fix(#279): fix compilation with older msvc

by avoiding known SFINAE problem in msvc 2017

appveyor.yml

@@ -2,15 +2,26 @@ version: "{build}"
 
 environment:
   matrix:
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      MSVC_VERSION: 2017
+      CXX_VERSION: 11
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      MSVC_VERSION: 2017
+      CXX_VERSION: 14
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      MSVC_VERSION: 2017
+      CXX_VERSION: 17
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
-      generator: Visual Studio 16 2019
+      MSVC_VERSION: 2019
-      systemver: 10.0.18362.0
+      CXX_VERSION: 11
-    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2022
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
-      generator: Visual Studio 17 2022
+      MSVC_VERSION: 2019
-      systemver: 10.0.22621.0
+      CXX_VERSION: 14
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
+      MSVC_VERSION: 2019
+      CXX_VERSION: 17
 
 configuration:
-  - Release
   - Debug
 
 clone_depth: 10
@@ -20,9 +31,11 @@ install:
   - git submodule update --init --recursive
 
 build_script:
+  - '"C:\Program Files (x86)\Microsoft Visual Studio\%MSVC_VERSION%\Community\VC\Auxiliary\Build\vcvarsall.bat" x64'
   - cd C:\toml11
-  - cmake -B build -G"%generator%" -DCMAKE_SYSTEM_VERSION="%systemver%" -A x64 -DCMAKE_CXX_STANDARD=11 -DTOML11_BUILD_TESTS=ON -DTOML11_PRECOMPILE=ON
+  - cmake -B build -G"NMake Makefiles" -DCMAKE_BUILD_TYPE=%configuration% -DCMAKE_CXX_STANDARD=%CXX_VERSION% -DTOML11_BUILD_TESTS=ON -DBUILD_TESTING=ON -DTOML11_PRECOMPILE=ON
-  - cmake --build build --config "%configuration%"
+  - cmake --build build
 
 test_script:
-  - ctest --test-dir build --build-config "%configuration%" --timeout 300 --output-on-failure
+  - cd build\tests\
+  - ctest --timeout 300 --output-on-failure

include/toml11/compat.hpp

@@ -386,6 +386,35 @@ using return_type_of_t = typename std::result_of<F(Args...)>::type;
 } // cxx
 } // toml
 
+// ---------------------------------------------------------------------------
+// C++17 void_t
+
+#if TOML11_CPLUSPLUS_STANDARD_VERSION >= TOML11_CXX17_VALUE
+#  if defined(__cpp_lib_void_t)
+#    if __cpp_lib_void_t >= 201411L
+#      define TOML11_HAS_STD_VOID_T 1
+#    endif
+#  endif
+#endif
+
+namespace toml
+{
+namespace cxx
+{
+#if defined(TOML11_HAS_STD_VOID_T)
+
+using std::void_t;
+
+#else
+
+template<typename ...>
+using void_t = void;
+
+#endif // TOML11_HAS_STD_VOID_T
+
+} // cxx
+} // toml
+
 // ----------------------------------------------------------------------------
 // (subset of) source_location
 

include/toml11/types.hpp

@@ -2,6 +2,7 @@
 #define TOML11_TYPES_HPP
 
 #include "comments.hpp"
+#include "compat.hpp"
 #include "error_info.hpp"
 #include "format.hpp"
 #include "ordered_map.hpp"
@@ -299,77 +300,53 @@ namespace detail
 // ----------------------------------------------------------------------------
 // check if type T has all the needed member types
 
-struct has_comment_type_impl
+template<typename T, typename U = void>
-{
+struct has_comment_type: std::false_type{};
-    template<typename T> static std::true_type  check(typename T::comment_type*);
-    template<typename T> static std::false_type check(...);
-};
 template<typename T>
-using has_comment_type = decltype(has_comment_type_impl::check<T>(nullptr));
+struct has_comment_type<T, cxx::void_t<typename T::comment_type>>: std::true_type{};
 
-struct has_integer_type_impl
+template<typename T, typename U = void>
-{
+struct has_integer_type: std::false_type{};
-    template<typename T> static std::true_type  check(typename T::integer_type*);
-    template<typename T> static std::false_type check(...);
-};
 template<typename T>
-using has_integer_type = decltype(has_integer_type_impl::check<T>(nullptr));
+struct has_integer_type<T, cxx::void_t<typename T::integer_type>>: std::true_type{};
 
-struct has_floating_type_impl
+template<typename T, typename U = void>
-{
+struct has_floating_type: std::false_type{};
-    template<typename T> static std::true_type  check(typename T::floating_type*);
-    template<typename T> static std::false_type check(...);
-};
 template<typename T>
-using has_floating_type = decltype(has_floating_type_impl::check<T>(nullptr));
+struct has_floating_type<T, cxx::void_t<typename T::floating_type>>: std::true_type{};
 
-struct has_string_type_impl
+template<typename T, typename U = void>
-{
+struct has_string_type: std::false_type{};
-    template<typename T> static std::true_type  check(typename T::string_type*);
-    template<typename T> static std::false_type check(...);
-};
 template<typename T>
-using has_string_type = decltype(has_string_type_impl::check<T>(nullptr));
+struct has_string_type<T, cxx::void_t<typename T::string_type>>: std::true_type{};
 
-struct has_array_type_impl
+template<typename T, typename U = void>
-{
+struct has_array_type: std::false_type{};
-    template<typename T> static std::true_type  check(typename T::template array_type<int>*);
-    template<typename T> static std::false_type check(...);
-};
 template<typename T>
-using has_array_type = decltype(has_array_type_impl::check<T>(nullptr));
+struct has_array_type<T, cxx::void_t<typename T::template array_type<int>>>: std::true_type{};
 
-struct has_table_type_impl
+template<typename T, typename U = void>
-{
+struct has_table_type: std::false_type{};
-    template<typename T> static std::true_type  check(typename T::template table_type<int, int>*);
-    template<typename T> static std::false_type check(...);
-};
 template<typename T>
-using has_table_type = decltype(has_table_type_impl::check<T>(nullptr));
+struct has_table_type<T, cxx::void_t<typename T::template table_type<int, int>>>: std::true_type{};
 
-struct has_parse_int_impl
+template<typename T, typename U = void>
-{
+struct has_parse_int: std::false_type{};
-    template<typename T> static std::true_type  check(decltype(std::declval<T>().parse_int(
-            std::declval<const std::string&>(),
-            std::declval<const source_location>(),
-            std::declval<const std::uint8_t>()
-        ))*);
-    template<typename T> static std::false_type check(...);
-};
 template<typename T>
-using has_parse_int = decltype(has_parse_int_impl::check<T>(nullptr));
+struct has_parse_int<T, cxx::void_t<decltype(std::declval<T>().parse_int(
+        std::declval<std::string const&>(),
+        std::declval<::toml::source_location const&>(),
+        std::declval<std::uint8_t>()
+    ))>>: std::true_type{};
 
-struct has_parse_float_impl
+template<typename T, typename U = void>
-{
+struct has_parse_float: std::false_type{};
-    template<typename T> static std::true_type  check(decltype(std::declval<T>().parse_float(
-            std::declval<const std::string&>(),
-            std::declval<const source_location>(),
-            std::declval<const bool>()
-        ))*);
-    template<typename T> static std::false_type check(...);
-};
 template<typename T>
-using has_parse_float = decltype(has_parse_float_impl::check<T>(nullptr));
+struct has_parse_float<T, cxx::void_t<decltype(std::declval<T>().parse_float(
+        std::declval<std::string const&>(),
+        std::declval<::toml::source_location const&>(),
+        std::declval<bool>()
+    ))>>: std::true_type{};
 
 template<typename T>
 using is_type_config = cxx::conjunction<

tests/CMakeLists.txt

@@ -21,6 +21,7 @@ set(TOML11_TEST_NAMES
     test_parse_inline_table
     test_parse_table_keys
     test_parse_table
+    test_parse
     test_result
     test_scanner
     test_serialize

tests/test_parse.cpp

@@ -0,0 +1,50 @@
+#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
+#include "doctest.h"
+
+#include <toml.hpp>
+
+#include <clocale>
+
+TEST_CASE("testing toml::parse(file)")
+{
+    using namespace toml::literals::toml_literals;
+
+    const std::string spec_example(R"(# This is a TOML document
+
+title = "TOML Example"
+
+[owner]
+name = "Tom Preston-Werner"
+dob = 1979-05-27T07:32:00-08:00
+
+[database]
+enabled = true
+ports = [ 8000, 8001, 8002 ]
+data = [ ["delta", "phi"], [3.14] ]
+temp_targets = { cpu = 79.5, case = 72.0 }
+
+[servers]
+
+[servers.alpha]
+ip = "10.0.0.1"
+role = "frontend"
+
+[servers.beta]
+ip = "10.0.0.2"
+role = "backend"
+)");
+
+    {
+        std::ofstream ofs("test_parse.toml");
+        ofs << spec_example;
+    }
+
+    const auto u = toml::parse_str(spec_example);
+    const auto v = toml::parse("test_parse.toml");
+
+    CHECK_EQ(u, v);
+
+    CHECK_EQ(toml::find<int>(v, "database", "ports", 0), 8000);
+    CHECK_EQ(toml::find<int>(v, "database", "ports", 1), 8001);
+    CHECK_EQ(toml::find<int>(v, "database", "ports", 2), 8002);
+}