Add clippy to lint rust code

.github/workflows/main.yml

@@ -9,8 +9,8 @@ on:
   workflow_dispatch:
 
 jobs:
-  tests:
-    name: Python ${{ matrix.python-version }}, ${{ matrix.os }}
+  check_python:
+    name: Check Python ${{ matrix.python-version }}, ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
 
     strategy:
@@ -22,14 +22,9 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-
       - uses: actions-rs/toolchain@v1
         with:
           toolchain: stable
-
-      - run: cargo test --no-default-features
-        working-directory: ./rust
-
       - uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
@@ -43,6 +38,21 @@ jobs:
       - name: Run tox targets for ${{ matrix.python-version }}
         run: python -m tox
 
+  check_rust:
+    name: Check Rust
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+      - name: Run tests
+        run: cargo test --no-default-features
+        working-directory: ./rust
+      - name: Run linter (clippy)
+        run: cargo clippy --all-targets --all-features -- -D warnings
+        working-directory: ./rust
+
   benchmarks:
       runs-on: ubuntu-22.04
       steps:

CONTRIBUTING.rst

@@ -61,6 +61,16 @@ To set up `grimp` for local development:
 
 6. Submit a pull request through the GitHub website.
 
+Rust code
+---------
+
+When working with the rust code (in the ``rust/`` directory):
+
+* Run tests with ``cargo test --no-default-features``.
+  The ``--no-default-features`` flag is needed to due to `this PYO3 issue <https://pyo3.rs/main/faq#i-cant-run-cargo-test-or-i-cant-build-in-a-cargo-workspace-im-having-linker-issues-like-symbol-not-found-or-undefined-reference-to-_pyexc_systemerror>`_.
+* Run `clippy <https://doc.rust-lang.org/clippy/index.html>`_ (a linter for rust) with ``cargo clippy --all-targets --all-features -- -D warnings``.
+  It's often possible to apply automatic fixes to clippy issues with the ``--fix`` flag e.g. ``cargo clippy --all-targets --all-features --fix --allow-staged``.
+
 Pull Request Guidelines
 -----------------------