[material-ui][TimelineItem] Fix extra ::before spacing when TimelineOppositeContent is present by tyalau · Pull Request #46663 · mui/material-ui (original) (raw)

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(2) Not sure about this on non-RSC SSR. With a 'use client' parent rendering on the server, initial state is false, so the SSR HTML has MuiTimelineItem-missingOppositeContent. After mount, the effect flips state and the class is removed — that gives a hydration class-attribute mismatch and a one-frame flash for any theme override keyed on that class.

The old render-time computation kept SSR and the first client render in sync. Same fix as (1) should cover this too.