Remove invalid nondependent static assert (microsoft#1186)

* Remove invalid static_assert(false).

* Turn on permissive-.

* clang-format

Release/CMakeLists.txt

@@ -188,6 +188,10 @@ elseif(CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
   if (WINDOWS_STORE OR WINDOWS_PHONE)
     add_compile_options(/ZW)
   endif()
+
+  if (NOT (MSVC_VERSION LESS 1920))
+	add_compile_options(/permissive-)
+  endif()
 else()
   message("-- Unknown compiler, success is doubtful.")
   message("CMAKE_CXX_COMPILER_ID=${CMAKE_CXX_COMPILER_ID}")

Release/include/cpprest/streams.h

@@ -528,9 +528,12 @@ class type_parser
 public:
     static pplx::task<T> parse(streams::streambuf<CharType> buffer)
     {
-        typename _type_parser_integral_traits<T>::_is_integral ii;
-        typename _type_parser_integral_traits<T>::_is_unsigned ui;
-        return _parse(buffer, ii, ui);
+        typedef typename _type_parser_integral_traits<T>::_is_integral ii;
+        typedef typename _type_parser_integral_traits<T>::_is_unsigned ui;
+
+        static_assert(ii::value || !ui::value, "type is not supported for extraction from a stream");
+
+        return _parse(buffer, ii {}, ui {});
     }
 
 private:
@@ -539,15 +542,6 @@ class type_parser
         _parse_floating_point(buffer);
     }
 
-    static pplx::task<T> _parse(streams::streambuf<CharType>, std::false_type, std::true_type)
-    {
-#ifdef _WIN32
-        static_assert(false, "type is not supported for extraction from a stream");
-#else
-        throw std::runtime_error("type is not supported for extraction from a stream");
-#endif
-    }
-
     static pplx::task<T> _parse(streams::streambuf<CharType> buffer, std::true_type, std::false_type)
     {
         return type_parser<CharType, int64_t>::parse(buffer).then([](pplx::task<int64_t> op) -> T {