Source maps aren't added to .mjs output files

[philipwalton]

Bug report

What is the current behavior?

Source maps don't get added when defining an output file with an mjs extension. If I change nothing about my config except for the output extension from mjs to js, it works as expected.

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

Here's a minimal repo:

webpack.config.js:

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

module.exports = {
  mode: 'development',
  entry: {
    main: "./main.mjs"
  },
  output: {
    path: path.resolve(__dirname),
    filename: "[name].[chunkhash].mjs",
  },
  devtool: '#source-map',
};

main.mjs:

console.log('Hello World');

Other relevant information:
webpack version: 4.17.0
Node.js version: 10.8
Operating System: MacOS 10.13.6
Additional tools: N/A

[montogeek]

Not sure this is even supported.

[montogeek]

Which source map options have you tried?

[mathiasbynens]

.mjs is supported by default elsewhere in webpack. I think applying the same logic (if *.js or *.mjs → generate source maps) would make sense here.

[philipwalton]

In my example I show that I'm using the option devtool: '#source-map'.

And I agree with @mathiasbynens, Webpack claims in many places that it supports .mjs, and it's able to process the file correctly. The only thing it's not doing is generating the source map and appending a reference to it in the original file.

[sokra]

Send a PR fixing this RegExp:

webpack/lib/SourceMapDevToolPlugin.js

Line 87 in 6f1f18f

options.test = options.test || /\.(js|css)($|\?)/i;

[philipwalton]

Filed #7947.