install.md

TypeScript rules for Bazel

The TypeScript rules integrate the TypeScript compiler with Bazel.

Alternatives

This package provides Bazel wrappers around the TypeScript compiler.

At a high level, there are two alternatives provided: ts_project and ts_library. This section describes the trade-offs between these rules.

ts_project simply runs tsc --project, with Bazel knowing which outputs to expect based on the TypeScript compiler options, and with interoperability with other TypeScript rules via a Bazel Provider (DeclarationInfo) that transmits the type information. It is intended as an easy on-boarding for existing TypeScript code and should be familiar if your background is in frontend ecosystem idioms. Any behavior of ts_project should be reproducible outside of Bazel, with a couple of caveats noted in the rule documentation below.

We used to recommend using the tsc rule directly from the typescript project, like load("@npm//typescript:index.bzl", "tsc") However ts_project is strictly better and should be used instead.

ts_library is an open-sourced version of the rule we use to compile TS code at Google. It should be familiar if your background is in Bazel idioms. It is very complex, involving code generation of the tsconfig.json file, a custom compiler binary, and a lot of extra features. It is also opinionated, and may not work with existing TypeScript code. For example:

• Your TS code must compile under the --declaration flag so that downstream libraries depend only on types, not implementation. This makes Bazel faster by avoiding cascading rebuilds in cases where the types aren't changed.
• We control the output format and module syntax so that downstream rules can rely on them.

On the other hand, ts_library is also fast and optimized. We keep a running TypeScript compile running as a daemon, using Bazel workers. This process avoids re-parse and re-JIT of the >1MB typescript.js and keeps cached bound ASTs for input files which saves time. We also produce JS code which can be loaded faster (using named AMD module format) and which can be consumed by the Closure Compiler (via integration with tsickle).

Installation

Add a devDependency on @bazel/typescript

$ yarn add -D @bazel/typescript
# or
$ npm install --save-dev @bazel/typescript

Watch for any peerDependency warnings - we assume you have already installed the typescript package from npm.

Some rules require you to add this to your WORKSPACE file:

# Set up TypeScript toolchain
load("@npm//@bazel/typescript:index.bzl", "ts_setup_workspace")
ts_setup_workspace()

Create a BUILD.bazel file in your workspace root. If your tsconfig.json file is in the root, use

exports_files(["tsconfig.json"], visibility = ["//visibility:public"])

otherwise create an alias:

alias(
    name = "tsconfig.json",
    actual = "//path/to/my:tsconfig.json",
)

Make sure to remove the --noEmit compiler option from your tsconfig.json. This is not compatible with the ts_library rule.

Self-managed npm dependencies

We recommend you use Bazel managed dependencies but if you would like Bazel to also install a node_modules in your workspace you can also point the node_repositories repository rule in your WORKSPACE file to your package.json.

node_repositories(package_json = ["//:package.json"])

You can then run yarn in your workspace with:

$ bazel run @nodejs//:yarn_node_repositories

To use your workspace node_modules folder as a dependency in ts_library and other rules, add the following to your root BUILD.bazel file:

filegroup(
    name = "node_modules",
    srcs = glob(
        include = [
          "node_modules/**/*.js",
          "node_modules/**/*.d.ts",
          "node_modules/**/*.json",
          "node_modules/.bin/*",
        ],
        exclude = [
          # Files under test & docs may contain file names that
          # are not legal Bazel labels (e.g.,
          # node_modules/ecstatic/test/public/中文/檔案.html)
          "node_modules/**/test/**",
          "node_modules/**/docs/**",
          # Files with spaces in the name are not legal Bazel labels
          "node_modules/**/* */**",
          "node_modules/**/* *",
        ],
    ),
)

# Create a tsc_wrapped compiler rule to use in the ts_library
# compiler attribute when using self-managed dependencies
nodejs_binary(
    name = "@bazel/typescript/tsc_wrapped",
    entry_point = "@bazel/typescript/internal/tsc_wrapped/tsc_wrapped.js",
    # Point bazel to your node_modules to find the entry point
    node_modules = ["//:node_modules"],
)

See https://github.com/bazelbuild/rules_nodejs#dependencies for more information on managing npm dependencies with Bazel.

Customizing the TypeScript compiler binary

An example use case is needing to increase the NodeJS heap size used for compilations.

Similar to above, you declare your own binary for running tsc_wrapped, e.g.:

nodejs_binary(
    name = "tsc_wrapped_bin",
    entry_point = "@npm//:node_modules/@bazel/typescript/internal/tsc_wrapped/tsc_wrapped.js",
    templated_args = [
        "--node_options=--max-old-space-size=2048",
    ],
    data = [
        "@npm//protobufjs",
        "@npm//source-map-support",
        "@npm//tsutils",
        "@npm//typescript",
        "@npm//@bazel/typescript",
    ],
)

then refer to that target in the compiler attribute of your ts_library rule.

Note that nodejs_binary targets generated by npm_install/yarn_install can include data dependencies on packages which aren't declared as dependencies. For example, if you use [tsickle] to generate Closure Compiler-compatible JS, then it needs to be a data dependency of tsc_wrapped so that it can be loaded at runtime.  [tsickle]: https://github.com/angular/tsickle

Usage

Compiling TypeScript: ts_library

The ts_library rule invokes the TypeScript compiler on one compilation unit, or "library" (generally one directory of source files).

Create a BUILD file next to your sources:

package(default_visibility=["//visibility:public"])
load("//packages/typescript:index.bzl", "ts_library")

ts_library(
    name = "my_code",
    srcs = glob(["*.ts"]),
    deps = ["//path/to/other:library"],
)

If your ts_library target has npm dependencies you can specify these with fine grained npm dependency targets created by the yarn_install or npm_install rules:

ts_library(
    name = "my_code",
    srcs = glob(["*.ts"]),
    deps = [
      "@npm//@types/node",
      "@npm//@types/foo",
      "@npm//foo",
      "//path/to/other:library",
    ],
)

You can also use the @npm//@types target which will include all packages in the @types scope as dependencies.

If you are using self-managed npm dependencies, you can use the node_modules attribute in ts_library and point it to the //:node_modules filegroup defined in your root BUILD.bazel file. You'll also need to override the compiler attribute if you do this as the Bazel-managed deps and self-managed cannot be used together in the same rule.

ts_library(
    name = "my_code",
    srcs = glob(["*.ts"]),
    deps = ["//path/to/other:library"],
    node_modules = "//:node_modules",
    compiler = "//:@bazel/typescript/tsc_wrapped",
)

To build a ts_library target run:

bazel build //path/to/package:target

The resulting .d.ts file paths will be printed. Additionally, the .js outputs from TypeScript will be written to disk, next to the .d.ts files ¹.

Note that the tsconfig.json file used for compilation should be the same one your editor references, to keep consistent settings for the TypeScript compiler. By default, ts_library uses the tsconfig.json file in the workspace root directory. See the notes about the tsconfig attribute in the ts_library API docs.

¹ The declarationDir compiler option will be silently overwritten if present.

Accessing JavaScript outputs

The default output of the ts_library rule is the .d.ts files. This is for a couple reasons:

• help ensure that downstream rules which access default outputs will not require a cascading re-build when only the implementation changes but not the types
• make you think about whether you want the devmode (named UMD) or prodmode outputs

You can access the JS output by adding a filegroup rule after the ts_library, for example

ts_library(
    name = "compile",
    srcs = ["thing.ts"],
)

filegroup(
    name = "thing.js",
    srcs = ["compile"],
    # Change to es6_sources to get the 'prodmode' JS
    output_group = "es5_sources",
)

my_rule(
    name = "uses_js",
    deps = ["thing.js"],
)

Serving TypeScript for development

There are two choices for development mode:

1. Use the ts_devserver rule to bring up our simple, fast development server. This is intentionally very simple, to help you get started quickly. However, since there are many development servers available, we do not want to mirror their features in yet another server we maintain.
2. Teach your real frontend server to serve files from Bazel's output directory. This is not yet documented. Choose this option if you have an existing server used in development mode, or if your requirements exceed what the ts_devserver supports. Be careful that your development round-trip stays fast (should be under two seconds).

To use ts_devserver, you simply load the rule, and call it with deps that point to your ts_library target(s):

load("//packages/typescript:index.bzl", "ts_devserver", "ts_library")

ts_library(
    name = "app",
    srcs = ["app.ts"],
)

ts_devserver(
    name = "devserver",
    # We'll collect all the devmode JS sources from these TypeScript libraries
    deps = [":app"],
    # This is the path we'll request from the browser, see index.html
    serving_path = "/bundle.js",
    # The devserver can serve our static files too
    static_files = ["index.html"],
)

The index.html should be the same one you use for production, and it should load the JavaScript bundle from the path indicated in serving_path.

If you don't have an index.html file, a simple one will be generated by the ts_devserver.

See examples/app in this repository for a working example. To run the devserver, we recommend you use ibazel:

$ ibazel run examples/app:devserver

ibazel will keep the devserver program running, and provides a LiveReload server so the browser refreshes the application automatically when each build finishes.

Writing TypeScript code for Bazel

Bazel's TypeScript compiler has your workspace path mapped, so you can import from an absolute path starting from your workspace.

/WORKSPACE:

workspace(name = "myworkspace")

/some/long/path/to/deeply/nested/subdirectory.ts:

import {thing} from 'myworkspace/place';

will import from /place.ts.

Since this is an extension to the vanilla TypeScript compiler, editors which use the TypeScript language services to provide code completion and inline type checking will not be able to resolve the modules. In the above example, adding

"paths": {
    "myworkspace/*": ["*"]
}

to tsconfig.json will fix the imports for the common case of using absolute paths. See path mapping for more details on the paths syntax.

Similarly, you can use path mapping to teach the editor how to resolve imports from ts_library rules which set the module_name attribute.

Notes

If you'd like a "watch mode", try ibazel.

At some point, we plan to release a tool similar to gazelle to generate the BUILD files from your source code.

API documentation