Rustfmt can generate invalid code when using `space_after_colon=false`

[lever1209]

formatting the following code with space_after_colon=false will generate invalid code

struct SomeStruct {
    some_field: ::some_crate::Thing,
}

since it removes the space between the field colon and the :: prefix on some_crate
i cant see this as very high priority because i dont know anyone who prefixes things with :: asides from maybe alloc or std, and space_after_colon=false isnt widely used, but this should probably be looked into

[ytmimi]

Thanks for the report! Confirming that I can reproduce this when using space_after_colon=false with rustfmt 1.8.0-nightly (054efdd 2025-02-07)

[ytmimi]

This is an issue anywhere that space_after_colon applies. For example:

Input:

const THING: ::some_crate::SomeType  = ::some_crate::SomeType::default();

fn main() {
    let x: ::some_crate::SomeType = ::some_crate::SomeType::default();
}

Output:

const THING:::some_crate::SomeType = ::some_crate::SomeType::default();

fn main() {
    let x:::some_crate::SomeType = ::some_crate::SomeType::default();
}