column tree distributes width more safely

[addepar-andy]

There is a bug where the width distributor will get into an infinite loop. The loop would check for delta being zero, but if delta started as a decimal, then the check would never pass. This does 3 things:

1. adds a loop guard so that the UI / tests don't freeze if something crazy happens to the loop.
2. rounds delta so the target is always an integer
3. makes delta chunks always integral and sum to the delta

Reviewers: @Addepar/web-core

[addepar-andy]

i can write some unit tests for the new function i wrote, but i'm not really sure how to actually trigger this bug, so i'm not sure what kind of component test to write.

[addepar-andy]

i have also verified that this does fix the frozen tests on my iverson branch

[pzuraq]

I like the divideRounded function a lot, it's what I was trying to do but better!

I think we should wrap the loopCount logic in a DEBUG flag so that it gets stripped out of production builds though. You can import the flag, and use it in if statements and they'll be stripped:

import { assert } from '@ember/debug';
import { DEBUG } from '@glimmer/env';

let loopCount;

if (DEBUG) {
  loopCount = 0;
}

// ...

if (DEBUG) {
  loopCount++;
  assert('loop count exceeded guard while distributing width', loopCount < LOOP_COUNT_GUARD);
}

[addepar-andy]

i think we should keep the flag in. if something goes wrong on prod and guard is there, users will see an error. without the guard, the entire tab will freeze.

[pzuraq]

We can keep it in for now, but I’d like to circle back and add a few more assertions that give us guarantees before we release 1.0.0. It shouldn’t be possible to get in that state.