Multi level "exports" not supported?

[achingbrain]

The multiformats module has the following fields in it's package.json:

{
  // ...other stuff
  "main": "./cjs/src/index.js",
  "browser": {
    ".": "./cjs/src/index.js",
    "./basics": "./cjs/src/basics.js",
    "./bases/base16": "./cjs/src/bases/base16.js"
    // ...other stuff
  },
  "exports": {
    ".": {
      "browser": "./esm/src/index.js",
      "require": "./cjs/src/index.js",
      "import": "./esm/src/index.js"
    },
    "./basics": {
      "browser": "./esm/src/basics.js",
      "require": "./cjs/src/basics.js",
      "import": "./esm/src/basics.js"
    },
    "./bases/base16": {
      "browser": "./esm/src/bases/base16.js",
      "require": "./cjs/src/bases/base16.js",
      "import": "./esm/src/bases/base16.js"
    }
    // ...other stuff
  }
}

and the following directory structure:

multiformats
|-- cjs
|    +-- src
|         |-- index.js
|         |-- basics.js
|         +-- bases
|              +-- base16.js
|-- esm
|    +-- src
|         |-- index.js
|         |-- basics.js
|         +-- bases
|              +-- base16.js
|-- src
|    |-- index.js
|    |-- basics.js
|    +-- bases
|         +-- base16.js

When using browserify on a project that depends on multiformats, I see errors when trying to require anything greater than one level deep in the module:

const mf = require('multiformats')
// ok

const basics = require('multiformats/basics')
// ok

const basics = require('multiformats/basics/base16')
// Error: Can't walk dependency graph: Cannot find module 'multiformats/bases/base16' from '/path/to/index.js'
//     required by /path/to/index.js
//     at /path/to/node_modules/resolve/lib/async.js:137:35
//     at processDirs (/path/to/node_modules/resolve/lib/async.js:291:39)
//     at isdir (/path/to/node_modules/resolve/lib/async.js:300:32)
//     at /path/to/node_modules/resolve/lib/async.js:25:69
//     at FSReqCallback.oncomplete (fs.js:183:21)

Is this intentional? I can't see where this module consults the exports field (though it's been a long day) or is it unsupported?

[ljharb]

resolve does not yet support the "exports" field in any way; see #224.

Regardless, for backwards compatibility, packages like multiformats should be mimicking the "exports" structure in a CJS-compatible directory structure - at which point, tools like resolve will Just Work.

[achingbrain]

After digging a bit deeper this has nothing to do with the "exports" field. Browserify won't consult the browser map in package.json to see if a file should be overridden if it can't resolve the original file in the first place.

That is, you can't use browser values as a hint to Browserify as to where to look for the file for a given path that's been required in the same way you can with "exports".

One thing is that the file at the given path doesn't need to actually have any content, it just needs to exist, and node will take exports over browser so there's no danger of it importing the wrong file.

[ljharb]

New node will, yes, but old node won't use exports or browser - so the "exports" structure should still be represented in actual requireable CJS files in the filesystem.

[achingbrain]

This has been fixed by the linked ipjs PR