Summary:
PreAllocation currently always happens at revision 0 (after ShadowNode creation), and all CREATE mutations are triggered for ShadowNodes at revision 1 or higher (since CREATE mutations are generated by the differ, it means that all ShadowNodes have revision 1 or higher when CompleteRoot is called). This means that between PreAllocation and CREATE, we /always/ expect at least one clone.
It is possible for a node to be "non-view-forming" at revision 0, causing view preallocation to be skipped, and "view-forming" at revision 1 (causing the CREATE mutation to be thrown away, since all CREATE mutations of revision 0 or 1 are thrown away). This causes a crash. It is extremely marginal, but there are repros in the wild.
Thus, I'm introducing one new UIManager and Scheduler delegate method that allows the mounting layer to be notified of clones. If a clone from rev 0->1 results in a node going from non-view-forming to view-forming, we can preallocate then, as well.
This resolves this crash, and allows us to keep experimenting safely with this View PreAllocation optimization. I believe all edge-cases are accounted for.
Changelog: [Internal]
Reviewed By: sammy-SC
Differential Revision: D29043426
fbshipit-source-id: dff11d3140ded1cbb02a5518a3aeb52dc812cc50
f2e0b2f45f