feat: expose this.cacheable in webpack and rspack load/transform hooks

docs/guide/index.md

@@ -363,11 +363,13 @@ const plugin = createUnplugin(() => ({
 | [`this.getWatchFiles`](https://rollupjs.org/plugin-development/#this-getwatchfiles)   |   ✅   |  ✅  |   ✅    |   ❌    |   ✅   |   ✅    |  ✅  |    ✅    | ✅  |
 | [`this.warn`](https://rollupjs.org/plugin-development/#this-warn)                     |   ✅   |  ✅  |   ✅    |   ✅    |   ✅   |   ✅    |  ✅  |    ✅    | ✅  |
 | [`this.error`](https://rollupjs.org/plugin-development/#this-error)                   |   ✅   |  ✅  |   ✅    |   ✅    |   ✅   |   ✅    |  ✅  |    ✅    | ✅  |
+| [`this.cacheable`](https://webpack.js.org/api/loaders/#thiscacheable)<sup>3</sup>     |   ❌   |  ❌  |   ✅    |   ❌    |   ✅   |   ✅    |  ❌  |    ❌    | ❌  |
 
 ::: info Notice
 
 1. For bundlers other than Rollup, Rolldown, or Vite, `setParseImpl` must be called to manually provide a parser implementation. Parsers such as [Acorn](https://github.com/acornjs/acorn), [Babel](https://babeljs.io/), or [Oxc](https://oxc.rs/) can be used.
 2. Currently, [`this.emitFile`](https://rollupjs.org/plugin-development/#thisemitfile) only supports the `EmittedAsset` variant.
+3. Only in the `load` and `transform` hooks. Call `this.cacheable(false)` when the result can't be cached, for example when it depends on state the bundler doesn't track, so the module is built again on every rebuild. On other bundlers `this.cacheable` is `undefined`, so call it as `this.cacheable?.(false)` in plugins that run on several bundlers.
 
 :::
 

src/rspack/context.ts

@@ -46,6 +46,7 @@ export function createContext(loader: LoaderContext): UnpluginContext {
   return {
     error: error => loader.emitError(normalizeMessage(error)),
     warn: message => loader.emitWarning(normalizeMessage(message)),
+    cacheable: flag => loader.cacheable(flag),
   }
 }
 

src/types.ts

@@ -242,4 +242,13 @@ export interface UnpluginMessage {
 export interface UnpluginContext {
   error: (message: string | UnpluginMessage) => void
   warn: (message: string | UnpluginMessage) => void
+  /**
+   * Pass `false` to tell the bundler that the result of this `load` or `transform` call can't be
+   * cached, so the module is built again on every rebuild instead of being restored from the cache.
+   *
+   * Only available in `load` and `transform` on webpack and Rspack (including Rsbuild).
+   *
+   * @see https://webpack.js.org/api/loaders/#thiscacheable
+   */
+  cacheable?: ((flag?: boolean) => void) | undefined
 }

src/webpack/context.ts

@@ -68,6 +68,7 @@ export function createContext(loader: LoaderContext<{ unpluginName: string }>):
   return {
     error: error => loader.emitError(normalizeMessage(error)),
     warn: message => loader.emitWarning(normalizeMessage(message)),
+    cacheable: flag => loader.cacheable(flag),
   }
 }
 

test/unit-tests/cacheable/cacheable.test.ts

@@ -0,0 +1,115 @@
+import type { UnpluginInstance } from 'unplugin'
+import { mkdtempSync, realpathSync, rmSync, writeFileSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { basename, join } from 'node:path'
+import { createUnplugin } from 'unplugin'
+import { afterAll, describe, expect, it } from 'vitest'
+import { rspackBuild, webpackBuild } from '../utils'
+
+const root = realpathSync(mkdtempSync(join(tmpdir(), 'unplugin-cacheable-')))
+
+writeFileSync(join(root, 'entry.js'), [
+  `import loaded from './loaded.js'`,
+  `import transformed from './transformed.js'`,
+  `console.log(loaded, transformed)`,
+].join('\n'))
+writeFileSync(join(root, 'loaded.js'), `export default 'loaded'`)
+writeFileSync(join(root, 'transformed.js'), `export default 'transformed'`)
+
+afterAll(() => rmSync(root, { recursive: true, force: true }))
+
+function createPlugin() {
+  const calls: Record<string, number> = {}
+  const count = (key: string) => {
+    calls[key] = (calls[key] ?? 0) + 1
+  }
+  const plugin = createUnplugin(() => ({
+    name: 'cacheable',
+    load(id) {
+      if (basename(id) === 'loaded.js') {
+        count('load loaded.js')
+        this.cacheable?.(false)
+      }
+    },
+    transform(_code, id) {
+      count(`transform ${basename(id)}`)
+      if (basename(id) === 'transformed.js')
+        this.cacheable?.(false)
+    },
+  }))
+  return { calls, plugin }
+}
+
+interface Compiler {
+  run: (callback: (error: Error | null, stats?: { hasErrors: () => boolean, toString: (options: any) => string }) => void) => void
+  close: (callback: () => void) => void
+}
+
+// Build twice with the same compiler so the second build can reuse the in-memory cache
+async function buildTwice(compiler: Compiler): Promise<void> {
+  const run = () => new Promise<void>((resolve, reject) => {
+    compiler.run((error, stats) => {
+      if (error)
+        reject(error)
+      else if (!stats || stats.hasErrors())
+        reject(new Error(stats?.toString({ all: false, errors: true }) ?? 'no stats'))
+      else
+        resolve()
+    })
+  })
+  await run()
+  await run()
+  await new Promise<void>(resolve => compiler.close(resolve))
+}
+
+const frameworks = [
+  [
+    'webpack',
+    (plugin: UnpluginInstance<any>) => webpackBuild({
+      mode: 'development',
+      cache: { type: 'memory' },
+      context: root,
+      entry: join(root, 'entry.js'),
+      output: {
+        path: join(root, 'dist-webpack'),
+      },
+      plugins: [
+        plugin.webpack(),
+      ],
+    }) as unknown as Compiler,
+  ],
+  [
+    'rspack',
+    (plugin: UnpluginInstance<any>) => rspackBuild({
+      mode: 'development',
+      cache: true,
+      context: root,
+      entry: join(root, 'entry.js'),
+      output: {
+        path: join(root, 'dist-rspack'),
+      },
+      plugins: [
+        plugin.rspack(),
+      ],
+    }) as unknown as Compiler,
+  ],
+] as const
+
+describe('this.cacheable', () => {
+  for (const [name, createCompiler] of frameworks) {
+    it(name, async () => {
+      const { calls, plugin } = createPlugin()
+
+      await buildTwice(createCompiler(plugin))
+
+      // `entry.js` comes from the cache on the second build, while the modules marked
+      // with `this.cacheable(false)` in `load` or `transform` are built again
+      expect(calls).toEqual({
+        'load loaded.js': 2,
+        'transform entry.js': 1,
+        'transform loaded.js': 2,
+        'transform transformed.js': 2,
+      })
+    })
+  }
+})

test/unit-tests/rspack/context.test.ts

@@ -86,4 +86,15 @@ describe('createBuildContext', () => {
     context.warn('testWarning')
     expect(loaderContext.emitWarning).toHaveBeenCalledWith(new Error('testWarning'))
   })
+
+  it('createContext - should forward cacheable to the loader', () => {
+    const loaderContext = {
+      cacheable: vi.fn(),
+    }
+
+    const context = createContext(loaderContext as any)
+    context.cacheable!(false)
+
+    expect(loaderContext.cacheable).toHaveBeenCalledWith(false)
+  })
 })

test/unit-tests/webpack/context.test.ts

@@ -103,6 +103,17 @@ describe('webpack - utils', () => {
       expect(mockLoader.emitError).toHaveBeenCalledWith(expect.any(Error))
       expect(mockLoader.emitWarning).toHaveBeenCalledWith(expect.any(Error))
     })
+
+    it('should forward cacheable to the loader', () => {
+      const mockLoader = {
+        cacheable: vi.fn(),
+      } as unknown as LoaderContext<{ unpluginName: string }>
+
+      const context = createContext(mockLoader)
+      context.cacheable!(false)
+
+      expect(mockLoader.cacheable).toHaveBeenCalledWith(false)
+    })
   })
 
   describe('normalizeMessage', () => {