Make filesystem::path safe for self assignment

The standard says "If *this and p are the same object, has no effect."
Previously we ended up clearing the path.

	* include/bits/fs_path.h (path::operator=(path&&)): Check for self
	assignment.
	* src/c++17/fs_path.cc (path::operator=(const path&)): Likewise.
	* testsuite/27_io/filesystem/path/assign/copy.cc: Test self
	assignment.

From-SVN: r270171

1 files changed, 18 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/27_io/filesystem/path/assign/copy.cc b/libstdc++-v3/testsuite/27_io/filesystem/path/assign/copy.cc
index 6c24e3ae7b9..775dbffad36 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/path/assign/copy.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/path/assign/copy.cc
@@ -20,6 +20,7 @@
 
 #include <filesystem>
 #include <testsuite_fs.h>
+#include <testsuite_hooks.h>
 
 using std::filesystem::path;
 using __gnu_test::compare_paths;
@@ -47,9 +48,26 @@ test02()
   }
 }
 
+void
+test03()
+{
+  // self assignment should have no effect
+  const path orig = "foo/bar/baz";
+  path p = orig;
+  const auto ptr1 = p.c_str();
+  const auto ptr2 = p.begin()->c_str();
+  p = std::move(p);
+  __gnu_test::compare_paths(p, orig);
+  p = p;
+  __gnu_test::compare_paths(p, orig);
+  VERIFY( ptr1 == p.c_str() );
+  VERIFY( ptr2 == p.begin()->c_str() );
+}
+
 int
 main()
 {
   test01();
   test02();
+  test03();
 }