Clean-up Flexbox Layout algorithm implementation

[NickAcPT]

Problem

While browsing the implementation of the algorithm in this project, I noticed some things that probably should be cleaned up in the future.

Missing Implementation

There's a few steps that are not implemented yet and probably should be.

https://github.com/DioxusLabs/stretch/blob/a50a4569c5dbcebdcb77408f804d9bf90ccdc508/src/algo.rs#L296-L302

https://github.com/DioxusLabs/stretch/blob/a50a4569c5dbcebdcb77408f804d9bf90ccdc508/src/algo.rs#L304-L310

https://github.com/DioxusLabs/stretch/blob/a50a4569c5dbcebdcb77408f804d9bf90ccdc508/src/algo.rs#L304-L310

Out of spec Implementation

It seems like there's some steps in the implemented algorithm that are outside of the Flexbox specification.

https://github.com/DioxusLabs/stretch/blob/a50a4569c5dbcebdcb77408f804d9bf90ccdc508/src/algo.rs#L269-L270

https://github.com/DioxusLabs/stretch/blob/a50a4569c5dbcebdcb77408f804d9bf90ccdc508/src/algo.rs#L360-L363

https://github.com/DioxusLabs/stretch/blob/a50a4569c5dbcebdcb77408f804d9bf90ccdc508/src/algo.rs#L454-L455

https://github.com/DioxusLabs/stretch/blob/a50a4569c5dbcebdcb77408f804d9bf90ccdc508/src/algo.rs#L605-L609

Tight coupling

Maintainability of the Flexbox algorithm in the future is important, more so if more algorithms are implemented side-by-side next to it.
Thus, I think that the flexbox (and future) algorithm implementation(s) should be divided by steps.
While it requires more code to setup and do properly, it will allow to have simpler and shorter methods for each step of the layouting.

I hope I didn't miss anything, first time I am opening an issue here.

[alice-i-cecile]

This is a fantastic issue, and I agree on all of the points you raised.

The only other suggestions I have to implementors is a) do the refactor in one PR, then add the other steps in a second PR b) remember to double-check benchmarks to avoid major regression and c) remember to use the #[inline] attribute macro on your little functions to help the compiler optimize this.

[TimJentzsch]

I suggest that we split this issue up as two as well, for the two steps you suggested.
Then it's easier to keep track and to assign the tasks to contributors.

[TimJentzsch]

I think now that the refactoring is merged, it would be a good idea to split this up into multiple smaller, actionable issues for each thing that needs to be improved.

This would make it easier to implement the features, review them and to keep progress of what needs to be done.

[alice-i-cecile]

Agreed. Closing; please do make scoped follow-up issues!

[TimJentzsch]

Not sure if I got all of them, but probably most.