Preserve the export statements of specific modules

[ChadKillingsworth]

Need a way to indicate specific modules which will have their export statements preserved through compilation. This will allow the compiler to both process modules and also output modules.

Supports google/closure-compiler-npm#56

I'm envisioning that module rewriting will look something like this:

module$a = function() {};
module$a.foo = 'foo';

// Synthentic extern to be replaced with a module export statement
// before code printing
JSCompiler_preserveExport(module$a);
JSCompiler_preserveExport(JSCompiler_renameProperty('foo', module$a), module$a.foo);

[TrySound]

Do I understand correctly this issue is about ignoring (not bundling) import statements and producing esm output? Then gcc is the main blocker in migrating react distribution to esm.

Currently I get this error in one of react modules with language_in/out 'ECMASCRIPT6' however there's not need in any resolution.

/var/folders/45/62sm5z9j7_79q17k3p17xl180000gn/T/tmp-30456KDpy739M3rD2.tmp:1: ERROR - Invalid module
path "react" for resolution mode "BROWSER"
import React from 'react';
^

1 error(s), 0 warning(s)

[ChadKillingsworth]

Has nothing to do with imports - only exports. If you are using SIMPLE optimizations, this is fairly easy to do with output wrappers:

--js_output_wraper="%output%;export default module$path$to$module.default"

This is much more challenging for ADVANCED mode compilations.

[TrySound]

It's possible to disable bundling cjs with process_common_js_modules. Does gcc have a plan to add similar for es modules with ECMASCRIPT6 output?

Yes compilation level is SIMPLE. Thanks for the tip.

[Jamesernator]

A kinda dream I'd have is that preserving exports in a set of modules would allow closure compiler to preserve public names and such automatically without resorting to things like ['someName'].

Combined with ES private fields it'd be easy to determine visibility of name.

e.g. Consider this set of modules:

// Queue.js
export default class Queue {
  enqueue() {

  }

  dequeue() {

  }
}

// Lock.js
import Queue from './Queue.js';

export default class Lock {
  #locked = false;
  #queue = new Queue();

  acquire() {
    // ...
  }
}

// Resource.js
import Lock from './lock.js';

export default class Resource {
  lock = new Lock();

  doThing() {

  }
}

If we have Resource.js as the only file where exports are preserved, then we can determine that all properties of Resource and Lock (because it's public on Resource) must be visible. However because Queue is not visible from any public symbol it's fair game for any minification.

[EatingW]

Created internal issue http://b/141261567