rustfmt silently deletes the word const when it appears before impl while using the experimental const_trait_impl feature #4084
Description
For example, this is valid / working code on nightly:
#![allow(incomplete_features)]
#![feature(const_trait_impl)]
#[derive(Debug)]
struct Struct {
f: f32,
}
impl const std::default::Default for Struct {
#[inline]
fn default() -> Self {
Self { f: 12.5 }
}
}
const S: Struct = Default::default();
fn main() {
println!("{:?}", S);
}However, if you run rustfmt, it will not error but simply quietly delete the word const between impl and std::default. This isn't great when using rustfmt at the crate level as it will of course delete all instances of const for trait impls, most likely breaking the build (and causing you to have to add them all back in).
The deletion seems like odd behavior in general, IMO: I'd expect rustfmt to give a hard error on syntax it thinks is legitimately invalid (as it usually does), and just do its best to normally format anything else.