fix: derive useDefineForClassFields value from tsconfig.compilerOptions.target (fixes #10296)

docs/guide/features.md

@@ -57,7 +57,7 @@ However, some libraries (e.g. [`vue`](https://github.com/vuejs/core/issues/1228)
 
 #### `useDefineForClassFields`
 
-Starting from Vite 2.5.0, the default value will be `true` if the TypeScript target is `ESNext`. It is consistent with the [behavior of `tsc` 4.3.2 and later](https://github.com/microsoft/TypeScript/pull/42663). It is also the standard ECMAScript runtime behavior.
+Starting from Vite 2.5.0, the default value will be `true` if the TypeScript target is `ESNext` or `ES2022` or newer. It is consistent with the [behavior of `tsc` 4.3.2 and later](https://github.com/microsoft/TypeScript/pull/42663). It is also the standard ECMAScript runtime behavior.
 
 But it may be counter-intuitive for those coming from other programming languages or older versions of TypeScript.
 You can read more about the transition in the [TypeScript 3.7 release notes](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#the-usedefineforclassfields-flag-and-the-declare-property-modifier).

packages/vite/src/node/__tests__/plugins/esbuild.spec.ts

@@ -1,7 +1,6 @@
 import { describe, expect, test } from 'vitest'
 import type { ResolvedConfig, UserConfig } from '../../config'
 import {
-  ESBuildTransformResult,
   resolveEsbuildTranspileOptions,
   transformWithEsbuild,
 } from '../../plugins/esbuild'
@@ -305,6 +304,81 @@ describe('transformWithEsbuild', () => {
       `/* @__PURE__ */ ${jsxFactory}(${jsxFragment}, null)`,
     )
   })
+
+  describe('useDefineForClassFields', async () => {
+    const transformClassCode = async (
+      target: string,
+      tsconfigCompilerOptions: {
+        target?: string
+        useDefineForClassFields?: boolean
+      },
+    ) => {
+      const result = await transformWithEsbuild(
+        `
+          class foo {
+            bar = 'bar'
+          }
+        `,
+        'bar.ts',
+        {
+          target,
+          tsconfigRaw: { compilerOptions: tsconfigCompilerOptions },
+        },
+      )
+      return result?.code
+    }
+
+    const [
+      defineForClassFieldsTrueTransformedCode,
+      defineForClassFieldsTrueLowerTransformedCode,
+      defineForClassFieldsFalseTransformedCode,
+    ] = await Promise.all([
+      transformClassCode('esnext', {
+        useDefineForClassFields: true,
+      }),
+      transformClassCode('es2021', {
+        useDefineForClassFields: true,
+      }),
+      transformClassCode('esnext', {
+        useDefineForClassFields: false,
+      }),
+    ])
+
+    test('target: esnext and tsconfig.target: esnext => true', async () => {
+      const actual = await transformClassCode('esnext', {
+        target: 'esnext',
+      })
+      expect(actual).toBe(defineForClassFieldsTrueTransformedCode)
+    })
+
+    test('target: es2021 and tsconfig.target: esnext => true', async () => {
+      const actual = await transformClassCode('es2021', {
+        target: 'esnext',
+      })
+      expect(actual).toBe(defineForClassFieldsTrueLowerTransformedCode)
+    })
+
+    test('target: es2021 and tsconfig.target: es2021 => false', async () => {
+      const actual = await transformClassCode('es2021', {
+        target: 'es2021',
+      })
+      expect(actual).toBe(defineForClassFieldsFalseTransformedCode)
+    })
+
+    test('target: esnext and tsconfig.target: es2021 => false', async () => {
+      const actual = await transformClassCode('esnext', {
+        target: 'es2021',
+      })
+      expect(actual).toBe(defineForClassFieldsFalseTransformedCode)
+    })
+
+    test('target: es2022 and tsconfig.target: es2022 => true', async () => {
+      const actual = await transformClassCode('es2022', {
+        target: 'es2022',
+      })
+      expect(actual).toBe(defineForClassFieldsTrueTransformedCode)
+    })
+  })
 })
 
 /**

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

@@ -125,6 +125,23 @@ export async function transformWithEsbuild(
         ...tsconfigRaw?.compilerOptions,
       },
     }
+
+    const { compilerOptions } = tsconfigRaw
+    if (compilerOptions) {
+      // esbuild derives `useDefineForClassFields` from `target` instead of `tsconfig.compilerOptions.target`
+      // https://github.com/evanw/esbuild/issues/2584
+      // but we want `useDefineForClassFields` to be derived from `tsconfig.compilerOptions.target`
+      if (compilerOptions.useDefineForClassFields === undefined) {
+        const lowercaseTarget = compilerOptions.target?.toLowerCase() ?? 'es3'
+        if (lowercaseTarget.startsWith('es')) {
+          const esVersion = lowercaseTarget.slice(2)
+          compilerOptions.useDefineForClassFields =
+            esVersion === 'next' || +esVersion >= 2022
+        } else {
+          compilerOptions.useDefineForClassFields = false
+        }
+      }
+    }
   }
 
   const resolvedOptions = {