Travis: cache bazel builds between runs. (#181)

Author: g-easy

.travis.yml

@@ -9,19 +9,32 @@ matrix:
       env: BAZEL_OS=darwin
 
 compiler: clang
+
+# - Limit memory.
+# - Enable thread safety analysis (only works with clang).
 env: BAZEL_OPTIONS="--local_resources=4096,2,1.0 --copt=-Werror=thread-safety"
 
+cache:
+  directories:
+    - $HOME/bazel-cache
+
 before_install:
   # OS X does not have clang-format by default, and has a different sed.
   - if \[ "$TRAVIS_OS_NAME" == "linux" \]; then
       tools/format.sh ;
     fi
-  - wget https://github.com/bazelbuild/bazel/releases/download/0.11.1/bazel-0.11.1-installer-${BAZEL_OS}-x86_64.sh
-  - chmod +x bazel-0.11.1-installer-${BAZEL_OS}-x86_64.sh
-  - ./bazel-0.11.1-installer-${BAZEL_OS}-x86_64.sh --user
+  - wget https://github.com/bazelbuild/bazel/releases/download/0.17.1/bazel-0.17.1-installer-${BAZEL_OS}-x86_64.sh
+  - chmod +x bazel-0.17.1-installer-${BAZEL_OS}-x86_64.sh
+  - ./bazel-0.17.1-installer-${BAZEL_OS}-x86_64.sh --user
+  - echo "build --disk_cache=$HOME/bazel-cache" > ~/.bazelrc
+  - echo "build --experimental_strict_action_env" >> ~/.bazelrc
 
 script:
-  # We can't use --noshow_progress because Travis terminates the
-  # build after 10 mins without output.
+  # Limit the amount of progress output. We can't use --noshow_progress because
+  # Travis terminates the build after 10 mins without output.
   - bazel build $BAZEL_OPTIONS --experimental_ui_actions_shown=1 -k $(bazel query "kind(rule, //...)" | grep -v :_)
   - bazel test $BAZEL_OPTIONS --experimental_ui_actions_shown=1 -k $(bazel query "kind(test, //...) except attr('tags', 'manual|noci', //...)" | grep -v :_)
+
+before_cache:
+  # Before uploading cache.
+  - du -sk $HOME/bazel-cache