fix: await locale manifest write

build/index.js

@@ -30,7 +30,7 @@ async function listLocaleJson(localeArr) {
       name: localeData.match(localeNameRegex)[1]
     })
   }))
-  promisifyWriteFile(path.join(__dirname, '../locale.json'), JSON.stringify(localeListArr), 'utf8')
+  await promisifyWriteFile(path.join(__dirname, '../locale.json'), JSON.stringify(localeListArr), 'utf8')
 }
 
 (async () => {

test/build/localeManifestAwait.test.js

@@ -0,0 +1,43 @@
+describe('locale manifest generation', () => {
+  beforeEach(() => {
+    jest.resetModules()
+  })
+
+  afterEach(() => {
+    jest.restoreAllMocks()
+  })
+
+  it('reports a locale manifest write failure through the build error handler', async () => {
+    const writeError = new Error('locale manifest write failed')
+    let rejectWrite
+    let reportError
+    const errorReported = new Promise((resolve) => {
+      reportError = resolve
+    })
+    const consoleError = jest.spyOn(console, 'error').mockImplementation((error) => {
+      reportError(error)
+    })
+
+    jest.doMock('rollup', () => ({
+      rollup: () => Promise.resolve({ write: () => Promise.resolve() })
+    }))
+    jest.doMock('../../build/rollup.config', () => config => config)
+    jest.doMock('ncp', () => ({ ncp: (source, destination, callback) => callback() }))
+    jest.doMock('fs', () => ({
+      readdir: (directory, callback) => callback(null, []),
+      readFile: (file, encoding, callback) => callback(null, ''),
+      writeFile: (file, contents, encoding, callback) => {
+        rejectWrite = () => callback(writeError)
+      }
+    }))
+
+    require('../../build') // eslint-disable-line global-require
+
+    await new Promise(resolve => setImmediate(resolve))
+    expect(rejectWrite).toEqual(expect.any(Function))
+
+    rejectWrite()
+    await expect(errorReported).resolves.toBe(writeError)
+    expect(consoleError).toHaveBeenCalledTimes(1)
+  })
+})