feat(gitlab): add CI component

This adds a GitLab CI/CD component that can be `included` in users
GitLab CI configuration to integrate releaser-pleaser.

Unlike the GitHub Action, this can not easily run whenever a merge
request description is changed, only when changes are pushed to main.

We also switch the container base image from `static` to `busybox`
as GitLab CI requires a shell (`sh`) binary to be present for the image
use to run jobs.

.github/workflows/mirror.yaml

@@ -0,0 +1,23 @@
+name: mirror
+on:
+  push:
+    branches: [main, gitlab] # TODO
+    tags: ["*"]
+
+jobs:
+  gitlab:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          # Need all to fetch all tags so we can push them
+          fetch-depth: 0
+
+      - name: Add Remote
+        env:
+          CLONE_URL: "https://releaser-pleaser:${{ secrets.GITLAB_COM_PUSH_TOKEN }}@gitlab.com/apricote/releaser-pleaser.git"
+        run: git remote add gitlab $CLONE_URL
+
+      - name: Push
+        run: git push --all --tags gitlab

.gitlab-ci.yml

@@ -0,0 +1,15 @@
+stages: [release]
+
+# For the GitLab CI/CD component to be usable, it needs to be published in
+# the CI/CD catalog. This happens on new releases.
+# As the primary tagging happens on GitHub, we only react to pushed tags
+# and create a corresponding GitLab Release.
+create-release:
+  stage: release
+  image: registry.gitlab.com/gitlab-org/release-cli:latest
+  script: echo "Creating release $CI_COMMIT_TAG"
+  rules:
+    - if: $CI_COMMIT_TAG
+  release:
+    tag_name: "$CI_COMMIT_TAG"
+    description: "$CI_COMMIT_TAG_MESSAGE"

.ko.yaml

@@ -1,3 +1,6 @@
 defaultPlatforms:
   - linux/arm64
-  - linux/amd64
+  - linux/amd64
+
+# Need a shell for gitlab-ci
+defaultBaseImage: cgr.dev/chainguard/busybox

docs/SUMMARY.md

@@ -5,7 +5,7 @@
 # Tutorials
 
 - [Getting started on GitHub](tutorials/github.md)
-- [Getting started on GitLab]()
+- [Getting started on GitLab](tutorials/gitlab.md)
 
 # Explanation
 
@@ -22,7 +22,7 @@
 - [Glossary](reference/glossary.md)
 - [Pull Request Options](reference/pr-options.md)
 - [GitHub Action](reference/github-action.md)
-- [GitLab CI]()
+- [GitLab CI/CD Component](reference/gitlab-cicd-component.md)
 
 ---
 

docs/reference/gitlab-cicd-component.md

@@ -0,0 +1 @@
+# GitLab CI/CD Component

templates/run.yml

@@ -0,0 +1,36 @@
+spec:
+  inputs:
+    # Remember to update docs/reference/gitlab-ci-component.md
+    branch:
+      default: main
+      description: "This branch is used as the target for releases."
+
+    token:
+      description: "GitLab token for creating and updating release MRs."
+
+    extra-files:
+      description: 'List of files that are scanned for version references.'
+      default: ""
+
+    stage:
+      default: build
+      description: 'Defines the build stage'
+    # Remember to update docs/reference/gitlab-ci-component.md
+---
+
+releaser-pleaser:
+  stage: $[[ inputs.stage ]]
+  rules:
+    # There is no way to run a pipeline when the MR description is updated :(
+    - if: $CI_COMMIT_BRANCH == "$[[ inputs.branch ]]"
+  image:
+    name: ghcr.io/apricote/releaser-pleaser:v0.4.0-beta.0 # x-releaser-pleaser-version
+    entrypoint: [""]
+  variables:
+    GITLAB_TOKEN: $[[ inputs.token ]]
+  script:
+    - |
+      rp run \
+        --forge=gitlab \
+        --branch=$[[ inputs.branch ]] \
+        --extra-files=$[[ inputs.extra-files ]]