Oxc Resolver

Rust port of enhanced-resolve.

• built-in tsconfig-paths-webpack-plugin
  • support extending tsconfig defined in tsconfig.extends
  • support paths alias defined in tsconfig.compilerOptions.paths
  • support project references defined tsconfig.references
• supports in-memory file system via the FileSystem trait
• contains tracing instrumentation

Usage

The following usages apply to both Rust and Node.js; the code snippets are written in JavaScript.

To handle the exports field in package.json, ESM and CJS need to be differentiated.

ESM

Per ESM Resolution algorithm

defaultConditions is the conditional environment name array, ["node", "import"].

This means when the caller is an ESM import (import "module"), resolve options should be

{
  "conditionNames": ["node", "import"]
}

CJS

Per CJS Resolution algorithm

LOAD_PACKAGE_EXPORTS(X, DIR)

5. let MATCH = PACKAGE_EXPORTS_RESOLVE(pathToFileURL(DIR/NAME), "." + SUBPATH, package.json "exports", ["node", "require"]) defined in the ESM resolver.

This means when the caller is a CJS require (require("module")), resolve options should be

{
  "conditionNames": ["node", "require"]
}

Cache

To support both CJS and ESM with the same cache:

const esmResolver = ResolverFactory({
  conditionNames: ["node", "import"]
});

const cjsResolver = esmResolver.cloneWithOptions({
  conditionNames: ["node", "import"]
});

Browser Field

From this non-standard spec:

The browser field is provided to JavaScript bundlers or component tools when packaging modules for client side use.

The option is

{
  "aliasFields": ["browser"]
}

Options

The options are aligned with enhanced-resolve.

Field	Default	Description
alias	[]	A list of module alias configurations or an object which maps key to value
aliasFields	[]	A list of alias fields in description files
extensionAlias	{}	An object which maps extension to extension aliases
conditionNames	[]	A list of exports field condition names
descriptionFiles	["package.json"]	A list of description files to read from
enforceExtension	false	Enforce that a extension from extensions must be used
exportsFields	["exports"]	A list of exports fields in description files
extensions	[".js", ".json", ".node"]	A list of extensions which should be tried for files
fallback	[]	Same as alias, but only used if default resolving fails
fileSystem		The file system which should be used
fullySpecified	false	Request passed to resolve is already fully specified and extensions or main files are not resolved for it (they are still resolved for internal requests)
mainFields	["main"]	A list of main fields in description files
mainFiles	["index"]	A list of main files in directories
modules	["node_modules"]	A list of directories to resolve modules from, can be absolute path or folder name
resolveToContext	false	Resolve to a context instead of a file
preferRelative	false	Prefer to resolve module requests as relative request and fallback to resolving as module
preferAbsolute	false	Prefer to resolve server-relative urls as absolute paths before falling back to resolve in roots
restrictions	[]	A list of resolve restrictions
roots	[]	A list of root paths
symlinks	true	Whether to resolve symlinks to their symlinked location

Unimplemented Options

Field	Default	Description
cachePredicate	function() { return true };	A function which decides whether a request should be cached or not. An object is passed to the function with path and request properties.
cacheWithContext	true	If unsafe cache is enabled, includes request.context in the cache key
plugins	[]	A list of additional resolve plugins which should be applied
resolver	undefined	A prepared Resolver to which the plugins are attached
unsafeCache	false	Use this cache object to unsafely cache the successful requests

Debugging

Rspack

The following environment variable will emit tracing information.

RSPACK_PROFILE='TRACE=filter=oxc_resolver=trace&layer=logger' rspack build

Test

Tests are ported from

• enhanced-resolve
• tsconfig-path and parcel-resolver for tsconfig-paths

Test cases are located in ./src/tests, fixtures are located in ./tests

• alias.test.js
• browserField.test.js
• dependencies.test.js
• exportsField.test.js
• extension-alias.test.js
• extensions.test.js
• fallback.test.js
• fullSpecified.test.js
• identifier.test.js (see unit test in crates/oxc_resolver/src/request.rs)
• importsField.test.js
• incorrect-description-file.test.js (need to add ctx.fileDependencies)
• missing.test.js
• path.test.js (see unit test in crates/oxc_resolver/src/path.rs)
• plugins.test.js
• pnp.test.js
• resolve.test.js
• restrictions.test.js (partially done, regex is not supported yet)
• roots.test.js
• scoped-packages.test.js
• simple.test.js
• symlink.test.js

Irrelevant tests

• CachedInputFileSystem.test.js
• SyncAsyncFileSystemDecorator.test.js
• forEachBail.test.js
• getPaths.test.js
• pr-53.test.js
• unsafe-cache.test.js
• yield.test.js

📖 License

oxc_resolver is free and open-source software licensed under the MIT License.

Oxc partially copies code from the following projects.

Project	License
webpack/enhanced-resolve	MIT
dividab/tsconfig-paths	MIT
parcel-bundler/parcel	MIT
tmccombs/json-comments-rs	Apache 2.0