Comment changeset status in PRs (#625)

* Initial implementation

* Fix

* fix

* fix

* Make it look nicer

* Update docs

* Rename to pr-status-comment

* Remove outputs

* Update path

* update name

* Checkout PR in a detached worktree (#626)

Co-authored-by: bluwy <bjornlu.dev@gmail.com>

* Move comment to separate job

* Loosen event requirement

* Update

* Apply suggestions from code review

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

* Use TLA

* use using

* Remove test log

---------

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

pr-status/README.md

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+# changesets/action/pr-status
+
+This action generates the changesets status in PRs, e.g. whether it has changeset files and which packages will be released if the PR is merged.
+
+It requires the repo to be checked out, and automatically fetches the PR head ref into a temporary detached worktree in order to infer the changed files and packages. It also requires the [`pull_request_target`](https://docs.github.com/en/actions/reference/workflows-and-actions/events-that-trigger-workflows#pull_request_target) event to be triggered in order to have permissions to comment on the PR and to work in PRs from forks.
+
+You can also use the [`pull_request`](https://docs.github.com/en/actions/reference/workflows-and-actions/events-that-trigger-workflows#pull_request) event if you prefer to lock permissions down and not run for PRs from forks. Make sure to add an if check to prevent the action from failing in fork PRs:
+
+```yaml
+jobs:
+  pr-status:
+    if: github.event.pull_request.head.repo.full_name == github.repository
+    # ...
+```
+
+See the [action metadata](action.yml) for details on the inputs and outputs.
+
+> [!WARNING]
+> **Do not run untrusted code** when using the `pull_request_target` event. The example below only checks out code and does not run any code from the PR. Read more about the `pull_request_target` event in the [GitHub documentation](https://docs.github.com/en/actions/reference/workflows-and-actions/events-that-trigger-workflows#pull_request_target).
+
+## Example setup
+
+```yaml
+# .github/workflows/comment-changesets-pr-status.yml
+name: Comment Changesets status in PRs
+
+on:
+  pull_request_target:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+jobs:
+  pr-status:
+    runs-on: ubuntu-slim
+    permissions:
+      contents: read # to check out files in the repo
+    outputs:
+      comment-body: ${{ steps.pr-status.outputs.comment-body }}
+    steps:
+      - name: Check out repo
+        uses: actions/checkout@v6
+
+      - name: Generate status
+        id: pr-status
+        uses: changesets/action/pr-status@v1
+
+  pr-comment:
+    needs: pr-status
+    runs-on: ubuntu-slim
+    permissions:
+      pull-requests: write # to create and update comments on PRs
+    steps:
+      - name: Comment on PR
+        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.

pr-status/action.yml

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+name: Changesets - PR Status
+description: Generate the changesets status in PRs
+runs:
+  using: node24
+  main: ../dist/pr-status.js
+inputs: {}
+outputs:
+  comment-body:
+    description: The generated comment body to present the changesets status in PRs.
+branding:
+  icon: package
+  color: blue