Add simple PR comment sub-action

.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

@@ -2,6 +2,10 @@
 
 This action for [Changesets](https://github.com/changesets/changesets) creates a pull request with all of the package versions updated and changelogs updated and when there are new changesets on [your configured `baseBranch`](https://github.com/changesets/changesets/blob/main/docs/config-file-options.md#basebranch-git-branch-name), the PR will be updated. When you're ready, you can merge the pull request and you can either publish the packages to npm manually or setup the action to do it for you.
 
+There are also sub-actions hosted in this repository. Check out their respective READMEs for more details:
+
+- [pr-comment](./pr-comment/README.md): Comment on PRs.
+
 ## Usage
 
 ### Inputs

pr-comment/README.md

@@ -0,0 +1,29 @@
+# @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!
+          # Optional. If provided, the action will update the comment that contains this id,
+          # or create a comment with this id to be updated later.
+          update-id: changesets
+```

pr-comment/action.yml

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+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: "If provided, the action will update the comment that contains this id, or create a comment with this id to be updated later."
+    required: false
+outputs:
+  comment-id:
+    description: "The comment id of the comment that was created or updated."
+branding:
+  icon: message-circle
+  color: blue

rolldown.config.js

@@ -1,7 +1,10 @@
 import { defineConfig } from "rolldown";
 
 export default defineConfig({
-  input: "src/index.ts",
+  input: {
+    index: "src/index.ts",
+    ["pr-comment"]: "src/pr-comment/index.ts",
+  },
   output: {
     dir: "dist",
     format: "esm",

src/pr-comment/index.ts

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+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", { required: false });
+
+  const commentMarker = updateId
+    ? `<!-- changesets-action-pr-comment:${updateId} -->`
+    : null;
+  const commentBody = commentMarker ? `${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!");
+}