Fix release workflow (#1157)

Ensure the release workflow will work consistently by limiting the
number of issues that are checked in addition to making use of a cache.
This should keep the requests below the API limit and overtime may be
increased should the cache be retained.

Add checks to determine the correct default branch and look to establish
if the tag that was created is reachable from this branch, using it as
the value for `commitish` to the create release action so that it
retains the `x commits since release` text and link.

In the case the workflow is re-run for a release after another release
look to pick up the next tag after this release in order to limit the
release notes from updating with additional fixes.

.github/workflows/release.yml

@@ -13,12 +13,63 @@ jobs:
       -
         name: Checkout code
         uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      -
+        name: Determine remote default branch
+        uses: actions/github-script@v3.0.0
+        id: remote_default_branch
+        with:
+          github-token: ${{secrets.GITHUB_TOKEN}}
+          script: |
+            repo = await github.repos.get({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+            })
+            return repo.data.default_branch
       -
         name: Prepare
         id: prep
         run: |
+          set -eu -o pipefail
+
+          # exclude unreleased in case re-running workflow
+          echo "unreleased=false" >> .github_changelog_generator
+          echo "max-issues=200" >> .github_changelog_generator
+          # in case we've tagged subsequently ensure consistent run
+          NEXT_TAG_SHA1="$(git rev-list --tags --skip=0 --no-walk | grep -B 1 ${{ github.sha }} || true)"
+          if [[ "${NEXT_TAG_SHA1:-}" != "${{ github.sha }}" ]]
+          then
+              NEXT_TAG=$(git describe --tags --abbrev=0 ${NEXT_TAG_SHA1})
+              echo "due-tag=${NEXT_TAG}" >> .github_changelog_generator
+          fi
+          # limit list to next tag if any
           LAST_TAG=$(git describe --tags --abbrev=0 HEAD~1 2>/dev/null || true)
+
+          # to ensure that releases continue to get 'x commits since release'
+          # need to pass the branch name in addition to the tag to the create
+          # release. Work out which branch the current tag is on
+          DEFAULT_BRANCH=origin/${{ steps.remote_default_branch.outputs.result }}
+          if git merge-base --is-ancestor ${{ github.ref }} ${DEFAULT_BRANCH}
+          then
+              # if the tag is in the history of the default remote branch
+              BRANCH=${DEFAULT_BRANCH}
+          else
+              # otherwise take the first match and hope for the best
+              BRANCH=$(git branch -r --format="%(refname:short)" --contains ${{ github.ref }} | head -n1)
+          fi
+          BRANCH=${BRANCH#origin/}
+
+          # set outputs for usage
           echo ::set-output name=previous_version::${LAST_TAG}
+          echo ::set-output name=release_branch::${BRANCH}
+      -
+        name: Cache Github API requests
+        id: cache-changelog-api-requests
+        uses: actions/cache@v2
+        with:
+          key: github-changelog-cache
+          path: .github_changelog_generator_cache
       -
         name: Changelog Generation
         uses: CharMixer/auto-changelog-action@v1.1
@@ -34,8 +85,6 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         with:
           tag_name: ${{ github.ref }}
+          commitish: ${{ steps.prep.outputs.release_branch }}
           release_name: Release ${{ github.ref }}
           body_path: release_notes.md
-          draft: false
-          prerelease: false
-