Bug report

What is the current behavior?

webpack shows a warning when rebuild:

Multiple assets emit different content to the same filename app.js.map

If the current behavior is a bug, please provide the steps to reproduce.

webpack.config.js

const path = require('path')
const webpack = require('webpack')

module.exports = {
  mode: 'development',
  entry: {
    app: './entry.js'
  },
  output: {
    path: path.resolve(__dirname, './dist'),
    filename: '[name].js'
  },
  devtool: false,
  plugins: [
    new webpack.SourceMapDevToolPlugin({
      filename: '[name].js.map'
    }),

    new webpack.HotModuleReplacementPlugin() // !!!!!!! remove this line, the warning will not display
  ]
}

entry.js

console.log(`
  modify this module, then webpack shows warning:
  WARNING in Conflict: Multiple assets emit different content to the same filename app.js.map
`)

reproduction steps:

1. use SourceMapDevToolPlugin and HotModuleReplacementPlugin (refer to webpack.config.js)
2. npx webpack --watch
3. modify content of entry.js, then save
4. webpack shows a warning: Multiple assets emit different content to the same filename app.js.map

webpack doesn’t show this warning if i remove the line new webpack.HotModuleReplacementPlugin()

What is the expected behavior?

webpack should not show a warning

Other relevant information: webpack version: 4.41.0 Node.js version: v10.15.3 Operating System: win10