Cross-build Intel macOS jobs on Apple Silicon

.github/workflows/ci.yml

@@ -59,19 +59,11 @@ jobs:
             buildtype: release,
             args: -Db_pch=false
           }
-          - name: macOS x86_64 Debug
-            os: macos-15-intel
-            buildtype: debugoptimized
-            args: &macos_debug_args >-
-              -Dmacos_deployment_target=15.0
-              -Dbuild_osx_bundle=false
-              -Dfftw3=enabled
-              -Dlibpulse=disabled
-              -Dopenal=enabled
           - name: macOS x86_64 Release
-            os: macos-15-intel
+            os: macos-15
+            cross_args: --cross-file tools/macos-release.ini --cross-file tools/macos-x86_64.ini
             buildtype: release
-            args: &macos_release_args >-
+            args: &macos_source_args >-
               -Ddefault_library=static
               -Dbuild_osx_bundle=true
               -Dfftw3=disabled
@@ -102,11 +94,17 @@ jobs:
           - name: macOS arm64 Debug
             os: macos-15
             buildtype: debugoptimized
-            args: *macos_debug_args
+            args: >-
+              -Dmacos_deployment_target=15.0
+              -Dbuild_osx_bundle=false
+              -Dfftw3=enabled
+              -Dlibpulse=disabled
+              -Dopenal=enabled
           - name: macOS arm64 Release
             os: macos-15
+            native_args: --native-file tools/macos-release.ini
             buildtype: release
-            args: *macos_release_args
+            args: *macos_source_args
 
     steps:
       - uses: actions/checkout@v6
@@ -159,17 +157,34 @@ jobs:
 
           echo "PKG_CONFIG_PATH=$(brew --prefix icu4c)/lib/pkgconfig:$(brew --prefix zlib)/lib/pkgconfig" >> "${GITHUB_ENV}"
 
-      - name: Install dependencies (macOS Release)
+      - name: Install build tools (macOS source dependencies)
         if: startsWith(matrix.config.os, 'macos-') && matrix.config.buildtype == 'release'
         run: |
           brew install ninja nasm
 
+      - name: Check Rosetta (macOS cross builds)
+        if: matrix.config.cross_args
+        run: |
+          if ! /usr/bin/arch -x86_64 /usr/bin/true; then
+            sudo softwareupdate --install-rosetta --agree-to-license
+          fi
+          /usr/bin/arch -x86_64 /usr/bin/true
+
       - name: Install test dependencies (macOS)
         if: startsWith(matrix.config.os, 'macos-')
+        env:
+          CROSS_ARGS: ${{ matrix.config.cross_args }}
         run: |
           # LuaJIT is Lua 5.1 to luarocks.
           brew install luajit luarocks
-          luarocks --lua-dir="$(brew --prefix luajit)" --lua-version=5.1 install busted
+          if test -n "${CROSS_ARGS}"; then
+            # Busted's native modules are loaded by the Intel test executable.
+            luarocks --lua-dir="$(brew --prefix luajit)" --lua-version=5.1 install busted \
+              CC='/usr/bin/clang -arch x86_64' \
+              LD='/usr/bin/clang -arch x86_64'
+          else
+            luarocks --lua-dir="$(brew --prefix luajit)" --lua-version=5.1 install busted
+          fi
 
       - name: Install dependencies (Linux)
         if: startsWith(matrix.config.os, 'ubuntu-')
@@ -184,7 +199,7 @@ jobs:
       - name: Configure
         run: |
           ${{ matrix.config.devenv }}
-          meson setup build ${{ matrix.config.args }} -Dbuildtype=${{ matrix.config.buildtype }} ${{ github.ref_type == 'tag' && '-Dofficial_release=true' || '' }}
+          meson setup build ${{ matrix.config.native_args }} ${{ matrix.config.cross_args }} ${{ matrix.config.args }} -Dbuildtype=${{ matrix.config.buildtype }} ${{ github.ref_type == 'tag' && '-Dofficial_release=true' || '' }}
 
       - name: Build FFTW (MacOS)
         if: startsWith(matrix.config.os, 'macos-') && matrix.config.buildtype == 'release'
@@ -199,6 +214,14 @@ jobs:
           ${{ matrix.config.devenv }}
           meson compile -C build
 
+      - name: Verify Intel cross-build architecture
+        if: matrix.config.cross_args
+        run: |
+          test "$(lipo -archs build/aegisub)" = x86_64
+          test "$(lipo -archs build/tests/gtest-main)" = x86_64
+          test "$(lipo -archs build/tests/luajit-52)" = x86_64
+          test "$(lipo -archs build/automation/tests/aegisub-lua)" = x86_64
+
       # The automation suite is registered at configure time only if the
       # busted probe succeeds, so make sure it can't silently drop out of CI
       - name: Check automation tests are registered
@@ -211,6 +234,18 @@ jobs:
           ${{ matrix.config.devenv }}
           meson test -C build --verbose --suite Aegisub
 
+      - name: Check cross-built tests executed
+        if: matrix.config.cross_args
+        run: |
+          python3 - <<'PY'
+          import json
+          from pathlib import Path
+
+          results = [json.loads(line) for line in Path('build/meson-logs/testlog.json').read_text().splitlines()]
+          if not results or any(result['result'] != 'OK' for result in results):
+              raise SystemExit('Cross-built tests must pass under Rosetta, not be skipped')
+          PY
+
       # Windows artifacts
       - name: Generate Windows installer
         if: matrix.config.os == 'windows-latest'

docs/developer_docs.md

@@ -109,6 +109,32 @@ the notary service and stapled. This follows Apple's nested-container guidance;
 the app and every nested Mach-O file are still Developer ID-signed before the
 DMG is created.
 
+## Intel macOS cross builds
+
+The Intel Release CI lane uses an Apple Silicon runner with
+`--cross-file tools/macos-release.ini --cross-file tools/macos-x86_64.ini`.
+Compilation uses native Apple Silicon tools targeting x86_64; Rosetta runs
+the resulting Intel test executables.
+This checks the Intel code path, but does not replace testing a release on
+real Intel hardware.
+
+The Intel lane builds its target dependencies from source using the shared
+macOS release dependency options in `.github/workflows/ci.yml`. Both Release
+lanes use `tools/macos-release.ini` to restrict pkg-config and CMake dependency
+discovery away from Homebrew; arm64 loads it with `--native-file`. Homebrew is
+still used for build tools. The native arm64 Debug lane still uses
+Homebrew libraries and is tested but not packaged. Intel coverage comes from
+the Release lane, including tests under Rosetta.
+
+For a local cross build, use the same dependency options and cross files as CI.
+After Meson setup, run `tools/macos-build-fftw.sh BUILD_DIR`, then reconfigure
+with `-Dpkg_config_path="$PWD/BUILD_DIR/fftw-prefix/lib/pkgconfig"`
+and `-Dfftw3=enabled`. The bootstrap reads the target architecture from Meson
+and only passes Autoconf's `--host` option when it differs from the build CPU.
+Automation tests also need Intel builds of Busted's native Lua modules; the
+workflow shows the LuaRocks compiler overrides. Use a separate LuaRocks tree
+if native arm64 tests need to run on the same machine.
+
 ## Running Doxygen
 
 You can run Doxygen with the following command:

tools/macos-build-fftw.sh

@@ -29,8 +29,17 @@ FFTW_SHA256="5630c24cdeb33b131612f7eb4b1a9934234754f9f388ff8617458d0be6f239a1"
 FFTW_URL="https://fftw.org/fftw-${FFTW_VERSION}.tar.gz"
 FFTW_PREFIX="${BUILD_DIR}/fftw-prefix"
 FFTW_STAMP="${FFTW_PREFIX}/.aegisub-build"
-ARCH="$(uname -m)"
-EXPECTED_STAMP="fftw=${FFTW_VERSION} arch=${ARCH} macos=${DEPLOYMENT_TARGET}"
+ARCH="$(meson introspect --machines "${BUILD_DIR}" | python3 -c '
+import json
+import sys
+
+machine = json.load(sys.stdin)["host"]
+if machine["system"] != "darwin":
+    raise SystemExit("FFTW macOS bootstrap requires a Darwin host")
+print({"aarch64": "arm64", "x86_64": "x86_64"}.get(machine["cpu_family"], machine["cpu_family"]))
+')"
+BUILD_ARCH="$(uname -m)"
+EXPECTED_STAMP="fftw=${FFTW_VERSION} arch=${ARCH} build=${BUILD_ARCH} macos=${DEPLOYMENT_TARGET}"
 
 if test -f "${FFTW_STAMP}" && test "$(cat "${FFTW_STAMP}")" = "${EXPECTED_STAMP}"; then
     echo "Using existing FFTW build: ${EXPECTED_STAMP}"
@@ -62,12 +71,19 @@ rm -rf "${FFTW_PREFIX}"
 mkdir -p "${FFTW_PREFIX}"
 
 cd "${WORK_DIR}/fftw-${FFTW_VERSION}"
-export CFLAGS="-O3 -mmacosx-version-min=${DEPLOYMENT_TARGET}"
-export LDFLAGS="-mmacosx-version-min=${DEPLOYMENT_TARGET}"
+export CC=/usr/bin/clang
+export CFLAGS="-O3 -arch ${ARCH} -mmacosx-version-min=${DEPLOYMENT_TARGET}"
+export LDFLAGS="-arch ${ARCH} -mmacosx-version-min=${DEPLOYMENT_TARGET}"
+
+# Keep runtime probes enabled for native builds.
+set -- "--build=$(./config.guess)"
+if test "${ARCH}" != "${BUILD_ARCH}"; then
+    set -- "$@" "--host=${ARCH}-apple-darwin"
+fi
 
 # Aegisub only uses FFTW's single-threaded, double-precision API.
 # shellcheck disable=SC2086
-./configure \
+./configure "$@" \
     --prefix="${FFTW_PREFIX}" \
     --disable-shared \
     --enable-static \
@@ -80,6 +96,10 @@ export LDFLAGS="-mmacosx-version-min=${DEPLOYMENT_TARGET}"
 
 make -s -j"$(sysctl -n hw.logicalcpu)"
 make -s install
+if test "$(lipo -archs "${FFTW_PREFIX}/lib/libfftw3.a")" != "${ARCH}"; then
+    echo "FFTW library architecture does not match Meson's host: ${ARCH}" >&2
+    exit 1
+fi
 printf '%s\n' "${EXPECTED_STAMP}" > "${FFTW_STAMP}"
 
 echo "Built FFTW ${FFTW_VERSION} for macOS ${DEPLOYMENT_TARGET} (${ARCH})"

tools/macos-release.ini

@@ -0,0 +1,9 @@
+# Use Homebrew build tools, but exclude its target libraries from discovery.
+[properties]
+pkg_config_libdir = ['/usr/lib/pkgconfig']
+
+[built-in options]
+pkg_config_path = []
+
+[cmake]
+CMAKE_IGNORE_PREFIX_PATH = ['/opt/homebrew', '/usr/local']

tools/macos-x86_64.ini

@@ -0,0 +1,24 @@
+# Build Intel binaries with native Apple Silicon tools; run tests via Rosetta.
+# Combine with macos-release.ini for target dependency search paths.
+[binaries]
+c = ['/usr/bin/clang', '-arch', 'x86_64']
+cpp = ['/usr/bin/clang++', '-arch', 'x86_64']
+objc = ['/usr/bin/clang', '-arch', 'x86_64']
+objcpp = ['/usr/bin/clang++', '-arch', 'x86_64']
+ar = '/usr/bin/ar'
+strip = '/usr/bin/strip'
+pkg-config = 'pkg-config'
+cmake = 'cmake'
+exe_wrapper = ['/usr/bin/arch', '-x86_64']
+
+[host_machine]
+system = 'darwin'
+cpu_family = 'x86_64'
+cpu = 'x86_64'
+endian = 'little'
+
+[properties]
+needs_exe_wrapper = true
+
+[cmake]
+CMAKE_OSX_ARCHITECTURES = 'x86_64'