fix(esbuild): enable experimentalDecorators by default (#13805)

packages/vite/src/node/optimizer/scan.ts

@@ -205,8 +205,11 @@ async function prepareEsbuildScanner(
 
   const plugin = esbuildScanPlugin(config, container, deps, missing, entries)
 
-  const { plugins = [], ...esbuildOptions } =
-    config.optimizeDeps?.esbuildOptions ?? {}
+  const {
+    plugins = [],
+    tsconfigRaw,
+    ...esbuildOptions
+  } = config.optimizeDeps?.esbuildOptions ?? {}
 
   return await esbuild.context({
     absWorkingDir: process.cwd(),
@@ -219,6 +222,16 @@ async function prepareEsbuildScanner(
     format: 'esm',
     logLevel: 'silent',
     plugins: [...plugins, plugin],
+    tsconfigRaw:
+      typeof tsconfigRaw === 'string'
+        ? tsconfigRaw
+        : {
+            ...tsconfigRaw,
+            compilerOptions: {
+              experimentalDecorators: true,
+              ...tsconfigRaw?.compilerOptions,
+            },
+          },
     ...esbuildOptions,
   })
 }

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

@@ -142,6 +142,14 @@ export async function transformWithEsbuild(
       compilerOptions.useDefineForClassFields = false
     }
 
+    // esbuild v0.18 only transforms decorators when `experimentalDecorators` is set to `true`.
+    // To preserve compat with the esbuild breaking change, we set `experimentalDecorators` to
+    // `true` by default if it's unset.
+    // TODO: Remove this in Vite 5
+    if (compilerOptions.experimentalDecorators === undefined) {
+      compilerOptions.experimentalDecorators = true
+    }
+
     // esbuild uses tsconfig fields when both the normal options and tsconfig was set
     // but we want to prioritize the normal options
     if (options) {

playground/tsconfig-json/__tests__/tsconfig-json.spec.ts

@@ -67,4 +67,16 @@ describe('transformWithEsbuild', () => {
       'import { MainTypeOnlyClass } from "./not-used-type";',
     )
   })
+
+  test('experimentalDecorators', async () => {
+    const main = path.resolve(__dirname, '../src/decorator.ts')
+    const mainContent = fs.readFileSync(main, 'utf-8')
+    // Should not error when transpiling decorators
+    // TODO: In Vite 5, this should require setting `tsconfigRaw.experimentalDecorators`
+    // or via the closest `tsconfig.json`
+    const result = await transformWithEsbuild(mainContent, main, {
+      target: 'es2020',
+    })
+    expect(result.code).toContain('__decorateClass')
+  })
 })

playground/tsconfig-json/src/decorator.ts

@@ -0,0 +1,11 @@
+function first() {
+  return function (...args: any[]) {}
+}
+
+export class Foo {
+  @first()
+  // @ts-expect-error we intentionally not enable `experimentalDecorators` to test esbuild compat
+  method(@first test: string) {
+    return test
+  }
+}

playground/tsconfig-json/src/main.ts

@@ -1,6 +1,7 @@
 // @ts-nocheck
 import '../nested/main'
 import '../nested-with-extends/main'
+import './decorator'
 
 // eslint-disable-next-line @typescript-eslint/consistent-type-imports
 import { MainTypeOnlyClass } from './not-used-type'