Implement LWG2989: path's streaming operators allow everything under the sun.

Because path can be constructed from a ton of different types, including string
and wide strings, this caused it's streaming operators to suck up all sorts
of silly types via silly conversions. For example:

using namespace std::experimental::filesystem::v1;
std::wstring w(L"wide");
std::cout << w; // converts to path.

This patch tentatively adopts the resolution to LWG2989 and fixes the issue
by making the streaming operators friends of path.

llvm-svn: 324189

1 files changed, 33 insertions, 0 deletions

diff --git a/libcxx/test/std/experimental/filesystem/class.path/path.nonmember/path.io.pass.cpp b/libcxx/test/std/experimental/filesystem/class.path/path.nonmember/path.io.pass.cpp
index 4b7ad735c7f..8dd82a845f2 100644
--- a/libcxx/test/std/experimental/filesystem/class.path/path.nonmember/path.io.pass.cpp
+++ b/libcxx/test/std/experimental/filesystem/class.path/path.nonmember/path.io.pass.cpp
@@ -26,6 +26,7 @@
 #include <type_traits>
 #include <sstream>
 #include <cassert>
+#include <iostream>
 
 #include "test_macros.h"
 #include "test_iterators.h"
@@ -35,6 +36,8 @@
 MultiStringType InStr =  MKSTR("abcdefg/\"hijklmnop\"/qrstuvwxyz/123456789");
 MultiStringType OutStr = MKSTR("\"abcdefg/\\\"hijklmnop\\\"/qrstuvwxyz/123456789\"");
 
+
+
 template <class CharT>
 void doIOTest() {
   using namespace fs;
@@ -56,10 +59,40 @@ void doIOTest() {
   }
 }
 
+namespace impl {
+using namespace fs;
+
+template <class Stream, class Tp, class = decltype(std::declval<Stream&>() << std::declval<Tp&>())>
+std::true_type is_ostreamable_imp(int);
+
+template <class Stream, class Tp>
+std::false_type is_ostreamable_imp(long);
+
+template <class Stream, class Tp, class = decltype(std::declval<Stream&>() >> std::declval<Tp&>())>
+std::true_type is_istreamable_imp(int);
+
+template <class Stream, class Tp>
+std::false_type is_istreamable_imp(long);
+
+
+} // namespace impl
+
+template <class Stream, class Tp>
+struct is_ostreamable : decltype(impl::is_ostreamable_imp<Stream, Tp>(0)) {};
+template <class Stream, class Tp>
+struct is_istreamable : decltype(impl::is_istreamable_imp<Stream, Tp>(0)) {};
+
+void test_LWG2989() {
+  static_assert(!is_ostreamable<decltype(std::cout), std::wstring>::value, "");
+  static_assert(!is_ostreamable<decltype(std::wcout), std::string>::value, "");
+  static_assert(!is_istreamable<decltype(std::cin), std::wstring>::value, "");
+  static_assert(!is_istreamable<decltype(std::wcin), std::string>::value, "");
+}
 
 int main() {
   doIOTest<char>();
   doIOTest<wchar_t>();
   //doIOTest<char16_t>();
   //doIOTest<char32_t>();
+  test_LWG2989();
 }