gitlab-ci: add test preview feature

.gitlab-ci.yml

@@ -1,25 +1,79 @@
-before_script:
-  - sudo apk add git ikiwiki po4a perl-yaml-tiny
+workflow:
+  rules: # disable tag pipelines and duplicate MR pipelines
+    - if: $CI_COMMIT_BRANCH
 
-test:
-  stage: test
-  script:
-  - ikiwiki --setup ikiwiki.setup
-  - ln -s index.en.html public/index.html
-  rules:
-    - if: $CI_COMMIT_REF_NAME != $CI_DEFAULT_BRANCH
-  tags:
-    - knit
+variables:
+  MAIN_BRANCH_PATH: "."
+  EPHEMERAL_BRANCHES_PATH: preview # subpath to ephemeral branches content for preview
 
 pages:
-  stage: deploy
+  stage: build
+  cache:
+    key: gitlab-pages
+    paths: [public]
+  before_script:
+    - sudo apk add git ikiwiki po4a perl-yaml-tiny tree
+    # CURRENT_CONTENT_PATH is defined in rules, different between main branch and ephemeral branches
+    - mkdir -p public/$CURRENT_CONTENT_PATH && ls public/$CURRENT_CONTENT_PATH/..
+    - | # create ephermetal branched path if not existent
+      if [ ! -d "public/$EPHEMERAL_BRANCHES_PATH" ]; then
+        mkdir -p public/$EPHEMERAL_BRANCHES_PATH
+      fi
+    - | # avoid deleting main branch content when cache has been erased
+      if [ "$CI_COMMIT_BRANCH" != "$CI_DEFAULT_BRANCH" ] && [ ! -f public/$MAIN_BRANCH_PATH/index.html ]; then
+        echo -e "💥\e[91;1m Unable to retrieve $CI_DEFAULT_BRANCH generated files from cache ; please regenerate $CI_DEFAULT_BRANCH files first\e[0m"
+        exit 1
+      fi
+    - rm -rf public/$CURRENT_CONTENT_PATH || true # remove last version of current branch
   script:
-  - ikiwiki --setup ikiwiki.setup
-  - ln -s index.en.html public/index.html
-  artifacts:
-    paths:
-    - public
+    - ikiwiki --setup ikiwiki.setup
+    - | # create symbolic link to index.en.html if public/index.html does not exist
+      if [ ! -L "public/index.html"  ]; then
+        ln -s index.en.html public/index.html
+      fi
+    - |
+      if [ -z "$CURRENT_CONTENT_PATH" ]; then
+        mv public output
+        mkdir -p public
+        mv public public/$CURRENT_CONTENT_PATH
+      fi
+    - cd public/$EPHEMERAL_BRANCHES_PATH
+    - tree -d -H '.' -L 1 --noreport --charset utf-8 -T "Versions" -o index.html # generate a root HTML listing all previews for easier access
+  environment:
+    name: pages/$CI_COMMIT_BRANCH
+    action: start
+    url: $CI_PAGES_URL/$CURRENT_CONTENT_PATH
+    on_stop: pages-clean-preview
   rules:
-    - if: $CI_COMMIT_REF_NAME == $CI_DEFAULT_BRANCH
+    # 'main branch' is exposed at GitLab Pages root
+    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
+      variables:
+        CURRENT_CONTENT_PATH: $MAIN_BRANCH_PATH
+    # other (short-lived) branches generation are exposed in 'EPHEMERAL_BRANCHES_PATH/branch-name-sanitized' sub path
+    - variables:
+        CURRENT_CONTENT_PATH: $EPHEMERAL_BRANCHES_PATH/$CI_COMMIT_REF_SLUG
+  artifacts:
+    paths: [public]
+    expire_in: 1h
+  tags:
+    - knit
+
+pages-clean-preview:
+  stage: build
+  cache:
+    key: gitlab-pages
+    paths: [public]
+  variables:
+    GIT_STRATEGY: none # git files not available after branch deletion
+    FOLDER_TO_DELETE: $EPHEMERAL_BRANCHES_PATH/$CI_COMMIT_REF_SLUG # an indirection to allow arbitrary deletion when launching this job
+  script:
+    - rm -rf public/$FOLDER_TO_DELETE
+  environment:
+    name: pages/$CI_COMMIT_BRANCH
+    action: stop
+  rules:
+    - if: $CI_COMMIT_BRANCH != $CI_DEFAULT_BRANCH
+      when: manual
+      allow_failure: true
   tags:
     - knit