Semantic Highlighting: impl Iterator is considered callable

[CryZe]

The newly introduced callable modifier (which I've used to mark variables the same color as functions) is for some reason being applied to impl Iterator here:

[lnicola]

CC @GrayJack

[GrayJack]

Hey @CryZe , can you give a code that this happens or point me to a code base where it happens?

[bjorn3]

The Callable modifier comes from https://github.com/rust-analyzer/rust-analyzer/blob/35ed3d2c005fdb0ec9ab78a52b31758bd7de298e/crates/ide/src/syntax_highlighting.rs#L773-L775

[bjorn3]

I think what happens is because of the + {error} the question if it implements FnOnce results in an ambiguous solution. This will then cause impls_fnonce to return true, as solution.is_some() is true.

[CryZe]

This replicates the issue:

fn look_up(word: &str) -> Option<impl Iterator<Item = char> + Clone + '_> {
    Some(word.chars())
}

fn foo() {
    if let Some(bar) = look_up("hi") {}
}

[CryZe]

It also seems to replicate with:

fn look_up() -> impl Clone {}

fn foo() {
    let bar = look_up();
}

which doesn't have the + {error} which apparently correlates with the lifetime. Any impl Trait seems to cause it.

[GrayJack]

@bjorn3 Changing method_resolution::implements_trait the function returns false when solution is Solution::Ambig solves the issue.

But, is it best to change method_resolution::implements_trait implementation or create a new function that only returns true when the solution is Solution::Unique?

[flodiebold]

It's worth investigating why impl Clone: Fn would return ambiguous though 🤔