fix: Throw error only when 'umd' or 'iife' are used

packages/vite/src/node/__tests__/build.spec.ts

@@ -1,8 +1,10 @@
 import { resolve } from 'node:path'
 import { fileURLToPath } from 'node:url'
-import { describe, expect, test } from 'vitest'
+import type { OutputOptions } from 'rollup'
+import { describe, expect, test, vi } from 'vitest'
 import type { LibraryFormats, LibraryOptions } from '../build'
-import { resolveLibFilename } from '../build'
+import { resolveBuildOutputs, resolveLibFilename } from '../build'
+import { createLogger } from '../logger'
 
 const __dirname = resolve(fileURLToPath(import.meta.url), '..')
 
@@ -12,6 +14,101 @@ const baseLibOptions: LibraryOptions = {
   entry: 'mylib.js'
 }
 
+describe('resolveBuildOutputs', () => {
+  test('resolves outputs correctly', () => {
+    const logger = createLogger()
+    const libOptions: LibraryOptions = { ...baseLibOptions }
+    const outputs: OutputOptions[] = [{ format: 'es' }]
+    const resolvedOutputs = resolveBuildOutputs(outputs, libOptions, logger)
+
+    expect(resolvedOutputs).toEqual([
+      {
+        format: 'es'
+      }
+    ])
+  })
+
+  test('resolves outputs from lib options', () => {
+    const logger = createLogger()
+    const libOptions: LibraryOptions = { ...baseLibOptions, name: 'lib' }
+    const resolvedOutputs = resolveBuildOutputs(void 0, libOptions, logger)
+
+    expect(resolvedOutputs).toEqual([
+      {
+        format: 'es'
+      },
+      {
+        format: 'umd'
+      }
+    ])
+  })
+
+  test('does not change outputs when lib options are missing', () => {
+    const logger = createLogger()
+    const outputs: OutputOptions[] = [{ format: 'es' }]
+    const resolvedOutputs = resolveBuildOutputs(outputs, false, logger)
+
+    expect(resolvedOutputs).toEqual(outputs)
+  })
+
+  test('logs a warning when outputs is an array and formats are specified', () => {
+    const logger = createLogger()
+    const loggerSpy = vi.spyOn(logger, 'warn').mockImplementation(() => {})
+    const libOptions: LibraryOptions = {
+      ...baseLibOptions,
+      formats: ['iife']
+    }
+    const outputs: OutputOptions[] = [{ format: 'es' }]
+
+    resolveBuildOutputs(outputs, libOptions, logger)
+
+    expect(loggerSpy).toHaveBeenCalledWith(
+      expect.stringContaining('"build.lib.formats" will be ignored because')
+    )
+  })
+
+  test('throws an error when lib.name is missing on iife format', () => {
+    const logger = createLogger()
+    const libOptions: LibraryOptions = {
+      ...baseLibOptions,
+      formats: ['iife']
+    }
+    const resolveBuild = () => resolveBuildOutputs(void 0, libOptions, logger)
+
+    expect(resolveBuild).toThrowError(/Option "build\.lib\.name" is required/)
+  })
+
+  test('throws an error when lib.name is missing on umd format', () => {
+    const logger = createLogger()
+    const libOptions: LibraryOptions = { ...baseLibOptions, formats: ['umd'] }
+    const resolveBuild = () => resolveBuildOutputs(void 0, libOptions, logger)
+
+    expect(resolveBuild).toThrowError(/Option "build\.lib\.name" is required/)
+  })
+
+  test('throws an error when output.name is missing on iife format', () => {
+    const logger = createLogger()
+    const libOptions: LibraryOptions = { ...baseLibOptions }
+    const outputs: OutputOptions[] = [{ format: 'iife' }]
+    const resolveBuild = () => resolveBuildOutputs(outputs, libOptions, logger)
+
+    expect(resolveBuild).toThrowError(
+      /Entries in "build\.rollupOptions\.output" must specify "name"/
+    )
+  })
+
+  test('throws an error when output.name is missing on umd format', () => {
+    const logger = createLogger()
+    const libOptions: LibraryOptions = { ...baseLibOptions }
+    const outputs: OutputOptions[] = [{ format: 'umd' }]
+    const resolveBuild = () => resolveBuildOutputs(outputs, libOptions, logger)
+
+    expect(resolveBuild).toThrowError(
+      /Entries in "build\.rollupOptions\.output" must specify "name"/
+    )
+  })
+})
+
 describe('resolveLibFilename', () => {
   test('custom filename function', () => {
     const filename = resolveLibFilename(

packages/vite/src/node/build.ts

@@ -644,36 +644,45 @@ export function resolveLibFilename(
   return `${name}.${format}.${extension}`
 }
 
-function resolveBuildOutputs(
+export function resolveBuildOutputs(
   outputs: OutputOptions | OutputOptions[] | undefined,
   libOptions: LibraryOptions | false,
   logger: Logger
 ): OutputOptions | OutputOptions[] | undefined {
   if (libOptions) {
-    const formats = libOptions.formats || ['es', 'umd']
-    if (
-      (formats.includes('umd') || formats.includes('iife')) &&
-      !libOptions.name
-    ) {
-      throw new Error(
-        `Option "build.lib.name" is required when output formats ` +
-          `include "umd" or "iife".`
-      )
+    const libFormats = libOptions.formats || ['es', 'umd']
+
+    if (!Array.isArray(outputs)) {
+      const requiresName =
+        libFormats.includes('umd') || libFormats.includes('iife')
+
+      if (requiresName && !libOptions.name) {
+        throw new Error(
+          'Option "build.lib.name" is required when output formats include "umd" or "iife".'
+        )
+      }
+
+      return libFormats.map((format) => ({ ...outputs, format }))
     }
-    if (!outputs) {
-      return formats.map((format) => ({ format }))
-    } else if (!Array.isArray(outputs)) {
-      return formats.map((format) => ({ ...outputs, format }))
-    } else if (libOptions.formats) {
-      // user explicitly specifying own output array
+
+    // By this point, we know "outputs" is an Array.
+    if (libOptions.formats) {
       logger.warn(
         colors.yellow(
-          `"build.lib.formats" will be ignored because ` +
-            `"build.rollupOptions.output" is already an array format`
+          '"build.lib.formats" will be ignored because "build.rollupOptions.output" is already an array format.'
         )
       )
     }
+
+    outputs.forEach((output) => {
+      if (['umd', 'iife'].includes(output.format!) && !output.name) {
+        throw new Error(
+          'Entries in "build.rollupOptions.output" must specify "name" when the format is "umd" or "iife".'
+        )
+      }
+    })
   }
+
   return outputs
 }