fix memo and add tests

packages/signals/tests/memo.rs

@@ -2,13 +2,14 @@
 use std::collections::HashMap;
 use std::rc::Rc;
 
+use dioxus::html::p;
 use dioxus::prelude::*;
 use dioxus_core::ElementId;
 use dioxus_signals::*;
 
 #[test]
 fn memos_rerun() {
-    simple_logger::SimpleLogger::new().init().unwrap();
+    let _ = simple_logger::SimpleLogger::new().init();
 
     #[derive(Default)]
     struct RunCounter {
@@ -48,3 +49,97 @@ fn memos_rerun() {
     assert_eq!(current_counter.component, 1);
     assert_eq!(current_counter.effect, 2);
 }
+
+#[test]
+fn memos_prevents_component_rerun() {
+    let _ = simple_logger::SimpleLogger::new().init();
+
+    #[derive(Default)]
+    struct RunCounter {
+        component: usize,
+        effect: usize,
+    }
+
+    let counter = Rc::new(RefCell::new(RunCounter::default()));
+    let mut dom = VirtualDom::new_with_props(
+        |cx| {
+            let mut signal = use_signal(cx, || 0);
+
+            if cx.generation() == 1 {
+                *signal.write() = 0;
+            }
+            if cx.generation() == 2 {
+                println!("Writing to signal");
+                *signal.write() = 1;
+            }
+
+            render! {
+                Child {
+                    signal: signal,
+                    counter: cx.props.clone(),
+                }
+            }
+        },
+        counter.clone(),
+    );
+
+    #[derive(Default, Props)]
+    struct ChildProps {
+        signal: Signal<usize>,
+        counter: Rc<RefCell<RunCounter>>,
+    }
+
+    impl PartialEq for ChildProps {
+        fn eq(&self, other: &Self) -> bool {
+            self.signal == other.signal
+        }
+    }
+
+    fn Child(cx: Scope<ChildProps>) -> Element {
+        let counter = &cx.props.counter;
+        let signal = cx.props.signal;
+        counter.borrow_mut().component += 1;
+
+        let memo = cx.use_hook(move || {
+            to_owned![counter];
+            memo(move || {
+                counter.borrow_mut().effect += 1;
+                println!("Signal: {:?}", signal);
+                signal.value()
+            })
+        });
+        match cx.generation() {
+            0 => {
+                assert_eq!(memo.value(), 0);
+            }
+            1 => {
+                assert_eq!(memo.value(), 1);
+            }
+            _ => panic!("Unexpected generation"),
+        }
+
+        render! {
+            div {}
+        }
+    }
+
+    let _ = dom.rebuild().santize();
+    dom.mark_dirty(ScopeId(0));
+    dom.render_immediate();
+
+    {
+        let current_counter = counter.borrow();
+        assert_eq!(current_counter.component, 1);
+        assert_eq!(current_counter.effect, 2);
+    }
+
+    dom.mark_dirty(ScopeId(0));
+    dom.render_immediate();
+    dom.render_immediate();
+
+    {
+        let current_counter = counter.borrow();
+        assert_eq!(current_counter.component, 2);
+        assert_eq!(current_counter.effect, 3);
+    }
+}