Automatically draft release notes on maintenance branches push (#2872)

This commit introduces Release-Drafter in a dedicated workflow,
for pushes categorized as "SNAPSHOT" (ie corresponding to the merging of
a PR).

The use of `filter-by-commitish` in the config and `commitish` (set to
the target branch) in the action config should ensure that drafts are
created for both the `main` branch and older maintenance branches.

Fixes #1445.

.github/release-drafter.yml

@@ -0,0 +1,45 @@
+name-template: 'v$RESOLVED_VERSION'
+tag-template: 'v$RESOLVED_VERSION'
+categories:
+  - title: ':warning: Update considerations and deprecations'
+    labels:
+      - 'warn/api-change'
+      - 'warn/behavior-change'
+      - 'warn/blocker'
+      - 'warn/deprecation'
+      - 'warn/regression'
+  - title: ':sparkles: New features and improvements'
+    label: 'type/enhancement'
+  - title: ':lady_beetle: Bug fixes'
+    label: 'type/bug'
+  - title: ':book: Documentation, Tests and Build'
+    labels:
+      - 'type/chores'
+      - 'type/documentation'
+  - title: ':up: Dependency Upgrades'
+    label: 'type/dependency-upgrade'
+change-template: '- $TITLE'
+exclude-contributors:
+  - 'simonbasle'
+  - 'OlegDokuka'
+  - 'violetagg'
+  - 'pderop'
+  - 'garyrussel'
+  - 'acogoluegnes'
+filter-by-commitish: true
+template: |
+  # :checklist: TODO below
+   - [ ] Replace release train references
+   - [ ] Replace older maintenance train references
+   - [ ] Ensure changes from other maintenance release are indeed grouped and extra-indented
+
+  ${{ github.event.repository.name }} `$RESOLVED_VERSION` is part of **`2020.0.{SR}` Release Train (`Europium` SR{SR})**.
+
+  This release contains {SHORT DESCRIPTION OF THE CONTENTS}.
+
+  All changes from [`{OLDER_TRAIN}`](https://github.com/${{ github.repository }}/releases/tag/v{OLDER_TRAIN}) are also included and these are listed below with an additional level of indentation.
+
+  $CHANGES
+
+  ## :+1: Thanks to all contributors who participated to this release
+  $CONTRIBUTORS

.github/workflows/release-drafter.yml

@@ -0,0 +1,37 @@
+name: Release Notes Drafter
+on:
+  push:
+    branches: # For branches, better to list them explicitly than regexp include
+      - main
+      - 3.3.x
+jobs:
+  releaseDraft:
+    # Note this job has no access to secrets, only github token. When possible we favor plain run of gradle tasks.
+    name: release-draft
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+      - name: setup java
+        uses: actions/setup-java@v2
+        with:
+          distribution: 'temurin'
+          java-version: 8
+      - name: interpret version
+        id: version
+        #we only run the qualifyVersionGha task so that no other console printing can hijack this step's output
+        #output:
+        #  versionType: ${{ steps.version.outputs.versionType }}
+        #  fullVersion: ${{ steps.version.outputs.fullVersion }}
+        #fails if versionType is BAD, which interrupts the workflow
+        run: ./gradlew qualifyVersionGha
+      - name: compile release notes
+        # Renovate Bot should suggest updates to the action
+        uses: release-drafter/[email protected]
+        id: notes
+        #draft release notes only if this is a snapshot commit (ie. a merge of a PR)
+        if: steps.version.outputs.versionType == 'SNAPSHOT'
+        with:
+          disable-autolabeler: true
+          commitish: ${{ github.ref_name }}
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

gradle/setup.gradle

@@ -61,6 +61,7 @@ task qualifyVersionGha() {
 			println "::error ::Unable to parse $version to a VersionNumber with recognizable qualifier"
 			throw new TaskExecutionException(tasks.getByName("qualifyVersionGha"), new IllegalArgumentException("Unable to parse $version to a VersionNumber with recognizable qualifier"))
 		}
+		println "Recognized $version as $versionType"
 	}
 }