Add a CI job which runs depgraph.

It can also push the results to GitHub pages.

.circleci/config.yml

@@ -41,6 +41,10 @@ workflows:
       #       # integration tests.
       #       - "debian-9"
 
+      # Generate the underlying data for a visualization to aid with Python 3
+      # porting.
+      - "build-porting-depgraph"
+
   images:
     # Build the Docker images used by the ci jobs.  This makes the ci jobs
     # faster and takes various spurious failures out of the critical path.
@@ -292,6 +296,18 @@ jobs:
       - store_artifacts: *STORE_OTHER_ARTIFACTS
       - run: *SUBMIT_COVERAGE
 
+  build-porting-depgraph:
+    # Generate up-to-date data for the dependency graph visualizer.
+    docker:
+      - image: "python:3.7-buster"
+
+    steps:
+      - "checkout"
+      - run:
+          name: "Generate dependency graph data"
+          command: |
+            ./misc/python3/depgraph.sh
+
   build-image: &BUILD_IMAGE
     # This is a template for a job to build a Docker image that has as much of
     # the setup as we can manage already done and baked in.  This cuts down on

misc/python3/depgraph.sh

@@ -0,0 +1,35 @@
+#!/bin/env bash
+
+set -x
+set -eo pipefail
+
+# if [ "${CIRCLE_BRANCH}" != "master" ]; then
+#     echo "Declining to update dependency graph for non-master build."
+#     exit 0
+# fi
+
+git config user.name 'Build Automation'
+git config user.email 'tahoe-dev@tahoe-lafs.org'
+
+TAHOE="${PWD}"
+git clone git@github.com:tahoe-lafs/tahoe-depgraph.git
+cd tahoe-depgraph
+
+# Generate the maybe-changed data.
+python tahoe-depgraph.py "${TAHOE}"
+
+if git diff-index --quiet --cached HEAD; then
+  echo "Declining to commit without any changes."
+  exit 0
+fi
+
+# Commit everything that changed.  It should be tahoe-deps.json and
+# tahoe-ported.json.
+git commit -am "\
+Built from ${CIRCLE_REPOSITORY_URL}@${CIRCLE_SHA1}
+
+tahoe-depgraph was $(git --git-dir ../.git rev-parse HEAD
+"
+
+# Publish it on GitHub.
+git push -q origin gh-pages