From 455836af8923b9ab423d6281f8ae9b9df49376d3 Mon Sep 17 00:00:00 2001
From: Stenzek <stenzek@gmail.com>
Date: Mon, 3 Feb 2025 00:30:39 +1000
Subject: [PATCH] CMake: Check C++20 features that are missing on some systems

---
 CMakeLists.txt                                | 11 +----
 CMakeModules/DuckStationBuildSummary.cmake    |  2 +
 .../DuckStationCompilerRequirement.cmake      | 16 +++++++
 CMakeModules/DuckStationUtils.cmake           | 47 +++++++++++++++++++
 src/common/heterogeneous_containers.h         |  1 +
 5 files changed, 68 insertions(+), 9 deletions(-)
 create mode 100644 CMakeModules/DuckStationCompilerRequirement.cmake

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8e8d37371..23ee264ae 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.16)
+cmake_minimum_required(VERSION 3.19)
 project(duckstation C CXX)
 
 # Policy settings.
@@ -16,10 +16,6 @@ if(NOT CMAKE_BUILD_TYPE MATCHES "Debug|Devel|MinSizeRel|RelWithDebInfo|Release")
   set(CMAKE_BUILD_TYPE "Release")
 endif()
 
-message(STATUS "CMake Version: ${CMAKE_VERSION}")
-message(STATUS "CMake System Name: ${CMAKE_SYSTEM_NAME}")
-message(STATUS "Build Type: ${CMAKE_BUILD_TYPE}")
-
 # Pull in modules.
 set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/CMakeModules/")
 include(DuckStationUtils)
@@ -34,6 +30,7 @@ detect_cache_line_size()
 # Build options. Depends on system attributes.
 include(DuckStationBuildOptions)
 include(DuckStationDependencies)
+include(DuckStationCompilerRequirement)
 
 # Enable PIC on Linux, otherwise the builds do not support ASLR.
 if(LINUX OR BSD)
@@ -120,10 +117,6 @@ endif()
 # Prevent fmt from being built with exceptions, or being thrown at call sites.
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DFMT_EXCEPTIONS=0")
 
-# Use C++20.
-set(CMAKE_CXX_STANDARD 20)
-set(CMAKE_CXX_STANDARD_REQUIRED ON)
-
 # Recursively include the source tree.
 add_subdirectory(dep)
 add_subdirectory(src)
diff --git a/CMakeModules/DuckStationBuildSummary.cmake b/CMakeModules/DuckStationBuildSummary.cmake
index adb69a259..6874b919a 100644
--- a/CMakeModules/DuckStationBuildSummary.cmake
+++ b/CMakeModules/DuckStationBuildSummary.cmake
@@ -1,3 +1,5 @@
+message(STATUS "Build Type: ${CMAKE_BUILD_TYPE}")
+
 if(ENABLE_OPENGL)
   message(STATUS "Building with OpenGL support.")
 endif()
diff --git a/CMakeModules/DuckStationCompilerRequirement.cmake b/CMakeModules/DuckStationCompilerRequirement.cmake
new file mode 100644
index 000000000..b7fabbf86
--- /dev/null
+++ b/CMakeModules/DuckStationCompilerRequirement.cmake
@@ -0,0 +1,16 @@
+# Use C++20.
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+# C++20 feature checks. Some Linux environments are incomplete.
+check_cpp20_feature("__cpp_structured_bindings" 201606)
+check_cpp20_feature("__cpp_constinit" 201907)
+check_cpp20_feature("__cpp_designated_initializers" 201707)
+check_cpp20_feature("__cpp_using_enum" 201907)
+check_cpp20_feature("__cpp_lib_bit_cast" 201806)
+check_cpp20_feature("__cpp_lib_bitops" 201907)
+check_cpp20_feature("__cpp_lib_int_pow2" 202002)
+check_cpp20_feature("__cpp_lib_starts_ends_with" 201711)
+check_cpp20_attribute("likely" 201803)
+check_cpp20_attribute("unlikely" 201803)
+check_cpp20_attribute("no_unique_address" 201803)
diff --git a/CMakeModules/DuckStationUtils.cmake b/CMakeModules/DuckStationUtils.cmake
index 9d7c5ad46..f0635f1ac 100644
--- a/CMakeModules/DuckStationUtils.cmake
+++ b/CMakeModules/DuckStationUtils.cmake
@@ -1,3 +1,5 @@
+include(CheckSourceCompiles)
+
 function(disable_compiler_warnings_for_target target)
 	if(MSVC)
 		target_compile_options(${target} PRIVATE "/W0")
@@ -245,3 +247,48 @@ function(install_imported_dep_library name)
   get_target_property(LOCATION "${name}" IMPORTED_LOCATION_RELEASE)
   install(FILES "${LOCATION}" RENAME "${SONAME}" DESTINATION "${CMAKE_INSTALL_LIBDIR}")
 endfunction()
+
+function(check_cpp20_feature MACRO MINIMUM_VALUE)
+  set(CACHE_VAR "CHECK_CPP20_FEATURE_${MACRO}")
+  if(NOT DEFINED ${CACHE_VAR})
+    # Create a small source code snippet that fails to compile if the feature is not available.
+    set(TEMP_FILE "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/src.cpp")
+    file(WRITE "${TEMP_FILE}" "#include <version>
+#if !defined(${MACRO}) || ${MACRO} < ${MINIMUM_VALUE}L
+#error Missing feature
+#endif
+    ")
+    set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+    try_compile(HAS_FEATURE
+      ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY} "${TEMP_FILE}"
+      CXX_STANDARD 20
+      CXX_STANDARD_REQUIRED TRUE
+    )
+    set(${CACHE_VAR} ${HAS_FEATURE} CACHE INTERNAL "Cached feature test result for ${MACRO}")
+  endif()
+  if(NOT HAS_FEATURE)
+    message(FATAL_ERROR "${MACRO} is not supported by your compiler, at least ${MINIMUM_VALUE} is required.")
+  endif()
+endfunction()
+
+function(check_cpp20_attribute ATTRIBUTE MINIMUM_VALUE)
+  set(CACHE_VAR "CHECK_CPP20_ATTRIBUTE_${MACRO}")
+  if(NOT DEFINED ${CACHE_VAR})
+    set(TEMP_FILE "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/src.cpp")
+    file(WRITE "${TEMP_FILE}" "#include <version>
+#if !defined(__has_cpp_attribute) || __has_cpp_attribute(${ATTRIBUTE}) < ${MINIMUM_VALUE}L
+#error Missing feature
+#endif
+    ")
+    set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+    try_compile(HAS_FEATURE
+      ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY} "${TEMP_FILE}"
+      CXX_STANDARD 20
+      CXX_STANDARD_REQUIRED TRUE
+    )
+    set(${CACHE_VAR} ${HAS_FEATURE} CACHE INTERNAL "Cached attribute test result for ${MACRO}")
+  endif()
+  if(NOT HAS_FEATURE)
+    message(FATAL_ERROR "${ATTRIBUTE} is not supported by your compiler, at least ${MINIMUM_VALUE} is required.")
+  endif()
+endfunction()
diff --git a/src/common/heterogeneous_containers.h b/src/common/heterogeneous_containers.h
index 2f7bf35ee..1549f36e7 100644
--- a/src/common/heterogeneous_containers.h
+++ b/src/common/heterogeneous_containers.h
@@ -13,6 +13,7 @@
 #include <string>
 #include <unordered_map>
 #include <unordered_set>
+#include <version>
 
 namespace detail {
 struct transparent_string_hash