fix: allow Option<String> and Option<AttrValue> as VNode children in html!

Generalize `IntoPropValue<VNode> for Option<VNode>` into a blanket
`IntoPropValue<VNode> for Option<T>` where `T: IntoPropValue<VNode>`.

The single-expression child path in the html! macro calls
`IntoPropValue::<VNode>::into_prop_value()` directly, which only had
an impl for `Option<VNode>`. This is a regression from the removal of
the `ToHtml` trait, which had a blanket `Option<T: ToHtml>` impl.

Author: Madoshakalaka

packages/yew-macro/tests/html_macro/html-element-pass.rs

@@ -123,6 +123,18 @@ fn compile_pass() {
 
     let option_vnode = ::std::option::Option::Some(::yew::html! {});
     _ = ::yew::html! { <div>{option_vnode}</div> };
+
+    // Option<String> and Option<AttrValue> as single children
+    let opt_string: ::std::option::Option<::std::string::String> =
+        ::std::option::Option::Some(::std::string::String::from("hello"));
+    _ = ::yew::html! { <div>{opt_string}</div> };
+
+    let opt_attr: ::std::option::Option<::yew::AttrValue> =
+        ::std::option::Option::Some(::yew::AttrValue::Static("hello"));
+    _ = ::yew::html! { <div>{opt_attr}</div> };
+
+    let opt_none: ::std::option::Option<::std::string::String> = ::std::option::Option::None;
+    _ = ::yew::html! { <div>{opt_none}</div> };
 }
 
 fn main() {}

packages/yew/src/html/conversion/into_prop_value.rs

@@ -214,10 +214,11 @@ impl IntoPropValue<VNode> for Vec<VNode> {
     }
 }
 
-impl IntoPropValue<VNode> for Option<VNode> {
+impl<T: IntoPropValue<VNode>> IntoPropValue<VNode> for Option<T> {
     #[inline]
     fn into_prop_value(self) -> VNode {
-        self.unwrap_or_default()
+        self.map(IntoPropValue::into_prop_value)
+            .unwrap_or_default()
     }
 }
 
@@ -350,6 +351,18 @@ mod test {
         let _: Option<AttrValue> = Cow::Borrowed("foo").into_prop_value();
     }
 
+    #[test]
+    fn test_option_to_vnode() {
+        let _: VNode = Some(String::from("hello")).into_prop_value();
+        let _: VNode = Some(AttrValue::Static("hello")).into_prop_value();
+        let _: VNode = Option::<String>::None.into_prop_value();
+        let _: VNode = Option::<AttrValue>::None.into_prop_value();
+        let _: VNode = Some(VNode::default()).into_prop_value();
+        let _: VNode = Option::<VNode>::None.into_prop_value();
+        let _: VNode = Some(42u32).into_prop_value();
+        let _: VNode = Some(true).into_prop_value();
+    }
+
     #[test]
     fn test_callback() {
         let _: Callback<String> = (|_: String| ()).into_prop_value();