@rolldown/plugin-transform-imports

@rolldown/plugin-transform-imports

Rolldown plugin for transforming imports and re-exports from barrel files into individual module imports. This improves performance by avoiding resolving all of imports in the barrel file. For example, it rewrites import { map } from "lodash" with import map from "lodash/map".

Install

pnpm add -D @rolldown/plugin-transform-imports

Usage

import transformImports from '@rolldown/plugin-transform-imports'

export default {
  plugins: [
    transformImports({
      lodash: {
        transform: 'lodash/{{member}}',
      },
    }),
  ],
}

This transforms:

import { map, filter } from 'lodash'

Into:

import map from 'lodash/map'
import filter from 'lodash/filter'

Options

The plugin takes a Record<string, TransformConfig> — a map of module names (or regex patterns) to their transform configuration.

Module names are converted to regex patterns: lodash matches exactly lodash, while ^lodash(/.*)?$ allows custom regex patterns (must start with ^ and end with $).

TransformConfig

transform

• Type: string | [pattern: string, template: string][]
• Required

The path template for transformed imports. Use {{member}} as a placeholder for the imported member name.

String form:

{
  transform: 'lodash/{{member}}'
}
// import { map } from 'lodash' → import map from 'lodash/map'

Array of tuples form for pattern-based routing:

{
  transform: [
    ['someFunc', 'some-lib/some-module'],
    ['*', 'some-lib/{{member}}'],
  ]
}

Each tuple is [pattern, template]. Patterns are treated as regex (except * which matches anything). The first matching pattern wins.

preventFullImport

• Type: boolean
• Default: false

When true, throws an error on namespace imports (import * as X) and side-effect imports (import 'mod').

skipDefaultConversion

• Type: boolean
• Default: false

When true, keeps the import as a named import instead of converting to a default import:

// skipDefaultConversion: false (default)
import { map } from 'lodash'
import map from 'lodash/map' // output

// skipDefaultConversion: true
import { map } from 'lodash'
import { map } from 'lodash/map' // output

handleDefaultImport

• Type: boolean
• Default: false

When true, transforms default imports using the local name as the member:

// handleDefaultImport: true
import myMap from 'lodash'
import myMap from 'lodash/myMap' // output

handleNamespaceImport

• Type: boolean
• Default: false

When true, transforms namespace imports using the local name as the member:

// handleNamespaceImport: true
import * as myMap from 'lodash'
import * as myMap from 'lodash/myMap' // output

Template Syntax

Templates use {{...}} placeholders with the following variables:

Variables

• {{member}} — the imported member name
• {{matches.[N]}} — capture group from the module name regex
• {{memberMatches.[N]}} — capture group from the member pattern (tuple form only)

Case Transforms

Apply a case transform by prefixing the variable:

• {{camelCase member}} — MyComponent → myComponent
• {{kebabCase member}} — MyComponent → my-component
• {{snakeCase member}} — MyComponent → my_component
• {{upperCase member}} — map → MAP

Example with regex capture groups

{
  '^my-lib/(.+)$': {
    transform: 'my-lib/dist/{{matches.[1]}}/{{kebabCase member}}',
  },
}
// import { MyButton } from 'my-lib/components'
// → import MyButton from 'my-lib/dist/components/my-button'

Re-exports

The plugin also transforms re-exports:

// input
export { map, filter } from 'lodash'
// output
export { default as map } from 'lodash/map'
export { default as filter } from 'lodash/filter'

With skipDefaultConversion: true:

// input
export { map, filter } from 'lodash'
// output
export { map } from 'lodash/map'
export { filter } from 'lodash/filter'

Dynamic Imports

Static dynamic imports are also transformed:

const mod = await import('lodash')
// source is rewritten based on the transform template

Benchmark

Results of the benchmark that can be run by pnpm bench in ./benchmark directory:

  name                                     hz      min      max     mean      p75      p99     p995     p999     rme  samples
· @rolldown/plugin-transform-imports  14.9081  65.9831  69.8849  67.0775  67.5907  69.8849  69.8849  69.8849  ±1.29%       10
· babel-plugin-transform-imports       5.1254   184.90   246.64   195.11   191.14   246.64   246.64   246.64  ±6.84%       10
· @swc/plugin-transform-imports       10.9555  88.5649  98.1298  91.2780  92.9843  98.1298  98.1298  98.1298  ±2.50%       10

@rolldown/plugin-transform-imports - bench/transform-imports.bench.ts > Transform Imports Benchmark
  1.36x faster than @swc/plugin-transform-imports
  2.91x faster than babel-plugin-transform-imports

The benchmark was ran on the following environment:

OS: macOS Tahoe 26.3
CPU: Apple M4
Memory: LPDDR5X-7500 32GB

License

MIT

Credits

The implementation is based on swc-project/plugins/packages/transform-imports (Apache License 2.0). Test cases are also adapted from it.