#Compiler

The Compiler is a core object in Rspack. A Compiler instance is created whenever you call Rspack's JavaScript API or CLI.

It provides methods like run and watch to start builds, while exposing various Compiler hooks that allow Rspack plugins to intervene at different stages of the build process.

#Compiler methods

#run

Start a compilation, and calls back when the compilation is completed or aborted due to an error.

function run(
  callback: (
    error: Error, // Only including compiler-related errors, such as configuration errors, not including compilation errors
    stats: Stats, // detailed information generated during the compilation
  ) => void,
  options?: {
    modifiedFiles?: ReadonlySet<string>; // Modified files included in this compilation
    removedFiles?: ReadonlySet<string>; // Deleted files included in this compilation
  },
): void;

compiler.run((err, stats) => {
  // Deal with the compiler errors
  handleCompilerError(err);
  // Deal with the compilation errors
  handleModuleErrors(stats.toJson().errors);
  // Deal with the result
  handleBuildResult(stats);
  // End this compilation
  compiler.close(closeErr => {
    // Start a new compilation
    compiler.run((err, stats) => {});
  });
});

#watch

Watching files and directories, start a compilation process after they change, and calls back every time the compilation is completed or aborted due to an error.

function watch(
  watchOptions: WatchOptions, // options for starting the watching
  handler: (error: Error, stats: Stats) => void, // callback when every compilation ends
): Watching; // watching controller

const watching = compiler.watch(
  {
    aggregateTimeout: 300,
    poll: undefined,
  },
  (err, stats) => {
    // Deal with the result
    handleBuildResult(stats);
  },
);

The Watching object provides the following methods:

• watch:
  • Type: (files: string[], dirs: string[], missing: string[]): void
  • Usage: Add the files and directories that need to be watched.
• invalidate:
  • Type: (callback: () => void): void
  • Usage: Immediately end this round of watching and start a compilation with the currently recorded file changes, without stopping the watcher.
• suspend:
  • Type: (): void
  • Usage: Enter the state of only watching and will not start a new compilation.
• resume:
  • Type: (): void
  • Usage: Exit the state of only watching and start a compilation with the currently recorded file changes.
• close:
  • Type: (callback: () => void): void
  • Usage: Stop the watcher.

#close

Close the current compiler, and handle low-priority tasks such as caching during this period.

function close(
  callback: (err: Error) => void, // callback after closing
): void;

#getInfrastructureLogger

Create a logger object that is not associated with any compilation, which is used to print global logs.

function getInfrastructureLogger(name: string): Logger;

#getCache

Create a cache object to share data in the build process.

function getCache(name: string): CacheFacade;

#purgeInputFileSystem

Stop the read loop of the input file system, which internally contains a timer and may cause the process to still not be able to exit after calling compiler.close.

function purgeInputFileSystem(): void;

#createChildCompiler

Allows running another instance of Rspack inside of Rspack. However, as a child with different settings and configurations applied. It copies all hooks and plugins from the parent (or top-level compiler) and creates a child Compiler instance. Returns the created Compiler.

function createChildCompiler(
  compilation: Compilation,
  compilerName: string,
  compilerIndex: number,
  outputOptions: OutputOptions,
  plugins: RspackPlugin[],
): Compiler;

#runAsChild

Running the child compiler, which will doing a complete compiling and generate the assets.

function runAsChild(
  callback(
    err: Error, // error related to the child compiler
    entries: Chunk[], // chunks generated by the child compiler
    compilation: Compilation, // the compilation created by the child compiler
  ): void;
): void;

#isChild

Whether this compiler is a child compiler.

function isChild(): boolean;

#Compiler properties

#hooks

See compiler hooks for more details.

#rspack

• Type: typeof rspack

Get the exports of @rspack/core to obtain the associated internal objects. This is especially useful when you cannot directly reference @rspack/core or there are multiple Rspack instances.

A common example is accessing the sources object in a Rspack plugin:

const { RawSource } = compiler.rspack.sources;
const source = new RawSource('console.log("Hello, world!");');

#webpack

• Type: typeof rspack

Equivalent to compiler.rspack, this property is used for compatibility with webpack plugins.

If the Rspack plugin you are developing needs to be webpack compatible, you can use this property instead of compiler.rspack.

console.log(compiler.webpack === compiler.rspack); // true

#name

• Type: string

Get the name:

• For the root compiler, it is equivalent to name.
• For the child compiler, it is the value passed into createChildCompiler.
• For the MultiCompiler and in the KV form, it is the key.

#context

Current project root directory:

• Created through new Compiler, it is the value passed in.
• Created through rspack({}), it is context configuration.

#root

• Type: Compiler

Get the root of the child compiler tree.

#options

• Type: RspackOptionsNormalized

Get the full options used by this compiler.

#watchMode

• Type: boolean

Whether started through compiler.watch.

#watching

• Type: Watching

Get the watching object, see watch method for more details.

#running

• Type: boolean

Whether the compilation is currently being executed.

#inputFileSystem

• Type: InputFileSystem

Get the proxy object used for reading from the file system, which has optimizations such as caching inside to reduce duplicate reading of the same file.

#outputFileSystem

• Type: OutputFileSystem

Get the proxy object used for writing to the file system, fs by default.

#watchFileSystem

• Type: WatchFileSystem

Get the proxy object used for watching files or directories changes, which provides a watch method to start watching, and passes in the changed and removed items in the callback.

#MultiCompiler

The MultiCompiler module allows Rspack to run multiple configurations in separate compilers. If the options parameter in the Rspack's JavaScript API is an array of options, Rspack applies separate compilers and calls the callback after all compilers have been executed.

const { rspack } = require('@rspack/core');

rspack(
  [
    { entry: './index1.js', output: { filename: 'bundle1.js' } },
    { entry: './index2.js', output: { filename: 'bundle2.js' } },
  ],
  (err, stats) => {
    process.stdout.write(stats.toString() + '\n');
  },
);

It can also be created through new MultiCompiler:

const compiler1 = new Compiler({
  /* */
});
const compiler2 = new Compiler({
  /* */
});

new MultiCompiler([compiler1, compiler2]);

new MultiCompiler([compiler1, compiler2], {
  parallelism: 1, // the maximum number of parallel compilers
});

new MultiCompiler({
  name1: compiler1,
  name2: compiler2,
});

MultiCompiler also provides some methods and attributes of the Compiler.

#MultiCompiler methods

#setDependencies

Specify the dependency relationship between the compilers, using compiler.name as the identifier, to ensure the execution order of the compilers.

setDependencies(compiler: Compiler, dependencies: string[]): void;

#validateDependencies

Check whether the dependency relationship between the compilers is legal. If there is a cycle or a missing dependency, it will trigger the callback.

validateDependencies(
  callback: (err: Error) => void; // callback when there is an error
): boolean

#run

Execute the run method of each compiler according to the dependency relationship to start the compilation process.

run(
  callback: (err: Error, stats: MultiStats) => void,
  options?: {
    modifiedFiles?: ReadonlySet<string>; // Modified files included in this compilation
    removedFiles?: ReadonlySet<string>; // Deleted files included in this compilation
  },
): void;

#watch

Execute the watch method of each compiler according to the dependency relationship to start watching, and start a compilation process after the file changes.

function watch(
  watchOptions: WatchOptions | WatchOptions[],
  handler: (err: Error, stats: MultiStats) => void,
): MultiWatching;

#close

Execute the close method of each compiler to close them, and handle low-priority tasks such as caching during this period.

close(callback: (err: Error) => void): void;

#purgeInputFileSystem

Execute the purgeInputFileSystem of each compiler to stop the read loop of the file system

purgeInputFileSystem(): void;

#getInfrastructureLogger

Create a logger object that is not associated with any compilation, which is used to print global logs.

getInfrastructureLogger(name: string): Logger;

Same with compilers[0].getInfrastructureLogger()

#MultiCompiler properties

#compilers

• Type: Compiler[]

Get all included compilers.

#options

• Type: RspackOptionsNormalized[]

Get all the full options used by the compilers.

#inputFileSystem

• Type: InputFileSystem

Set the proxy object used for reading from the file system for each compiler.

#outputFileSystem

• Type: OutputFileSystem

Set the proxy object used for writing from the file system for each compiler.

#watchFileSystem

• Type: WatchFileSystem

Set the proxy object used for watching files or directories changes for each compiler.

#running

• Type: boolean

Whether the compilation is currently being executed.