Markdown link check in CI (#2543)

* check using xargs

* fix broken BC link

* install npm, run precommit before unit tests

* try to install npm

* try a node image build

* add workflow

* don't use precommit on node run

* sudo make me a sandwich

* pass config arg

* revert CI order change

* retry precommit

* sudo apt-get

* sudo npm

* make sure fails on bad link

* cleanup and refix link

.circleci/config.yml

       - store_artifacts:
           path: htmlcov
           destination: htmlcov
+
+  markdown_link_check:
+    docker:
+      - image: circleci/node:12.6.0
+    working_directory: ~/repo
+
+    steps:
+      - checkout
+
+      - restore_cache:
+          keys:
+          - v1-node-dependencies-{{ checksum ".pre-commit-config.yaml" }}
+          # fallback to using the latest cache if no exact match is found
+          - v1-node-dependencies-
+
+      - run:
+          name: Install Dependencies
+          command: |
+            sudo apt-get install python3-venv
+            python3 -m venv venv
+            . venv/bin/activate
+            pip install pre-commit
+      - run: sudo npm install -g markdown-link-check
+
+      - save_cache:
+          paths:
+            - ./venv
+          key: v1-node-dependencies-{{ checksum ".pre-commit-config.yaml" }}
+
+      - run:
+          name: Run markdown-link-check via precommit
+          command: |
+            . venv/bin/activate
+            pre-commit run --hook-stage manual markdown-link-check --all-files
+
+workflows:
+  version: 2
+  build_and_test:
+    jobs:
+      - build
+      - markdown_link_check

.pre-commit-config.yaml

                 .*_pb2.py|
                 .*_pb2_grpc.py
             )$
+# "Local" hooks, see https://pre-commit.com/#repository-local-hooks
+-   repo: local
+    hooks:
+    -   id: markdown-link-check
+        name: markdown-link-check
+        # markdown-link-check doesn't support multiple files on the commandline, so this hacks around that.
+        # Note that you must install the package separately via npm. For example:
+        #  brew install npm; npm install -g markdown-link-check
+        entry: bash -xc 'echo "$@" | xargs -n1 -t markdown-link-check -c markdown-link-check.config.json' --
+        language: system
+        types: [markdown]
+        # Don't check localized files since their target might not be localized.
+        exclude: ".*localized.*"
+        # Only run manually, e.g. pre-commit run --hook-stage manual markdown-link-check
+        stages: [manual]

docs/Training-SAC.md

 In some cases, you might want to bootstrap the agent's policy using behavior recorded
 from a player. This can help guide the agent towards the reward. Pretraining adds
 training operations that mimic a demonstration rather than attempting to maximize reward.
-It is essentially equivalent to running [behavioral cloning](./Training-BehavioralCloning.md)
+It is essentially equivalent to running [behavioral cloning](./Training-Behavioral-Cloning.md)
 in-line with SAC.
 
 To use pretraining, add a `pretraining` section to the trainer_config. For instance:

markdown-link-check.config.json

+{
+    "ignorePatterns": [
+        {
+            "pattern": "^http://localhost",
+            "comment": "Ignore local tensorboard links"
+        },
+        {
+            "pattern": "^https://developer.nvidia.com/compute/machine-learning/cudnn/secure",
+            "comment": "Requires login"
+        }
+    ]
+}