Writing Rust Plugins

Rust plugins are the recommended way to write your plugins cause Rust plugins are much faster and powerful than Js Plugins. A Rust plugin is a struct that implements farmfe_core::plugin::Plugin trait, example:

Note for a Rust plugin struct:

• The struct must be pub and #[farm_plugin] attribute is required.
• The struct must implement Plugin trait, and the name method must be implemented.
• The struct must export a new method that accepts 2 arguments for initialization, the first argument is &Config and the second argument is String. The new method is called when the plugin is loaded, and the Config is the farm project config, and the String is the plugin options.

We also provide a Rust plugin example repository: farm-rust-plugin-example.

note

This document only covers how to create, develop and publish a rust plugin, for more detail about the plugin hooks, see Plugin Hooks.

Conventions

For farm specific Rust plugins:

• The Farm plugin should have a name with a farm-plugin- prefix and clear semantics.
• Include the farm-plugin- keyword in package.json.

If your plugin is only applicable to a specific framework, its name should follow the following prefix format:

• farm-plugin-vue-: Prefix as a Vue plugin
• farm-plugin-react-: Prefix as a React plugin
• farm-plugin-svelte-: Prefix as a svelte plugin
• ...

Concepts

Before you start to write your rust plugin, you should know the following concepts:

• module_type: The type of the module, it can be js, ts, css, sass, json, etc. Farm supports js/ts/jsx/tsx, css, html, json, static assets(png, svg, etc) natively. module_type is returned by load hook. You can extend natively supported module type by Rust plugins the same as Farm internal plugins.
• resolved_path and module_id: resolved_path is the absolute path of the module, and module_id is the unique id of the module, it's usually relative path of the module from the project root + query. For example, we import a module as import './a?query', the resolved_path is /project/src/a.ts and the module_id is src/a.ts?query.
• context: All the hooks in the plugin accept a context argument, it's the compilation context of the farm project, you can use it to get the ModuleGraph, Module, Resources, etc.
• Resource and Resource Pot: Resource is the final output bundle file, and Resource Pot is the abstract representation of the resource, similar to Chunk of other bundlers. Inside Farm, first we will generate Resource Pots from ModuleGraph, render Resource Pots and finally generate Resources from Resource Pots.

Module Type

In Farm, every thing is First Class Citizens, so Farm designs module_type to identify the type of a module and handle different kinds of ModuleTypes in different plugins.

module_type returned by load hook, and can be transformed by transform hook. Farm supports js/ts/jsx/tsx, css, html, json, static assets(png, svg, etc) natively. For these module types, you can return them directly in load or transform hook directly. But if you want to handle custom module types, you may need to implement ohter hooks like parse, render_resource_pot_modules, generate resources, etc to control how to parse, render and generate resources for the custom module types.

Create Plugin

Farm provides official templates to help your create your rust plugins quickly:

pnpm

npm

yarn

then follow the prompts to create your plugin.

or you can create a plugin derectly by running the following command:

pnpm

npm

yarn

Above command will create new rust plugin with name my-farm-plugin in the current directory. --type can be rust or js

Plugin Project Structure

The plugin project structure is as follows:

Notable files and directories:

• src/lib.rs: The main file of the plugin, where you define your plugin.
• Cargo.toml: The manifest file for Rust.
• package.json: The manifest file for npm.
• npm: Where your platform specific binary packages placed. These packages should be published to npm registry before publish the plugin.
• .github/workflows: Used to cross build and publish your plugin in github actions.
• rust-toolchain.toml: The rust toolchain file, it should not be modified manually, it should always using the same version as the farm core.

Farm provides a tool(@farmfe/plugin-tools) to help you build and publish your rust plugin, see package.json:

More detail about building and publishing your plugin, see buidling and publishing sections.

Develop Plugin

To develop and test your plugin locally, you should build your plugin for your platform first, run:

Then you can use the built plugin in your farm project by adding the plugin to the plugins field in farm.config.ts:

and execute pnpm i in your farm project, and run farm start to start your farm project with your plugin.

when you make changes to your plugin, you should rebuild your plugin and restart your farm project to see the changes. for example, add load hook to your plugin:

src/lib.rs

Then rebuild your plugin with pnpm build and restart your farm project with farm start, you will see the load hook is called when compiling your farm project.

note

For more detail about the plugin hooks, see Plugin Hooks.

Handle ModuleType

module_type is returned by the load hook or transform hook. Your set any module type to the module in the load hook, and the module will be processed by the corresponding plugin that supports the module type.

For native supported module types, you can just return the module type in the load hook:

src/lib.rs

For non-native supported module types, you should use transform hook to transform the module type to a native supported module type, otherwise you need to implement parse, renderResourcePot hook to handle your custom module type:

src/lib.rs

note

Module type guard like matches!(param.module_type, ModuleType::Custom("sass")) is required in the transform hook, cause the transform hook will be called for all module types, and you should only handle your custom module type in the transform hook. So do the parse and other hooks.

or implement parse, render_resource_pot_modules hook to handle your custom module type, see how native farm css plugin handle css module type in farm-plugin-css.

Handle Plugin Options

The rust plugin options can be configured in farm.config.ts:

The Option will be json serialized and passed to the new method of your plugin, you can handle the options in the new method:

src/lib.rs

Note that you should add dependencies serde and serde_json to your Cargo.toml to support options deserialization:

note

Non json serializable options are not supported. Which means you can only use types like string, number, boolean, array, object, etc. function options are not supported.

Using farm_core In Plugin

Farm exposes all core structures and utilities in farmfe_core crate. Refer to the farmfe_core documentation for more detail.

note

If you want to use swc structures like Module, Program, etc. in your plugin, you should use farmfe_core::swc_ast that re-exposed by farm core. Cause the swc version used by farm core may be different from the swc version you used in your plugin, and the swc version used by farm core is guaranteed to be compatible with farm core.

Caveats

Using SWC In Plugin

Note that your rust plugin should not use any SWC related packages like swc_common, swc_transforms, etc. Cause SWC stores the global state in the process, it may cause dead lock when you use SWC in your plugin.

Farm recommended to write SWC Plugin if you want to make changes to the AST of your farm project. For how to write SWC plugin, see Write SWC Plugin.

Choosing Rust toolchain

Cause Farm Rust Plugin is a dynamic linked library, you should always use the same version of the rust toolchain as the farm core. The rust toolchain is defined in rust-toolchain.toml, it should not be modified manually. And should should always build your plugin from Rust, cause Farm Core does not support FFI and not promise ABI stability to provide best performance.

Plugin Compatibility

Farm core maintains a API version that exposes to the plugin. If you met a message like Incompatible Rust Plugin: Current core's version..., it means your plugin is not compatible with the current farm core version. You should update your plugin to the latest version to fix the issue.

For plugin authors, you should rebuild and publish your plugin for the latest farm core version to make your plugin compatible with the latest farm core version.

note

Farm promises API Compatibility for the same major version, for example, if your plugin is compatible with farm core 1.0.0, it should also be compatible with farm core 1.1.0, 1.2.0, etc. which means your plugin will always work for the same major version of farm.

Cross Build

A Farm Rust Plugin is a platform specific dynamic linked library, you should build your plugin for all platforms you want to support. Farm provided a example for how to build your plugin using github actions, see .github/workflows/build.yml

By default, A farm rust plugin should be built for the following platforms:

• linux-x64-gnu
• linux-x64-musl
• darwin-x64
• win32-x64-msvc
• linux-arm64-musl
• linux-arm64-gnu
• darwin-arm64
• win32-ia32-msvc
• win32-arm64-msvc

For a public plugin that published to npm registry, we recommend you to publish your plugin for all platforms above. For a private rust plugin, you can build your plugin for any platform you want to support.

tip

Cause a rust plugin is a pure dynamic linked library, if you have questions about how to build your plugin for a specific platform, just google how to build a dynamic linked library for that platform in Rust.

Publish

Steps to publish your Rust plugin:

1. Cross build the Rust plugin to dynamic linked library, see Cross Build for detail.
2. Copy the binary artifacts to npm dir, for example: Copy to npm/linux-x64-gnu/index.farm.
3. Publish platform specific packages under npm dir, you can use farm-plugin-tool prepublish to publish packages under npm dir.
4. Publish the package itself

see example github actions publish workflow

Examples

We will use @farmfe/plugin-sass as demostration to a real Rust plugin example. This plugin will support compiling .scss and .sass file in your farm project.

Define Plugin

Exports a Rust struct named FarmPluginSass.

src/lib.rs

• The struct must be pub and #[farm_plugin] attribute is required.
• The struct must export a new method that accepts 2 arguments for initialization, the first argument is &Config and the second argument is String.

Implement Plugin Trait

Plugin trait is used to define hooks that can hook into Farm compiler.

Load .scss File

Implement load hook to support load .scss files.

In the load hook, we only read the file that ends with .scss or .sass, return the file content and maked its module_type as ModuleType::Custom(String::from("sass")).

Transform sass File

After we load the .scss file, we need to transform it to css in transform hook, then Farm will treat it as css in following process.

tip

This example only covers how to implement a transformer plugin. For more abilities that Farm support, refer to Plugin Hooks.