Add changelog-existence workflow

.github/workflows/changelog-existence.yml

@@ -0,0 +1,106 @@
+# **what?**
+# Checks that a file has been committed under the /.changes directory
+# as a new CHANGELOG entry.  Cannot check for a specific filename as
+# it is dynamically generated by change type and timestamp.
+#
+
+# **why?**
+# Ensure code change gets reflected in the CHANGELOG.
+
+# **when?**
+# This will run when called in a workflow.
+
+# Example Usage including required permissions
+
+# permissions:
+#   contents: read
+#   pull-requests: write
+#
+# name: Check Changelog Entry
+# jobs:
+#   changelog:
+#     uses: dbt-labs/actions/.github/workflows/changelog-check.yml@main
+#    with:
+#      changelog_comment: 'Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see [the contributing guide](https://github.com/dbt-labs/dbt-core/blob/main/CONTRIBUTING.md#adding-changelog-entry).'
+#      skip_label: 'Skip Changelog'
+#    secrets: inherit # this is only acceptable because we own the action we're calling
+#
+
+name: Check Changelog Entry Exists
+
+on:
+  workflow_call:
+    inputs:
+      changelog_comment:
+        description: The comment text when no changelog is found
+        type: string
+        required: true
+      skip_label:
+        description: Label on the PR that indicates CHANGELOGs are not required.
+        type: string
+        required: true
+
+jobs:
+  changelog_existence:
+    name: Check if Changelog Exists
+    if: "!contains(github.event.pull_request.labels.*.name, inputs.skip_label)"
+    runs-on: ubuntu-latest
+
+    steps:
+
+      - name: "[DEBUG] - Print Inputs"
+        shell: bash
+        id: echo_inputs
+        run: |
+          echo "all variables defined as inputs"
+          echo "Input Comment Text:        ${{ inputs.changelog_comment }}"
+          echo "Input Label for Skipping:  ${{ inputs.skip_label }}"
+      - name: Check if changelog file was added
+        # https://github.com/marketplace/actions/paths-changes-filter
+        # For each filter, it sets output variable named by the filter to the text:
+        #  'true' - if any of changed files matches any of filter rules
+        #  'false' - if none of changed files matches any of filter rules
+        uses: dorny/paths-filter@v2
+        id: changelog_check
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          filters: |
+            exists:
+              - added: '.changes/unreleased/**.yaml'
+      # this step uses the read permission from the GITHUB_TOKEN it inherits
+      - name: Check for comment
+        if: steps.changelog_check.outputs.exists == 'false'
+        uses: peter-evans/find-comment@v1
+        id: changelog_comment
+        with:
+          issue-number: ${{ github.event.pull_request.number }}
+          comment-author: 'github-actions[bot]'
+          body-includes: ${{ inputs.changelog_comment }}
+
+      - name: Set if comment already exists
+        if: steps.changelog_check.outputs.exists == 'false'
+        shell: bash
+        id: comment_check
+        run: |
+          if [ '${{ steps.changelog_comment.outputs.comment-body }}' = '' ]; then
+            echo "::set-output name=exists::false"
+            echo "Comment does not exist for this PR"
+          else
+            echo "::set-output name=exists::true"
+            echo "Comment already exists for this PR"
+          fi
+      # this step uses the write permission on the PR from the GITHUB_TOKEN it inherits
+      - name: Create PR comment if changelog entry is missing, required, and does not exist
+        if: |
+          steps.changelog_check.outputs.exists == 'false' &&
+          steps.comment_check.outputs.exists == 'false'
+        uses: peter-evans/create-or-update-comment@v1
+        with:
+          issue-number: ${{ github.event.pull_request.number }}
+          body: ${{ inputs.changelog_comment }}
+
+      - name: Fail job if changelog entry is missing and required
+        if: steps.changelog_check.outputs.exists == 'false'
+        uses: actions/github-script@v6
+        with:
+          script: core.setFailed('Changelog entry required to merge.')