fix(Controller): handle the cancel prop in runAsync start callback

Remove `cancel` handling from the `runAsync` function, forcing callers to implement cancellation manually.

Author: aleclarson

packages/core/src/Controller.ts

@@ -2,7 +2,7 @@ import { is, each, OneOrMore, toArray, UnknownProps, noop } from 'shared'
 import * as G from 'shared/globals'
 
 import { Lookup, Falsy } from './types/common'
-import { inferTo, flush } from './helpers'
+import { inferTo, flush, isDefaultProp } from './helpers'
 import { FrameValue } from './FrameValue'
 import { SpringPhase, CREATED, ACTIVE, IDLE } from './SpringPhase'
 import { SpringValue, createLoopUpdate, createUpdate } from './SpringValue'
@@ -303,7 +303,14 @@ export function flushUpdate(
           pause: noop,
           start(props, resolve) {
             props.onRest = onRest as any
-            resolve(runAsync(asyncTo, props, state, ctrl))
+            if (!props.cancel) {
+              resolve(runAsync(asyncTo, props, state, ctrl))
+            }
+            // Prevent `cancel: true` from ending the current `runAsync` call,
+            // except when the default `cancel` prop is being set.
+            else if (isDefaultProp(props, 'cancel')) {
+              cancelAsync(state, props.callId)
+            }
           },
         },
       })

packages/core/src/helpers.ts

@@ -49,6 +49,12 @@ export const getProps = <T, Arg = never>(
   props &&
   (is.fun(props) ? props(i, arg) : is.arr(props) ? props[i] : { ...props })
 
+/** Returns `true` if the given prop is having its default value set. */
+export const isDefaultProp = <T extends Lookup>(props: T, key: keyof T) =>
+  !is.und(
+    props.default === true ? props[key] : props.default && props.default[key]
+  )
+
 export const mergeDefaultProps = (
   defaultProps: Lookup,
   props: Lookup & { default?: boolean | Lookup }

packages/core/src/runAsync.ts

@@ -53,13 +53,6 @@ export async function runAsync<T>(
   state: RunAsyncState<T>,
   target: AnimationTarget<T>
 ): AsyncResult<T> {
-  if (props.cancel) {
-    // Stop the active `asyncTo` only on "default cancel".
-    if (props.default) {
-      state.asyncTo = undefined
-    }
-    return getCancelledResult(target)
-  }
   if (props.pause) {
     await new Promise(resume => {
       state.resumeQueue.add(resume)