Broken sourcemaps for two outputs of different entryFileNames in same dir

[danimoh]

• Rollup Version: 2.0.2
• Operating System: Fedora
• Node Version: 12.13.1
• Link to reproduction: https://repl.it/repls/GraveProudCore

Expected Behavior

Generated sourcemaps for individual bundles generated in an output dir should reference their respective bundle file.

Actual Behavior

All sourcemaps for bundles named via entryFileNames in the same output dir reference the last generated file ("file":"bundle.cjs.js" in the example repl).
Chrome DevTools fails to parse the erroneous sourcemaps.

Use case

The repl setup is somewhat artificial. The desired behavior can in the example be achieved more elegantly and without issues by using output.file instead of output.dir in combination with output.entryFileNames. However, there are uses cases where such a setup makes sense, for example when one wants to generate declaration files with the typescript plugin which requires specifying the dir option.

[danimoh]

For anyone running into this issue:
This can be fixed with a very simple output plugin, for example for the repl linked in the issue:

import path from 'path';

// Fixes broken sourcemaps generated by rollup which might mess up association to a sourcemap's bundle file when writing
// multiple outputs to the same directory, see https://github.com/rollup/rollup/issues/3439.
function fixSourcemaps() {
    return {
        name: 'fix-sourcemaps',
        generateBundle: (options, bundle) => {
            for (const assetOrChunkInfo of Object.values(bundle)) {
                if (!assetOrChunkInfo.map) return; // has no sourcemap
                assetOrChunkInfo.map.file = path.basename(assetOrChunkInfo.fileName);
            }
        },
    };
}

export default {
  input: 'input.js',
  output: [
    {
      dir: 'output',
      format: 'es',
      entryFileNames: 'bundle.es.js',
      sourcemap: true,
      plugins: [fixSourcemaps()],
    },
    {
      dir: 'output',
      format: 'cjs',
      entryFileNames: 'bundle.cjs.js',
      sourcemap: true,
      plugins: [fixSourcemaps()],
    },
  ],
};

[lukastaegert]

Sorry, for this, fix at #3440

[lukastaegert]

Respect you found such an easy workaround using the plugin API 👍

[danimoh]

Awesome, thank you for the fix :)