fix: rethrow falsy errors thrown in flushPending (#2820)

src/vanilla/store.ts

@@ -199,13 +199,15 @@ const addPendingFunction = (pending: Pending, fn: () => void) => {
 }
 
 const flushPending = (pending: Pending) => {
-  let error: unknown | undefined
+  let error: AnyError
+  let hasError = false
   const call = (fn: () => void) => {
     try {
       fn()
     } catch (e) {
-      if (!error) {
+      if (!hasError) {
         error = e
+        hasError = true
       }
     }
   }
@@ -218,7 +220,7 @@ const flushPending = (pending: Pending) => {
     atomStates.forEach((atomState) => atomState.m?.l.forEach(call))
     functions.forEach(call)
   }
-  if (error) {
+  if (hasError) {
     throw error
   }
 }

tests/vanilla/store.test.tsx

@@ -876,3 +876,23 @@ describe('should mount and trigger listeners even when an error is thrown', () =
     expect(listener).toHaveBeenCalledOnce()
   })
 })
+
+it('throws falsy errors in onMount, onUnmount, and listeners', () => {
+  const store = createStore()
+  const a = atom(0)
+  a.onMount = () => {
+    throw ''
+  }
+  expect(() => store.sub(a, () => {})).toThrow('')
+  const b = atom(0)
+  b.onMount = () => () => {
+    throw ''
+  }
+  const unsub = store.sub(b, () => {})
+  expect(() => unsub()).toThrow('')
+  const c = atom(0)
+  store.sub(c, () => {
+    throw ''
+  })
+  expect(() => store.set(c, 1)).toThrow('')
+})