chore(test): run hook tests under React.StrictMode#2431
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Flip `configure({ reactStrictMode: true })` globally in
`packages/core/test/setup.ts` so every `render` and `renderHook` from
`vitest-browser-react` is automatically wrapped in `<React.StrictMode>`.
If a test passes under StrictMode it passes without; the inverse hides
real bugs (see #1991).
Simplifies `useSprings.test.tsx`: the local `isStrictMode` flag and
`<React.StrictMode>` wrapper in `createUpdater` are now redundant, so
both are dropped. The `strictModeFunctionCallMultiplier` is preserved
(still 2) because props functions are still invoked twice per render.
Refs #1991.
The `reverse` and `passedRef` flags were accumulated as side effects inside the `useSprings` wrapper, expecting it to fire at least once per render. Under React.StrictMode's second render pass `useSprings` skips the wrapper — its `useMemo([length])` deps are unchanged and the `[deps]` `useMemo` calls `declareUpdates(0, min(prevLength, length))` which is `(0, 0)` on a first render — so the accumulators stay at their initial values. `reverse` defaults to `true`, which inverts the chaining direction in the layout effect. For object-form props every spring receives the same props, so derive `reverse` and `passedRef` directly from `propsArg` instead of mutating them via the wrapper. The function-form path still uses the accumulator pattern; same latent issue, tracked as follow-up. Fixes #1991.
…sed springs `SpringValue.stop()` unconditionally called `_focus(this.get())` to snap `animation.to` to the current value. That is the right move when freezing an active animation, but it incorrectly establishes a goal where none existed on a paused or never-started spring (`_prepareNode` seeds the underlying value via `from`, so `this.get()` returns that value). The bug became observable under React.StrictMode, whose simulated unmount fires `useSprings`'s cleanup (`ctrl.stop(true)`) on every controller — including a freshly-mounted spring whose initial update was paused by `SpringContext`. The cleanup wrote `from` into `animation.to`, leaving `t.goal` equal to `0` instead of `undefined` on the subsequent remount. Gate the `_focus` call on `animation.to` already being defined. The "only merges when changed" test gets an updated first assertion that acknowledges the StrictMode mount → simulated unmount → remount cycle double-fires the layout effect: the user update fires twice, and the default-context update fires on the remount because `defaultProps` now has `onProps` set. Fixes #1991.
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🦋 Changeset detectedLatest commit: 8a43db7 The changes in this PR will be included in the next version bump. This PR includes changesets to release 12 packages
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This was referenced May 21, 2026
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Run every hook test under
React.StrictModeby default. The premise: if a test passes under StrictMode it passes without, and the inverse hides real React-correctness bugs. The two fixes in this PR are exactly the kind of bug the inverse was hiding — both fall out the moment StrictMode is on.Bugs StrictMode caught
useTrailchained in the wrong direction.reverseandpassedRefwere accumulated as side effects inside theuseSpringswrapper, relying on the wrapper firing at least once per render. StrictMode's second render pass skips it —useMemo([length])deps are unchanged so the cache holds, and the[deps]useMemoinvokesdeclareUpdates(0, min(prevLength=0, length=2))which iterates zero times on the first render.reversestayed at its initialtrue, flipping the trail direction. Fixed by derivingreverse/passedReffrompropsArgdirectly for the object form. The function form has the same latent issue and is noted as follow-up.SpringValue.stop()established a phantom goal.stop()unconditionally called_focus(this.get())to snapanimation.toto the current value — correct for an active animation, wrong for a paused or never-started spring whose underlying value was seeded by_prepareNodeviafrom. StrictMode's simulated unmount firesuseSprings's cleanup (ctrl.stop(true)) on every controller, so a freshly-mounted paused spring ended up withanimation.to = 0instead ofundefined. Fixed by gating the_focuscall onanimation.toalready being defined.Stale assertion
SpringContext > only merges when changedneeded an updated first assertion — not a library bug, an unavoidable consequence of StrictMode double-firing effects on initial mount. The user update fires twice, and the default-context update fires on the remount becausedefaultProps.onPropswas set by the first pass. Subsequent rerenders are unaffected.