Implement Attribute for Either<A, B>

[alexisfontaine]

This implementation allows to define HtmlElement<Tag, (Either<FooAttribute, BarAttribute>,), Children> as the output of a fully-typed reusable component.

The current workaround of having to write Either<HtmlElement<Tag, FooAttribute, Children>, HtmlElement<Tag, BarAttribute, Children>>, besides being more verbose, also lacks an implementation of ElementExt.

[gbj]

Thanks!

[luxalpa]

Sadly, this broke rustflags = ["--cfg=erase_components"] on nightly with a bunch of errors like these:

error[E0277]: the trait bound `(Either<<A as Attribute>::AsyncOutput, ...>,): Attribute` is not satisfied
   --> C:\Users\Luxalpa\.cargo\git\checkouts\leptos-79e4740403520456\88b1b2d\tachys\src\view\either.rs:147:24
    |
147 |     type AsyncOutput = (Either<A::AsyncOutput, B::AsyncOutput>,);
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unsatisfied trait bound

[alexisfontaine]

Hum, have you tried the current release? I just did, and it looks like these errors were introduced between v0.7.4 and v0.7.5. Unfortunately I don't know much about the erase_components config to be able to help...

[luxalpa]

There's in fact another error like this in the current release (v0.7.5) which was fixed earlier: #3536