Use "rules" and run certain CI jobs automatically

* Switch to 'rules' for specifying when certain CI jobs are executed.
* Execute 'setup' and 'prep' jobs when respective Dockerfiles change.

.gitlab-ci.yml

@@ -32,6 +32,10 @@ variables:
 
 image: $DUNE_ENV_IMAGE
 
+# Run pipelines on branches
+include:
+  - template: 'Workflows/Branch-Pipelines.gitlab-ci.yml'
+
 # Move into top-level DUNE directory
 before_script:
   - cd $DUNE_DIR
@@ -64,13 +68,8 @@ stages:
   - test
   - deploy
 
-
-# --- Preparation of Docker Images ---
-setup:dune-env: &setup
-  stage: setup
-  only:
-    variables:
-      - $REBUILD_BASE_IMAGE # must be defined and have non-empty value
+# --- Job Template for Docker in Docker (DinD) Runner Setup ---
+.dind:
   tags:
     - dind
   image: docker:stable
@@ -80,6 +79,14 @@ setup:dune-env: &setup
     DOCKER_DRIVER: overlay2
   before_script:
     - $DOCKER_LOGIN
+
+# --- Preparation of Docker Images ---
+setup:dune-env: &setup
+  stage: setup
+  extends: .dind
+  rules:
+    - changes:
+        - docker/dune-env.dockerfile
   script:
     - docker build -f docker/dune-env.dockerfile
       --build-arg PROCNUM=$CPUS_DIND
@@ -97,12 +104,17 @@ setup:dune-env-clang:
     - docker push ${DUNE_ENV_IMAGE}-clang
 
 prep:update-dune: &update
-  <<: *setup
   stage: prep
+  extends: .dind
   allow_failure: true
-  only:
-    - master
-    - tags
+  rules:
+    # Run after pushes to master and tags in original repo, not forks
+    - if: '$CI_COMMIT_BRANCH == "master" && $CI_PROJECT_PATH == "dorie/dorie"'
+    - if: '$CI_COMMIT_TAG && $CI_PROJECT_PATH == "dorie/dorie"'
+    # Run after Dockerfile changed. Do not allow failure then.
+    - changes:
+        - docker/dune-env-update.dockerfile
+      allow_failure: false
   script:
     - docker build -f docker/dune-env-update.dockerfile
       --build-arg DUNE_ENV_IMAGE=$DUNE_ENV_IMAGE
@@ -255,10 +267,9 @@ test:examples:
 
 test:python-tests:
   <<: *test
+  # May run immediately
   dependencies: []
-  # TODO: Make empty once https://gitlab.com/gitlab-org/gitlab/issues/30631
-  #       is resolved
-  needs: ["build:docs"] # Any quick job from previous stage
+  needs: []
   script:
     - $DUNECONTROL --only=dorie configure
     - $DUNECONTROL --only=dorie make test_python
@@ -266,18 +277,10 @@ test:python-tests:
 # --- Deploy jobs ---
 deploy:dockerhub-devel: &deploy
   stage: deploy
-  only:
-    - master@dorie/dorie
-  tags:
-    - dind
-  image: docker:stable
-  services:
-    - docker:dind
-  variables:
-    DOCKER_DRIVER: overlay2
-  dependencies: []
-  before_script:
-    - $DOCKER_LOGIN
+  extends: .dind
+  rules:
+    # Run after pushes to master in original repo, not forks
+    - if: '$CI_COMMIT_BRANCH == "master" && $CI_PROJECT_PATH == "dorie/dorie"'
   script:
     - docker build -f docker/dorie.dockerfile
       --build-arg BASE_IMG_VERSION=$IMAGE_VERSION --build-arg PROCNUM=$CPUS_DIND
@@ -289,8 +292,9 @@ deploy:dockerhub-devel: &deploy
 
 deploy:dockerhub-stable:
   <<: *deploy
-  only:
-    - tags@dorie/dorie
+  rules:
+    # Run after pushes to tags in original repo, not forks
+    - if: '$CI_COMMIT_TAG && $CI_PROJECT_PATH == "dorie/dorie"'
   script:
     - docker build -f docker/dorie.dockerfile
       --build-arg BASE_IMG_VERSION=$IMAGE_VERSION --build-arg PROCNUM=$CPUS_DIND

CHANGELOG.md

@@ -8,6 +8,7 @@
 * Coding style tools and instructions.
     [`clang-format-hook`](https://github.com/barisione/clang-format-hooks)
     as Git submodule !203
+* Automatically trigger DUNE Docker image builds using `rules` !213
 
 ### Changed
 

docker/README.md

@@ -25,15 +25,11 @@ Both images are updated by the GitLab CI/CD Pipeline defined in
 [`.gitlab-ci.yml`](../gitlab-ci.yml).
 
 The `setup` build stage is builds a new DUNE environment image "from scratch".
-It is triggered by running a pipeline with the CI variable `REBUILD_BASE_IMAGE`
-set to a non-empty value. This is achieved by manually starting the pipeline
-from the GitLab web interface ("CI/CD" - "Pipelines" - "Run Pipeline") and
-entering the variable as well as an arbitrary value. This should only be
-necessary if dependencies or their required versions change.
-
 The `prep` stage updates all APT and DUNE packages in the DUNE environment image
 and is run whenever a pipeline includes the deployment of a new application
-image.
+image. Both stages are automatically triggered if the respective Dockerfiles
+are changed. The `prep` stage is additionally executed for every push to
+the `master` branch or a tag.
 
 The `deploy` stage deploys DORiE application images. It compiles DORiE into the
 DUNE environment image. This stage is only run if tags are pushed or commits