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

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

[Jonathan Wakely]

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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/80762.cc: New test.
	* testsuite/experimental/filesystem/path/construct/80762.cc: New test.

Tested x86_64-linux (and manually verified it fixes the clang errors).

Committed to trunk. This is worth backporting too, I think.


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commit 39d7ca64fdd9ad94c80655ac79c84259a33b3306
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Dec 12 14:51:08 2018 +0000

    PR libstdc++/80762 avoid ambiguous __constructible_from<void, void>
    
    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/80762.cc: New test.
            * testsuite/experimental/filesystem/path/construct/80762.cc: New test.

diff --git a/libstdc++-v3/include/bits/fs_path.h b/libstdc++-v3/include/bits/fs_path.h
index 0eee684a2f6..cbaea7343a3 100644
--- a/libstdc++-v3/include/bits/fs_path.h
+++ b/libstdc++-v3/include/bits/fs_path.h
@@ -110,7 +110,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
     template<typename _Tp1, typename _Tp2 = void>
       using _Path = typename
-	std::enable_if<__and_<__not_<is_same<_Tp1, path>>,
+	std::enable_if<__and_<__not_<is_same<remove_cv_t<_Tp1>, path>>,
+			      __not_<is_void<_Tp1>>,
 			      __constructible_from<_Tp1, _Tp2>>::value,
 		       path>::type;
 
diff --git a/libstdc++-v3/include/experimental/bits/fs_path.h b/libstdc++-v3/include/experimental/bits/fs_path.h
index 653b4a3fe85..340cc59d541 100644
--- a/libstdc++-v3/include/experimental/bits/fs_path.h
+++ b/libstdc++-v3/include/experimental/bits/fs_path.h
@@ -125,7 +125,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
     template<typename _Tp1, typename _Tp2 = void>
       using _Path = typename
-	std::enable_if<__and_<__not_<is_same<_Tp1, path>>,
+	std::enable_if<__and_<__not_<is_same<typename remove_cv<_Tp1>::type,
+					     path>>,
+			      __not_<is_void<_Tp1>>,
 			      __constructible_from<_Tp1, _Tp2>>::value,
 		       path>::type;
 
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/path/construct/80762.cc b/libstdc++-v3/testsuite/27_io/filesystem/path/construct/80762.cc
new file mode 100644
index 00000000000..15a79fd4e12
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/filesystem/path/construct/80762.cc
@@ -0,0 +1,29 @@
+// Copyright (C) 2018 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do compile { target c++17 } }
+
+#include <filesystem>
+
+using std::filesystem::path;
+
+static_assert( !std::is_constructible_v<path, void> );
+static_assert( !std::is_constructible_v<path, volatile path> );
+static_assert( !std::is_constructible_v<path, volatile path&> );
+static_assert( !std::is_constructible_v<path, const volatile path> );
+static_assert( !std::is_constructible_v<path, const volatile path&> );
diff --git a/libstdc++-v3/testsuite/experimental/filesystem/path/construct/80762.cc b/libstdc++-v3/testsuite/experimental/filesystem/path/construct/80762.cc
new file mode 100644
index 00000000000..fdd9f768f78
--- /dev/null
+++ b/libstdc++-v3/testsuite/experimental/filesystem/path/construct/80762.cc
@@ -0,0 +1,28 @@
+// Copyright (C) 2018 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do compile { target c++11 } }
+
+#include <experimental/filesystem>
+
+using std::experimental::filesystem::path;
+
+static_assert( !std::is_constructible<path, void>::value, "" );
+static_assert( !std::is_constructible<path, volatile path>::value, "" );
+static_assert( !std::is_constructible<path, volatile path&>::value, "" );
+static_assert( !std::is_constructible<path, const volatile path>::value, "" );
+static_assert( !std::is_constructible<path, const volatile path&>::value, "" );

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

[Christophe Lyon]

On Wed, 12 Dec 2018 at 17:13, Jonathan Wakely <jwakely@redhat.com> 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/80762.cc: New test.
>         * testsuite/experimental/filesystem/path/construct/80762.cc: New test.
>

Hi Jonathan,

One of the new tests fails on bare-metal/newlib targets (aarch64-elf/arm-eabi):
FAIL: experimental/filesystem/path/construct/80762.cc (test for excess errors)
/libstdc++-v3/testsuite/experimental/filesystem/path/construct/80762.cc:20:
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?

Thanks


> Tested x86_64-linux (and manually verified it fixes the clang errors).
>
> Committed to trunk. This is worth backporting too, I think.
>

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

[Jonathan Wakely]

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On 13/12/18 08:56 +0100, Christophe Lyon wrote:
>On Wed, 12 Dec 2018 at 17:13, Jonathan Wakely <jwakely@redhat.com> 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/80762.cc: New test.
>>         * testsuite/experimental/filesystem/path/construct/80762.cc: New test.
>>
>
>Hi Jonathan,
>
>One of the new tests fails on bare-metal/newlib targets (aarch64-elf/arm-eabi):
>FAIL: experimental/filesystem/path/construct/80762.cc (test for excess errors)
>/libstdc++-v3/testsuite/experimental/filesystem/path/construct/80762.cc:20:
>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.

Aside:
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 libstdc++.so 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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commit e9d4b85b9d8f91743617729d0a1e6a9f9a39e37d
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Dec 13 10:56:46 2018 +0000

    Disable new tests for configurations with no libstdc++fs.a
    
            * testsuite/27_io/filesystem/path/construct/80762.cc: Skip test if
            the Filesystem TS support is not configured.
            * testsuite/experimental/filesystem/path/construct/80762.cc: Likewise.

diff --git a/libstdc++-v3/testsuite/27_io/filesystem/path/construct/80762.cc b/libstdc++-v3/testsuite/27_io/filesystem/path/construct/80762.cc
index 15a79fd4e12..0137e4466d0 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/path/construct/80762.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/path/construct/80762.cc
@@ -17,6 +17,7 @@
 
 // { dg-options "-std=gnu++17" }
 // { dg-do compile { target c++17 } }
+// { dg-require-filesystem-ts "" }
 
 #include <filesystem>
 
diff --git a/libstdc++-v3/testsuite/experimental/filesystem/path/construct/80762.cc b/libstdc++-v3/testsuite/experimental/filesystem/path/construct/80762.cc
index fdd9f768f78..84ea48b11b1 100644
--- a/libstdc++-v3/testsuite/experimental/filesystem/path/construct/80762.cc
+++ b/libstdc++-v3/testsuite/experimental/filesystem/path/construct/80762.cc
@@ -16,6 +16,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-do compile { target c++11 } }
+// { dg-require-filesystem-ts "" }
 
 #include <experimental/filesystem>
 

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

[Christophe Lyon]

On Thu, 13 Dec 2018 at 12:00, Jonathan Wakely <jwakely@redhat.com> wrote:
>
> On 13/12/18 08:56 +0100, Christophe Lyon wrote:
> >On Wed, 12 Dec 2018 at 17:13, Jonathan Wakely <jwakely@redhat.com> 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/80762.cc: New test.
> >>         * testsuite/experimental/filesystem/path/construct/80762.cc: New test.
> >>
> >
> >Hi Jonathan,
> >
> >One of the new tests fails on bare-metal/newlib targets (aarch64-elf/arm-eabi):
> >FAIL: experimental/filesystem/path/construct/80762.cc (test for excess errors)
> >/libstdc++-v3/testsuite/experimental/filesystem/path/construct/80762.cc:20:
> >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.

>
> Aside:
> 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 libstdc++.so library, so only the tests for
> std::experimental::filesystem::path will depend on libstdc++fs.a being
> available. Until then, this patch is needed.
>
Great!

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

[Jonathan Wakely]

On 13/12/18 13:10 +0100, Christophe Lyon wrote:
>On Thu, 13 Dec 2018 at 12:00, Jonathan Wakely <jwakely@redhat.com> wrote:
>>
>> On 13/12/18 08:56 +0100, Christophe Lyon wrote:
>> >On Wed, 12 Dec 2018 at 17:13, Jonathan Wakely <jwakely@redhat.com> 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/80762.cc: New test.
>> >>         * testsuite/experimental/filesystem/path/construct/80762.cc: New test.
>> >>
>> >
>> >Hi Jonathan,
>> >
>> >One of the new tests fails on bare-metal/newlib targets (aarch64-elf/arm-eabi):
>> >FAIL: experimental/filesystem/path/construct/80762.cc (test for excess errors)
>> >/libstdc++-v3/testsuite/experimental/filesystem/path/construct/80762.cc:20:
>> >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 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86756 :-)

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.

>>
>> Aside:
>> 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 libstdc++.so library, so only the tests for
>> std::experimental::filesystem::path will depend on libstdc++fs.a being
>> available. Until then, this patch is needed.
>>
>Great!