ci: prebuild the fedora toolchain as a container image

.dockerignore

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+# The image is a toolchain only -- the dockerfile COPYs nothing, and the
+# scripts arrive via actions/checkout at run time. Keep the build context empty.
+*
+!dockerfile

.gitea/workflows/build-image.yaml

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+---
+name: Build Autoupdater Image
+
+concurrency:
+  group: build-image
+  cancel-in-progress: false
+
+on:
+  schedule:
+    # Monthly. fedora:latest moves to a new release twice a year and gets
+    # updates in between; :latest is overwritten each time.
+    - cron: "0 3 1 * *"
+  push:
+    branches:
+      - main
+    paths:
+      - dockerfile
+      - .dockerignore
+      - .gitea/workflows/build-image.yaml
+  workflow_dispatch:
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  build:
+    # No Fedora needed here -- this only drives docker. The *image* is Fedora.
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Log in to the Gitea container registry
+        env:
+          GIT_HOST: ${{ vars.GIT_HOST || 'git.bjphoster.com' }}
+          REGISTRY_USER: ${{ vars.REGISTRY_USER }}
+          GIT_TOKEN: ${{ secrets.GIT_TOKEN }}
+        run: |
+          set -euo pipefail
+          # NB: this is the Gitea *username*, not vars.GIT_NAME -- that one is
+          # the display name used for git commit authorship and contains spaces.
+          printf '%s' "${GIT_TOKEN}" \
+            | docker login "${GIT_HOST}" \
+                --username "${REGISTRY_USER}" \
+                --password-stdin
+
+      - name: Build and push
+        env:
+          GIT_HOST: ${{ vars.GIT_HOST || 'git.bjphoster.com' }}
+        run: |
+          set -euo pipefail
+          # The repo is `.autoupdate`, but OCI names cannot start with a dot.
+          image="${GIT_HOST}/rpm/autoupdate"
+
+          # --pull so a monthly rebuild actually picks up a new base image
+          # rather than reusing a cached one.
+          docker build --pull --tag "${image}:latest" .
+          docker push "${image}:latest"
+
+          echo "pushed ${image}:latest"
+
+      - name: Log out
+        if: always()
+        env:
+          GIT_HOST: ${{ vars.GIT_HOST || 'git.bjphoster.com' }}
+        run: docker logout "${GIT_HOST}" || true

dockerfile

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+# Build environment for the RPM autoupdater.
+#
+# Rebuilt monthly by .gitea/workflows/build-image.yaml and pushed as :latest, so
+# the nightly package jobs start with the toolchain already in place instead
+# of each running a full dnf transaction first.
+#
+# Fedora specifically: rpmbuild, rpmspec and rpmlint are native there and
+# current. Packages are built with `dist` undefined, so the noarch result is not
+# tied to the Fedora release that built it and installs on EL and openSUSE too.
+FROM fedora:latest
+
+LABEL org.opencontainers.image.title="rpm-autoupdate"
+LABEL org.opencontainers.image.description="Fedora build environment for the RPM package autoupdater"
+LABEL org.opencontainers.image.source="https://git.bjphoster.com/rpm/.autoupdate"
+
+# nodejs       actions/checkout is a JavaScript action; the runner executes it
+#              with `node` from inside this image, and fedora ships none.
+# rpm-build    rpmbuild and rpmspec
+# rpmdevtools  spectool, to resolve Source0's file name
+# rpmlint      advisory lint of the spec and the built package
+# util-linux   runuser, to drop from root to the build user
+# make         the usual BuildRequires of a script package
+RUN dnf -y install --setopt=install_weak_deps=False \
+      nodejs \
+      git \
+      curl \
+      jq \
+      rpm-build \
+      rpmdevtools \
+      rpmlint \
+      util-linux \
+      shadow-utils \
+      make \
+      tar \
+      gzip \
+      findutils \
+      diffutils \
+ && dnf clean all
+
+# The nightly job drops to this user rather than building as root (CI
+# containers are root by default). Baked in here rather than created per run.
+RUN useradd --create-home --shell /bin/bash builder
+
+# Sanity check: fail the image build rather than the nightly job if the
+# toolchain ever stops working in this environment.
+RUN runuser -u builder -- bash -c 'rpmbuild --version && rpmspec --version && command -v spectool rpmlint node'