Fix defaulted type parameter. (yewstack#2284)

* Fix defaulted type parameter.

* Add test.

packages/yew-macro/src/function_component.rs

@@ -201,7 +201,7 @@ pub fn function_component_impl(
         #[doc(hidden)]
         #[allow(non_camel_case_types)]
         #[allow(unused_parens)]
-        #vis struct #function_name #impl_generics {
+        #vis struct #function_name #generics {
             _marker: ::std::marker::PhantomData<(#phantom_generics)>,
         }
 
@@ -215,7 +215,7 @@ pub fn function_component_impl(
 
         #(#attrs)*
         #[allow(type_alias_bounds)]
-        #vis type #component_name #impl_generics = ::yew::functional::FunctionComponent<#function_name #ty_generics>;
+        #vis type #component_name #generics = ::yew::functional::FunctionComponent<#function_name #ty_generics>;
     };
 
     Ok(quoted)

packages/yew-macro/tests/function_component_attr/with-defaulted-type-param-pass.rs

@@ -0,0 +1,25 @@
+use yew::prelude::*;
+
+#[derive(Properties, Debug)]
+pub struct CompProps<A> {
+    #[prop_or_default]
+    _phantom: std::marker::PhantomData<A>,
+}
+
+impl<A> PartialEq for CompProps<A> {
+    fn eq(&self, _rhs: &Self) -> bool {
+        true
+    }
+}
+
+#[function_component(Comp)]
+pub fn comp<A = ()>(_props: &CompProps<A>) -> Html {
+    todo!()
+}
+
+#[function_component(App)]
+pub fn app() -> Html {
+    html! { <Comp /> } // No generics here.
+}
+
+fn main() {}