libstdc++: Implement LWG 3070 in path::lexically_relative

	* src/c++17/fs_path.cc [_GLIBCXX_FILESYSTEM_IS_WINDOWS]
	(is_disk_designator): New helper function.
	(path::_Parser::root_path()): Use is_disk_designator.
	(path::lexically_relative(const path&)): Implement resolution of
	LWG 3070.
	* testsuite/27_io/filesystem/path/generation/relative.cc: Check with
	path components that look like a root-name.

From-SVN: r278313

1 files changed, 16 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/27_io/filesystem/path/generation/relative.cc b/libstdc++-v3/testsuite/27_io/filesystem/path/generation/relative.cc
index dde08d46f2c..b2ac27293b2 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/path/generation/relative.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/path/generation/relative.cc
@@ -77,10 +77,26 @@ test03()
   compare_paths( path("/dir/.").lexically_relative("/dir/."), "." );
 }
 
+void
+test04()
+{
+#if defined(__MING32__) || defined(__MINGW64__)
+  // DR 3070
+  compare_paths(path("c:/f:o/bar").lexically_relative("c:/f:o/bar"), ".");
+  compare_paths(path("c:/foo/bar").lexically_relative("c:/foo/b:r"), "..\\bar");
+  compare_paths(path("c:/foo/b:r").lexically_relative("c:/foo/bar"), "..\\b:r");
+  compare_paths(path("c:/foo/b:").lexically_relative("c:/foo/b:"), "");
+  compare_paths(path("c:/foo/bar").lexically_relative("c:/foo/b:"), "");
+  compare_paths(path("c:/f:/bar").lexically_relative("c:/foo/bar"), "");
+  compare_paths(path("foo/bar").lexically_relative("foo/b:/bar"), "");
+#endif
+}
+
 int
 main()
 {
   test01();
   test02();
   test03();
+  test04();
 }