Add slash command "/format" to automatically format PRs (#646)

This PR adds a special github action to enable slash commands in comments. 
With the feature enabled, anyone, who have written permission to a pull request, 
can write /format at the first line of a comment to trigger the "format" action, 
which can format the codes automatically.


Co-authored-by: Wei Ji <[email protected]>

Author: seisman

.github/PULL_REQUEST_TEMPLATE.md

@@ -15,3 +15,7 @@ Fixes #
 - [ ] Add new public functions/methods/classes to `doc/api/index.rst`.
 - [ ] Write detailed docstrings for all functions/methods.
 - [ ] If adding new functionality, add an example to docstrings or tutorials.
+
+**Notes**
+
+- You can write `/format` in the first line of a comment to lint the code automatically

.github/workflows/format-command.yml

@@ -0,0 +1,47 @@
+name: format-command
+on:
+  repository_dispatch:
+    types: [format-command]
+jobs:
+  format:
+    runs-on: ubuntu-latest
+    steps:
+      # Generate token from GenericMappingTools bot
+      - uses: tibdex/github-app-token@v1
+        id: generate-token
+        with:
+          app_id: ${{ secrets.APP_ID }}
+          private_key: ${{ secrets.APP_PRIVATE_KEY }}
+
+      # Checkout the pull request branch
+      - uses: actions/checkout@v2
+        with:
+          token: ${{ steps.generate-token.outputs.token }}
+          repository: ${{ github.event.client_payload.pull_request.head.repo.full_name }}
+          ref: ${{ github.event.client_payload.pull_request.head.ref }}
+
+      # Setup Python environment
+      - uses: actions/setup-python@v1
+
+      # Install formatting tools
+      - name: Install formatting tools
+        run: pip install black blackdoc flake8
+
+      # Run "make format" and commit the change to the PR branch
+      - name: Commit to the PR branch if any changes
+        run: |
+          make format
+          if [[ $(git ls-files -m) ]]; then
+            git config --global user.name 'actions-bot'
+            git config --global user.email '[email protected]'
+            git commit -am "[format-command] fixes"
+            git push
+          fi
+
+      - name: Add reaction
+        uses: peter-evans/create-or-update-comment@v1
+        with:
+          token: ${{ steps.generate-token.outputs.token }}
+          repository: ${{ github.event.client_payload.github.payload.repository.full_name }}
+          comment-id: ${{ github.event.client_payload.github.payload.comment.id }}
+          reaction-type: hooray

.github/workflows/slash-command-dispatch.yml

@@ -0,0 +1,24 @@
+name: Slash Command Dispatch
+on:
+  issue_comment:
+    types: [created]
+    # Add "edited" type for test purposes. Where possible, avoid using to prevent processing unnecessary events.
+    # types: [created, edited]
+jobs:
+  slashCommandDispatch:
+    runs-on: ubuntu-latest
+    steps:
+      # Generate token from GenericMappingTools bot
+      - uses: tibdex/github-app-token@v1
+        id: generate-token
+        with:
+          app_id: ${{ secrets.APP_ID }}
+          private_key: ${{ secrets.APP_PRIVATE_KEY }}
+
+      - name: Slash Command Dispatch
+        uses: peter-evans/slash-command-dispatch@v2
+        with:
+          token: ${{ steps.generate-token.outputs.token }}
+          commands: |
+            format
+          issue-type: pull-request

CONTRIBUTING.md

@@ -255,9 +255,10 @@ Before committing, run it to automatically format your code:
 make format
 ```
 
-Don't worry if you forget to do it.
-Our continuous integration systems will warn us and you can make a new commit with the
-formatted code.
+Don't worry if you forget to do it. Our continuous integration systems will
+warn us and you can make a new commit with the formatted code.
+Even better, you can just write `/format` in the first line of any comment in a
+Pull Request to lint the code automatically.
 
 We also use [flake8](http://flake8.pycqa.org/en/latest/) and
 [pylint](https://www.pylint.org/) to check the quality of the code and quickly catch