Add IntoPropValue implementation to convert from Cows to `AttrVal…

…ue` (#3346)

* added IntoPropValue impls to & from Cows

* fixed formatting & test's expected output

* fixed formatting

* fixed macro test's expected output

* removed conversion to String & Rc

* fixed macro tests

* fixed macro tests

packages/yew-macro/tests/html_macro/element-fail.stderr

@@ -505,6 +505,7 @@ error[E0277]: the trait bound `Option<NotToString>: IntoPropValue<Option<implici
    = help: the following other types implement trait `IntoPropValue<T>`:
              <Option<&'static str> as IntoPropValue<Option<String>>>
              <Option<&'static str> as IntoPropValue<Option<implicit_clone::unsync::IString>>>
+             <Option<Cow<'static, str>> as IntoPropValue<Option<implicit_clone::unsync::IString>>>
              <Option<F> as IntoPropValue<Option<yew::Callback<I, O>>>>
              <Option<Rc<str>> as IntoPropValue<Option<implicit_clone::unsync::IString>>>
              <Option<String> as IntoPropValue<Option<implicit_clone::unsync::IString>>>
@@ -519,6 +520,7 @@ error[E0277]: the trait bound `Option<{integer}>: IntoPropValue<Option<implicit_
    = help: the following other types implement trait `IntoPropValue<T>`:
              <Option<&'static str> as IntoPropValue<Option<String>>>
              <Option<&'static str> as IntoPropValue<Option<implicit_clone::unsync::IString>>>
+             <Option<Cow<'static, str>> as IntoPropValue<Option<implicit_clone::unsync::IString>>>
              <Option<F> as IntoPropValue<Option<yew::Callback<I, O>>>>
              <Option<Rc<str>> as IntoPropValue<Option<implicit_clone::unsync::IString>>>
              <Option<String> as IntoPropValue<Option<implicit_clone::unsync::IString>>>
@@ -632,6 +634,7 @@ error[E0277]: the trait bound `Option<yew::NodeRef>: IntoPropValue<yew::NodeRef>
    = help: the following other types implement trait `IntoPropValue<T>`:
              <Option<&'static str> as IntoPropValue<Option<String>>>
              <Option<&'static str> as IntoPropValue<Option<implicit_clone::unsync::IString>>>
+             <Option<Cow<'static, str>> as IntoPropValue<Option<implicit_clone::unsync::IString>>>
              <Option<F> as IntoPropValue<Option<yew::Callback<I, O>>>>
              <Option<Rc<str>> as IntoPropValue<Option<implicit_clone::unsync::IString>>>
              <Option<String> as IntoPropValue<Option<implicit_clone::unsync::IString>>>

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

@@ -1,3 +1,4 @@
+use std::borrow::Cow;
 use std::rc::Rc;
 
 use implicit_clone::unsync::{IArray, IMap};
@@ -186,6 +187,7 @@ impl_into_prop!(|value: &'static str| -> String { value.to_owned() });
 impl_into_prop!(|value: &'static str| -> AttrValue { AttrValue::Static(value) });
 impl_into_prop!(|value: String| -> AttrValue { AttrValue::Rc(Rc::from(value)) });
 impl_into_prop!(|value: Rc<str>| -> AttrValue { AttrValue::Rc(value) });
+impl_into_prop!(|value: Cow<'static, str>| -> AttrValue { AttrValue::from(value) });
 
 impl<T: ImplicitClone + 'static> IntoPropValue<IArray<T>> for &'static [T] {
     fn into_prop_value(self) -> IArray<T> {
@@ -226,6 +228,7 @@ mod test {
         let _: AttrValue = "foo".into_prop_value();
         let _: Option<AttrValue> = "foo".into_prop_value();
         let _: Option<AttrValue> = Rc::<str>::from("foo").into_prop_value();
+        let _: Option<AttrValue> = Cow::Borrowed("foo").into_prop_value();
     }
 
     #[test]