Enable C++20 and re-enable MSVC build

Also switched to standard-conforming __VA_OPT__ for logging.

CMakeLists.txt

@@ -1,5 +1,9 @@
-# CMake 3.8 required for 17 to be a valid value for CXX_STANDARD
-cmake_minimum_required(VERSION 3.8)
+# CMake 3.12.4 required for 20 to be a valid value for CXX_STANDARD
+cmake_minimum_required(VERSION 3.15)
+# Add MSVC runtime library selection flags automatically:
+cmake_policy(SET CMP0091 OLD)
+# Don't override the warning flags in MSVC:
+cmake_policy(SET CMP0092 NEW)
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/CMakeModules")
 include(DownloadExternals)
 include(CMakeDependentOption)
@@ -73,8 +77,12 @@ message(STATUS "Target architecture: ${ARCHITECTURE}")
 
 # Configure C++ standard
 # ===========================
-set(CMAKE_CXX_STANDARD 17)
-set(CMAKE_CXX_STANDARD_REQUIRED ON)
+if (MSVC)
+    add_compile_options(/std:c++latest)
+else()
+    set(CMAKE_CXX_STANDARD 20)
+    set(CMAKE_CXX_STANDARD_REQUIRED ON)
+endif()
 
 # set up output paths for executable binaries
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/bin)

appveyor.yml

@@ -10,7 +10,7 @@ environment:
   CHERE_INVOKING: 1
   matrix:
     - BUILD_TYPE: mingw
-    # - BUILD_TYPE: msvc
+    - BUILD_TYPE: msvc
 
 platform:
   - x64
@@ -37,7 +37,7 @@ before_build:
   - ps: |
         if ($env:BUILD_TYPE -eq 'msvc') {
           # redirect stderr and change the exit code to prevent powershell from cancelling the build if cmake prints a warning
-          cmd /C 'cmake -G "Visual Studio 16 2019" -DUSE_BUNDLED_QT=OFF -DQt5_DIR=C:\Qt\5.14\msvc2017_64\lib\cmake\qt5 -DWARNINGS_AS_ERRORS=OFF - .. 2>&1 && exit 0'
+          cmd /C 'cmake -G "Visual Studio 16 2019" -DUSE_BUNDLED_QT=OFF -DQt5_DIR=C:\Qt\5.14\msvc2017_64\lib\cmake\qt5 -DWARNINGS_AS_ERRORS=OFF .. 2>&1 && exit 0'
         } else {
           C:\msys64\usr\bin\bash.exe -lc "cmake -G 'MSYS Makefiles' -DCMAKE_BUILD_TYPE=Release -DMINGW_STATIC_BUILD=ON -DCOMPILE_WITH_DWARF=OFF .. 2>&1"
         }

src/CMakeLists.txt

@@ -39,7 +39,7 @@ if (MSVC)
     # /Zc:externConstexpr        - Allow extern constexpr variables to have external linkage, like the standard mandates
     # /Zc:inline                 - Let codegen omit inline functions in object files
     # /Zc:throwingNew            - Let codegen assume `operator new` (without std::nothrow) will never return null
-    # /experimental:preprocessor - Work around bugs within MSVC's crappy preprocessor
+    # /Zc:preprocessor           - Use std-conforming MSVC preprocessor
     add_compile_options(
         /W4
         /w34263
@@ -60,7 +60,7 @@ if (MSVC)
         /Zc:externConstexpr
         /Zc:inline
         /Zc:throwingNew
-        /experimental:preprocessor
+        /Zc:preprocessor
     )
 
     # /GS- - No stack buffer overflow checks

src/common/logging/log.h

@@ -15,12 +15,11 @@
 std::uint64_t GetLoggingTime();
 std::string StandardizeLogClass(const std::string& log_class);
 
-// TODO: Use a standard variant of ##__VA_ARGS__?
 #define LOG_PRINT(log_class, level, text_style, file, line, func, format, ...)                     \
     {                                                                                              \
         fmt::print(stderr, text_style, "[{:12.6f}] {} <{}> {}:{}:{}: " format "\n",                \
                    GetLoggingTime() / 1000000.0, StandardizeLogClass(log_class), level, file,      \
-                   line, func, ##__VA_ARGS__);                                                     \
+                   line, func __VA_OPT__(, ) __VA_ARGS__);                                         \
         fflush(stderr);                                                                            \
     }
 

src/core/inner_fat.h

@@ -23,7 +23,8 @@ struct ArchiveFormatInfo {
     u32_le number_files;       ///< The pre-defined number of files in the archive.
     u8 duplicate_data;         ///< Whether the archive should duplicate the data.
 };
-static_assert(std::is_pod<ArchiveFormatInfo>::value, "ArchiveFormatInfo is not POD");
+static_assert(std::is_standard_layout_v<ArchiveFormatInfo> && std::is_trivial_v<ArchiveFormatInfo>,
+              "ArchiveFormatInfo is not POD");
 
 union TableOffset {
     // This has different meanings for different savegame layouts