Add script to merge master/main into PR branch

This script automates merging the master or main branch into a pull request branch when triggered by a specific comment on GitHub.

Author: sbijarnia-eightfold

merge_master.sh

@@ -0,0 +1,129 @@
+#!/bin/bash
+#
+# This script merges master (or main) into a PR branch when a PR comment contains
+# "merge master" or "merge main".
+#
+# It is meant to be triggered by a GitHub Action on `issue_comment.created`.
+
+set -euo pipefail
+
+# ----------- ENVIRONMENT CHECKS -----------
+if [[ -z "${GITHUB_TOKEN:-}" ]]; then
+  echo "Set the GITHUB_TOKEN env variable."
+  exit 1
+fi
+
+if [[ -z "${GITHUB_REPOSITORY:-}" ]]; then
+  echo "Set the GITHUB_REPOSITORY env variable."
+  exit 1
+fi
+
+if [[ -z "${GITHUB_EVENT_PATH:-}" ]]; then
+  echo "Set the GITHUB_EVENT_PATH env variable."
+  exit 1
+fi
+
+# ----------- CONSTANTS -----------
+URI="https://api.github.com"
+API_HEADER="Accept: application/vnd.github.v3+json"
+AUTH_HEADER="Authorization: token ${GITHUB_TOKEN}"
+
+# ----------- PARSE EVENT DATA -----------
+action=$(jq --raw-output .action "$GITHUB_EVENT_PATH")
+comment_body=$(jq --raw-output .comment.body "$GITHUB_EVENT_PATH" | tr -d '\r' | tr -d '\n' | xargs)
+issue_number=$(jq --raw-output .issue.number "$GITHUB_EVENT_PATH")
+
+echo "Action: $action"
+echo "Comment: $comment_body"
+echo "PR Number: $issue_number"
+
+# Only process new comments on PRs
+if [[ "$action" != "created" ]]; then
+  echo "This script only runs for new comments."
+  exit 0
+fi
+
+is_pr=$(jq --raw-output '.issue.pull_request | if . != null then "true" else "false" end' "$GITHUB_EVENT_PATH")
+if [[ "$is_pr" != "true" ]]; then
+  echo "Comment is not on a pull request."
+  exit 0
+fi
+
+# ----------- COMMAND CHECK -----------
+if [[ "$comment_body" != "merge master" && "$comment_body" != "merge main" ]]; then
+  echo "No merge command found."
+  exit 0
+fi
+
+# ----------- FETCH PR DETAILS -----------
+echo "Fetching PR details..."
+pr_data=$(curl -sSL \
+  -H "${AUTH_HEADER}" \
+  -H "${API_HEADER}" \
+  "${URI}/repos/${GITHUB_REPOSITORY}/pulls/${issue_number}")
+
+head_ref=$(echo "$pr_data" | jq -r .head.ref)
+base_ref=$(echo "$pr_data" | jq -r .base.ref)
+
+echo "Base branch: $base_ref"
+echo "PR branch: $head_ref"
+
+# ----------- DETERMINE SOURCE BRANCH -----------
+merge_source="master"
+if [[ "$comment_body" == "merge main" ]]; then
+  merge_source="main"
+fi
+
+# ----------- CLONE AND MERGE -----------
+echo "Cloning repository and merging $merge_source into $head_ref..."
+git config --global user.name "github-actions[bot]"
+git config --global user.email "github-actions[bot]@users.noreply.github.com"
+
+git clone "https://x-access-token:${GITHUB_TOKEN}@github.com/${GITHUB_REPOSITORY}.git" repo
+cd repo
+
+git fetch origin "$merge_source"
+git fetch origin "$head_ref"
+
+git checkout "$head_ref"
+
+# Attempt merge
+set +e
+git merge "origin/${merge_source}" --no-edit
+merge_exit=$?
+set -e
+
+# ----------- HANDLE MERGE RESULT -----------
+if [[ $merge_exit -eq 0 ]]; then
+  # Check if there’s anything to push
+  if git diff --quiet HEAD "origin/${head_ref}"; then
+    echo "No changes to push (branch already up to date)."
+    curl -sSL \
+      -H "${AUTH_HEADER}" \
+      -H "${API_HEADER}" \
+      -X POST \
+      -d "{\"body\":\":information_source: ${merge_source} is already up to date with ${head_ref}.\"}" \
+      "${URI}/repos/${GITHUB_REPOSITORY}/issues/${issue_number}/comments"
+    exit 0
+  fi
+
+  echo "Pushing merged branch..."
+  git push origin "HEAD:${head_ref}"
+
+  # Comment success
+  curl -sSL \
+    -H "${AUTH_HEADER}" \
+    -H "${API_HEADER}" \
+    -X POST \
+    -d "{\"body\":\":white_check_mark: Successfully merged ${merge_source} into ${head_ref}.\"}" \
+    "${URI}/repos/${GITHUB_REPOSITORY}/issues/${issue_number}/comments"
+else
+  echo "Merge conflict detected."
+  curl -sSL \
+    -H "${AUTH_HEADER}" \
+    -H "${API_HEADER}" \
+    -X POST \
+    -d "{\"body\":\":x: Merge from ${merge_source} failed due to conflicts. Please resolve manually.\"}" \
+    "${URI}/repos/${GITHUB_REPOSITORY}/issues/${issue_number}/comments"
+  exit 1
+fi