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.
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,
--- /dev/null
+// { 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);
+}
--- /dev/null
+// { 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);
+}