Fix hot reload diffing to empty rsx (#3567)

* Fix hot reloading to empty rsx

* Only normalize the template when hot reloading and rendering

* add a test for emptying out an rsx block in hot reloading

packages/rsx-hotreload/src/diff.rs

@@ -122,7 +122,10 @@ impl HotReloadResult {
         new: &TemplateBody,
         name: String,
     ) -> Option<Self> {
-        let full_rebuild_state = LastBuildState::new(full_rebuild_state, name);
+        // Normalize both the full rebuild state and the new state for rendering
+        let full_rebuild_state = full_rebuild_state.normalized();
+        let new = new.normalized();
+        let full_rebuild_state = LastBuildState::new(&full_rebuild_state, name);
         let mut s = Self {
             full_rebuild_state,
             templates: Default::default(),
@@ -131,7 +134,7 @@ impl HotReloadResult {
             literal_component_properties: Default::default(),
         };
 
-        s.hotreload_body::<Ctx>(new)?;
+        s.hotreload_body::<Ctx>(&new)?;
 
         Some(s)
     }

packages/rsx-hotreload/tests/hotreload_pattern.rs

@@ -467,6 +467,32 @@ fn invalid_cases() {
     assert!(added.is_none());
 }
 
+#[test]
+fn invalid_empty_rsx() {
+    let old_template = quote! {
+        div {
+            for item in vec![1, 2, 3, 4] {
+                div { "asasddasdasd" }
+                div { "123" }
+            }
+            for item in vec![4, 5, 6] {
+                span { "asasddasdasd" }
+                span { "123" }
+            }
+        }
+    };
+
+    // empty out the whole rsx block
+    let new_template = quote! {};
+
+    let location = "file:line:col:0";
+
+    let old_template: CallBody = syn::parse2(old_template).unwrap();
+    let new_template: CallBody = syn::parse2(new_template).unwrap();
+
+    assert!(hotreload_callbody::<Mock>(&old_template, &new_template).is_none());
+}
+
 #[test]
 fn attributes_reload() {
     let old = quote! {

packages/rsx/src/template_body.rs

@@ -91,6 +91,7 @@ impl Parse for TemplateBody {
         myself
             .diagnostics
             .extend(children.diagnostics.into_diagnostics());
+
         Ok(myself)
     }
 }
@@ -99,51 +100,39 @@ impl Parse for TemplateBody {
 /// This is because the parsing phase filled in all the additional metadata we need
 impl ToTokens for TemplateBody {
     fn to_tokens(&self, tokens: &mut TokenStream2) {
-        // If the nodes are completely empty, insert a placeholder node
-        // Core expects at least one node in the template to make it easier to replace
-        if self.is_empty() {
-            // Create an empty template body with a placeholder and diagnostics + the template index from the original
-            let empty = Self::new(vec![BodyNode::RawExpr(parse_quote! {()})]);
-            let default = Self {
-                diagnostics: self.diagnostics.clone(),
-                template_idx: self.template_idx.clone(),
-                ..empty
-            };
-            // And then render the default template body
-            default.to_tokens(tokens);
-            return;
-        }
+        // First normalize the template body for rendering
+        let node = self.normalized();
 
         // If we have an implicit key, then we need to write its tokens
-        let key_tokens = match self.implicit_key() {
+        let key_tokens = match node.implicit_key() {
             Some(tok) => quote! { Some( #tok.to_string() ) },
             None => quote! { None },
         };
 
-        let roots = self.quote_roots();
+        let roots = node.quote_roots();
 
         // Print paths is easy - just print the paths
-        let node_paths = self.node_paths.iter().map(|it| quote!(&[#(#it),*]));
-        let attr_paths = self.attr_paths.iter().map(|(it, _)| quote!(&[#(#it),*]));
+        let node_paths = node.node_paths.iter().map(|it| quote!(&[#(#it),*]));
+        let attr_paths = node.attr_paths.iter().map(|(it, _)| quote!(&[#(#it),*]));
 
         // For printing dynamic nodes, we rely on the ToTokens impl
         // Elements have a weird ToTokens - they actually are the entrypoint for Template creation
-        let dynamic_nodes: Vec<_> = self.dynamic_nodes().collect();
+        let dynamic_nodes: Vec<_> = node.dynamic_nodes().collect();
         let dynamic_nodes_len = dynamic_nodes.len();
 
         // We could add a ToTokens for Attribute but since we use that for both components and elements
         // They actually need to be different, so we just localize that here
-        let dyn_attr_printer: Vec<_> = self
+        let dyn_attr_printer: Vec<_> = node
             .dynamic_attributes()
             .map(|attr| attr.rendered_as_dynamic_attr())
             .collect();
         let dynamic_attr_len = dyn_attr_printer.len();
 
-        let dynamic_text = self.dynamic_text_segments.iter();
+        let dynamic_text = node.dynamic_text_segments.iter();
 
-        let diagnostics = &self.diagnostics;
-        let index = self.template_idx.get();
-        let hot_reload_mapping = self.hot_reload_mapping();
+        let diagnostics = &node.diagnostics;
+        let index = node.template_idx.get();
+        let hot_reload_mapping = node.hot_reload_mapping();
 
         tokens.append_all(quote! {
             dioxus_core::Element::Ok({
@@ -255,6 +244,23 @@ impl TemplateBody {
         body
     }
 
+    /// Normalize the Template body for rendering. If the body is completely empty, insert a placeholder node
+    pub fn normalized(&self) -> Self {
+        // If the nodes are completely empty, insert a placeholder node
+        // Core expects at least one node in the template to make it easier to replace
+        if self.is_empty() {
+            // Create an empty template body with a placeholder and diagnostics + the template index from the original
+            let empty = Self::new(vec![BodyNode::RawExpr(parse_quote! {()})]);
+            let default = Self {
+                diagnostics: self.diagnostics.clone(),
+                template_idx: self.template_idx.clone(),
+                ..empty
+            };
+            return default;
+        }
+        self.clone()
+    }
+
     pub fn is_empty(&self) -> bool {
         self.roots.is_empty()
     }