Typing: use WebpackError type definition from webpack

src/webpack/compiler/registerReadyCallback.ts

@@ -3,9 +3,11 @@ import { MOCHAPACK_NAME } from '../../util/constants'
 
 export default function registerReadyCallback(
   compiler: Compiler,
-  cb: (err: (Error | string) | null, stats: Stats | null) => void
+  cb: (err: Error, stats: Stats | null) => void
 ) {
-  compiler.hooks.failed.tap(MOCHAPACK_NAME, cb)
+  compiler.hooks.failed.tap(MOCHAPACK_NAME, (err: Error) => {
+    cb(err, null)
+  });
   compiler.hooks.done.tap(MOCHAPACK_NAME, (stats: Stats) => {
     if (stats.hasErrors()) {
       const jsonStats = stats.toJson()

src/webpack/util/createStatsFormatter.ts

@@ -2,8 +2,8 @@ import { EOL } from 'os'
 import chalk from 'chalk'
 import { Stats } from 'webpack'
 import RequestShortener from 'webpack/lib/RequestShortener'
+import WebpackError from 'webpack/lib/WebpackError'
 import { formatErrorMessage, stripLoaderFromPath } from './formatUtil'
-import { WebpackError } from '../types'
 
 const createGetFile = (requestShortener: RequestShortener) => (
   e: WebpackError
@@ -29,14 +29,7 @@ const createGetFile = (requestShortener: RequestShortener) => (
 const ensureWebpackErrors = (
   errors: Array<string | WebpackError>
 ): Array<WebpackError> =>
-  errors.map((e: string | WebpackError) => {
-    /* istanbul ignore if */
-    if (typeof e === 'string') {
-      // webpack does this also, so there must be case when this happens
-      return ({ message: e } as any) as WebpackError
-    }
-    return e
-  })
+  errors.map((e: WebpackError) => e.toString())
 
 const prependWarning = (message: string) =>
   `${chalk.yellow('Warning')} ${message}`