Upstream Bug (?): Arcane resolution rules with package.json

[ryan-roemer]

For a contrived example like:

// pkgs/index.js
const dep = require("./dep");
console.log("TODO HERE", { dep });

// pkgs/dep/deeper/index.js
module.exports = "deeper index";

// pkgs/dep/deeper/package.json
{
  "main": "diff.js"
}

// pkgs/dep/deeper/diff.js
module.exports = "diff";

// pkgs/dep/index.js
module.exports = "dep index";

// pkgs/dep/package.json
{
  "main": "deeper"
}

Node.js resolves thusly:

$ node pkgs
TODO HERE { dep: 'deeper index' }

which means pkgs/dep/package.json is read, but pkgs/dep/deeper/package.json is not, instead just using pkgs/dep/deeper/index.js.

In trace-deps, the resolve library instead comes up with our traced deps as:

// out/pkgs/index.js
const dep = require("./dep");
console.log("TODO HERE", { dep });

// out/pkgs/dep/deeper/package.json
{
  "main": "diff.js"
}

// out/pkgs/dep/deeper/diff.js
module.exports = "diff";

// out/pkgs/dep/package.json
{
  "main": "deeper"
}

// out/package.json
{
  /* snipped */
}

The problem is for the nested load of deeper, resolve() is using deeper/package.json:main and real Node.js doesn't instead using deeper/index.js directly, which we see in output here:

$ node out/pkgs/index.js 
internal/modules/cjs/loader.js:305
      throw err;
      ^

Error: Cannot find module '/Users/rye/Desktop/TD_TEST/out/pkgs/dep/deeper'. Please verify that the package.json has a valid "main" entry
    at tryPackage (internal/modules/cjs/loader.js:297:19)
    at Function.Module._findPath (internal/modules/cjs/loader.js:528:18)
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:780:27)
    at Function.Module._load (internal/modules/cjs/loader.js:686:27)
    at Module.require (internal/modules/cjs/loader.js:848:19)
    at require (internal/modules/cjs/helpers.js:74:18)
    at Object.<anonymous> (/Users/rye/Desktop/TD_TEST/out/pkgs/index.js:1:13)
    at Module._compile (internal/modules/cjs/loader.js:955:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:991:10)
    at Module.load (internal/modules/cjs/loader.js:811:32) {
  code: 'MODULE_NOT_FOUND',
  path: '/Users/rye/Desktop/TD_TEST/out/pkgs/dep/package.json',
  requestPath: './dep'
}