Remove Component validation in html! to allow for generic components

[mankinskin]

Because this validation check tries to impl Component for the component
type, generic components could not have been used, because the impl has to define the generic type parameter itself, but it can only see the <C> part directly, and thus can not define the type parameters trait bounds properly.

With this change, it is possible to write a component like this, with a generic type parameter with trait bounds.

impl<C> Component for TreeView<C>
    where C: Component,
{
    type Message = Msg;
    type Properties = TreeData<<C as Component>::Properties>;
    ...
    fn view(&self) -> Html {
        if self.props.expanded {
            html! {
                <div>{
                    for self.props.children.iter().cloned()
                            .map(|child| html! {
                                <TreeView<C>
                                    element={child.element}
                                    children={child.children}
                                    expanded={child.expanded}
                                />
                            })
                }</div>
            }
        } else {
            html!{}
        }
    }
    ...
}

See more details in this issue: #1064

[jstarry]

Take a look at the tests that we run in CI.. The macro test is going to fail because the compiler error message will be different

[jstarry]

Oops, macro tests were not running. Could you please rebase off last master and fix the tests?

[jstarry]

Guide: https://github.com/yewstack/yew/blob/master/CONTRIBUTING.md#macro-tests

[mankinskin]

Guide: https://github.com/yewstack/yew/blob/master/CONTRIBUTING.md#macro-tests

There is a broken link in the guide for the stderr file.
Because I had some problems, I checked out master at 393eb8 and when I run

TRYBUILD=overwrite cargo test --test macro_test

I get

error: no test target named `macro_test`

Running the tests with

./ci/run_tests.sh

yields

...
error: test failed, to rerun pass '--lib'

Caused by:
  could not execute process `wasm-bindgen-test-runner /home/linusb/git/yew/target/wasm32-unknown-unknown/debug/deps/yew-88efceb071029c6b.wasm` (never executed)

Not sure where this is coming from. Do you have any problems running the tests on the current master?

[jstarry]

@mankinskin you'll have to run that command from ./crates/macro

[jstarry]

Thanks! Now you can see why I added that validation check 😉

[mankinskin]

Yes indeed, it might be confusing at first, but at least it contains the helpful error at the end :) But it would still be interesting to know how to get the trait bounds of a generic type argument from a proc macro ..
But well, thank you for helping me contribute to this awesome project!

[jstarry]

but at least it contains the helpful error at the end :)

Haha yes very true!

But it would still be interesting to know how to get the trait bounds of a generic type argument from a proc macro ..

Yeah, I think it's possible. We can inspect and validate the generics from the component type if present. Just don't have time to do so now :)

[jstarry]

🎉 released in v0.14.3