Rewrite path parsing using the `path` module instead of regexes

In the recent weeks we had multiple high priority bugs, which were caused by the same reason: parsing paths with regexes.

I happily create a PR for this, but I have no idea what does the getModuleName function do. Are there some test cases for that?

I don't believe there are tests for it. getModuleName() accepts a file path (a package main) and attempts to pluck out the NPM package name from it. Basically the next directory within the deepest node_modules directory. There is a slight twist in that namespaced modules consist of two path segments. I don't mind writing some tests for the function, or refactoring it to split on path.separator and inspect the parts.

It turns out nodejs still does not have path.split, we cant bypass regexes entirely

We could use something like this, but I don't particularly like the idea of a loop that I can't prove it will terminate.

var path = require("path");
function pathSplit(pathname) {
  var parts = [];
  for (;;) {
    var basename = path.basename(pathname);
    var dirname = path.dirname(pathname);
    if (dirname === pathname) {
      break;
    }
    pathname = dirname;
    parts.push(basename);
  }
  parts.reverse();
  return parts;
}

console.log(pathSplit("a/b/sdfsdf//cccv/node_modules/dsgdgfh")); // [ 'a', 'b', 'sdfsdf', 'cccv', 'node_modules', 'dsgdgfh' ]

This looks better, only that it still doesn't use the path module:

function getModuleName(pathname) {
  var parts = pathname.split(/[\\/]/g).filter(p => p !== "" && p !== "." && p !== "..");
  if (parts.length <= 0) {
    return null;
  }
  var nodeModulesIdx = parts.lastIndexOf("node_modules");
  if (nodeModulesIdx < 0 || nodeModulesIdx + 1 >= parts.length) {
    return parts[parts.length - 1];
  }
  return parts[nodeModulesIdx + 1];
}

console.log(getModuleName("../../babel-plugin-asd")); // babel-plugin-asd
console.log(getModuleName("../..//babel-plugin-asd")); // babel-plugin-asd
console.log(getModuleName("..//../babel-plugin-asd")); // babel-plugin-asd
console.log(getModuleName("c:\\node_modules/babel-plugin-asd")); // babel-plugin-asd
console.log(getModuleName("../node_modules/xxx/../node_modules///babel-plugin-asd/xyz")); // babel-plugin-asd
console.log(getModuleName("xxx/../node_modules/..//babel-plugin-asd/xyz")); // babel-plugin-asd

What do you think?

@sorgloomer Needs some extra logic to support namespaced packages. @foo/bar - they show up as directories within node_modules.

Also, it might be easier to use path.resolve(pathname) so we don't have to worry about jumps? For the split(), could do: pathname.split(path.separator).