feat(check-merge-safety): Comment Matching Feature for Merge Safety Check

README.md

@@ -136,6 +136,68 @@ The following parameters can be used for additional control over when it is safe
 - `override_filter_paths`: These are the file paths that, if out of date on a PR, will prevent merge no matter what files the PR is changing
     - example: `override_filter_paths: package.json,package-lock.json`
 - `override_filter_globs`: These are glob patterns for `override_filter_paths`
+- `match_comment_paths`: When set to `'true'`, enables comment path matching. This reads paths from a specially formatted PR comment and checks if the branch is behind on any of those paths. This is useful when a PR's scope extends beyond the files it directly modifies (e.g., due to transitive dependencies in a monorepo triggering tests in other packages).
+
+#### Comment Path Matching
+
+When `match_comment_paths` is enabled, the helper looks for a PR comment containing the marker `<!-- check-merge-safety-paths -->` followed by a JSON array of paths in a fenced code block:
+
+````markdown
+<!-- check-merge-safety-paths -->
+
+```json
+["path/to/package1", "path/to/package2"]
+```
+````
+
+````
+
+This is useful for monorepos with selective testing, where changing one package (e.g., a shared data model) triggers tests for dependent packages. Without this feature, merging could introduce bugs if the dependent packages were updated on main after the PR's tests ran.
+
+Example workflow integration:
+
+```yaml
+# After determining affected paths, post them as a comment
+- name: Post affected paths
+  uses: actions/github-script@v7
+  with:
+    script: |
+      const marker = '<!-- check-merge-safety-paths -->';
+      const paths = ${{ steps.get-affected-paths.outputs.paths }};
+      const body = `${marker}\n\`\`\`json\n${JSON.stringify(paths)}\n\`\`\``;
+
+      const { data: comments } = await github.rest.issues.listComments({
+        owner: context.repo.owner,
+        repo: context.repo.repo,
+        issue_number: context.issue.number
+      });
+      const existing = comments.find(c => c.body.includes(marker));
+
+      if (existing) {
+        await github.rest.issues.updateComment({
+          owner: context.repo.owner,
+          repo: context.repo.repo,
+          comment_id: existing.id,
+          body
+        });
+      } else {
+        await github.rest.issues.createComment({
+          owner: context.repo.owner,
+          repo: context.repo.repo,
+          issue_number: context.issue.number,
+          body
+        });
+      }
+
+# Then run check-merge-safety with comment path matching enabled
+- uses: ExpediaGroup/github-helpers@v1
+  with:
+    helper: check-merge-safety
+    paths: |
+      packages/package-1
+      packages/package-2
+    match_comment_paths: 'true'
+````
 
 ### [close-pr](.github/workflows/close-pr.yml)
 

action.yml

@@ -167,6 +167,9 @@ inputs:
     description: 'The commit message to use'
     required: false
     default: 'Automated PR creation'
+  match_comment_paths:
+    description: 'Enable comment path matching for check-merge-safety. When enabled, reads paths from a specially formatted PR comment to determine if the branch needs rebasing.'
+    required: false
 outputs:
   output:
     description: 'The output of the helper'

dist/helpers/check-merge-safety.js

@@ -27,7 +27,8 @@ import"../main-9m3k9gt0.js";
 import {
   error,
   info,
-  setFailed
+  setFailed,
+  warning
 } from "../main-q70tmm6g.js";
 import {
   __toESM
@@ -38,6 +39,7 @@ var import_micromatch = __toESM(require_micromatch(), 1);
 var import_bluebird = __toESM(require_bluebird(), 1);
 var git = simpleGit();
 var maxBranchNameLength = 50;
+var COMMENT_PATHS_MARKER = "<!-- check-merge-safety-paths -->";
 
 class CheckMergeSafety extends HelperInputs {
 }
@@ -140,7 +142,7 @@ var getDiff = async (compareBase, compareHead, basehead) => {
   }
   return changedFileNames;
 };
-var getMergeSafetyStateAndMessage = async (pullRequest, { paths, ignore_globs, override_filter_paths, override_filter_globs }) => {
+var getMergeSafetyStateAndMessage = async (pullRequest, { paths, ignore_globs, override_filter_paths, override_filter_globs, match_comment_paths }) => {
   const {
     base: {
       repo: {
@@ -165,6 +167,24 @@ var getMergeSafetyStateAndMessage = async (pullRequest, { paths, ignore_globs, o
   }
   const truncatedRef = ref.length > maxBranchNameLength ? `${ref.substring(0, maxBranchNameLength)}...` : ref;
   const truncatedBranchName = `${username}:${truncatedRef}`;
+  if (match_comment_paths === "true") {
+    const commentPaths = await getPathsFromComment(pullRequest.number);
+    if (commentPaths.length) {
+      info(`Found ${commentPaths.length} paths from PR comment`);
+      const outdatedCommentPaths = commentPaths.filter((commentPath) => fileNamesWhichBranchIsBehindOn.some((file) => file.startsWith(commentPath + "/") || file === commentPath));
+      if (outdatedCommentPaths.length) {
+        error(buildErrorMessage(outdatedCommentPaths, "comment paths", truncatedBranchName));
+        const displayPaths = outdatedCommentPaths.slice(0, 3).join(", ");
+        const suffix = outdatedCommentPaths.length > 3 ? "..." : "";
+        return {
+          state: "failure",
+          message: `Branch is behind on paths from comment: ${displayPaths}${suffix}. Please update with ${default_branch}.`
+        };
+      }
+    } else {
+      info("No paths found in PR comment, skipping comment path matching check");
+    }
+  }
   const globalFilesOutdatedOnBranch = override_filter_globs ? import_micromatch.default(fileNamesWhichBranchIsBehindOn, override_filter_globs.split(/[\n,]/)) : override_filter_paths ? fileNamesWhichBranchIsBehindOn.filter((changedFile) => override_filter_paths.split(/[\n,]/).includes(changedFile)) : [];
   if (globalFilesOutdatedOnBranch.length) {
     error(buildErrorMessage(globalFilesOutdatedOnBranch, "global files", truncatedBranchName));
@@ -209,9 +229,33 @@ ${paths.map((path) => `* ${path}`).join(`
 var diffErrorMessage = (basehead, message = "") => `Failed to generate diff for ${basehead}. Please verify SHAs are valid and try again.${message ? `
 Error: ${message}` : ""}`;
 var buildSuccessMessage = (branchName) => `Branch ${branchName} is safe to merge!`;
+var getPathsFromComment = async (pullNumber) => {
+  const { data: comments } = await octokit.issues.listComments({
+    ...context.repo,
+    issue_number: pullNumber
+  });
+  const pathsComment = comments.find((c) => c.body?.includes(COMMENT_PATHS_MARKER));
+  if (!pathsComment?.body) {
+    return [];
+  }
+  const jsonMatch = pathsComment.body.match(/```json\n([\s\S]*?)\n```/);
+  if (!jsonMatch?.[1]) {
+    return [];
+  }
+  try {
+    const parsed = JSON.parse(jsonMatch[1]);
+    if (Array.isArray(parsed) && parsed.every((item) => typeof item === "string")) {
+      return parsed;
+    }
+    return [];
+  } catch {
+    warning(`Failed to parse paths from PR #${pullNumber} comment`);
+    return [];
+  }
+};
 export {
   checkMergeSafety,
   CheckMergeSafety
 };
 
-//# debugId=852D8F69D0103B1E64756E2164756E21
+//# debugId=8CCB3211353B88AF64756E2164756E21

src/helpers/check-merge-safety.ts

@@ -25,12 +25,15 @@ import * as core from '@actions/core';
 const git = simpleGit();
 
 const maxBranchNameLength = 50;
+const COMMENT_PATHS_MARKER = '<!-- check-merge-safety-paths -->';
+
 export class CheckMergeSafety extends HelperInputs {
   declare context?: string;
   declare paths?: string;
   declare ignore_globs?: string;
   declare override_filter_paths?: string;
   declare override_filter_globs?: string;
+  declare match_comment_paths?: string;
 }
 
 export const checkMergeSafety = async (inputs: CheckMergeSafety) => {
@@ -147,7 +150,7 @@ const getDiff = async (compareBase: DiffRefs, compareHead: DiffRefs, basehead: s
 
 const getMergeSafetyStateAndMessage = async (
   pullRequest: PullRequest,
-  { paths, ignore_globs, override_filter_paths, override_filter_globs }: CheckMergeSafety
+  { paths, ignore_globs, override_filter_paths, override_filter_globs, match_comment_paths }: CheckMergeSafety
 ) => {
   const {
     base: {
@@ -175,6 +178,31 @@ const getMergeSafetyStateAndMessage = async (
 
   const truncatedRef = ref.length > maxBranchNameLength ? `${ref.substring(0, maxBranchNameLength)}...` : ref;
   const truncatedBranchName = `${username}:${truncatedRef}`;
+
+  if (match_comment_paths === 'true') {
+    const commentPaths = await getPathsFromComment(pullRequest.number);
+
+    if (commentPaths.length) {
+      core.info(`Found ${commentPaths.length} paths from PR comment`);
+
+      const outdatedCommentPaths = commentPaths.filter(commentPath =>
+        fileNamesWhichBranchIsBehindOn.some(file => file.startsWith(commentPath + '/') || file === commentPath)
+      );
+
+      if (outdatedCommentPaths.length) {
+        core.error(buildErrorMessage(outdatedCommentPaths, 'comment paths', truncatedBranchName));
+        const displayPaths = outdatedCommentPaths.slice(0, 3).join(', ');
+        const suffix = outdatedCommentPaths.length > 3 ? '...' : '';
+        return {
+          state: 'failure',
+          message: `Branch is behind on paths from comment: ${displayPaths}${suffix}. Please update with ${default_branch}.`
+        } as const;
+      }
+    } else {
+      core.info('No paths found in PR comment, skipping comment path matching check');
+    }
+  }
+
   const globalFilesOutdatedOnBranch = override_filter_globs
     ? micromatch(fileNamesWhichBranchIsBehindOn, override_filter_globs.split(/[\n,]/))
     : override_filter_paths
@@ -223,7 +251,7 @@ const getMergeSafetyStateAndMessage = async (
   } as const;
 };
 
-const buildErrorMessage = (paths: string[], pathType: 'projects' | 'global files', branchName: string) =>
+const buildErrorMessage = (paths: string[], pathType: 'projects' | 'global files' | 'comment paths', branchName: string) =>
   `
 The following ${pathType} are outdated on branch ${branchName}
 
@@ -234,3 +262,31 @@ const diffErrorMessage = (basehead: string, message = '') =>
   `Failed to generate diff for ${basehead}. Please verify SHAs are valid and try again.${message ? `\nError: ${message}` : ''}`;
 
 const buildSuccessMessage = (branchName: string) => `Branch ${branchName} is safe to merge!`;
+
+const getPathsFromComment = async (pullNumber: number): Promise<string[]> => {
+  const { data: comments } = await octokit.issues.listComments({
+    ...githubContext.repo,
+    issue_number: pullNumber
+  });
+
+  const pathsComment = comments.find(c => c.body?.includes(COMMENT_PATHS_MARKER));
+  if (!pathsComment?.body) {
+    return [];
+  }
+
+  const jsonMatch = pathsComment.body.match(/```json\n([\s\S]*?)\n```/);
+  if (!jsonMatch?.[1]) {
+    return [];
+  }
+
+  try {
+    const parsed: unknown = JSON.parse(jsonMatch[1]);
+    if (Array.isArray(parsed) && parsed.every(item => typeof item === 'string')) {
+      return parsed;
+    }
+    return [];
+  } catch {
+    core.warning(`Failed to parse paths from PR #${pullNumber} comment`);
+    return [];
+  }
+};

src/types/generated.ts

@@ -67,4 +67,5 @@ export class HelperInputs {
   declare packages?: string;
   declare branch_name?: string;
   declare commit_message?: string;
+  declare match_comment_paths?: string;
 }