mypy_primer: add to CI (#4629)

Co-authored-by: hauntsaninja <>

.github/workflows/mypy_primer.yml

@@ -0,0 +1,34 @@
+name: Run mypy_primer
+
+on:
+  # Only run on PR, since we diff against master
+  pull_request:
+
+jobs:
+  mypy_primer:
+    name: Run mypy_primer
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          path: typeshed_to_test
+          fetch-depth: 0
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.8
+      - name: Install dependencies
+        run: |
+          python -m pip install -U pip
+          pip install git+https://github.com/hauntsaninja/mypy_primer.git
+      - name: Run mypy_primer
+        run: |
+          cd typeshed_to_test
+          echo "new commit"
+          git rev-list --format=%s --max-count=1 $GITHUB_SHA
+          git checkout -b upstream_master origin/master
+          echo "base commit"
+          git rev-list --format=%s --max-count=1 upstream_master
+          cd ..
+          echo "ATTENTION: failures here shouldn't be treated as blocking; use your judgement"
+          echo "(Unfortunately, Github doesn't seem to have an \"allowed_failures\" equivalent)"
+          mypy_primer --new v0.790 --old v0.790 --custom-typeshed-repo typeshed_to_test --new-typeshed $GITHUB_SHA --old-typeshed upstream_master -o concise