From ce0604e08a931f8d50ab41fe7607eb48cc022449 Mon Sep 17 00:00:00 2001
From: Greg Johnston <greg.johnston@gmail.com>
Date: Mon, 16 Dec 2024 08:58:31 -0500
Subject: [PATCH] fix: rebuilding of `InertElement` (closes #3368)

---
 tachys/src/html/mod.rs     | 42 ++++++++++++++++++++++++++++++++------
 tachys/src/renderer/dom.rs |  3 ++-
 2 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/tachys/src/html/mod.rs b/tachys/src/html/mod.rs
index c4225be702..67af1a5bd3 100644
--- a/tachys/src/html/mod.rs
+++ b/tachys/src/html/mod.rs
@@ -2,8 +2,11 @@ use self::attribute::Attribute;
 use crate::{
     hydration::Cursor,
     no_attrs,
-    prelude::AddAnyAttr,
-    renderer::{CastFrom, Rndr},
+    prelude::{AddAnyAttr, Mountable},
+    renderer::{
+        dom::{Element, Node},
+        CastFrom, Rndr,
+    },
     view::{Position, PositionState, Render, RenderHtml},
 };
 use std::borrow::Cow;
@@ -90,14 +93,41 @@ impl InertElement {
     }
 }
 
+/// Retained view state for [`InertElement`].
+pub struct InertElementState(Cow<'static, str>, Element);
+
+impl Mountable for InertElementState {
+    fn unmount(&mut self) {
+        self.1.unmount();
+    }
+
+    fn mount(&mut self, parent: &Element, marker: Option<&Node>) {
+        self.1.mount(parent, marker)
+    }
+
+    fn insert_before_this(&self, child: &mut dyn Mountable) -> bool {
+        self.1.insert_before_this(child)
+    }
+}
+
 impl Render for InertElement {
-    type State = crate::renderer::types::Element;
+    type State = InertElementState;
 
     fn build(self) -> Self::State {
-        Rndr::create_element_from_html(&self.html)
+        let el = Rndr::create_element_from_html(&self.html);
+        InertElementState(self.html, el)
     }
 
-    fn rebuild(self, _state: &mut Self::State) {}
+    fn rebuild(self, state: &mut Self::State) {
+        let InertElementState(prev, el) = state;
+        if &self.html != prev {
+            let mut new_el = Rndr::create_element_from_html(&self.html);
+            el.insert_before_this(&mut new_el);
+            el.unmount();
+            *el = new_el;
+            *prev = self.html;
+        }
+    }
 }
 
 impl AddAnyAttr for InertElement {
@@ -157,6 +187,6 @@ impl RenderHtml for InertElement {
         let el = crate::renderer::types::Element::cast_from(cursor.current())
             .unwrap();
         position.set(Position::NextChild);
-        el
+        InertElementState(self.html, el)
     }
 }
diff --git a/tachys/src/renderer/dom.rs b/tachys/src/renderer/dom.rs
index 11addfc7d5..bcac94fe52 100644
--- a/tachys/src/renderer/dom.rs
+++ b/tachys/src/renderer/dom.rs
@@ -444,7 +444,8 @@ impl Dom {
         // TODO can be optimized to cache HTML strings or cache <template>?
         let tpl = document().create_element("template").unwrap();
         tpl.set_inner_html(html);
-        Self::clone_template(tpl.unchecked_ref())
+        let tpl = Self::clone_template(tpl.unchecked_ref());
+        tpl.first_element_child().unwrap_or(tpl)
     }
 }