On 17/05/21 15:25 +0100, Jonathan Wakely wrote:
On 17/05/21 15:02 +0100, Jonathan Wakely wrote:
The constraint check for filesystem::path construction uses
decltype(__is_path_src(declval<Source>())) which mean it considers
conversion from an rvalue. When Source is a volatile-qualified type
it cannot use is_path_src(const Unknown&) because a const lvalue
reference can only bind to a non-volatile rvalue.
Since the relevant path members all have a const Source& parameter,
the constraint should be defined in terms of declval<const Source&>(),
not declval<Source>(). This avoids the problem of volatile-qualified
rvalues, because we no longer use an rvalue at all.
libstdc++-v3/ChangeLog:
PR libstdc++/100630
* include/bits/fs_path.h (__is_constructible_from): Test
construction from a const lvalue, not an rvalue.
* include/experimental/bits/fs_path.h (__is_constructible_from):
Likewise.
* testsuite/27_io/filesystem/path/construct/100630.cc: New test.
* testsuite/experimental/filesystem/path/construct/100630.cc:
New test.
Tested x86_64-linux, pushed to gcc-10 (this isn't needed for gcc-11 or
trunk, but I also plan to backport it to gcc-9).
Oh actually this is needed for experimental::filesystem::path on trun
kand gcc-11 (as I found when I added to the new tests to trunk) so
I'll fix it there too.
Here's the patch for trunk and gcc-11.
commit 45aa7a447652e8541cc381d7ab128544f81ed857
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Mon May 17 11:54:06 2021
libstdc++: Fix filesystem::path constraints for volatile [PR 100630]
The constraint check for filesystem::path construction uses
decltype(__is_path_src(declval<Source>())) which mean it considers
conversion from an rvalue. When Source is a volatile-qualified type
it cannot use is_path_src(const Unknown&) because a const lvalue
reference can only bind to a non-volatile rvalue.
Since the relevant path members all have a const Source& parameter,
the constraint should be defined in terms of declval<const Source&>(),
not declval<Source>(). This avoids the problem of volatile-qualified
rvalues, because we no longer use an rvalue at all.
libstdc++-v3/ChangeLog:
PR libstdc++/100630
* include/experimental/bits/fs_path.h (__is_constructible_from):
Test construction from a const lvalue, not an rvalue.
* testsuite/27_io/filesystem/path/construct/100630.cc: New test.
* testsuite/experimental/filesystem/path/construct/100630.cc:
New test.
diff --git a/libstdc++-v3/include/experimental/bits/fs_path.h b/libstdc++-v3/include/experimental/bits/fs_path.h
index 2df2bba3dcd..1ecf2f3a7bd 100644
--- a/libstdc++-v3/include/experimental/bits/fs_path.h
+++ b/libstdc++-v3/include/experimental/bits/fs_path.h
@@ -124,7 +124,7 @@ namespace __detail
template<typename _Source>
struct __constructible_from<_Source, void>
- : decltype(__is_path_src(std::declval<_Source>(), 0))
+ : decltype(__is_path_src(std::declval<const _Source&>(), 0))
{ };
template<typename _Tp1, typename _Tp2 = void,
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/path/construct/100630.cc b/libstdc++-v3/testsuite/27_io/filesystem/path/construct/100630.cc
new file mode 100644
index 00000000000..eb8473e600e
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/filesystem/path/construct/100630.cc
@@ -0,0 +1,14 @@
+// { dg-options "-std=gnu++17" }
+// { dg-do compile { target c++17 } }
+
+#include <filesystem>
+
+void f(bool) { }
+void f(const std::filesystem::path&) { }
+
+void
+test_100630()
+{
+ volatile bool b = true;
+ f(b);
+}
diff --git a/libstdc++-v3/testsuite/experimental/filesystem/path/construct/100630.cc b/libstdc++-v3/testsuite/experimental/filesystem/path/construct/100630.cc
new file mode 100644
index 00000000000..b2428ff74cf
--- /dev/null
+++ b/libstdc++-v3/testsuite/experimental/filesystem/path/construct/100630.cc
@@ -0,0 +1,14 @@
+// { dg-do compile { target c++11 } }
+// { dg-require-filesystem-ts "" }
+
+#include <experimental/filesystem>
+
+void f(bool) { }
+void f(const std::experimental::filesystem::path&) { }
+
+void
+test_100630()
+{
+ volatile bool b = true;
+ f(b);
+}
