migrate to C++20

Author: nschimme

BUILD.md

@@ -8,7 +8,7 @@ This guide describes how to build **MMapper** from source on Linux, macOS, and W
 
 Ensure the following tools are installed:
 
-- A C++17-compatible compiler (e.g., GCC, Clang, MSVC)
+- A C++20-compatible compiler (e.g., GCC 11+, Clang 16+, MSVC 19.29+)
 - [CMake 3.20+](https://cmake.org/)
 - [Ninja](https://ninja-build.org/)
 - [Qt 6.4+](https://www.qt.io/) (6.8.3 recommended) with `QtWebSockets` and `QtMultimedia`

CMakeLists.txt

@@ -3,7 +3,7 @@ project(mmapper CXX)
 
 list(APPEND CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/cmake)
 
-set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 
@@ -419,6 +419,7 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
         endif()
 
         add_compile_options(-Weverything)
+        add_compile_options(-Wno-c++20-compat)
         add_compile_options(-Wno-c++98-c++11-compat-binary-literal) # never useful.
         add_compile_options(-Wno-c++98-compat) # never useful.
         add_compile_options(-Wno-c++98-compat-pedantic) # sometimes useful.
@@ -461,7 +462,7 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
         add_compile_options(-Werror=shorten-64-to-32)
         add_compile_options(-Werror=sign-conversion) # can warn about hard-to-spot bugs.
         add_compile_options(-Werror=switch)
-        add_compile_options(-Werror=unused-result) # required for c++17 [[nodiscard]]
+        add_compile_options(-Werror=unused-result) # required for [[nodiscard]]
         add_compile_options(-Werror=weak-vtables) # can result in crashes for ODR violations.
 
         # remove noise (most of these cannot be fixed)
@@ -472,6 +473,7 @@ if(MSVC)
     add_definitions(-DNOMINMAX)
     # modernize the __cplusplus value
     add_compile_options(/Zc:__cplusplus)
+    add_compile_options(/Zc:preprocessor)
     add_compile_options(/utf-8)
     add_compile_options(/permissive-)
     if(CMAKE_BUILD_TYPE_UPPER MATCHES "^RELWITHDEBINFO$")

src/CMakeLists.txt

@@ -771,7 +771,7 @@ endif()
 
 set_target_properties(
   mmapper PROPERTIES
-  CXX_STANDARD 17
+  CXX_STANDARD 20
   CXX_STANDARD_REQUIRED ON
   CXX_EXTENSIONS OFF
   COMPILE_FLAGS "${WARNING_FLAGS}"
@@ -781,15 +781,15 @@ set_target_properties(
 
 set_target_properties(
   mm_global PROPERTIES
-  CXX_STANDARD 17
+  CXX_STANDARD 20
   CXX_STANDARD_REQUIRED ON
   CXX_EXTENSIONS OFF
   COMPILE_FLAGS "${WARNING_FLAGS}"
 )
 
 set_target_properties(
   mm_map PROPERTIES
-  CXX_STANDARD 17
+  CXX_STANDARD 20
   CXX_STANDARD_REQUIRED ON
   CXX_EXTENSIONS OFF
   COMPILE_FLAGS "${WARNING_FLAGS}"

src/display/Textures.h

@@ -232,9 +232,8 @@ namespace mctp {
 namespace detail {
 // converts from EnumIndexedArray<SharedMMTexture, ...> to EnumIndexedArray<MMTexArrayPosition, ...>
 template<typename T>
-auto typeHack(const T &)
-    -> std::enable_if_t<std::is_same_v<typename T::value_type, SharedMMTexture>,
-                        EnumIndexedArray<MMTexArrayPosition, typename T::index_type, T::SIZE>>;
+    requires(std::is_same_v<typename T::value_type, SharedMMTexture>)
+auto typeHack(const T &) -> EnumIndexedArray<MMTexArrayPosition, typename T::index_type, T::SIZE>;
 
 template<typename T>
 struct NODISCARD Proxy

src/global/AnsiOstream.h

@@ -135,13 +135,17 @@ class NODISCARD AnsiOstream final
     void write(char16_t codepoint);
     void write(char32_t codepoint);
     void write(std::string_view sv);
+    void write(std::u8string_view sv)
+    {
+        write(std::string_view{reinterpret_cast<const char *>(sv.data()), sv.size()});
+    }
 
     template<typename T>
-    auto write(const T n)
-        -> std::enable_if_t<(std::is_integral_v<T> && !std::is_same_v<char32_t, std::decay_t<T>>
-                             && sizeof(char) < sizeof(T))
-                                || std::is_floating_point_v<T>,
-                            void>
+        requires((std::is_integral_v<T> and sizeof(T) > sizeof(char)
+                  and not(std::is_same_v<char16_t, std::decay_t<T>>
+                          or std::is_same_v<char32_t, std::decay_t<T>>))
+                 or std::is_floating_point_v<T>)
+    void write(const T n)
     {
         auto s = std::to_string(n);
         write(std::string_view{s});

src/global/Array.h

@@ -35,16 +35,15 @@ class NODISCARD Array : public std::array<T, N>
 
 public:
     template<typename First, typename... Types>
+        requires(std::is_same_v<First, Types> && ...)
     explicit constexpr Array(First &&first, Types &&...args)
         : std::array<T, N>{std::forward<First>(first), std::forward<Types>(args)...}
     {
         static_assert(N == 1 + sizeof...(Types), "missing initializers");
     }
 };
 
-#if __cpp_deduction_guides >= 201606
-// deducation guide copied from std::array
 template<typename T, typename... U>
-Array(T, U...) -> Array<std::enable_if_t<(std::is_same_v<T, U> && ...), T>, 1 + sizeof...(U)>;
-#endif
+    requires(std::is_same_v<T, U> && ...)
+Array(T, U...) -> Array<T, 1 + sizeof...(U)>;
 } // namespace MMapper

src/global/Charset-Utf8.cpp

@@ -552,13 +552,7 @@ NODISCARD static constexpr bool is7bit(const char c) noexcept
 }
 NODISCARD static constexpr bool is7bit(const std::string_view sv) noexcept
 {
-    // NOLINTNEXTLINE (can't use std::all_of() in constexpr in c++17)
-    for (const char c : sv) {
-        if (!is7bit(c)) {
-            return false;
-        }
-    }
-    return true;
+    return std::all_of(sv.begin(), sv.end(), [](char c) { return is7bit(c); });
 }
 
 NODISCARD static constexpr Utf8ValidationEnum validateUtf8(std::string_view sv) noexcept

src/global/Charset.cpp

@@ -348,7 +348,6 @@ ALLOW_DISCARD QString &toAsciiInPlace(QString &str)
 
     // NOTE: 128 (0x80) was not converted to 'z' before.
     for (QChar &qc : str) {
-        // c++17 if statement with initializer
         if (const char ch = mmqt::toLatin1(qc); !isAscii(ch)) {
             qc = QLatin1Char{charset::conversion::latin1ToAscii(ch)};
         }

src/global/ConfigConsts-Computed.h

@@ -4,6 +4,7 @@
 
 #include "ConfigEnums.h"
 
+#include <functional>
 #include <stdexcept>
 #include <string_view>
 
@@ -44,7 +45,7 @@ static inline constexpr PackageEnum CURRENT_PACKAGE = [] {
     throw std::runtime_error("unsupported package type");
 }();
 
-static inline constexpr const PlatformEnum CURRENT_PLATFORM = [] {
+static inline constexpr PlatformEnum CURRENT_PLATFORM = std::invoke([]() constexpr -> PlatformEnum {
 #if defined(Q_OS_WIN)
     return PlatformEnum::Windows;
 #elif defined(Q_OS_MAC)
@@ -56,14 +57,15 @@ static inline constexpr const PlatformEnum CURRENT_PLATFORM = [] {
 #else
     throw std::runtime_error("unsupported platform");
 #endif
-}();
+});
 
-static inline constexpr const EnvironmentEnum CURRENT_ENVIRONMENT = [] {
+static inline constexpr EnvironmentEnum CURRENT_ENVIRONMENT = std::invoke(
+    []() constexpr -> EnvironmentEnum {
 #if Q_PROCESSOR_WORDSIZE == 4
-    return EnvironmentEnum::Env32Bit;
+        return EnvironmentEnum::Env32Bit;
 #elif Q_PROCESSOR_WORDSIZE == 8
-    return EnvironmentEnum::Env64Bit;
+        return EnvironmentEnum::Env64Bit;
 #else
-    throw std::runtime_error("unsupported environment");
+        throw std::runtime_error("unsupported environment");
 #endif
-}();
+    });

src/global/MakeQPointer.h

@@ -12,8 +12,8 @@
 
 namespace mmqt {
 template<typename T, typename... Args>
-NODISCARD auto makeQPointer(Args &&...args)
-    -> std::enable_if_t<std::is_base_of_v<QObject, T>, QPointer<T>>
+    requires(std::is_base_of_v<QObject, T>)
+NODISCARD QPointer<T> makeQPointer(Args &&...args)
 {
     auto ptr = std::make_unique<T>(std::forward<Args>(args)...);
     if (ptr->QObject::parent() == nullptr) {