feat: implement ID cycling

packages/core/tests/cycle.rs

@@ -0,0 +1,51 @@
+use dioxus::core::{ElementId, Mutation::*};
+use dioxus::prelude::*;
+
+/// As we clean up old templates, the ID for the node should cycle
+#[test]
+fn cycling_elements() {
+    let mut dom = VirtualDom::new(|cx| {
+        cx.render(match cx.generation() % 2 {
+            0 => rsx! { div { "wasd" } },
+            1 => rsx! { div { "abcd" } },
+            _ => unreachable!(),
+        })
+    });
+
+    let edits = dom.rebuild().santize();
+    assert_eq!(
+        edits.edits,
+        [
+            LoadTemplate { name: "template", index: 0, id: ElementId(1,) },
+            AppendChildren { m: 1 },
+        ]
+    );
+
+    dom.mark_dirty_scope(ScopeId(0));
+    assert_eq!(
+        dom.render_immediate().santize().edits,
+        [
+            LoadTemplate { name: "template", index: 0, id: ElementId(2,) },
+            ReplaceWith { id: ElementId(1,), m: 1 },
+        ]
+    );
+
+    // notice that the IDs cycle back to ElementId(1), preserving a minimal memory footprint
+    dom.mark_dirty_scope(ScopeId(0));
+    assert_eq!(
+        dom.render_immediate().santize().edits,
+        [
+            LoadTemplate { name: "template", index: 0, id: ElementId(1,) },
+            ReplaceWith { id: ElementId(2,), m: 1 },
+        ]
+    );
+
+    dom.mark_dirty_scope(ScopeId(0));
+    assert_eq!(
+        dom.render_immediate().santize().edits,
+        [
+            LoadTemplate { name: "template", index: 0, id: ElementId(2,) },
+            ReplaceWith { id: ElementId(1,), m: 1 },
+        ]
+    );
+}