refs #81, work on incomplete string_view support when using c++17

Author: gulrak

.clang-tidy

@@ -0,0 +1,3 @@
+---
+Checks: -modernize-use-nodiscard
+...

include/ghc/filesystem.hpp

@@ -1569,14 +1569,14 @@ inline StringType fromUtf8(const std::string& utf8String, const typename StringT
     return result;
 }
 
-template <typename charT, typename traits, typename Alloc, typename std::enable_if<(sizeof(charT) == 1), int>::type size = 1>
-inline std::string toUtf8(const std::basic_string<charT, traits, Alloc>& unicodeString)
+template <typename strT, typename std::enable_if<path::_is_basic_string<strT>::value && (sizeof(typename strT::value_type) == 1), int>::type size = 1>
+inline std::string toUtf8(const strT& unicodeString)
 {
     return std::string(unicodeString.begin(), unicodeString.end());
 }
 
-template <typename charT, typename traits, typename Alloc, typename std::enable_if<(sizeof(charT) == 2), int>::type size = 2>
-inline std::string toUtf8(const std::basic_string<charT, traits, Alloc>& unicodeString)
+template <typename strT, typename std::enable_if<path::_is_basic_string<strT>::value && (sizeof(typename strT::value_type) == 2), int>::type size = 2>
+inline std::string toUtf8(const strT& unicodeString)
 {
     std::string result;
     for (auto iter = unicodeString.begin(); iter != unicodeString.end(); ++iter) {
@@ -1604,8 +1604,8 @@ inline std::string toUtf8(const std::basic_string<charT, traits, Alloc>& unicode
     return result;
 }
 
-template <typename charT, typename traits, typename Alloc, typename std::enable_if<(sizeof(charT) == 4), int>::type size = 4>
-inline std::string toUtf8(const std::basic_string<charT, traits, Alloc>& unicodeString)
+template <typename strT, typename std::enable_if<path::_is_basic_string<strT>::value && (sizeof(typename strT::value_type) == 4), int>::type size = 4>
+inline std::string toUtf8(const strT& unicodeString)
 {
     std::string result;
     for (auto c : unicodeString) {

test/CMakeLists.txt

@@ -44,6 +44,23 @@ else()
         endif()
         ParseAndAddCatchTests(filesystem_test_wchar)
     endif()
+    if("cxx_std_17" IN_LIST CMAKE_CXX_COMPILE_FEATURES)
+        add_executable(filesystem_test_cpp17 filesystem_test.cpp catch.hpp)
+        set_property(TARGET filesystem_test_cpp17 PROPERTY CXX_STANDARD 17)
+        target_link_libraries(filesystem_test_cpp17 ghc_filesystem)
+        target_compile_options(filesystem_test_cpp17 PRIVATE
+                $<$<BOOL:${EMSCRIPTEN}>:-s DISABLE_EXCEPTION_CATCHING=0>
+                $<$<CXX_COMPILER_ID:Clang>:-Wall -Wextra -Wshadow -Wconversion -Wsign-conversion -Wpedantic -Werror>
+                $<$<CXX_COMPILER_ID:GNU>:-Wall -Wextra -Wshadow -Wconversion -Wsign-conversion -Wpedantic -Wno-psabi -Werror>
+                $<$<CXX_COMPILER_ID:MSVC>:/WX>)
+        if(CMAKE_CXX_COMPILER_ID MATCHES MSVC)
+            target_compile_definitions(filesystem_test_cpp17 PRIVATE _CRT_SECURE_NO_WARNINGS)
+        endif()
+        if(EMSCRIPTEN)
+            set_target_properties(filesystem_test_cpp17 PROPERTIES LINK_FLAGS "-g4 -s DISABLE_EXCEPTION_CATCHING=0 -s ALLOW_MEMORY_GROWTH=1")
+        endif()
+        ParseAndAddCatchTests(filesystem_test_cpp17)
+    endif()
 endif()
 
 add_executable(multifile_test multi1.cpp multi2.cpp catch.hpp)

test/filesystem_test.cpp

@@ -2689,6 +2689,7 @@ TEST_CASE("30.10.15.39 weakly_canonical", "[filesystem][operations][fs.op.weakly
 TEST_CASE("std::string_view support", "[filesystem][fs.string_view]")
 {
 #if __cpp_lib_string_view
+    using namespace std::literals;
     {
         std::string p("foo/bar");
         std::string_view sv(p);
@@ -2698,7 +2699,11 @@ TEST_CASE("std::string_view support", "[filesystem][fs.string_view]")
         CHECK(p2 == "foo");
         CHECK(p2.compare(std::string_view("foo")) == 0);
     }
-
+    {
+        auto p = fs::path{"XYZ"};
+        p /= "Appendix"sv;
+        CHECK(p == "XYZ/Appendix");
+    }
 #if defined(IS_WCHAR_PATH) || defined(GHC_USE_WCHAR_T)
     {
         std::wstring p(L"foo/bar");