# TypeScript rules for Bazel

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**WARNING: this is beta-quality software. Breaking changes are likely. Not recommended for production use without expert support.**

The TypeScript rules integrate the TypeScript compiler with Bazel.

## API Docs

Generated documentation for using each rule is at:
http://tsetse.info/api/

## Installation

First, install a current Bazel distribution.

Create a `BUILD.bazel` file in your project root:

```python
package(default_visibility = ["//visibility:public"])
exports_files(["tsconfig.json"])

# NOTE: this will move to node_modules/BUILD in a later release
filegroup(name = "node_modules", srcs = glob([
    "node_modules/**/*.js",
    "node_modules/**/*.d.ts",
    "node_modules/**/*.json",
]))
```

Next create a `WORKSPACE` file in your project root (or edit the existing one)
containing:

```python
# TypeScript rules depend on running Node.js.
http_archive(
    name = "build_bazel_rules_nodejs",
    url = "https://github.com/bazelbuild/rules_nodejs/archive/0.8.0.zip",
    strip_prefix = "rules_nodejs-0.8.0",
    sha256 = "4e40dd49ae7668d245c3107645f2a138660fcfd975b9310b91eda13f0c973953",
)

# ts_web_test depends on the web testing rules to provision browsers.
http_archive(
    name = "io_bazel_rules_webtesting",
    url = "https://github.com/bazelbuild/rules_webtesting/archive/v0.2.0.zip",
    strip_prefix = "rules_webtesting-0.2.0",
    sha256 = "cecc12f07e95740750a40d38e8b14b76fefa1551bef9332cb432d564d693723c",
)

# ts_devserver depends on the Go rules.
# See https://github.com/bazelbuild/rules_go#setup for the latest version.
http_archive(
    name = "io_bazel_rules_go",
    url = "https://github.com/bazelbuild/rules_go/releases/download/0.8.1/rules_go-0.8.1.tar.gz",
    sha256 = "90bb270d0a92ed5c83558b2797346917c46547f6f7103e648941ecdb6b9d0e72",
)

# Include @bazel/typescript in package.json#devDependencies
local_repository(
    name = "build_bazel_rules_typescript",
    path = "node_modules/@bazel/typescript",
)

load("@build_bazel_rules_nodejs//:defs.bzl", "node_repositories")

# Point to the package.json file so Bazel can run the package manager for you.
node_repositories(package_json = ["//:package.json"])

load("@io_bazel_rules_go//go:def.bzl", "go_rules_dependencies", "go_register_toolchains")

go_rules_dependencies()
go_register_toolchains()

load("@io_bazel_rules_webtesting//web:repositories.bzl", "browser_repositories", "web_test_repositories")

web_test_repositories()
browser_repositories(
    chromium = True,
)

load("@build_bazel_rules_typescript//:defs.bzl", "ts_setup_workspace")

ts_setup_workspace()
```

We recommend using the Yarn package manager, because it has a built-in command
to verify the integrity of your `node_modules` directory.
You can run the version Bazel has already installed:

```sh
$ bazel run @yarn//:yarn
```

## 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:

```python
package(default_visibility=["//visibility:public"])
load("@build_bazel_rules_typescript//:defs.bzl", "ts_library")

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

Then build it:

`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 <sup>1</sup>.

> <sup>1</sup> The
> [declarationDir](https://www.typescriptlang.org/docs/handbook/compiler-options.html)
> compiler option will be silently overwritten if present.

### 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.
1. 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):

```python
load("@build_bazel_rules_typescript//:defs.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]:

```sh
$ 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.

[ibazel]: https://github.com/bazelbuild/bazel-watcher

## 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`:
```python
workspace(name = "myworkspace")
```

`/some/long/path/to/deeply/nested/subdirectory.ts`:
```javascript
import {thing} from 'myworkspace/place';
```

will import from `/place.ts`.


Since this is an extension to the vanillia 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
```json
"paths": {
    "myworkspace/*": ["*"]
}
```
to `tsconfig.json` will fix the imports for the common case of using absolute paths.
See https://www.typescriptlang.org/docs/handbook/module-resolution.html#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 https://github.com/bazelbuild/bazel-watcher
(note, it's also quite new).

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

In the meantime, we suggest associating the `.bazel` extension with Python in
your editor, so that you get useful syntax highlighting.

[gazelle]: https://github.com/bazelbuild/rules_go/tree/master/go/tools/gazelle

### Releasing

Start from a clean checkout at master/HEAD. Check if there are any breaking
changes since the last tag - if so, this will be a minor, if not, it's a patch.
(This may not sound like semver - but since our major version is a zero, the
rule is that minors are breaking changes and patches are new features).

```sh
yarn skydoc
git commit -a -m 'Update docs for release'
npm config set tag-version-prefix ''
npm version minor -m 'rel: %s' # Replace minor with patch if no breaking changes
git push
git push --tags
npm publish
```