Passing closure inside another closure makes it `FnOne` instead of `Fn`

[reef pier]

I have this small code snippet that I created with the leptos framework:

use leptos::*;

pub struct MarkdownClickEvent;

#[component]
pub fn Markdown<F: Fn(MarkdownClickEvent) + 'static>(
    cx: Scope,
    source: ReadSignal<String>,
    #[prop(optional)] 
    onclick: Option<F>,
    ) 
    -> impl IntoView {
    let onclick = onclick.unwrap();
    view! {cx,
        <div style="width:100%"> 
            {move || parse(&source.get(), &onclick)}
        </div>
    }
}

fn parse<F>(source: &str, onclick: &F) -> impl IntoView 
where F: Fn(MarkdownClickEvent) + 'static
{
    unimplemented!()
}

This code works, but I would like to avoid cloning source (source.get clones the signal)
So I changed the code to

use leptos::*;

pub struct MarkdownClickEvent;

#[component]
pub fn Markdown<F: Fn(MarkdownClickEvent) + 'static>(
    cx: Scope,
    source: ReadSignal<String>,
    #[prop(optional)] 
    onclick: Option<F>,
    ) 
    -> impl IntoView {
    let onclick = onclick.unwrap();
    view! {cx,
        <div style="width:100%"> 
            {move || source.with(|x| parase(x, &onclick))}
        </div>
    }
}

fn parse<F>(source: &str, onclick: &F) -> impl IntoView 
where F: Fn(MarkdownClickEvent) + 'static
{
    unimplemented!()
}

Now, I get a compile error
```error[E0525]: expected a closure that implements the Fn trait, but this closure only implements FnOnce
--> src/lib.rs:17:14
|
14 | / view! {cx,
15 | | <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/katex.min.css" integrity="sha384-3UiQGuEI4TTMaFmGIZumfRPtfKQ3trwQE2JgosJxCnGmQpL/lJdjpcHkaaFwHl...
16 | | <div style="width:100%">
17 | | {move || source.with(move |x| parse(x, &onclick))}
| | ^^^^^^^ ------- closure is FnOnce because it moves the variable onclick out of its environment
| | |
| | this closure implements FnOnce, not Fn
18 | | </div>
19 | | }
| | -
| | |
| |_____the requirement to implement Fn derives from here
| required by a bound introduced by this call

I don't see why adding a level of closures creates this compile error ...

[tranquil inlet]

the code you quoted isn't the code with the error

in the error, the inner closure is a move closure, which means it always moves all of the variables it captures when it is constructed

so, it moves onclick out of its environment, i.e.. the outer move || closure, which makes it impossible to call the outer closure more than once

the answer may be to remove the move, if it's okay for the inner closure to borrow things

or you may have to clone onclick so that the inner closure can have it