ci: build in a prebuilt Arch image with ccache and no QML cachegen

.gitea/workflows/ci-image.yml

@@ -0,0 +1,31 @@
+name: CI image
+
+# Builds the Arch image that ci.yml runs in, with the build dependencies preinstalled.
+# Rebuilt weekly to pick up Arch updates.
+on:
+  push:
+    branches: [main]
+    paths: ['.gitea/ci-image/**', '.gitea/workflows/ci-image.yml']
+  schedule:
+    - cron: '0 3 * * 1'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  packages: write
+
+jobs:
+  image:
+    # The build runs on the runner's own Docker daemon, so the amd64 runner has the new
+    # image locally right away. It does not re-pull tags it already has.
+    runs-on: amd64
+    env:
+      IMAGE: git.trivk.dev/tri/qtpotato-ci:latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Build
+        run: docker build --pull -t "$IMAGE" .gitea/ci-image
+      - name: Push
+        run: |
+          echo "${{ secrets.GITHUB_TOKEN }}" | docker login git.trivk.dev -u "${{ github.actor }}" --password-stdin
+          docker push "$IMAGE"

.gitea/workflows/ci.yml

@@ -3,24 +3,39 @@ name: CI
 on:
   push:
     branches: [main]
+    paths-ignore: ['README.md', 'LICENSES/**']
   pull_request:
+    paths-ignore: ['README.md', 'LICENSES/**']
 
 jobs:
   build:
     # Arch Linux only ships x86_64 images, so pick an amd64 runner.
     runs-on: amd64
-    container: archlinux:latest
+    # Arch with the build dependencies preinstalled; see ci-image.yml.
+    container: git.trivk.dev/tri/qtpotato-ci:latest
+    env:
+      CCACHE_DIR: ${{ github.workspace }}/.ccache
+      # Keep hits across weekly image rebuilds when the compiler did not change.
+      CCACHE_COMPILERCHECK: content
+      CCACHE_MAXSIZE: 500M
     steps:
-      - name: Install dependencies
-        run: |
-          pacman -Syu --noconfirm --needed git nodejs base-devel cmake ninja extra-cmake-modules \
-              qt6-base qt6-declarative kirigami ki18n kcoreaddons kcrash kconfig \
-              mpvqt qcoro qtkeychain-qt6 ffmpeg
       - uses: actions/checkout@v4
+      - uses: actions/cache@v4
+        with:
+          path: .ccache
+          key: ccache-${{ github.sha }}
+          restore-keys: ccache-
       - name: Configure
-        run: cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Debug -DBUILD_TESTING=ON
+        # The tests do not load QML, so skip QML cachegen and debug info: they take over
+        # half of the build. Release and AUR builds keep both.
+        run: |
+          cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Debug -DCMAKE_CXX_FLAGS_DEBUG=-O0 \
+              -DQT_QML_NO_CACHEGEN=ON -DCMAKE_CXX_COMPILER_LAUNCHER=ccache -DBUILD_TESTING=ON
       - name: Build
-        run: cmake --build build
+        run: |
+          ccache -z
+          cmake --build build
+          ccache -s
       - name: Test
         env:
           QT_QPA_PLATFORM: offscreen