Cyclic dependencies in es6 modules

[jonathanolson]

(JO, [SR?] 2-4 hours) [sprintable, JO investigated] Cyclic Dependencies: ES6 modules support cyclic dependencies. So places like scenery and dot, where we had to "trick" the runtime with an assignment-less require statement and then loading things from the namespace will no longer be necessary.
What to do with this pattern and cycles in general? window.require = function(){}; // TODO: #820 this supports like require( 'DOT/Utils' ); in Vector2
JO: Cyclic dependencies in our classic style look fine. See #820 (comment) for details, use empty imports (import ‘../repo/js/Blah.js’) if we just need to ensure code runs (our migrate will need to change to include this).
JO: Commented-out require statements could be added back in, and use the cyclic form

I'll investigate commented-out require statements, we can potentially just uncomment those and test.

After the fact, I'll also want to do some cleanup in those cases

[jonathanolson]

Handled, we're now uncommenting those require statements and it's working nicely.

Keeping open to handle cleanup after full migrate, but dropping priority.

[samreid]

Balloons and static electricity exhibits a problem where scenery.Image does not exist when Node.rasterized is called. @jonathanolson how do you recommend to proceed?

[samreid]

From slack:

Jonathan Olson 5:55 PM
Just have an empty import in Node?

Sam Reid 6:00 PM
I tried but that creates a cycle and fails to load. Image cannot be defined until Node definition completes

Jonathan Olson 6:01 PM
Then put an empty import where we use rasterize?

Sam Reid 6:02 PM
At each of the top-level call sites?

[jonathanolson]

Created phetsims/scenery#1038 for handling that case. I presume we aren't running into any other issues?

[samreid]

As far as I can tell, this only triggered in Balloons and Static Electricity, and the workaround I committed seems to be working OK.

[chrisklus]

@jonathanolson is there anything to do here? @samreid thinks this might be ready to close.

[jonathanolson]

Keeping it open for #871 (comment), since things like Vector2/Vector3 will want to not JUST import each other, but USE those imports (which I can't do easily in master before migration).

[jonathanolson]

Handled most circular dependency issues. Things like Block/Drawable seem like an issue (where interestingly if we try to import Block from Drawable, it will fail out and I can't identify where that import would cause issues.

@samreid thoughts to continue?

[jonathanolson]

The above commit seems to resolve scenery builds, but that's really concerning. @samreid have time to discuss this sometime?

[samreid]

Since the commit includes sorting, it is difficult to tell what part is concerning. Can you please clarify?

[jonathanolson]

That removing the import for ParallelDOM in the scenery main.js now allows it to run correctly after building.

And the fact that there were a lot of reasons I couldn't add back in all the imports we wanted (Block/Drawable being most easy to reproduce).

[jbphet]

We discussed this in the 6/4/202 dev meeting and the memorable quote was "[T]his is low priority until it becomes a problem." So, we are going to mark it as deferred and assign it to @ariel-phet. He'll set a reminder to check it in six months and, if it's not a problem by then, we will close it.

[ariel-phet]

Calendar reminder set