fix createWritableMemo (fixes #772)

Author: thetarnav

packages/memo/src/index.ts

@@ -191,10 +191,12 @@ export function createWritableMemo<T>(
   options?: MemoOptions<T | undefined>,
 ): [signal: Accessor<T>, setter: Setter<T>] {
   let combined: Accessor<T> = () => value as T;
+  
   const [signal, setSignal] = createSignal(value as T, EQUALS_FALSE_OPTIONS),
     memo = createMemo(
       callbackWith(fn, () => combined()),
       value,
+      EQUALS_FALSE_OPTIONS,
     );
 
   return [

packages/memo/test/writable.test.ts

@@ -32,7 +32,7 @@ describe("createWritableMemo", () => {
     const [count, setCount] = createSignal(1);
     let prevCb: number | undefined;
     const { result, setResult, dispose } = createRoot(dispose => {
-      const [result, setResult] = createWritableMemo(p => ((prevCb = p), count() * 2), -2);
+      const [result, setResult] = createWritableMemo((p?: number) => ((prevCb = p), count() * 2), -2);
       expect(prevCb).toBe(-2);
       expect(result()).toBe(2);
       return { result, dispose, setResult };
@@ -101,4 +101,23 @@ describe("createWritableMemo", () => {
       expect(memo()).toBe(-2);
       dispose();
     }));
+
+  // https://github.com/solidjs-community/solid-primitives/issues/772
+  test("issue 772", () => {
+    const [source, setSource] = createSignal(0);
+    const [[value, setValue], dispose] = createRoot(dispose => [createWritableMemo(() => !!source()), dispose])
+
+    expect(value()).toBe(false)
+
+    setSource(1);
+    expect(value()).toBe(true)
+
+    setValue(false);
+    expect(value()).toBe(false)
+
+    setSource(2);
+    expect(value()).toBe(true)
+
+    dispose()
+  })
 });