Docker layer caching in CI (#273)

* docker push

* use cached docker image

.github/workflows/tests.yml

@@ -2,26 +2,38 @@ name: Tests
 
 on: [push, pull_request]
 
+env:
+  RUN: docker run --shm-size 1G --rm opendbc /bin/sh -c
+  BUILD: |
+      docker pull $(grep -ioP '(?<=^from)\s+\S+' Dockerfile) || true
+      docker pull docker.io/commaai/opendbc:latest || true
+      docker build --cache-from docker.io/commaai/opendbc:latest -t opendbc -f Dockerfile .
+
 jobs:
   test:
     runs-on: ubuntu-16.04
 
     steps:
       - uses: actions/checkout@v2
-      - run: |
-          set -e
-          docker build -t opendbc .
-        name: "Build"
+      - name: Build Docker image
+        run: eval "$BUILD"
       - name: Static analysis
         run: |
           docker run opendbc bash -c "cd opendbc && git init && git add -A && pre-commit run --all"
-      - run: |
+      - name: Unit tests
+        run: |
           docker run opendbc bash -c "python -m unittest discover opendbc"
-        name: "Unit tests"
-      - run: |
+      - name: Python linter
+        run: |
           docker run opendbc bash -c "cd opendbc/can/tests/linter_python; PYTHONPATH=/ ./flake8_opendbc.sh"
           docker run opendbc bash -c "cd opendbc/can/tests/linter_python; PYTHONPATH=/ ./pylint_opendbc.sh"
-        name: "Python linter"
-      - run: |
+      - name: Generator test
+        run: |
           docker run opendbc bash -c "cd opendbc/can/tests/; PYTHONPATH=/ ./test_generator.sh"
-        name: "Generator test"
+      - name: Push to dockerhub
+        if: github.ref == 'refs/heads/master' && github.event_name != 'pull_request' && github.repository == 'commaai/opendbc'
+        run: |
+          docker login -u wmelching -p ${{ secrets.DOCKERHUB_TOKEN }}
+          docker tag opendbc docker.io/commaai/opendbc:latest
+          docker push docker.io/commaai/opendbc:latest
+