fix: useSprings with props function

This regression was introduced in the previous canary version.

It caused the props function to be called on every render.

The deps no longer have the "length" argument included by default, because we handle length changes in a separate useMemo call now.

If you want to update all springs when the length changes, you must include the length in your deps array explicitly.

packages/core/src/useSprings.ts

@@ -1,4 +1,4 @@
-import { useMemo, RefObject, useImperativeHandle } from 'react'
+import { useMemo, RefObject, useImperativeHandle, useState } from 'react'
 import { useLayoutEffect } from 'react-layout-effect'
 import { is, each, usePrev, useOnce, UnknownProps, Merge } from 'shared'
 
@@ -70,23 +70,36 @@ export function useSprings(
   deps?: any[]
 ): any {
   const propsFn = is.fun(props) && props
-  if (deps) deps = deps.concat(length)
+  if (propsFn && !deps) deps = []
 
   // The "ref" prop is taken from the props of the first spring only.
   // The ref is assumed to *never* change after the first render.
   let ref: RefObject<SpringHandle> | undefined
 
-  const ctrls: Controller[] = useMemoOne(() => [], [])
+  const [ctrls] = useState<Controller[]>([])
   const updates: ControllerProps[] = []
   const prevLength = usePrev(length) || 0
+
+  // Create new controllers when "length" increases, and destroy
+  // the affected controllers when "length" decreases.
   useMemoOne(() => {
+    // Note: Length changes are unsafe in React concurrent mode.
     if (prevLength > length) {
       for (let i = length; i < prevLength; i++) {
         ctrls[i].dispose()
       }
     }
     ctrls.length = length
-    for (let i = 0; i < length; i++) {
+    getUpdates(prevLength, length)
+  }, [length])
+
+  // Update existing controllers when "deps" are changed.
+  useMemoOne(() => {
+    getUpdates(0, prevLength)
+  }, deps)
+
+  function getUpdates(startIndex: number, endIndex: number) {
+    for (let i = startIndex; i < endIndex; i++) {
       const ctrl = ctrls[i] || (ctrls[i] = new Controller())
       const update: UseSpringProps<any> = propsFn
         ? propsFn(i, ctrl)
@@ -106,7 +119,19 @@ export function useSprings(
         }
       }
     }
-  }, deps)
+  }
+
+  // Controllers are not updated until the commit phase.
+  useLayoutEffect(() => {
+    each(updates, (update, i) => ctrls[i].update(update))
+    if (!ref) {
+      each(ctrls, ctrl => ctrl.start())
+    }
+  })
+
+  useOnce(() => () => {
+    each(ctrls, ctrl => ctrl.dispose())
+  })
 
   const api = useMemo(
     (): SpringHandle => ({
@@ -136,20 +161,8 @@ export function useSprings(
 
   useImperativeHandle(ref, () => api)
 
-  const isRenderDriven = !propsFn && arguments.length < 3
-  if (isRenderDriven) deps = undefined
-
-  useLayoutEffect(() => {
-    each(updates, (update, i) => ctrls[i].update(update))
-    if (!ref) {
-      each(ctrls, ctrl => ctrl.start())
-    }
-  }, deps)
-
-  useOnce(() => () => {
-    each(ctrls, ctrl => ctrl.dispose())
-  })
-
   const values = ctrls.map(ctrl => ({ ...ctrl.springs }))
-  return isRenderDriven ? values : [values, api.update, api.stop]
+  return propsFn || arguments.length == 3
+    ? [values, api.update, api.stop]
+    : values
 }