Add mypy to ci and precommit (#5969)

* Add mypy to ci and precommit

* Run precommit mypy in venv

* Fix issues raised in latest version of mypy

.github/workflows/ci.yaml

@@ -10,6 +10,7 @@ on:
 env:
   DEFAULT_PYTHON: "3.13"
   PRE_COMMIT_CACHE: ~/.cache/pre-commit
+  MYPY_CACHE_VERSION: 1
 
 concurrency:
   group: "${{ github.workflow }}-${{ github.ref }}"
@@ -286,6 +287,52 @@ jobs:
           . venv/bin/activate
           pylint supervisor tests
 
+  mypy:
+    name: Check mypy
+    runs-on: ubuntu-latest
+    needs: prepare
+    steps:
+      - name: Check out code from GitHub
+        uses: actions/checkout@v4.2.2
+      - name: Set up Python ${{ needs.prepare.outputs.python-version }}
+        uses: actions/setup-python@v5.6.0
+        id: python
+        with:
+          python-version: ${{ needs.prepare.outputs.python-version }}
+      - name: Generate partial mypy restore key
+        id: generate-mypy-key
+        run: |
+          mypy_version=$(cat requirements_test.txt | grep mypy | cut -d '=' -f 3)
+          echo "version=$mypy_version" >> $GITHUB_OUTPUT
+          echo "key=mypy-${{ env.MYPY_CACHE_VERSION }}-$mypy_version-$(date -u '+%Y-%m-%dT%H:%M:%s')" >> $GITHUB_OUTPUT
+      - name: Restore Python virtual environment
+        id: cache-venv
+        uses: actions/cache@v4.2.3
+        with:
+          path: venv
+          key: >-
+            ${{ runner.os }}-venv-${{ needs.prepare.outputs.python-version }}-${{ hashFiles('requirements.txt') }}-${{ hashFiles('requirements_tests.txt') }}
+      - name: Fail job if Python cache restore failed
+        if: steps.cache-venv.outputs.cache-hit != 'true'
+        run: |
+          echo "Failed to restore Python virtual environment from cache"
+          exit 1
+      - name: Restore mypy cache
+        uses: actions/cache@v4.2.3
+        with:
+          path: .mypy_cache
+          key: >-
+            ${{ runner.os }}-mypy-${{ needs.prepare.outputs.python-version }}-${{ steps.generate-mypy-key.outputs.key }}
+          restore-keys: >-
+            ${{ runner.os }}-venv-${{ needs.prepare.outputs.python-version }}-mypy-${{ env.MYPY_CACHE_VERSION }}-${{ steps.generate-mypy-key.outputs.version }}
+      - name: Register mypy problem matcher
+        run: |
+          echo "::add-matcher::.github/workflows/matchers/mypy.json"
+      - name: Run mypy
+        run: |
+          . venv/bin/activate
+          mypy --ignore-missing-imports supervisor
+
   pytest:
     runs-on: ubuntu-latest
     needs: prepare

.github/workflows/matchers/mypy.json

@@ -0,0 +1,16 @@
+{
+    "problemMatcher": [
+        {
+            "owner": "mypy",
+            "pattern": [
+                {
+                    "regexp": "^(.+):(\\d+):\\s(error|warning):\\s(.+)$",
+                    "file": 1,
+                    "line": 2,
+                    "severity": 3,
+                    "message": 4
+                }
+            ]
+        }
+    ]
+}