fix(reactivity): once watcher should stop when its callback throws (#15755)

Author: patienry

packages/reactivity/__tests__/watch.spec.ts

@@ -330,4 +330,16 @@ describe('watch', () => {
     value.value = true
     expect(value.value).toBe(false)
   })
+
+  test('once watcher should stop when its callback throws', () => {
+    const source = ref(0)
+    const callback = vi.fn(() => {
+      throw new Error('oops')
+    })
+    watch(source, callback, { once: true })
+
+    expect(() => (source.value = 1)).toThrow('oops')
+    expect(() => (source.value = 2)).not.toThrow()
+    expect(callback).toHaveBeenCalledTimes(1)
+  })
 })

packages/reactivity/src/watch.ts

@@ -221,9 +221,11 @@ export function watch(
   if (once && cb) {
     const _cb = cb
     cb = (...args) => {
-      const res = _cb(...args)
-      watchHandle()
-      return res
+      try {
+        return _cb(...args)
+      } finally {
+        watchHandle()
+      }
     }
   }