Twirl Template Rules for Bazel

Status	Stardoc
	Stardoc

Overview

rules_twirl compiles Twirl templates to Scala, so they can be used with bazelbuild/rules_scala and lucidsoftware/rules_scala.

Simple Core API: twirl_templates

For more information about Twirl templates, see the Play Twirl documentation.

Installation

rules_twirl isn't yet on the Bazel Central Registry, so you'll need to pull it in via archive_override. Be sure to replace <COMMIT> with latest commit on master and <INTEGRITY> with the hash suggested by Bazel after the dependency is first loaded.

/MODULE.bazel

bazel_dep(name = "rules_twirl")

rules_twirl_version = "<COMMIT>"

archive_override(
    module_name = "rules_twirl",
    integrity = "<INTEGRITY>",
    strip_prefix = "rules_twirl-{}".format(rules_twirl_version),
    urls = ["https://github.com/lucidsoftware/rules_twirl/archive/refs/heads/{}.zip".format(rules_twirl_version)],
)

By default, the Scala 3 version of the Twirl compiler will be used. To change the default to Scala 2.13, add the --@rules_twirl//twirl-toolchain=twirl-2-13 flag to your .bazelrc file.

If you want to use a custom Twirl compiler, you can set up a custom toolchain like so:

/BUILD.bazel

load("@rules_twirl//twirl-toolchain:create-toolchain.bzl", "create_twirl_toolchain")

create_twirl_toolchain(
    name = "twirl-custom",
    twirl_compiler = "<label of your custom Twirl templates compiler>",
)

Then, register your toolchain with Bazel and set it as the default in your .bazelrc file:

/MODULE.bazel

register_toolchains("//:twirl-custom")

/.bazelrc

common --@rules_twirl//twirl-toolchain=twirl-custom

You can find the available versions of the Twirl Compiler CLI on maven: https://mvnrepository.com/artifact/com.lucidchart/twirl-compiler-cli.

Usage

The twirl_templates rule compiles Twirl templates to a source jar that can be used with the rules_scala rules. For example,

twirl_templates(
    name = "twirl-templates",
    source_directory = "app",
    srcs = glob(["app/**/*.scala.html"])
        + glob(["app/**/*.scala.xml"])
        + glob(["app/**/*.scala.js"])
        + glob(["app/**/*.scala.txt"]),
)

scala_binary(
    name = "foo-service",
    srcs = glob(["app/**/*.scala"]) + [":twirl-templates"],
    main_class = "foo.server.RunServer",
    deps = [...],
)

Overriding the default Twirl compiler

To override the default Twirl compiler for a single target, you can change the twirl_toolchain_name attribute on the twirl_routes target. That attribute can be set to the name of any twirl_toolchain registered with twirl_register_toolchains (and created using create_twirl_toolchain). By default twirl-3 and twirl-2-13 are valid values.

For example:

twirl_templates(
    name = "twirl-templates",
    source_directory = "app",
    srcs = glob(["app/**/*.scala.html"])
        + glob(["app/**/*.scala.xml"])
        + glob(["app/**/*.scala.js"])
        + glob(["app/**/*.scala.txt"]),
    twirl_toolchain_name = "twirl-2-13",
)

See the Stardoc documentation for the full list of options for twirl_templates.

Use with the Play Framework

twirl_templates can be used with the rules_play_routes to run a Play Framework service. For example

twirl_templates(
    name = "twirl-templates",
    source_directory = "app",
    include_play_imports = True,
    srcs = glob(["app/**/*.scala.html"])
        + glob(["app/**/*.scala.xml"])
        + glob(["app/**/*.scala.js"])
        + glob(["app/**/*.scala.txt"]),
    additional_imports = [...],
)

play_routes(
    name = "play-routes",
    srcs = ["conf/routes"] + glob(["conf/*.routes"]),
    include_play_imports = True,
    generate_reverse_router = True,
    routes_imports = [...],
)

scala_binary(
    name = "foo-service",
    srcs = glob(["app/**/*.scala"])  + [":twirl-templates", ":play-routes"],
    visibility = ["//visibility:public"],
    main_class = "play.core.server.ProdServerStart",
    resources = ["conf/logback.xml"] + glob(["conf/resources/**/*"]),
    resource_strip_prefix = native.package_name(),
    classpath_resources = ["conf/application.conf"],
    jvm_flags = [
    	  "-Dhttp.port=9000",
    	  "-Dapplication.name=foo-service",
    ],
    deps = [...],
)

Development

Command Line Twirl Compiler

This project consists of the Twirl Bazel rules and a command line Twirl compiler. The command line compiler can be built with

bazel build //twirl-compiler

It can be run with

bazel run //twirl-compiler

Testing

All tests can be run using

test/run_all_tests.sh

They can also be run using

bazel test //test/...

Updating Third Party Dependencies

We use rules_jvm_external to import third party dependencies.

To make changes to the dependencies, simply update the appropriate maven.install call in MODULE.bazel, and then update the dependencies json file used by rules_jvm_external by running the following script:

scripts/gen-deps.sh

Never modify the dependencies json file directly.

Updating Stardoc

Before pushing your changes, make sure you update the documentation by running the following script:

scripts/gen-docs.sh

Failure to do so will result in CI failing.

Releasing

To release a new version to Maven Central:

1. Push a tag with this syntax: P1.P2.P3 where P1.P2.P3 is the Twirl version, e.g., 2.0.7
2. Once the build completes (including the publish step), find the staging repo in Sonatype (assuming you're signed in and have access to the project)
3. Verify all the artifacts are on the staging Repository, and then close it through the Sonatype GUI
4. Once Sonatype's pre-release checks on the repository complete, release it through the Sonatype GUI
5. Verify the artifact's present in Maven Central (it can take multiple hours for everything to sync)