Update dotfiles, test with GitHub actions

.github/workflows/pre-commit.yml

@@ -17,4 +17,21 @@ jobs:
           # where we are not using black > 21. Older black versions won't work with
           # Python 3.9.8+, and we can't bump black without reformatting.
           python-version: "3.9.7"
-      - uses: pre-commit/action@v2.0.0
+      - name: Get python version
+        run: echo "PY=$(python -VV | sha256sum | cut -d' ' -f1)" >> $GITHUB_ENV
+      - uses: actions/cache@v1
+        with:
+          path: ~/.cache/pre-commit
+          key: pre-commit|${{ env.PY }}|${{ hashFiles('.pre-commit-config.yaml') }}
+      - name: Install pre-commit
+        run: pip install pre-commit
+      - name: Run pre-commit
+        run: pre-commit run --all-files --show-diff-on-failure --color=always
+      - name: Check that all files generated by pre-commit are in git
+        run: |
+          newfiles="$(git ls-files --others --exclude-from=.gitignore)"
+          if [ "$newfiles" != "" ] ; then
+              echo "Please check-in the following files:"
+              echo "$newfiles"
+              exit 1
+          fi