feat: support importing ts files using their corresponding js extesions

To align with `tsc` default behavior, mentioned in microsoft/TypeScript#46452

Fixes vitejs#3040

packages/vite/src/node/plugins/resolve.ts

@@ -25,7 +25,10 @@ import {
   cleanUrl,
   slash,
   nestedResolveFrom,
-  isFileReadable
+  isFileReadable,
+  isTsRequest,
+  isPossibleTsOutput,
+  getTsSrcPath
 } from '../utils'
 import { ViteDevServer, SSROptions } from '..'
 import { createFilter } from '@rollup/pluginutils'
@@ -65,6 +68,11 @@ export interface InternalResolveOptions extends ResolveOptions {
   skipPackageJson?: boolean
   preferRelative?: boolean
   isRequire?: boolean
+  // #3040
+  // when the importer is a ts module,
+  // if the specifier requests a non-existent `.js/jsx/mjs/cjs` file,
+  // should also try import from `.ts/tsx/mts/cts` source file as fallback,
+  isFromTsImporter?: boolean
 }
 
 export function resolvePlugin(baseOptions: InternalResolveOptions): Plugin {
@@ -75,10 +83,6 @@ export function resolvePlugin(baseOptions: InternalResolveOptions): Plugin {
     ssrConfig,
     preferRelative = false
   } = baseOptions
-  const requireOptions: InternalResolveOptions = {
-    ...baseOptions,
-    isRequire: true
-  }
   let server: ViteDevServer | undefined
 
   const { target: ssrTarget, noExternal: ssrNoExternal } = ssrConfig ?? {}
@@ -104,13 +108,19 @@ export function resolvePlugin(baseOptions: InternalResolveOptions): Plugin {
       const targetWeb = !ssr || ssrTarget === 'webworker'
 
       // this is passed by @rollup/plugin-commonjs
-      const isRequire =
+      const isRequire = !!(
         resolveOpts &&
         resolveOpts.custom &&
         resolveOpts.custom['node-resolve'] &&
         resolveOpts.custom['node-resolve'].isRequire
+      )
 
-      const options = isRequire ? requireOptions : baseOptions
+      const options: InternalResolveOptions = {
+        ...baseOptions,
+
+        isRequire,
+        isFromTsImporter: isTsRequest(importer ?? '')
+      }
 
       const preserveSymlinks = !!server?.config.resolve.preserveSymlinks
 
@@ -450,6 +460,22 @@ function tryResolveFile(
       if (index) return index + postfix
     }
   }
+
+  const tryTsExtension = options.isFromTsImporter && isPossibleTsOutput(file)
+  if (tryTsExtension) {
+    const tsSrcPath = getTsSrcPath(file)
+    return tryResolveFile(
+      tsSrcPath,
+      postfix,
+      options,
+      tryIndex,
+      targetWeb,
+      preserveSymlinks,
+      tryPrefix,
+      skipPackageJson
+    )
+  }
+
   if (tryPrefix) {
     const prefixed = `${path.dirname(file)}/${tryPrefix}${path.basename(file)}`
     return tryResolveFile(

packages/vite/src/node/utils.ts

@@ -164,6 +164,14 @@ export const isJSRequest = (url: string): boolean => {
   return false
 }
 
+const knownTsRE = /\.(ts|mts|cts|tsx)$/
+const knownTsOutputRE = /\.(js|mjs|cjs|jsx)$/
+export const isTsRequest = (url: string) => knownTsRE.test(cleanUrl(url))
+export const isPossibleTsOutput = (url: string) =>
+  knownTsOutputRE.test(cleanUrl(url))
+export const getTsSrcPath = (filename: string) =>
+  filename.replace(/\.([cm])?(js)(x?)$/, '.$1ts$3')
+
 const importQueryRE = /(\?|&)import=?(?:&|$)/
 const internalPrefixes = [
   FS_PREFIX,