ci: implements merge tool (#2)

.github/workflows/merge-pr.yml

@@ -0,0 +1,108 @@
+name: /merge handler
+
+on:
+  repository_dispatch:
+    types: [merge-command]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+concurrency: merge-handler-${{ github.event.client_payload.pull_request.node_id || github.run_id }}
+
+jobs:
+  merge:
+    if: github.event.client_payload.pull_request != null
+
+    name: Trim description and merge
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - id: pr-data
+        name: Get PR data and trim PR body
+        uses: actions/github-script@v6
+        with:
+          script: |
+            const pull_id = context.payload.client_payload.pull_request.node_id;
+
+            core.debug(`Pull request ID: ${pull_id}.`);
+            const query = `query($id: ID!) {
+              node(id: $id) {
+                ... on PullRequest {
+                  autoMergeRequest {
+                    mergeMethod
+                  }
+                  closed
+                  body
+                }
+              }
+            }`;
+
+            const { node: pr_info } = await github.graphql(query, { id: pull_id });
+            core.debug(`PR data: ${pr_info}`);
+
+            if (node.autoMergeRequest || node.closed) {
+              core.notice("PR is already merged or is in queue.");
+              return;
+            }
+
+            const [ body, body_tail ] = pr_info.body.split(/^---\s*$/, 2)
+            body = body.trimEnd()
+            body_tail = body_tail?.trimEnd() || ""
+            core.setOutput('run', 'true')
+            core.setOutput('body', body)
+            core.setOutput('body-tail', body_tail)
+            core.setOutput('update-body', pr_info.body !== result.body)
+
+      - if: steps.pr-data.outputs.run
+        id: find-comment
+        uses: peter-evans/find-comment@v2
+        with:
+          issue-number: ${{ github.event.client_payload.pull_request.number }}
+          comment-author: github-actions[bot]
+          body-includes: <!-- /merge info comment -->
+          direction: last
+
+      - if: steps.pr-data.outputs.run && !(steps.find-comment.outputs.comment-id && steps.pr-data.outputs.body_tail == "")
+        name: Create or update informational comment
+        uses: peter-evans/create-or-update-comment@v3
+        with:
+          comment-id: ${{ steps.find-comment.outputs.comment-id }}
+          issue-number: ${{ github.event.client_payload.pull_request.number }}
+          body: |
+            <!-- /merge info comment -->
+            Merge requested by: @${{ github.event.client_payload.github.payload.comment.user.login }}
+
+            Contents after the first section break of this PR's description has been removed and preserved below:
+
+            ---
+
+            <blockquote>
+            ${{ steps.pr-data.outputs.body-tail }}
+            </blockquote>
+          edit-mode: replace
+
+      - if: steps.pr-data.outputs.run && steps.pr-data.outputs.update-body
+        name: Update PR description
+        uses: actions/github-script@v6
+        env:
+          NEW_PR_BODY: ${{ steps.pr-data.outputs.body }}
+        with:
+          script: |
+            const pull_id = context.payload.client_payload.pull_request.node_id;
+            const update = `mutation ($input: UpdatePullRequestInput!) {
+              updatePullRequest(input: $input) {
+                clientMutationId
+              }
+            }`;
+
+            await github.graphql(update, {
+              pullRequestId: pull_id,
+              body: process.env.NEW_PR_BODY
+            });
+
+      - name: Queue for merging
+        env:
+          URL: ${{ github.event.client_payload.pull_request.html_url }}
+        run: gh pr merge "$URL" --auto

.github/workflows/slash-commands.yml

@@ -0,0 +1,23 @@
+name: Dispatch slash commands
+
+on:
+  issue_comment:
+    types:
+      - created
+
+permissions:
+  pull-requests: write
+
+jobs:
+  dispatch:
+    name: Dispatch command
+    runs-on: ubuntu-latest
+    environment: pr-merge
+    steps:
+      - uses: peter-evans/slash-command-dispatch@v3
+        with:
+          token: ${{ secrets.PAT }}
+          commands: |
+            merge
+          issue-type: pull-request
+          permission: write