fix(useTransition): fix regression with non-linear transition functio…

…ns (#2973)

packages/core/useTransition/index.test.ts

@@ -158,6 +158,26 @@ describe('useTransition', () => {
     expect(transition.value).toBe(1)
   })
 
+  it('supports non-linear custom easing functions', async () => {
+    const source = ref(0)
+    const easeInQuad = vi.fn(n => n * n)
+    const transition = useTransition(source, {
+      duration: 100,
+      transition: easeInQuad,
+    })
+
+    expect(easeInQuad).not.toBeCalled()
+
+    source.value = 1
+
+    await promiseTimeout(50)
+    expect(easeInQuad).toBeCalled()
+    expectBetween(transition.value, 0, 1)
+
+    await promiseTimeout(100)
+    expect(transition.value).toBe(1)
+  })
+
   it('supports delayed transitions', async () => {
     const source = ref(0)
 

packages/core/useTransition/index.ts

@@ -148,7 +148,9 @@ export function executeTransition<T extends number | number[]>(
   const duration = toValue(options.duration) ?? 1000
   const startedAt = Date.now()
   const endAt = Date.now() + duration
-  const trans = toValue(options.transition) ?? linear
+  const trans = typeof options.transition === 'function'
+    ? options.transition
+    : (toValue(options.transition) ?? linear)
 
   const ease = typeof trans === 'function'
     ? trans