> >         * include/bits/fs_path.h (operator==, operator<=>): Use new
> >         _S_compare function.
> >         (path::_S_compare): New function to call path::compare in a
> >         context where path::iterator is complete.
> >         * include/experimental/bits/fs_path.h (operator<, operator==):
> >         Define after path::iterator is complete.
> >         * testsuite/27_io/filesystem/path/native/conv_c++23.cc: New
> >         test.
> >         * testsuite/experimental/filesystem/path/native/conv_c++23.cc:
> >         New test.
> >
> > Tested powerpc64le-linux. Committed to trunk.
> >
> > This also needs to be backported to gcc-11 where the string_view
> > constructor is present for C++23 mode.
> >
>
> The new test experimental/filesystem/path/native/conv_c++23.cc
> fails on arm-eabi and aarch64-elf:
> /libstdc++-v3/testsuite/experimental/filesystem/path/native/conv_c++23.cc:4:
> fatal error: experimental/filesystem: No such file or directory
> (both trunk and gcc-11)
>
> I guess that's easy to fix? :-)

Yes, fixed on trunk now by the attached patch. Tests running for the
gcc-11 backport.

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commit a40d2293a7a417fc7711f8f4e52dbd4c48c2a43f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Jun 14 14:22:07 2021

    libstdc++: Only run Filesystem TS test if supported
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/experimental/filesystem/path/native/conv_c++23.cc:
            Add dg-require-filesystem-ts directive.

diff --git a/libstdc++-v3/testsuite/experimental/filesystem/path/native/conv_c++23.cc b/libstdc++-v3/testsuite/experimental/filesystem/path/native/conv_c++23.cc
index f3c3f884965..81f57549ac9 100644
--- a/libstdc++-v3/testsuite/experimental/filesystem/path/native/conv_c++23.cc
+++ b/libstdc++-v3/testsuite/experimental/filesystem/path/native/conv_c++23.cc
@@ -1,5 +1,6 @@
 // { dg-options "-std=gnu++23" }
 // { dg-do compile { target c++23 } }
+// { dg-require-filesystem-ts "" }
 
 #include <experimental/filesystem>