Add an api for TemplateElement definition.

macros/Cargo.toml

@@ -17,3 +17,6 @@ str_inflector = "0.12.0"
 [dependencies.syn]
 version = "1.0.101"
 features = ["full"]
+
+[features]
+HtmlTemplateElement = []

macros/src/lib.rs

@@ -96,7 +96,11 @@ fn expand_component_def(
     }
 }
 
-fn expand_struct_trait_shim(struct_name: &Ident, once_name: &Ident, observed_attrs: Literal) -> syn::ItemImpl {
+fn expand_wc_struct_trait_shim(
+    struct_name: &Ident,
+    once_name: &Ident,
+    observed_attrs: Literal,
+) -> syn::ItemImpl {
     let trait_path = expand_crate_ref("wasm-web-component", parse_quote!(WebComponentDef));
     let handle_path = expand_crate_ref("wasm-web-component", parse_quote!(WebComponentHandle));
     parse_quote! {
@@ -239,16 +243,20 @@ fn expand_binding(struct_name: &Ident) -> syn::ItemImpl {
     )
 }
 
-fn expand_struct(
+fn expand_web_component_struct(
     item_struct: ItemStruct,
     class_name: Literal,
     element_name: Literal,
     observed_attributes: Literal,
 ) -> TokenStream {
     let struct_name = item_struct.ident.clone();
-    let struct_once_name = Ident::new(&(struct_name.to_string().to_snake_case().to_uppercase() + "_ONCE"), Span::call_site());
+    let struct_once_name = Ident::new(
+        &(struct_name.to_string().to_snake_case().to_uppercase() + "_ONCE"),
+        Span::call_site(),
+    );
     let component_def = expand_component_def(&struct_name, &class_name, &element_name);
-    let non_wasm_impl = expand_struct_trait_shim(&struct_name, &struct_once_name, observed_attributes);
+    let non_wasm_impl =
+        expand_wc_struct_trait_shim(&struct_name, &struct_once_name, observed_attributes);
     let wasm_shim = expand_wasm_shim(&struct_name);
     let binding_trait = expand_binding(&struct_name);
     let expanded = quote! {
@@ -268,6 +276,36 @@ fn expand_struct(
     TokenStream::from(expanded)
 }
 
+#[cfg(feature = "HtmlTemplateElement")]
+fn expand_template_struct(item_struct: ItemStruct) -> TokenStream {
+    let struct_name = item_struct.ident.clone();
+    let struct_once_name = Ident::new(
+        &(struct_name.to_string().to_snake_case().to_uppercase() + "_ONCE"),
+        Span::call_site(),
+    );
+    let trait_path = expand_crate_ref("wasm-web-component", parse_quote!(TemplateElement));
+    let expanded = quote! {
+        use std::sync::Once;
+        use web_sys::Node;
+        static #struct_once_name: Once = Once::new();
+        #item_struct
+        impl #trait_path for #struct_name {}
+        impl #struct_name {
+            #[doc = "Defines this HtmlTemplateElement and adds it to the document exactly once. Subsequent calls are noops."]
+            pub fn define_once() { // TODO(jwall): Should this return the element?
+                #struct_once_name.call_once(|| {
+                    let template_element = Self::render();
+                    let body = web_sys::window().expect("Failed to get window")
+                        .document().expect("Failed to get window document").
+                        body().expect("Failed to get document body");
+                    body.append_child(template_element.as_ref()).expect("Failed to add template element to document");
+                })
+            }
+        }
+    };
+    TokenStream::from(expanded)
+}
+
 /// Creates the necessary Rust and Javascript shims for a Web Component.
 #[proc_macro_attribute]
 pub fn web_component(attr: TokenStream, item: TokenStream) -> TokenStream {
@@ -279,5 +317,13 @@ pub fn web_component(attr: TokenStream, item: TokenStream) -> TokenStream {
     let (class_name, element_name, observed_attributes) =
         get_class_and_element_names(args, &item_struct.ident);
 
-    expand_struct(item_struct, class_name, element_name, observed_attributes)
+    expand_web_component_struct(item_struct, class_name, element_name, observed_attributes)
+}
+
+/// Creates the neccessary Rust and Javascript shims for rendering an HtmlTemplateElement
+#[cfg(feature = "HtmlTemplateElement")]
+#[proc_macro_attribute]
+pub fn template_element(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    let item_struct = parse_macro_input!(item as ItemStruct);
+    expand_template_struct(item_struct)
 }

wasm-web-component/Cargo.toml

@@ -2,15 +2,14 @@
 name = "wasm-web-component"
 version = "0.1.1"
 edition = "2021"
-author = "Jeremy Wall <jeremy@marzhillstudios.com>"
 
 [lib]
 crate-type = ["cdylib", "rlib"]
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
-[dependencies]
-wasm-web-component-macros = { path = "../macros" }
+[dependencies.wasm-web-component-macros]
+path = "../macros"
 
 [dependencies.wasm-bindgen-test]
 version = "0.3"
@@ -26,7 +25,6 @@ version = "0.3"
 features = [
     "CustomElementRegistry",
     "Document",
-    #"DocumentFragment",
     "KeyboardEvent",
     "Event",
     "EventTarget",
@@ -35,7 +33,6 @@ features = [
     "Text",
     "HtmlBaseElement",
     "HtmlElement",
-    "HtmlTemplateElement",
     "HtmlSlotElement",
     "Node",
     "ShadowRoot",
@@ -44,3 +41,10 @@ features = [
     "Window",
     "console"
 ]
+
+[features]
+default = ["HtmlTemplateElement"]
+HtmlTemplateElement = [
+    "web-sys/HtmlTemplateElement",
+    "wasm-web-component-macros/HtmlTemplateElement",
+]

wasm-web-component/src/lib.rs

@@ -1,5 +1,7 @@
 use js_sys::Function;
 use wasm_bindgen::{convert::IntoWasmAbi, JsValue};
+#[cfg(feature = "HtmlTemplateElement")]
+use web_sys::HtmlTemplateElement;
 use web_sys::{window, Element, Event, HtmlElement, Window};
 
 /// This attribute proc-macro will generate the following trait implementations
@@ -82,10 +84,22 @@ pub trait WebComponentBinding: WebComponentDef {
     }
 }
 
-/// Marker trait used in the generated shims to assert that their are Rust implemtntations
+/// Marker trait used in the generated shims to assert that there are Rust implemtntations
 /// of the callback functions for the component.
 pub trait WebComponent: WebComponentBinding {}
 
+/// Defines the template element rendering method.
+#[cfg(feature = "HtmlTemplateElement")]
+pub trait TemplateElementRender {
+    // Creates and returns an HtmlTemplateElement.
+    fn render() -> HtmlTemplateElement;
+}
+
+/// Marker trait used in the generated shims to assert that there are Rust implemtntations
+/// of the rendering function for the component.
+#[cfg(feature = "HtmlTemplateElement")]
+pub trait TemplateElement: TemplateElementRender {}
+
 /// A handle for your WebComponent Definition. Offers easy access to construct your
 /// element.
 pub struct WebComponentHandle {
@@ -301,4 +315,32 @@ mod tests {
         assert_eq!(ThisElement::class_name(), "ThisElement");
         assert_eq!(ThisElement::element_name(), "this-old-element");
     }
+
+    // TODO(jwall): Benchmarks for TemplateElements?
+    #[cfg(feature = "HtmlTemplateElement")]
+    #[wasm_bindgen_test]
+    fn test_template_element_render_once() {
+        use wasm_web_component_macros::template_element;
+
+        #[template_element]
+        pub struct MyTemplate();
+        impl TemplateElementRender for MyTemplate {
+            fn render() -> HtmlTemplateElement {
+                let val: JsValue = window()
+                    .unwrap()
+                    .document()
+                    .unwrap()
+                    .create_element("template")
+                    .unwrap()
+                    .into();
+                let el: HtmlTemplateElement = val.into();
+                el
+            }
+        }
+
+        let body = window().unwrap().document().unwrap().body().unwrap();
+        assert!(!body.last_child().unwrap().has_type::<HtmlTemplateElement>());
+        MyTemplate::define_once();
+        assert!(body.last_child().unwrap().has_type::<HtmlTemplateElement>());
+    }
 }