Add macOS (Apple Silicon) build support

.gitmodules

@@ -1,7 +1,11 @@
 [submodule "lib/APCpp"]
 	path = lib/APCpp
-	url = https://github.com/RecompRando/APCpp.git
-	branch = main
+	# TEMPORARY: the macOS build needs the size_t->Json::Value fix that is
+	# still pending upstream (see PR referenced in the commit/PR description).
+	# Pointing at the fork so CI can build; revert to RecompRando/APCpp once
+	# the fix is merged.
+	url = https://github.com/MarcDufresne/APCpp.git
+	branch = macos-arm64-fix
 [submodule "Archipelago-MM"]
 	path = archipelago
 	url = https://github.com/RecompRando/Archipelago-MM

CMakeLists.txt

@@ -6,7 +6,12 @@ set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 set(CMAKE_SKIP_BUILD_RPATH FALSE)
 set(CMAKE_BUILD_WITH_INSTALL_RPATH TRUE)
-set(CMAKE_INSTALL_RPATH "$\{ORIGIN\}")
+if(APPLE)
+    # macOS dyld uses @loader_path (dir of the loading binary), not $ORIGIN.
+    set(CMAKE_INSTALL_RPATH "@loader_path")
+else()
+    set(CMAKE_INSTALL_RPATH "$\{ORIGIN\}")
+endif()
 
 # Include the script to download and set up the Python binary
 if(WIN32)
@@ -29,6 +34,8 @@ elseif(CMAKE_SYSTEM_NAME MATCHES "Linux")
     else()
         message(FATAL_ERROR "Unknown pointer size.")
     endif()
+elseif(CMAKE_SYSTEM_NAME MATCHES "Darwin")
+    include(${CMAKE_SOURCE_DIR}/PythonStandalone_macOS_arm64.cmake)
 endif()
 
 add_library(APCpp-Glue SHARED 
@@ -41,6 +48,14 @@ add_library(APCpp-Glue SHARED
 
 target_include_directories(APCpp-Glue PRIVATE lib/APCpp)
 
+# The recomp engine resolves the native_libraries manifest entry by bare name
+# ("APCpp-Glue") + platform extension, matching the Windows APCpp-Glue.dll and
+# Linux APCpp-Glue.so in the release. macOS would otherwise get CMake's default
+# "lib" prefix (libAPCpp-Glue.dylib) and fail to resolve, so drop the prefix.
+if(APPLE)
+    set_target_properties(APCpp-Glue PROPERTIES PREFIX "")
+endif()
+
 if (WIN32)
     target_link_libraries(APCpp-Glue PRIVATE ws2_32)
 else()

PythonStandalone_macOS_arm64.cmake

@@ -0,0 +1,52 @@
+cmake_minimum_required(VERSION 3.20)
+project(UsePythonStandalone)
+
+include(FetchContent)
+
+set(PYTHON_URL "https://github.com/astral-sh/python-build-standalone/releases/download/20250409/cpython-3.11.12+20250409-aarch64-apple-darwin-install_only_stripped.tar.gz")
+set(PYTHON_ARCHIVE "${CMAKE_BINARY_DIR}/cpython.tar.gz")
+set(PYTHON_EXTRACT_DIR "${CMAKE_BINARY_DIR}/python-standalone")
+
+if(NOT EXISTS "${PYTHON_ARCHIVE}")
+    message(STATUS "Downloading Python artifact...")
+    file(DOWNLOAD "${PYTHON_URL}" "${PYTHON_ARCHIVE}" SHOW_PROGRESS)
+endif()
+
+if(NOT EXISTS "${PYTHON_EXTRACT_DIR}")
+    message(STATUS "Extracting Python artifact...")
+    file(MAKE_DIRECTORY "${PYTHON_EXTRACT_DIR}")
+    execute_process(
+        COMMAND ${CMAKE_COMMAND} -E tar xzf "${PYTHON_ARCHIVE}"
+        WORKING_DIRECTORY "${PYTHON_EXTRACT_DIR}"
+    )
+endif()
+
+file(GLOB EXTRACTED_DIRS LIST_DIRECTORIES true "${PYTHON_EXTRACT_DIR}/*")
+list(GET EXTRACTED_DIRS 0 PYTHON_ROOT)
+
+add_library(python_standalone INTERFACE)
+target_include_directories(python_standalone INTERFACE "${PYTHON_ROOT}/include/python3.11")
+target_link_directories(python_standalone INTERFACE "${PYTHON_ROOT}/lib")
+target_link_libraries(python_standalone INTERFACE "${PYTHON_ROOT}/lib/libpython3.11.dylib")
+
+function(link_python_standalone TARGET_NAME)
+    target_link_libraries(${TARGET_NAME} PRIVATE python_standalone)
+    # Copy the interpreter next to the target so it ships with the mod.
+    add_custom_command(TARGET ${TARGET_NAME} POST_BUILD
+        COMMAND ${CMAKE_COMMAND} -E copy_if_different
+            "${PYTHON_ROOT}/lib/libpython3.11.dylib"
+            "$<TARGET_FILE_DIR:${TARGET_NAME}>/libpython3.11.dylib"
+    )
+    # The python-build-standalone dylib has install_name /install/lib/libpython3.11.dylib,
+    # which gets baked into the target as an absolute dependency that won't exist on the
+    # user's machine. Rewrite it to @loader_path so dyld finds the copy placed alongside.
+    add_custom_command(TARGET ${TARGET_NAME} POST_BUILD
+        COMMAND install_name_tool -change
+            "/install/lib/libpython3.11.dylib"
+            "@loader_path/libpython3.11.dylib"
+            "$<TARGET_FILE:${TARGET_NAME}>"
+    )
+endfunction()
+
+set(PYTHON_EXE "${PYTHON_ROOT}/bin/python3.11" CACHE PATH "Python executable")
+set(PYTHON_STANDALONE_ROOT "${PYTHON_ROOT}" CACHE PATH "Root of extracted Python standalone distribution")