refactor(dts): implement cjsReexport stub via Rolldown plugin

Author: mandarini

src/build.ts

@@ -1,5 +1,3 @@
-import { writeFile } from 'node:fs/promises'
-import path from 'node:path'
 import { bold, green } from 'ansis'
 import { clearRequireCache } from 'import-without-cache'
 import {
@@ -311,10 +309,6 @@ async function buildSingle(
     await copy(config)
     await buildExe(config, chunks)
 
-    if (format === 'cjs' && dts && dts.cjsReexport && isDualFormat) {
-      await writeCjsDtsReexports(chunks, outDir, config.write !== false)
-    }
-
     if (!hasBuilt) {
       await done(bundle)
     }
@@ -326,27 +320,3 @@ async function buildSingle(
     ab = executeOnSuccess(config)
   }
 }
-
-async function writeCjsDtsReexports(
-  chunks: RolldownChunk[],
-  outDir: string,
-  write: boolean,
-): Promise<void> {
-  for (const chunk of chunks) {
-    if (chunk.type !== 'chunk') continue
-
-    // Match CJS JS output files: .cjs (fixed extension) or .js (non-fixed)
-    const match = chunk.fileName.match(/^(.*)\.(cjs|js)$/)
-    if (!match) continue
-
-    const baseName = match[1]
-    const dCtsName =
-      match[2] === 'cjs' ? `${baseName}.d.cts` : `${baseName}.d.ts`
-    const dMtsBasename = path.basename(`${baseName}.d.mts`)
-    const content = `export * from './${dMtsBasename}'\n`
-
-    if (write) {
-      await writeFile(path.join(outDir, dCtsName), content)
-    }
-  }
-}

src/features/rolldown.ts

@@ -133,6 +133,8 @@ async function resolveInputOptions(
           cjsDefault,
         }),
       )
+    } else if (dts.cjsReexport && isDualFormat) {
+      plugins.push(CjsDtsReexportPlugin())
     }
   }
   let cssPostPlugins: Plugin[] | undefined
@@ -340,6 +342,28 @@ function handlePluginInspect(plugins: RolldownPluginOption) {
   }
 }
 
+export function CjsDtsReexportPlugin(): Plugin {
+  return {
+    name: 'tsdown:cjs-dts-reexport',
+    generateBundle(_options, bundle) {
+      for (const chunk of Object.values(bundle)) {
+        if (chunk.type !== 'chunk') continue
+
+        const match = chunk.fileName.match(/^(.*)\.(cjs|js)$/)
+        if (!match) continue
+
+        const baseName = match[1]
+        const dCtsName =
+          match[2] === 'cjs' ? `${baseName}.d.cts` : `${baseName}.d.ts`
+        const dMtsBasename = path.basename(`${baseName}.d.mts`)
+        const content = `export * from './${dMtsBasename}'\n`
+
+        this.emitFile({ type: 'asset', fileName: dCtsName, source: content })
+      }
+    },
+  }
+}
+
 export function CssGuardPlugin(): Plugin {
   return {
     name: 'tsdown:css-guard',