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Building Angular with Bazel

Note: this doc is for developing Angular, it is not public documentation for building an Angular application with Bazel.

The Bazel build tool (http://bazel.build) provides fast, reliable incremental builds. We plan to migrate Angular's build scripts to Bazel.

Installation

In order to ensure that everyone builds Angular in a consistent way, Bazel will be installed through NPM and therefore it's not necessary to install Bazel manually.

The binaries for Bazel will be provided by the @bazel/bazel NPM package and its platform-specific dependencies.

You can access Bazel with the yarn bazel command

Configuration

The WORKSPACE file indicates that our root directory is a Bazel project. It contains the version of the Bazel rules we use to execute build steps, from build_bazel_rules_typescript. The sources on GitHub are published from Google's internal repository (google3).

Bazel accepts a lot of options. We check in some options in the .bazelrc file. See the bazelrc doc. For example, if you don't want Bazel to create several symlinks in your project directory (bazel-*) you can add the line build --symlink_prefix=/ to your .bazelrc file.

Building Angular

  • Build a package: yarn bazel build packages/core
  • Build all packages: yarn bazel build packages/...

You can use ibazel to get a "watch mode" that continuously keeps the outputs up-to-date as you save sources. Note this is new as of May 2017 and not very stable yet.

Testing Angular

  • Test package in node: yarn bazel test packages/core/test:test
  • Test package in karma: yarn bazel test packages/core/test:test_web
  • Test all packages: yarn bazel test packages/...

You can use ibazel to get a "watch mode" that continuously keeps the outputs up-to-date as you save sources.

Various Flags Used For Tests

If you're experiencing problems with seemingly unrelated tests failing, it may be because you're not using the proper flags with your Bazel test runs in Angular.

See also: //.bazelrc where --define=compile=legacy is defined as default.

  • --config=debug: build and launch in debug mode (see debugging instructions below)
  • --test_arg=--node_options=--inspect=9228: change the inspector port.
  • --define=compile=<option> Controls if ivy or legacy mode is enabled. This switches which compiler is used (ngc, ngtsc, or a tsc pass-through mode).
    • legacy: (default behavior) compile against View Engine, e.g. --define=compile=legacy
    • jit: Compile in ivy JIT mode, e.g. --define=compile=jit
    • aot: Compile in ivy AOT move, e.g. --define=compile=aot
  • --test_tag_filters=<tag>: filter tests down to tags defined in the tag config of your rules in any given BUILD.bazel.
    • no-ivy-aot: Useful for excluding build and test targets that are not meant to be executed in Ivy AOT mode (--define=compile=aot).
    • no-ivy-jit: Useful for excluding build and test targets that are not meant to be executed in Ivy JIT mode (--define=compile=jit).
    • ivy-only: Useful for excluding all Ivy build and tests targets with --define=compile=legacy.
    • fixme-ivy-aot: Useful for including/excluding build and test targets that are currently broken in Ivy AOT mode (--define=compile=aot).
    • fixme-ivy-jit: Useful for including/excluding build and test targets that are currently broken in Ivy JIT mode (--define=compile=jit).

Debugging a Node Test

  • Open chrome at: chrome://inspect
  • Click on Open dedicated DevTools for Node to launch a debugger.
  • Run test: yarn bazel test packages/core/test:test --config=debug

The process should automatically connect to the debugger. For additional info and testing options, see the nodejs_test documentation.

Debugging a Node Test in VSCode

First time setup:

  • Go to Debug > Add configuration (in the menu bar) to open launch.json
  • Add the following to the configurations array:
        {
            "name": "Attach (inspect)",
            "type": "node",
            "request": "attach",
            "port": 9229,
            "address": "localhost",
            "restart": false,
            "sourceMaps": true,
            "localRoot": "${workspaceRoot}",
            "remoteRoot": null
        },
        {
            "name": "Attach (no-sm,inspect)",
            "type": "node",
            "request": "attach",
            "port": 9229,
            "address": "localhost",
            "restart": false,
            "sourceMaps": false,
            "localRoot": "${workspaceRoot}",
            "remoteRoot": null
        },

Setting breakpoints directly in your code files may not work in VSCode. This is because the files you're actually debugging are built files that exist in a ./private/... folder. The easiest way to debug a test for now is to add a debugger statement in the code and launch the bazel corresponding test (yarn bazel test <target> --config=debug).

Bazel will wait on a connection. Go to the debug view (by clicking on the sidebar or Apple+Shift+D on Mac) and click on the green play icon next to the configuration name (ie Attach (inspect)).

Debugging a Karma Test

Debugging Bazel rules

Open external directory which contains everything that bazel downloaded while executing the workspace file:

open $(bazel info output_base)/external

See subcommands that bazel executes (helpful for debugging):

yarn bazel build //packages/core:package -s

To debug nodejs_binary executable paths uncomment find . -name rollup 1>&2 (~ line 96) in

open $(bazel info output_base)/external/build_bazel_rules_nodejs/internal/node_launcher.sh

Stamping

Bazel supports the ability to include non-hermetic information from the version control system in built artifacts. This is called stamping. You can see an overview at https://www.kchodorow.com/blog/2017/03/27/stamping-your-builds/ In our repo, here is how it's configured:

  1. In tools/bazel_stamp_vars.sh we run the git commands to generate our versioning info.
  2. In .bazelrc we register this script as the value for the workspace_status_command flag. Bazel will run the script when it needs to stamp a binary.

Note that Bazel has a --stamp argument to yarn bazel build, but this has no effect since our stamping takes place in Skylark rules. See https://github.com/bazelbuild/bazel/issues/1054

Remote cache

Bazel supports fetching action results from a cache, allowing a clean build to pick up artifacts from prior builds. This makes builds incremental, even on CI. It works because Bazel assigns a content-based hash to all action inputs, which is used as the cache key for the action outputs. Thanks to the hermeticity property, we can skip executing an action if the inputs hash is already present in the cache.

Of course, non-hermeticity in an action can cause problems. At worst, you can fetch a broken artifact from the cache, making your build non-reproducible. For this reason, we are careful to implement our Bazel rules to depend only on their inputs.

Currently we only use remote caching on CircleCI. We could enable it for developer builds as well, which would make initial builds much faster for developers by fetching already-built artifacts from the cache.

This feature is experimental, and developed by the CircleCI team with guidance from Angular. Contact Alex Eagle with questions.

How it's configured:

  1. In .circleci/config.yml, each CircleCI job downloads a proxy binary, which is built from https://github.com/notnoopci/bazel-remote-proxy. The download is done by running .circleci/setup_cache.sh. When the feature graduates from experimental, this proxy will be installed by default on every CircleCI worker, and this step will not be needed.
  2. Next, each job runs the setup-bazel-remote-cache anchor. This starts up the proxy running in the background. In the CircleCI UI, you'll see this step continues running while later steps run, and you can see logging from the proxy process.
  3. Bazel must be configured to connect to the proxy on a local port. This configuration lives in .circleci/bazel.rc and is enabled because we overwrite the system Bazel settings in /etc/bazel.bazelrc with this file.
  4. Each bazel command in .circleci/config.yml picks up and uses the caching flags.

Known issues

Webstorm

The autocompletion in WebStorm can be added via a Bazel plugin intended for IntelliJ IDEA, but the plugin needs to be installed in a special way. See bazelbuild/intellij#246 for more info.

Xcode

If you see the following error:

$ yarn bazel build packages/...
ERROR: /private/var/tmp/[...]/external/local_config_cc/BUILD:50:5: in apple_cc_toolchain rule @local_config_cc//:cc-compiler-darwin_x86_64: Xcode version must be specified to use an Apple CROSSTOOL
ERROR: Analysis of target '//packages/core/test/render3:render3' failed; build aborted: Analysis of target '@local_config_cc//:cc-compiler-darwin_x86_64' failed; build aborted

It might be linked to an interaction with VSCode. If closing VSCode fixes the issue, you can add the following line to your VSCode configuration:

"files.exclude": {"bazel-*": true}

source: https://github.com/bazelbuild/bazel/issues/4603

If VSCode is not the root cause, you might try:

  • Quit VSCode (make sure no VSCode is running).
bazel clean --expunge
sudo xcode-select -s /Applications/Xcode.app/Contents/Developer
sudo xcodebuild -license
yarn bazel build //packages/core    # Run a build outside VSCode to pre-build the xcode; then safe to run VSCode

Source: https://stackoverflow.com/questions/45276830/xcode-version-must-be-specified-to-use-an-apple-crosstool