Add armhf cross-compilation support via candidate-armhf branch (#119)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: lengau <4305943+lengau@users.noreply.github.com>

Author: Copilot

.github/workflows/pull-request.yaml

@@ -11,10 +11,7 @@ concurrency:
 jobs:
   build:
     name: 🧪 Build snap
-    strategy:
-      matrix:
-        os: [ubuntu-latest, ubuntu-24.04-arm]
-    runs-on: ${{ matrix.os }}
+    runs-on: ubuntu-24.04-arm
     steps:
       - name: 🧪 Build snap
         uses: snapcrafters/ci/test-snap-build@main

.github/workflows/release-to-candidate-armhf.yaml

@@ -0,0 +1,56 @@
+name: Release (armhf)
+
+on:
+  # Run the workflow each time new commits are pushed to the candidate-armhf branch.
+  push:
+    branches: [ "candidate-armhf" ]
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+  issues: write
+
+jobs:
+  release:
+    name: 🚢 Release armhf to latest/candidate
+    runs-on: ubuntu-latest
+    environment: "Candidate Branch"
+    steps:
+      - name: 🚢 Release to latest/candidate
+        uses: snapcrafters/ci/release-to-candidate@main
+        with:
+          architecture: armhf
+          launchpad-token: ${{ secrets.LP_BUILD_SECRET }}
+          repo-token: ${{ secrets.SNAPCRAFTERS_BOT_COMMIT }}
+          store-token: ${{ secrets.SNAP_STORE_CANDIDATE }}
+
+  call-for-testing:
+    name: 📣 Create call for testing
+    needs: release
+    environment: "Candidate Branch"
+    runs-on: ubuntu-latest
+    outputs:
+      issue-number: ${{ steps.issue.outputs.issue-number }}
+    steps:
+      - name: 📣 Create call for testing
+        id: issue
+        uses: snapcrafters/ci/call-for-testing@main
+        with:
+          architectures: armhf
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+
+  test:
+    name: 🗒️ Test snap on armhf
+    needs: call-for-testing
+    runs-on: ubuntu-24.04-arm
+    steps:
+      - name: 🗒️ Run tests
+        uses: snapcrafters/ci/run-tests@main
+        with:
+          issue-number: ${{ needs.call-for-testing.outputs.issue-number }}
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          test-script: ./test.sh

.github/workflows/sync-to-armhf.yaml

@@ -0,0 +1,32 @@
+name: Sync to armhf branch
+
+on:
+  push:
+    branches:
+      - candidate
+  workflow_dispatch:
+  workflow_call:
+
+permissions:
+  issues: write
+  contents: write
+
+jobs:
+  sync-armhf:
+    name: 🔄 Sync candidate branch to candidate-armhf
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout the source
+      uses: actions/checkout@v4
+      with:
+        token: ${{ secrets.SNAPCRAFTERS_BOT_COMMIT }}
+        fetch-depth: 0
+        ref: candidate-armhf
+    - name: Merge from candidate
+      run: |
+        git pull
+        git config --global user.name "Snapcrafters Bot"
+        git config --global user.email "bot@snapcrafters.org"
+
+        git merge origin/candidate -m 'chore: merge candidate to candidate-armhf'
+        git push

snap/snapcraft.yaml

@@ -30,14 +30,19 @@ issues:
 source-code: https://github.com/astral-sh/ruff
 website: https://github.com/astral-sh/ruff
 
+package-repositories:
+  - type: apt
+    architectures: [$CRAFT_ARCH_BUILD_FOR]
+    formats: [deb, deb-src]
+    components: [main]
+    suites: [noble, noble-updates, noble-backports]
+    key-id: F6ECB3762474EDA9D21B7022871920D1991BC93C
+    url: http://ports.ubuntu.com/ubuntu-ports
+
 platforms:
-  amd64:
-  arm64:
-  # Disabled until we can fix https://github.com/snapcrafters/ruff/issues/117
-  # armhf:
-  ppc64el:
-  riscv64:
-  s390x:
+  armhf:
+    build-on: [arm64, amd64]
+    build-for: [armhf]
 
 parts:
   ruff:
@@ -49,15 +54,26 @@ parts:
     source-tag: $SNAPCRAFT_PROJECT_VERSION
     source-depth: 1
     build-environment:
-      # See: https://github.com/lengau/uv-snap/issues/10
-      - to arm64:
-        - JEMALLOC_SYS_WITH_LG_PAGE: 16
-      - to ppc64el:
-        - JEMALLOC_SYS_WITH_LG_PAGE: 16
-    stage:
-      - bin/ruff
-    organize:
-      ruff: bin/ruff
+      # Build a static binary. Needed for armhf because of https://github.com/canonical/snapcraft/issues/5836
+      - CARGO_BUILD_TARGET: armv7-unknown-linux-musleabihf
+      - CARGO_TARGET_ARMV7_UNKNOWN_LINUX_MUSLEABIHF_LINKER: rust-lld
+      - CARGO_CFG_TARGET_FEATURE: crt-static
+      - CC: clang-20
+      - CARGO_PROFILE_RELEASE_LTO: "off"
+    build-packages:
+      - libclang-20-dev
+      - cmake
+      - gcc-arm-linux-gnueabihf
+      - libc6-dev-armhf-cross
+      # Use clang for the armhf build so we can build for musl.
+      - clang-20
+      - musl-dev
+      - musl-tools
+    override-build: |
+      rustup target add ${CARGO_BUILD_TARGET}
+      craftctl default
+      # manually install the ruff binary as its target dir differs
+      install -Dvm755 ./target/${CARGO_BUILD_TARGET}/release/ruff "${CRAFT_PART_INSTALL}/bin/ruff"
 
 apps:
   ruff: