Support ES6 modules in minimally-compiled bundles

Feature request: it seems possible that ES6 modules would work in minimally compiled bundles (e.g. compile=False js_binary rules) by converting them to goog.module form. Something like:

// foo.js
import {bar} from './bar.js';

export const foo = bar + 10;

might be transformed to:

// bundle.js
goog.loadModule('module$foo', function() {
  const {bar} = goog.require('$module$bar');
  
  exports.foo = bar + 10;
});

[jplaisted]

Already working on this! Note that goog.loadModule accepts one argument currently; the module definition function. We’re planning on adding a second argument, the path of the module. And we’re planning on support for relative, path goog.requires in a goog.module that resolve against the path that was passed in as the argument. Mostly this is for interop between goog and ES6 modules, but it makes this bundled case nice as well.

So your above example would be transformed to

goog.loadModule(function() {
  const {bar} = goog.require('./bar.js');
  
  exports.foo = bar + 10;
}, '/foo.js');

bar.js would also be similarly transformed and its exports would be registered under its path (/bar.js). So when the goog.require(‘./bar.js’) is called, it resolves to /bar.js, and the exports can be retrieved.

This will be done path based rather than symbol based since we need a similar mechanism for the debug loading case, and this way we don’t need to rewrite any paths at all (either to full paths or substitutes for symbols), which would require unnecessary rewriting of goog modules in the debug loading case.

[jplaisted]

Support for this landed awhile ago.