ci: cut PR CI time with a prebuilt image, ccache, and no QML cachegen (#22)

CI took about 5 min 10 s per PR on vm-201: 1.5 min of `pacman -Syu` and 3.5 min of build, half of it qmlcachegen compiling QML the tests never load. Now it takes **1 min 49 s with a cold ccache and 26 s with a warm one**.

- CI runs in a prebuilt Arch image with the build deps (`git.trivk.dev/tri/qtpotato-ci:latest`). `ci-image.yml` rebuilds it weekly, when its Dockerfile changes, or on demand. It builds on the runner's own Docker daemon, so vm-201 has the new image right away, since the runner does not re-pull tags it already has.
- CI configures with `QT_QML_NO_CACHEGEN=ON` and no debug info. Release and AUR builds keep both.
- ccache, kept between runs with `actions/cache`.
- Docs-only changes (`README.md`, `LICENSES/`) skip CI.

Pushing the image to the registry needed two workarounds. Gitea's Actions token cannot push container images, so it uses the `PACKAGE_TOKEN` secret from #21. Cloudflare rejects request bodies over 100 MB and `docker push` sends each layer in one request, so `regctl` (pinned by sha256) pushes the layers in 50 MB chunks.

Giving vm-201 more vCPUs is left out; it is an infra change.

Refs #20

Proof: on this PR, CI run 328 (cold ccache) took 1 min 49 s and run 332 (warm, 41/44 hits) took 26 s, both 8/8 tests. Image run 333 pushed the image, and the registry digest matches the runner's local image. A local build with the CI flags takes 74 steps instead of 154.

Reviewed with sol-loop: 3 rounds with gpt-6.1-sol. Sol verdict: approved

Created with Claude Opus 5.5 in Claude Code (T3 Code).
Reviewed-on: #22
Co-authored-by: Tri Vo Khac <git@trivk.dev>

.gitea/ci-image/Dockerfile

@@ -0,0 +1,7 @@
+# Arch Linux with QtPotato's build dependencies, so CI skips the pacman step.
+# Built and pushed by .gitea/workflows/ci-image.yml.
+FROM archlinux:latest
+RUN pacman -Syu --noconfirm --needed git nodejs base-devel cmake ninja ccache extra-cmake-modules \
+        qt6-base qt6-declarative kirigami ki18n kcoreaddons kcrash kconfig \
+        mpvqt qcoro qtkeychain-qt6 ffmpeg \
+    && rm -rf /var/cache/pacman/pkg/*

.gitea/workflows/arch-package.yml

@@ -0,0 +1,58 @@
+name: Arch package
+
+# Builds the qtpotato package from a release tag and publishes it to this Gitea's Arch
+# registry, so users can install it with pacman until it is on the AUR.
+on:
+  push:
+    tags: ['v*']
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: Release tag to package, e.g. v0.1.0
+        required: true
+
+permissions:
+  contents: read
+
+jobs:
+  package:
+    # Arch Linux only ships x86_64 images, so pick an amd64 runner.
+    runs-on: amd64
+    container: archlinux:latest
+    env:
+      TAG: ${{ inputs.tag || github.ref_name }}
+    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 hicolor-icon-theme
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.tag || github.ref }}
+      - name: Build
+        run: |
+          version="${TAG#v}"
+          dir=/tmp/pkg
+          mkdir -p "$dir"
+          git config --global --add safe.directory "$PWD"
+          git archive --format=tar --prefix="qtpotato-$version/" HEAD | gzip -n > "$dir/qtpotato-$version.tar.gz"
+          sum="$(sha256sum "$dir/qtpotato-$version.tar.gz" | cut -d' ' -f1)"
+          sed -e "s/^pkgver=.*/pkgver=$version/" -e "s/^pkgrel=.*/pkgrel=1/" \
+              -e 's/^source=.*/source=("$pkgname-$pkgver.tar.gz")/' \
+              -e "s/^sha256sums=.*/sha256sums=('$sum')/" \
+              packaging/aur/qtpotato/PKGBUILD > "$dir/PKGBUILD"
+          # makepkg refuses to run as root.
+          useradd -m builder
+          chown -R builder "$dir"
+          su builder -c "cd $dir && makepkg --noconfirm"
+      - name: Publish
+        env:
+          # The package registry rejects the job token, so this is a personal access token
+          # with the write:package scope.
+          TOKEN: ${{ secrets.PACKAGE_TOKEN }}
+        run: |
+          for f in /tmp/pkg/qtpotato-[0-9]*.pkg.tar.zst; do
+              curl -fsS -X PUT -H "Authorization: token $TOKEN" --upload-file "$f" \
+                  "$GITHUB_SERVER_URL/api/packages/${GITHUB_REPOSITORY%%/*}/arch/qtpotato"
+          done

.gitea/workflows/ci-image.yml

@@ -0,0 +1,40 @@
+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:
+
+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
+        # No layer cache, so each rebuild picks up the week's Arch updates.
+        run: docker build --pull --no-cache -t "$IMAGE" .gitea/ci-image
+      - name: Push
+        # Gitea's Actions token cannot push to the container registry, so this uses an
+        # access token with the write:package scope. Cloudflare rejects request bodies over
+        # 100 MB and docker push sends each layer in one request, so regctl pushes the
+        # layers in 50 MB chunks instead.
+        env:
+          TOKEN: ${{ secrets.PACKAGE_TOKEN }}
+        run: |
+          curl -fsSL -o /usr/local/bin/regctl \
+              https://github.com/regclient/regclient/releases/download/v0.11.7/regctl-linux-amd64
+          echo "3737fbbdd791e04e7a831640b681f3397a376498e80e2ad9b1b2d27296f239bc  /usr/local/bin/regctl" | sha256sum -c
+          chmod +x /usr/local/bin/regctl
+          echo "$TOKEN" | regctl registry login git.trivk.dev -u "${{ github.repository_owner }}" --pass-stdin
+          regctl registry set git.trivk.dev --blob-chunk 52428800 --blob-max 52428800
+          docker save "$IMAGE" -o "$RUNNER_TEMP/image.tar"
+          regctl image import "$IMAGE" "$RUNNER_TEMP/image.tar"

.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

.gitea/workflows/release.yml

@@ -15,10 +15,7 @@ jobs:
     steps:
       - name: Install dependencies
         run: |
-          pacman -Syu --noconfirm --needed git nodejs base-devel cmake ninja extra-cmake-modules \
+          pacman -Syu --noconfirm --needed git nodejs curl jq
-              qt6-base qt6-declarative qt6-svg qt6-wayland kirigami ki18n kcoreaddons kcrash kconfig \
-              mpvqt qcoro qtkeychain-qt6 ffmpeg plasma-integration qqc2-desktop-style breeze union \
-              curl jq file
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0
@@ -29,10 +26,6 @@ jobs:
           mkdir -p dist
           git archive --format=tar --prefix="qtpotato-$version/" "$GITHUB_REF_NAME" \
               | gzip -n > "dist/qtpotato-$version.tar.gz"
-      - name: AppImage
-        run: |
-          LDAI_OUTPUT="$PWD/dist/QtPotato-${GITHUB_REF_NAME#v}-x86_64.AppImage" \
-              packaging/appimage/build-appimage.sh "$PWD/build-appimage"
       - name: Publish release
         env:
           TOKEN: ${{ secrets.GITHUB_TOKEN }}

README.md

@@ -24,6 +24,42 @@ translate a whole subtitle track with any OpenAI-compatible API and show the res
   auto-hiding controls.
 - Follows your Plasma style, colours and icons.
 
+## Installing on Arch Linux
+
+### From the pacman repository
+
+Every release is built and published to this Gitea's package registry. Import the signing key
+once:
+
+```sh
+curl -O https://git.trivk.dev/api/packages/tri/arch/repository.key
+sudo pacman-key --add repository.key
+sudo pacman-key --lsign-key 9C48725295A5F54A6A491CF86B273DD49890E8A7
+```
+
+Then add the repository to `/etc/pacman.conf` and install:
+
+```ini
+[qtpotato]
+SigLevel = Required
+Server = https://git.trivk.dev/api/packages/tri/arch/$repo/$arch
+```
+
+```sh
+sudo pacman -Syu qtpotato
+```
+
+The package is built against Arch's current Qt and KDE Frameworks. If it breaks after a system
+update before a new release is out, build it from source as below.
+
+### From the PKGBUILD
+
+```sh
+git clone https://git.trivk.dev/tri/QtPotato.git
+cd QtPotato/packaging/aur/qtpotato   # or qtpotato-git for the latest main
+makepkg -si
+```
+
 ## Building
 
 ### Dependencies

packaging/aur/qtpotato/.SRCINFO

@@ -23,6 +23,6 @@ pkgbase = qtpotato
 	optdepends = qqc2-desktop-style: Plasma look for the interface
 	optdepends = plasma-integration: Plasma file dialogs, colours and icons
 	source = https://git.trivk.dev/tri/QtPotato/releases/download/v0.1.0/qtpotato-0.1.0.tar.gz
-	sha256sums = SKIP
+	sha256sums = 8ac4cd95e04880411f16009478765f698c1ba84538c776e68a431033e10ae837
 
 pkgname = qtpotato

packaging/aur/qtpotato/PKGBUILD

@@ -14,7 +14,7 @@ optdepends=('qqc2-desktop-style: Plasma look for the interface'
             'plasma-integration: Plasma file dialogs, colours and icons')
 source=("$url/releases/download/v$pkgver/$pkgname-$pkgver.tar.gz")
 # Filled in by update-pkgbuild.sh from the release's SHA256SUMS.
-sha256sums=('SKIP')
+sha256sums=('8ac4cd95e04880411f16009478765f698c1ba84538c776e68a431033e10ae837')
 
 build() {
   cmake -B build -S "$pkgname-$pkgver" -G Ninja \