build(macos): bundle libSDL3.dylib for sdl2-compat

cmake/macos/BundleSDL3Compat.cmake

@@ -0,0 +1,68 @@
+# Bundle libSDL3.dylib when libSDL2 is sdl2-compat.
+# BUNDLE_DIR   - the app bundle's Contents/Frameworks directory
+# APP_BINARY   - the main executable inside the app bundle
+# SDL2_LIBRARY - the SDL2 library the executable was linked against
+#
+# Homebrew's sdl2 formula ships sdl2-compat (2.32+), which dlopens
+# libSDL3.dylib at runtime (first candidate: @loader_path/libSDL3.dylib).
+# dylibbundler only walks LC_LOAD_DYLIB entries, so the SDL3 dependency
+# never lands in the bundle and the app aborts with
+# "Failed loading SDL3 library." on launch.
+
+set(bundled_sdl2 "${BUNDLE_DIR}/libSDL2-2.0.0.dylib")
+if(NOT EXISTS "${bundled_sdl2}")
+    # Static or monolithic SDL2 build: nothing to do.
+    return()
+endif()
+
+# sdl2-compat embeds the literal name "libSDL3.dylib" in its dlopen
+# search list; real SDL2 does not.
+execute_process(
+    COMMAND grep -q libSDL3.dylib "${bundled_sdl2}"
+    RESULT_VARIABLE is_sdl2_compat
+    OUTPUT_QUIET ERROR_QUIET)
+if(NOT is_sdl2_compat EQUAL 0)
+    # Real SDL2: no runtime SDL3 dependency.
+    return()
+endif()
+
+get_filename_component(sdl2_lib_dir "${SDL2_LIBRARY}" DIRECTORY)
+find_library(SDL3_LIBRARY
+    NAMES SDL3 libSDL3
+    HINTS "${sdl2_lib_dir}" /opt/homebrew/lib /usr/local/lib)
+
+if(NOT SDL3_LIBRARY)
+    message(WARNING
+        "libSDL2 is sdl2-compat but libSDL3.dylib was not found; "
+        "the bundled app will fail to launch with "
+        "'Failed loading SDL3 library.' Install SDL3 (brew install sdl3) "
+        "and rebuild.")
+    return()
+endif()
+
+execute_process(
+    COMMAND ${CMAKE_COMMAND} -E copy_if_different
+    "${SDL3_LIBRARY}" "${BUNDLE_DIR}/libSDL3.dylib"
+    RESULT_VARIABLE copy_result)
+if(NOT copy_result EQUAL 0)
+    message(WARNING "failed to copy ${SDL3_LIBRARY} into ${BUNDLE_DIR}")
+    return()
+endif()
+execute_process(
+    COMMAND codesign --force --sign - "${BUNDLE_DIR}/libSDL3.dylib"
+    RESULT_VARIABLE codesign_result)
+if(NOT codesign_result EQUAL 0)
+    message(WARNING "codesign failed for bundled libSDL3.dylib")
+endif()
+
+# libSDL3.dylib was added after dylibbundler signed the bundle. Nested code
+# must be signed before the enclosing bundle, so sign libSDL3.dylib first
+# (above), then re-seal the whole .app bundle.
+get_filename_component(app_bundle "${APP_BINARY}/../../.." ABSOLUTE)
+execute_process(
+    COMMAND codesign --force --deep --sign - "${app_bundle}"
+    RESULT_VARIABLE app_codesign_result)
+if(NOT app_codesign_result EQUAL 0)
+    message(WARNING "codesign failed for ${app_bundle}")
+endif()
+message(STATUS "Bundled ${SDL3_LIBRARY} for sdl2-compat")

cmake/macos/CMakeLists.txt

@@ -31,6 +31,15 @@ add_custom_command(TARGET ${PROJECT_NAME} POST_BUILD
 add_custom_command(TARGET ${PROJECT_NAME} POST_BUILD
         COMMAND dylibbundler -od -b -x $<TARGET_FILE:${PROJECT_NAME}> -d $<TARGET_FILE_DIR:${PROJECT_NAME}>/../Frameworks/ -p @executable_path/../Frameworks/)
 
+# Homebrew's sdl2 formula is sdl2-compat, which dlopens libSDL3.dylib at
+# runtime; dylibbundler can't see dlopen dependencies, so bundle SDL3 here.
+add_custom_command(TARGET ${PROJECT_NAME} POST_BUILD
+        COMMAND ${CMAKE_COMMAND}
+        -DBUNDLE_DIR=$<TARGET_FILE_DIR:${PROJECT_NAME}>/../Frameworks
+        -DAPP_BINARY=$<TARGET_FILE:${PROJECT_NAME}>
+        -DSDL2_LIBRARY=$<TARGET_FILE:SDL2::SDL2>
+        -P ${CMAKE_CURRENT_LIST_DIR}/BundleSDL3Compat.cmake)
+
 if (NOT "${CMAKE_GENERATOR}" MATCHES "Xcode")
     install(FILES $<TARGET_FILE:capsimage>
             DESTINATION $<TARGET_FILE_DIR:${PROJECT_NAME}>/../Resources/plugins/)