RPM: build for arm64 too, under emulation

Flutter can't cross-compile, so arm64 builds in an arm64 Fedora under the
runner's QEMU emulation, with its own SDK (the release tarball's Dart SDK
is x64, so arm64 fetches its own). quine-linux's arm64 image installs it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.forgejo/workflows/rpm.yml

@@ -25,11 +25,15 @@ jobs:
           fetch-depth: 0
 
       - name: Build
-        # /var/cache/quine-rpm-build outlives the job (host-mode runner): the Flutter SDK and pub packages.
+        # /var/cache/quine-rpm-build outlives the job (host-mode runner): the Flutter SDKs and pub packages.
+        # Once per architecture: Flutter can't cross-compile, so arm64 builds in an arm64 Fedora under
+        # the runner's QEMU emulation (slow). quine-linux's arm64 image installs that one.
         run: |
           mkdir -p out /var/cache/quine-rpm-build
-          podman run --rm -v "$PWD":/src -v /var/cache/quine-rpm-build:/cache -v "$PWD/out":/out \
-            registry.fedoraproject.org/fedora:44 bash /src/packaging/build-flutter-rpm.sh layer-wizard
+          for arch in amd64 arm64; do
+            podman run --rm --platform "linux/$arch" -v "$PWD":/src -v /var/cache/quine-rpm-build:/cache -v "$PWD/out":/out \
+              registry.fedoraproject.org/fedora:44 bash /src/packaging/build-flutter-rpm.sh layer-wizard
+          done
           ls -l out
 
       - name: Upload to the quine RPM group

packaging/build-flutter-rpm.sh

@@ -18,14 +18,20 @@ dnf install -y --setopt=install_weak_deps=False \
   clang cmake ninja-build pkgconf-pkg-config gtk3-devel xz-devel libstdc++-devel \
   git xz which unzip rpm-build desktop-file-utils
 
-sdk=/cache/flutter-$FLUTTER_VERSION
+# Flutter builds for the machine it runs on: x64 natively, arm64 in an arm64
+# container (the runner's QEMU emulation). One SDK per architecture.
+case $(uname -m) in x86_64) arch=x64 ;; aarch64) arch=arm64 ;; *) echo "unsupported: $(uname -m)" >&2; exit 1 ;; esac
+sdk=/cache/flutter-$FLUTTER_VERSION-$arch
 if [ ! -x "$sdk/bin/flutter" ]; then
-  curl -fL --retry 3 -o /cache/flutter.tar.xz \
+  curl -fL --retry 3 -o "/cache/flutter-$arch.tar.xz" \
     "https://storage.googleapis.com/flutter_infra_release/releases/stable/linux/flutter_linux_$FLUTTER_VERSION-stable.tar.xz"
-  echo "$FLUTTER_SHA256  /cache/flutter.tar.xz" | sha256sum -c
+  echo "$FLUTTER_SHA256  /cache/flutter-$arch.tar.xz" | sha256sum -c
   rm -rf "$sdk.tmp" && mkdir -p "$sdk.tmp"
-  tar -xJf /cache/flutter.tar.xz -C "$sdk.tmp" --strip-components=1
-  mv "$sdk.tmp" "$sdk" && rm /cache/flutter.tar.xz
+  tar -xJf "/cache/flutter-$arch.tar.xz" -C "$sdk.tmp" --strip-components=1
+  # The release tarball carries an x64 Dart SDK; without it, the first run
+  # fetches the one for this machine.
+  [ "$arch" = x64 ] || rm -rf "$sdk.tmp/bin/cache"
+  mv "$sdk.tmp" "$sdk" && rm "/cache/flutter-$arch.tar.xz"
 fi
 # The SDK and this checkout belong to other users than the container's root.
 git config --global --add safe.directory '*'
@@ -40,5 +46,5 @@ release=$(date -u +%Y%m%d%H%M).git$(git rev-parse --short=7 HEAD)
 rpmbuild -bb "packaging/$NAME.spec" \
   --define "_topdir /tmp/rpmbuild" \
   --define "version_ $version" --define "release_ $release" \
-  --define "bundle /src/build/linux/x64/release/bundle" --define "srcdir /src"
+  --define "bundle /src/build/linux/$arch/release/bundle" --define "srcdir /src"
 cp -v /tmp/rpmbuild/RPMS/*/*.rpm /out/

packaging/layer-wizard.spec

@@ -14,7 +14,7 @@ Release:        %{release_}%{?dist}
 Summary:        Layer an RPM onto a bootc system, with a guided reboot and rollback
 License:        LicenseRef-Not-Specified
 URL:            https://forge.quinefoundation.com/quine-global-labs/layer-wizard
-ExclusiveArch:  x86_64
+ExclusiveArch:  x86_64 aarch64
 
 Requires:       gtk3
 Requires:       polkit