From 6abb008f072567c1f226785b9ef04799a6ba2f40 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andreas=20M=C3=B6ller?= <am@localheinz.com>
Date: Mon, 24 Jan 2022 19:39:34 +0100
Subject: [PATCH] Enhancement: Add github/merge-pull-request action

---
 .github/workflows/merge.yaml                  | 12 +---
 CHANGELOG.md                                  |  2 +
 actions/github/merge-pull-request/action.yaml | 66 +++++++++++++++++++
 3 files changed, 69 insertions(+), 11 deletions(-)
 create mode 100644 actions/github/merge-pull-request/action.yaml

diff --git a/.github/workflows/merge.yaml b/.github/workflows/merge.yaml
index 184fd7d..61e26b7 100644
--- a/.github/workflows/merge.yaml
+++ b/.github/workflows/merge.yaml
@@ -54,16 +54,6 @@ jobs:
           github-token: "${{ secrets.ERGEBNIS_BOT_TOKEN }}"
 
       - name: "Merge pull request"
-        uses: "actions/github-script@v5"
+        uses: "./.github/actions/github/merge-pull-request"
         with:
           github-token: "${{ secrets.ERGEBNIS_BOT_TOKEN }}"
-          script: |
-            const pullRequest = context.payload.workflow_run.pull_requests[0];
-            const repository = context.repo;
-
-            await github.rest.pulls.merge({
-              merge_method: "merge",
-              owner: repository.owner,
-              pull_number: pullRequest.number,
-              repo: repository.repo,
-            });
diff --git a/CHANGELOG.md b/CHANGELOG.md
index cb34413..69c15c8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ For a full diff see [`1.2.1...main`][1.2.1...main].
 
 - Added composite action `github/add-assignee-to-pull-request` ([#59]), by [@localheinz]
 - Added composite action `github/approve-pull-request` ([#60]), by [@localheinz]
+- Added composite action `github/merge-pull-request` ([#64]), by [@localheinz]
 
 ## [`1.2.1`][1.2.1]
 
@@ -62,5 +63,6 @@ For a full diff see [`1.0.0...main`][1.0.0...main].
 [#54]: https://github.com/ergebnis/.github/pull/54
 [#59]: https://github.com/ergebnis/.github/pull/59
 [#60]: https://github.com/ergebnis/.github/pull/60
+[#64]: https://github.com/ergebnis/.github/pull/64
 
 [@localheinz]: https://github.com/localheinz
diff --git a/actions/github/merge-pull-request/action.yaml b/actions/github/merge-pull-request/action.yaml
new file mode 100644
index 0000000..3d3e74f
--- /dev/null
+++ b/actions/github/merge-pull-request/action.yaml
@@ -0,0 +1,66 @@
+# https://docs.github.com/en/actions/creating-actions/creating-a-composite-action
+# https://docs.github.com/en/actions/creating-actions/metadata-syntax-for-github-actions#inputs
+# https://docs.github.com/en/actions/creating-actions/metadata-syntax-for-github-actions#runs-for-composite-run-steps-actions
+# https://docs.github.com/en/rest/reference/pulls#merge-a-pull-request
+# https://docs.github.com/en/developers/webhooks-and-events/webhooks/webhook-events-and-payloads#pull_request
+# https://docs.github.com/en/developers/webhooks-and-events/webhooks/webhook-events-and-payloads#workflow_run
+
+name: "Merge pull request"
+
+description: "Merges a pull request"
+
+inputs:
+  github-token:
+    description: "GitHub token of a user with permission to merge a pull request"
+    required: true
+  merge-method:
+    default: "merge"
+    description: "Which merge method to use, one \"merge\", \"rebase\", \"squash\""
+    required: true
+
+runs:
+  using: "composite"
+
+  steps:
+    - name: "Determine pull request number"
+      uses: "actions/github-script@v5"
+      with:
+        github-token: "${{ inputs.github-token }}"
+        script: |
+          if (context.eventName == 'pull_request') {
+            core.exportVariable("PULL_REQUEST_NUMBER", context.payload.pull_request.number);
+
+            return;
+          }
+
+          if (context.eventName == 'workflow_run') {
+            core.exportVariable("PULL_REQUEST_NUMBER", context.payload.workflow_run.pull_requests[0].number);
+
+            return;
+          }
+
+          core.setFailed(`Unable to determine the pull request number for event "${context.eventName}"`);
+
+    - name: "Merge pull request"
+      uses: "actions/github-script@v5"
+      env:
+        MERGE_METHOD: "${{ inputs.merge-method }}"
+      with:
+        github-token: "${{ inputs.github-token }}"
+        script: |
+          if (!process.env.PULL_REQUEST_NUMBER) {
+            core.setFailed("The environment variable PULL_REQUEST_NUMBER is not defined.")
+
+            return;
+          }
+
+          try {
+            await github.rest.pulls.merge({
+              merge_method: process.env.MERGE_METHOD,
+              owner: context.repo.owner,
+              pull_number: process.env.PULL_REQUEST_NUMBER,
+              repo: context.repo.repo,
+            });
+          } catch (error) {
+            core.setFailed(error.message);
+          }