Update CI workflow for nbfmt and nblint

Author: lamberta

.github/workflows/ci.yaml

@@ -1,8 +1,13 @@
+# Pass/fail checks for continuous integration testing.
+# Webhook events: Pull requests
 name: CI
-on: pull_request
+on:
+  pull_request:
+    paths:
+    - "site/en/**"
 
 jobs:
-  notebook_format:
+  nbfmt:
     name: Notebook format
     runs-on: ubuntu-latest
     steps:
@@ -15,10 +20,34 @@ jobs:
     - name: Check notebook formatting
       run: |
         # Only check notebooks modified in this pull request.
-        notebooks="$(git diff --name-only master | grep '\.ipynb$' || true)"
-        if [[ -n "$notebooks" ]]; then
-          echo "Check formatting with nbfmt:"
-          python3 -m tensorflow_docs.tools.nbfmt --test $notebooks
+        readarray -t changed_notebooks < <(git diff --name-only master | grep '\.ipynb$' || true)
+        if [[ ${#changed_notebooks[@]} == 0 ]]; then
+          echo "No notebooks modified in this pull request."
+          exit 0
         else
+          echo "Check formatting with nbfmt:"
+          python3 -m tensorflow_docs.tools.nbfmt --test "${changed_notebooks[@]}"
+        fi
+
+  nblint:
+    name: Notebook lint
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/setup-python@v1
+    - uses: actions/checkout@v2
+    - name: Fetch master branch
+      run: git fetch -u origin master:master
+    - name: Install tensorflow-docs
+      run: python3 -m pip install -U git+https://github.com/tensorflow/docs
+    - name: Lint notebooks
+      run: |
+        # Only check notebooks modified in this pull request. (Ignore en-snapshot)
+        readarray -t changed_notebooks < <(git diff --name-only master | grep '\.ipynb$' || true)
+        if [[ ${#changed_notebooks[@]} == 0 ]]; then
           echo "No notebooks modified in this pull request."
+          exit 0
+        else
+          echo "Lint check with nblint:"
+          python3 -m tensorflow_docs.tools.nblint \
+            --arg=repo:tensorflow/docs "${changed_notebooks[@]}"
         fi