output.entryFileNames - accept a function?

[PatNeedham]

Feature Use Case

Is it possible for entryFileNames option to accept a function in addition to a string?

For background context, this is what my rollup.config.js looks like:

import commonjs from 'rollup-plugin-commonjs';
import nodeResolve from 'rollup-plugin-node-resolve';
import globals from 'rollup-plugin-node-globals';
import builtins from 'rollup-plugin-node-builtins';
import babel from 'rollup-plugin-babel';
import json from 'rollup-plugin-json';

module.exports = {
  experimentalCodeSplitting: true,
  optimizeChunks: true,
  external: […],
  input: [
    'src/components/Alert.jsx',
    'src/components/Anchor.jsx',
    'src/components/Button.jsx’,
    'src/components/Dropdown/index.jsx', // inside own folder
    ‘src/components/SomethingElse/index.jsx’,  // inside own folder
    …
  ],
  output: {
    dir: 'dist',
    format: 'esm'
  },
  plugins: [
    json(),
    nodeResolve({
      jsnext: true,
      preferBuiltins: false,
      extensions: ['.js', '.jsx', '.json'],
    }),
    commonjs({
      include: [
        'node_modules/**'
      ],
      exclude: [
        'node_modules/process-es6/**'
      ],
      namedExports: {
        'node_modules/downshift/node_modules/react-is/index.js': ['isForwardRef'],
        'node_modules/prop-types/index.js': [ ... ],
        'node_modules/react/index.js': [ ... ],
        'node_modules/react-dom/index.js': ['createPortal', 'findDOMNode', 'render']
      }
    }),
    babel({
      exclude: 'node_modules/**',
      presets: ['@babel/preset-env', 'react-app'],
      plugins: [
        ['syntax-trailing-function-commas', { loose: true }],
        ['@babel/plugin-proposal-class-properties', { loose: true }],
      ],
      runtimeHelpers: true,
    }),
    globals(),
    builtins(),
  ],
}

The default [name].js value for output.entryFileNames field this leads to a dist folder which contains the majority of the components necessary, except for those like Dropdown, SomethingElse, etc. the ones inside their own folders. However, they do appear inside files named like index.js, index1.js, index2.js, etc.

What can be done to make Rollup create output files like Dropdown.js and SomethingElse.js instead of index.js and index.1.js?

Feature Proposal

If entryFileNames accepted a function, that would address this issue because I could then write something like

output: {
    dir: 'dist',
    entryFileNames: (filePath) => endsWithIndexJSX(filePath) ? `${getLastFolderName(filePath)}.js` : `[name].js`
    format: 'esm'
  },

[lukastaegert]

This is definitely doable but might take some time. Note that you can already achieve the same (though maybe not as elegantly) today by using the object form of input:

input: {
  Alert: 'src/components/Alert.jsx',
  Dropdown: 'src/components/Dropdown/index.jsx', 
  // if you actually do want it in a special sub-folder
  'separate/SomethingElse': 'src/components/SomethingElse.jsx', 
  …
},

[jakearchibald]

The same feature would solve a slightly different use-case:

Most names should feature a [hash], but some resources (like a service worker, or in some cases a favicon) should not, so a single rule doesn't quite work.

[shellscape]

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[lukastaegert]

For me, making the file name output properties functions is definitely a desirable feature which could also solve some other issues. Reopening it to track this.

[shellscape]

@lukastaegert I'd like to tackle this one but I'll need some direction on when and where the function should be called. I've tracked down where the options are fetched from config, but unsure on the best place to call the fn. Is renderNamePattern in renderNamePattern.ts the right spot for that?

We're also going to get requests for async functions I'm sure, so I'll have to take that into consideration.

[lukastaegert]

I would not go for async functions unless there is actual demand. Also there are hardly any places in the user facing options where you can do something async.

Also I think this should make all three XYfileNames options replaceable with functions.

As for the right place, yes, renderNamePattern could be a good choice. I assume the idea is that if pattern is a function, it is called to get the actual pattern? Sounds good!

[frank-dspeed]

I did implement it in #3658 and added a test it works also with assets and all other filds that support a pattern.