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Re: [PATCH] PR libstdc++/80762 avoid ambiguous __constructible_from<void, void>

On 13/12/18 13:10 +0100, Christophe Lyon wrote:
On Thu, 13 Dec 2018 at 12:00, Jonathan Wakely <> wrote:

On 13/12/18 08:56 +0100, Christophe Lyon wrote:
>On Wed, 12 Dec 2018 at 17:13, Jonathan Wakely <> wrote:
>> Ensure we don't try to instantiate __is_constructible_from<void, void>,
>> because there are two partial specializations that are equally good
>> matches.
>>         PR libstdc++/80762
>>         * include/bits/fs_path.h (path::_Path): Use remove_cv_t and is_void.
>>         * include/experimental/bits/fs_path.h (path::_Path): Likewise.
>>         * testsuite/27_io/filesystem/path/construct/ New test.
>>         * testsuite/experimental/filesystem/path/construct/ New test.
>Hi Jonathan,
>One of the new tests fails on bare-metal/newlib targets (aarch64-elf/arm-eabi):
>FAIL: experimental/filesystem/path/construct/ (test for excess errors)
>fatal error: experimental/filesystem: No such file or directory
>I think there was a similar issue recently, but I don't remember how
>you fixed it?

Like this. Sorry for forgetting it. Committed to trunk.
OK thanks.
Note that only the one in "experimental" failed, the 27_io one did pass.

Because of :-)

The <filesystem> header is installed unconditionally, and that test
only needs the header not the library, so it happens to work.

The <experimental/filesystem> header is only installed when
libstdc++fs.a is available.

There's actually no reason the filesystem::path type can't be enabled
unconditionally for all targets, as it only relies on portable
features like std::string, but currently the definitions of its member
functions are in the libstdc++fs.a library which is only enabled
conditionally. Later today I plan to move the std::filesystem::path
type into the main library, so only the tests for
std::experimental::filesystem::path will depend on libstdc++fs.a being
available. Until then, this patch is needed.


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