switch Circle from Python 3.7 to 3.9

...by migrating from the google/cloud-sdk Docker image to cimg/python

.circleci/config.yml

@@ -1,52 +1,58 @@
 # CircleCI automatically reads this file from our repo and uses it for
 # configuration. Docs:
-# https://circleci.com/docs/2.0/configuration-reference/
-# https://circleci.com/docs/2.0/sample-config/
-version: 2
+# https://circleci.com/docs/2.1/configuration-reference/
+# https://circleci.com/docs/2.1/sample-config/
+version: 2.1
 
 jobs:
   build:
     docker:
-      # https://circleci.com/docs/2.0/google-auth/#installing-the-google-cloud-sdk
-      - image: google/cloud-sdk
+      - image: cimg/python:3.9
 
     environment:
       # https://github.com/GoogleCloudPlatform/google-cloud-datastore/issues/168#issuecomment-294418422
-      - APPLICATION_ID: dev~bridgy-federated
+      # - APPLICATION_ID: dev~bridgy-federated
 
     steps:
       - checkout
 
       - restore_cache:
-          key: venv-2-{{ .Branch }}-{{ checksum "requirements.txt" }}
+          key: venv-3-{{ .Branch }}-{{ checksum "requirements.txt" }}
 
       - run:
-          name: Dependencies
+          name: Base dependencies
+          command: |
+            # google-cloud-sdk: https://cloud.google.com/sdk/docs/install#deb
+            echo "deb [signed-by=/usr/share/keyrings/cloud.google.gpg] https://packages.cloud.google.com/apt cloud-sdk main" | sudo tee -a /etc/apt/sources.list.d/google-cloud-sdk.list
+            curl https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key --keyring /usr/share/keyrings/cloud.google.gpg add -
+            sudo apt-get update
+            sudo apt-get install -y apt-transport-https ca-certificates gnupg google-cloud-sdk google-cloud-sdk-datastore-emulator default-jre
+
+      - run:
+          name: Python dependencies
           command: |
-            apt-get update
-            apt-get install -y python3.7 python3.7-venv python3.7-dev
-            python3.7 -m venv local3
-            . local3/bin/activate
             pip install -U pip
-            pip install cython  # avoids grpcio install bug (search _needs_stub)
+            pip  -V
+            # make sure we install these at head, below
+            pip uninstall -y granary oauth-dropins
             pip install -U -r requirements.txt
-            pip install mox3
             pip install coverage coveralls
 
       - run:
           name: Build and test
           command: |
-            . local3/bin/activate
             CLOUDSDK_CORE_PROJECT=bridgy-federated gcloud beta emulators datastore start --no-store-on-disk --consistency=1.0 --host-port=localhost:8089 < /dev/null >& /dev/null &
             sleep 5s
-            python -m coverage run --source=. --omit=appengine_config.py,local3/\*,logs.py,tests/\* -m unittest discover -v
+            python -m coverage run --source=. --omit=appengine_config.py,logs.py,tests/\* -m unittest discover -v
             python -m coverage html -d /tmp/coverage_html
             if [ "$COVERALLS_REPO_TOKEN" != "" ]; then coveralls || true; fi
 
       - save_cache:
-          key: venv-2-{{ .Branch }}-{{ checksum "requirements.txt" }}
+          key: venv-3-{{ .Branch }}-{{ checksum "requirements.txt" }}
           paths:
-            - local
+            - /home/circleci/.pyenv
+            - /usr/lib/google-cloud-sdk
+            - /usr/lib/jvm/java-11-openjdk-amd64
 
       - store_artifacts:
           path: /tmp/coverage_html