Add simple PR comment sub-action (#636)

* Add simple PR comment sub-action

* Update rolldown config

* Add changeset

* Update readme

* Use TLA

* Add prefix

* fix merge

* Update

.changeset/curly-cameras-matter.md

@@ -0,0 +1,5 @@
+---
+"@changesets/action": minor
+---
+
+Add a new `@changesets/action/pr-comment` sub-action to comment on PRs

README.md

@@ -5,6 +5,7 @@ This action for [Changesets](https://github.com/changesets/changesets) creates a
 There are also sub-actions hosted in this repository. Check out their respective READMEs for more details:
 
 - [pr-status](./pr-status/README.md): Generate changeset status in PRs.
+- [pr-comment](./pr-comment/README.md): Comment on PRs.
 
 ## Usage
 

pr-comment/README.md

@@ -0,0 +1,52 @@
+# @changesets/action/pr-comment
+
+A simple GitHub Action to comment on PRs aimed to complement [`@changesets/action/pr-status`](../pr-status/README.md).
+
+This action is intentionally simple without advanced features. Check out other actions if so, such as [mshick/add-pr-comment](https://github.com/marketplace/actions/add-pr-comment) and [peter-evans/create-or-update-comment](https://github.com/marketplace/actions/create-or-update-comment).
+
+See the [action metadata](action.yml) for details on the inputs and outputs.
+
+## Example setup
+
+```yaml
+name: PR Comment
+
+on:
+  pull_request:
+
+jobs:
+  pr-comment:
+    runs-on: ubuntu-slim
+    permissions:
+      pull-requests: write # to create and update comments on PRs
+    steps:
+      - uses: changesets/action/pr-comment@v1
+        with:
+          body: Hello world!
+```
+
+When called repeatedly, the action will update the comment it created by default. If you use this action to create different types of comments, pass an `update-id` value to differentiate them.
+
+```yaml
+jobs:
+  pr-comment:
+    # ...
+    steps:
+      - uses: changesets/action/pr-comment@v1
+        with:
+          body: Hello world!
+          update-id: my-tag
+```
+
+If you want to always create new comments, pass an empty value to `update-id`.
+
+```yaml
+jobs:
+  pr-comment:
+    # ...
+    steps:
+      - uses: changesets/action/pr-comment@v1
+        with:
+          body: Hello world!
+          update-id: ""
+```

pr-comment/action.yml

@@ -0,0 +1,25 @@
+name: Changesets - PR Comment
+description: A simple GitHub Action to comment on PRs
+runs:
+  using: node24
+  main: ../dist/pr-comment.js
+inputs:
+  github-token:
+    description: "The GitHub token to use for authentication. Defaults to the GitHub-provided token."
+    required: false
+    default: ${{ github.token }}
+  body:
+    description: "The comment body to post on the PR."
+    required: true
+  update-id:
+    description: >
+      By default, the action will create and update a comment with this id. Pass a different id to
+      create and update a new comment, or pass an empty string to disable updating comments.
+    required: false
+    default: "changesets-action-pr-comment"
+outputs:
+  comment-id:
+    description: "The comment id of the comment that was created or updated."
+branding:
+  icon: message-circle
+  color: blue

pr-status/README.md

@@ -56,7 +56,6 @@ jobs:
         uses: changesets/action/pr-comment@v1
         with:
           body: ${{ needs.pr-status.outputs.comment-body }}
-          update-id: changesets-pr-status
 ```
 
 The workflow uses [`@changesets/action/pr-comment`](../pr-comment/README.md), which is a simple GitHub Action to comment on PRs.

rolldown.config.js

@@ -4,6 +4,7 @@ export default defineConfig({
   input: {
     index: "src/index.ts",
     ["pr-status"]: "src/pr-status/index.ts",
+    ["pr-comment"]: "src/pr-comment/index.ts",
   },
   output: {
     dir: "dist",

src/pr-comment/index.ts

@@ -0,0 +1,77 @@
+import * as core from "@actions/core";
+import * as github from "@actions/github";
+
+type Octokit = ReturnType<typeof github.getOctokit>;
+type CreateCommentParams = NonNullable<
+  Parameters<Octokit["rest"]["issues"]["createComment"]>[0]
+>;
+type UpdateCommentParams = NonNullable<
+  Parameters<Octokit["rest"]["issues"]["updateComment"]>[0]
+>;
+
+try {
+  await main();
+} catch (err) {
+  core.setFailed((err as Error).message);
+}
+
+async function main() {
+  const context = github.context.payload.pull_request;
+  if (!context) {
+    throw new Error(
+      "This action should only be run on `pull_request_target` or `pull_request` events",
+    );
+  }
+
+  const githubToken = core.getInput("github-token", { required: true });
+  const body = core.getInput("body", { required: true });
+  const updateId = core.getInput("update-id");
+
+  const commentMarker = updateId ? getCommentMarker(updateId) : null;
+  const commentBody = commentMarker ? `${commentMarker}\n\n${body}` : body;
+  const commentParam: CreateCommentParams | UpdateCommentParams = {
+    repo: context.base.repo.name,
+    owner: context.base.repo.owner.login,
+    issue_number: context.number,
+    body: commentBody,
+  };
+
+  const octokit = github.getOctokit(githubToken);
+
+  let existingCommentId: number | undefined;
+  if (commentMarker) {
+    core.info("Checking for existing comment...");
+    existingCommentId = await octokit.rest.issues
+      .listComments({
+        repo: context.base.repo.name,
+        owner: context.base.repo.owner.login,
+        issue_number: context.number,
+      })
+      .then((res) => {
+        const comment = res.data.find((c) => c.body?.includes(commentMarker));
+        return comment?.id;
+      });
+  }
+
+  if (existingCommentId) {
+    core.info(`Updating existing comment (id: ${existingCommentId})...`);
+    await octokit.rest.issues.updateComment({
+      ...commentParam,
+      comment_id: existingCommentId,
+    });
+    core.setOutput("comment-id", existingCommentId);
+  } else {
+    core.info("Creating new comment...");
+    const result = await octokit.rest.issues.createComment(commentParam);
+    core.setOutput("comment-id", result.data.id);
+  }
+
+  core.info("Done!");
+}
+
+function getCommentMarker(updateId: string) {
+  const prefix = "changesets-action-pr-comment";
+  return prefix === updateId
+    ? `<!-- ${prefix} -->`
+    : `<!-- ${prefix}:${updateId} -->`;
+}