PoC: automated linting on CI

This PR is to support the discussion on enforcing consistent formatting
on the CI [1].

[1] #1804

.github/workflows/linting.yml

@@ -0,0 +1,27 @@
+name: Code Quality
+
+on:
+  push:
+    branches: [ main, ci-fix, v1/maintenance ]
+  pull_request:
+    branches: [ main, ci-fix, v1/maintenance ]
+
+jobs:
+  linting:
+    if: "!contains(github.event.pull_request.labels.*.name, 'no-ci')"
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        submodules: 'recursive'
+
+    - uses: actions/setup-python@v5
+      with:
+        python-version: '3.13'
+
+    - name: Install pre-commit
+          run: pip install pre-commit yapf
+
+    - name: Run lint via pre-commit
+      run: pre-commit run --all-files

.pre-commit-config.yaml

@@ -0,0 +1,20 @@
+default_language_version:
+  python: python3
+
+repos:
+- repo: https://github.com/pre-commit/pre-commit-hooks
+  rev: v2.3.0
+  hooks:
+  - id: check-merge-conflict
+  - id: check-yaml
+  - id: end-of-file-fixer
+  - id: trailing-whitespace
+- repo: https://github.com/google/yapf
+  rev: v0.43.0
+  hooks:
+    - id: yapf
+      name: yapf
+      language: python
+      entry: yapf
+      args: [-i]
+      types: [python]

CONTRIBUTING.md

@@ -38,9 +38,28 @@ def example_function(param_a: str, *args: Optional[SDFG]) -> bool:
     ...
 ```
 
+For automatic styling, we rely on [pre-commit](https://pre-commit.com/) and use the [yapf](https://github.com/google/yapf) file formatter.
+**Please run `pre-commit` before making your pull request ready for review.**
 
-For automatic styling, we use the [yapf](https://github.com/google/yapf) file formatter.
-**Please run `yapf` before making your pull request ready for review.**
+```bash
+pre-commit run --all-files
+```
+
+Formatting will be evaluated as part of CI and you won't be able to merge unless formatting issues are resolved. To get `pre-commit` and `yapf`, be sure to install the `linting` extra, e.g. for contributors we recommend
+
+```bash
+pip install -e ".[testing,linting]"
+```
+
+to get testing and linting extras in an editable install.
+
+One way to always ensure consistency with our coding standards is to install pre-commit hooks, which will check formatting issues of changed files before every commit. If you wish to do so, run
+
+```bash
+pre-commit install
+```
+
+to install the `git` hooks for this repository.
 
 ## Tests
 

setup.py

@@ -79,7 +79,8 @@
       ] + cmake_requires,
       extras_require={
           'testing': ['coverage', 'pytest-cov', 'scipy', 'absl-py', 'opt_einsum', 'pymlir', 'click'],
-          'docs': ['jinja2<3.2.0', 'sphinx-autodoc-typehints', 'sphinx-rtd-theme>=0.5.1']
+          'docs': ['jinja2<3.2.0', 'sphinx-autodoc-typehints', 'sphinx-rtd-theme>=0.5.1'],
+          'linting': ['pre-commit', 'yapf'],
       },
       entry_points={
           'console_scripts': [