fix: allow passing defer:boolean to on (#1885)

* fix types of `defer` for `on`

* add changelog

---------

Co-authored-by: Ryan Carniato <ryansolid@gmail.com>

.changeset/red-pears-rush.md

@@ -0,0 +1,5 @@
+---
+"solid-js": patch
+---
+
+Allow passing defer:boolean to `on`

packages/solid/src/reactive/signal.ts

@@ -922,7 +922,7 @@ export function on<S, Next extends Prev, Prev = Next>(
 export function on<S, Next extends Prev, Prev = Next>(
   deps: AccessorArray<S> | Accessor<S>,
   fn: OnEffectFunction<S, undefined | NoInfer<Prev>, Next>,
-  options: OnOptions & { defer: true }
+  options: OnOptions | { defer: true }
 ): EffectFunction<undefined | NoInfer<Next>>;
 export function on<S, Next extends Prev, Prev = Next>(
   deps: AccessorArray<S> | Accessor<S>,

packages/solid/test/signals.type-tests.ts

@@ -710,6 +710,25 @@ const onMemo3 = createMemo(
 );
 // @ts-expect-error when deferred the type includes undefined
 const onMemo4: Accessor<number> = onMemo3;
+// Allow passing boolean to defer
+const memoCreator = (defer: boolean) =>
+  createMemo(
+    on(
+      [one, two],
+      (input, prevInput, prev) => {
+        const [one, two]: [number, boolean] = input;
+        if (prevInput) {
+          const [prevOne, prevTwo]: [number, boolean] = prevInput;
+        }
+        // @ts-expect-error FIXME computed type is unknown, should be `number`.
+        const _prev: number = prev;
+        return one + +two;
+      },
+      { defer }
+    )
+  );
+const memoCreator1: Accessor<number | undefined> = memoCreator(true);
+const memoCreator2: Accessor<number | undefined> = memoCreator(false);
 
 //////////////////////////////////////////////////////////////////////////
 // createSelector ////////////////////////////////////////////////////////