Building with Bazel

This guide explains how to build and test Angular apps with Bazel.

This guide assumes you are already familiar with developing and building Angular applications using the CLI.

It describes features which are part of Angular Labs, and are not considered a stable, supported API.

Using Bazel with the Angular CLI

The @angular/bazel package provides a builder that allows Angular CLI to use Bazel as the build tool.

To opt-in an existing application, run

ng add @angular/bazel

To use Bazel in a new application, first install @angular/bazel globally

npm install -g @angular/bazel

then create the new application with

ng new --collection=@angular/bazel

Now when you use Angular CLI build commands such as ng build and ng serve, Bazel is used behind the scenes. Outputs from Bazel appear in the dist/bin folder.

The command-line output includes extra logging from Bazel. We plan to reduce this in the future.

Removing Bazel

If you need to opt-out from using Bazel, you can restore the backup files:

• /angular.json.bak replaces /angular.json

Advanced configuration

Editing the Bazel configuration may prevent you opting out of Bazel. Custom behaviors driven by Bazel won't be available in other Builders.

This section assumes you are familiar with Bazel.

You can manually adjust the Bazel configuration to:

• customize the build steps
• parallellize the build for scale and incrementality

Create the initial Bazel configuration files by running the following command:

ng build --leaveBazelFilesOnDisk

Now you'll find new files in the Angular workspace:

• /WORKSPACE tells Bazel how to download external dependencies.
• /BUILD.bazel and /src/BUILD.bazel tell Bazel about your source code.

You can find a full-featured example with custom Bazel configurations at https://github.com/bazelbuild/rules_nodejs/tree/master/examples/angular.

Documentation for using Bazel for frontend projects is linked from https://docs.bazel.build/versions/master/bazel-and-javascript.html.

Running Bazel directly

In some cases you'll want to bypass the Angular CLI builder, and run the Bazel CLI directly. The Bazel tool is managed by the @bazel/bazelisk package (similar to how Node.js can be managed by nvm). You can install it globally to get the bazelisk command in your path, or use $(npm bin)/bazelisk in place of bazelisk below.

The common commands in Bazel are:

• bazelisk build [targets]: Compile the default output artifacts of the given targets.
• bazelisk test [targets]: For whichever *_test targets are found in the patterns, run the tests.
• bazelisk run [target]: Compile the program represented by target, and then run it.

To repeat the command any time the inputs change (watch mode), replace bazelisk with ibazel in these commands.

The output locations are printed in the output.

Full documentation for the Bazel CLI is at https://docs.bazel.build/versions/master/command-line-reference.html.

Querying the build graph

Because Bazel constructs a graph out of your targets, you can find lots of useful information.

Using the graphviz optional dependency, you'll have a program dot, which you can use with bazel query:

$ bazel query --output=graph ... | dot -Tpng > graph.png

See https://docs.bazel.build/versions/master/query-how-to.html for more details on bazel query.

Customizing BUILD.bazel files

"Rules" are like plugins for Bazel. Many rule sets are available. This guide documents the ones maintained by the Angular team at Google.

Rules are used in BUILD.bazel files, which are markers for the packages in your workspace. Each BUILD.bazel file declares a separate package to Bazel, though you can have more coarse-grained distributions so that the packages you publish (for example, to npm) can be made up of many Bazel packages.

In the BUILD.bazel file, each rule must first be imported, using the load statement. Then the rule is called with some attributes, and the result of calling the rule is that you've declared to Bazel how it can derive some outputs given some inputs and dependencies. Then later, when you run a bazel command line, Bazel loads all the rules you've declared to determine an absolute ordering of what needs to be run. Note that only the rules needed to produce the requested output will actually be executed.

A list of common rules for frontend development is documented in the README at https://github.com/bazelbuild/rules_nodejs/.