Add a warning for keys after the first node which do nothing (#4978)

* add a warning for keys after the first node which do nothing

* warnings on stable

* better warnings on nightly

packages/rsx/src/template_body.rs

@@ -109,6 +109,8 @@ impl ToTokens for TemplateBody {
             None => quote! { None },
         };
 
+        let key_warnings = self.check_for_duplicate_keys();
+
         let roots = node.quote_roots();
 
         // Print paths is easy - just print the paths
@@ -138,6 +140,8 @@ impl ToTokens for TemplateBody {
             dioxus_core::Element::Ok({
                 #diagnostics
 
+                #key_warnings
+
                 // Components pull in the dynamic literal pool and template in debug mode, so they need to be defined before dynamic nodes
                 #[cfg(debug_assertions)]
                 fn __original_template() -> &'static dioxus_core::internal::HotReloadedTemplate {
@@ -273,11 +277,7 @@ impl TemplateBody {
     }
 
     pub fn implicit_key(&self) -> Option<&AttributeValue> {
-        match self.roots.first() {
-            Some(BodyNode::Element(el)) => el.key(),
-            Some(BodyNode::Component(comp)) => comp.get_key(),
-            _ => None,
-        }
+        self.roots.first().and_then(BodyNode::key)
     }
 
     /// Ensure only one key and that the key is not a static str
@@ -304,6 +304,22 @@ impl TemplateBody {
         }
     }
 
+    fn check_for_duplicate_keys(&self) -> TokenStream2 {
+        let mut warnings = TokenStream2::new();
+
+        // Make sure there are not multiple keys or keys on nodes other than the first in the block
+        for root in self.roots.iter().skip(1) {
+            if let Some(key) = root.key() {
+                warnings.extend(new_diagnostics::warning_diagnostic(
+                    key.span(),
+                    "Keys are only allowed on the first node in the block.",
+                ));
+            }
+        }
+
+        warnings
+    }
+
     pub fn get_dyn_node(&self, path: &[u8]) -> &BodyNode {
         let mut node = self.roots.get(path[0] as usize).unwrap();
         for idx in path.iter().skip(1) {