False syntax errors with associated_const_equality

[thorjelly]

The following code works in nightly with cargo check but rust-analyzer reports HasCount<COUNT = {N}> as containing syntax errors:

#![feature(associated_const_equality)]

trait HasCount {
    const COUNT: usize;
}

trait Foo {}

impl<T, const N: usize> Foo for T where T: HasCount<COUNT = {N}> {}

Using pre-release VSCode extension. The official Rust plugin works fine.

[memoryruins]

The rustc tracking issue is rust-lang/rust#92827. It doesn't currently link to a doc/mcp/rfc describing the feature, but I imagine the syntax could be handled by r-a even before implementing lowering/analysis for them.

In the meantime, rust-analyzer syntax's built-in diagnostics can be configured/disabled by users until the syntax is handled (if the current diagnostic is distracting for anyone).

syn similarly updated to handle this case recently dtolnay/syn@99560af.

[Veykril]

This rule here needs to be updated, https://github.com/rust-analyzer/rust-analyzer/blob/faaec86ff0cf10dbd822a7abbeb381b3b5578141/crates/syntax/rust.ungram#L53-L54

Then cargo test -p syntax has to be run to update our syntax tree, and finally the parser has to be adjusted here https://github.com/rust-analyzer/rust-analyzer/blob/faaec86ff0cf10dbd822a7abbeb381b3b5578141/crates/parser/src/grammar/generic_args.rs#L43-L49

[xffxff]

I'm working on this