Add checkout steps

.azure/build_and_test.yml

@@ -17,13 +17,13 @@ variables:
 - template: variables/common.yml
 
 stages:
-  - stage: Build
-    jobs:
-    - template: jobs/build.yml
-      parameters:
-        container: release
-  - stage: Test
-    jobs:
-    - template: jobs/test.yml
-      parameters:
-        container: release
+- stage: Build
+  jobs:
+  - template: jobs/build.yml
+    parameters:
+      container: release
+- stage: Test
+  jobs:
+  - template: jobs/test.yml
+    parameters:
+      container: release

.azure/jobs/build.yml

@@ -8,4 +8,4 @@ jobs:
   pool: ${{ parameters.pool }}
   container: ${{ parameters.container }}
   steps:
-  - script: echo Building!
+  - template: steps/checkout_source.yml

.azure/jobs/steps/checkout_source.yml

@@ -0,0 +1,36 @@
+parameters:
+  name: 'Build'
+  pool: 'Default'
+  container: ''
+
+steps:
+- script: |
+    mkdir -p $ROS_WS
+    ln -s /opt/ros/$ROS_DISTRO $ROS_WS/install
+    echo $CACHE_NONCE | \
+      (echo cache_nonce && cat) >> $ROS_WS/checksum.txt
+    sha256sum $ROS_WS/checksum.txt >> $ROS_WS/checksum.txt
+    TZ=utc stat -c '%y' /ros_entrypoint.sh | \
+      (echo ros_entrypoint && cat) >> $ROS_WS/checksum.txt
+    sha256sum $ROS_WS/checksum.txt >> $ROS_WS/checksum.txt
+    rm -rf $OVERLAY_WS/*
+  displayName: Pre Checkout
+  name: pre_checkout
+- checkout: self
+  path: "${{ variables.OVERLAY_WS }}/src/navigation2"
+- script: |
+    rm $OVERLAY_WS/src/navigation2/nav2_system_tests/COLCON_IGNORE
+    if ! cmp \
+      $OVERLAY_WS/src/navigation2/tools/ros2_dependencies.repos \
+      $UNDERLAY_WS/ros2_dependencies.repos >/dev/null 2>&1
+    then
+      echo "Cleaning Underlay"
+      rm -rf $UNDERLAY_WS/*
+      cp $OVERLAY_WS/src/navigation2/tools/ros2_dependencies.repos \
+        $UNDERLAY_WS/ros2_dependencies.repos
+      mkdir -p $UNDERLAY_WS/src
+      vcs import $UNDERLAY_WS/src \
+        < $UNDERLAY_WS/ros2_dependencies.repos
+    fi
+  displayName: Post Checkout
+  name: post_checkout