Workaround rustfmt panic on quote!(Self(#var)) in Rust 1.93.0

[natepiano]

Objective

Fix CI failure caused by a rustfmt regression in Rust 1.93.0.

The cargo fmt --all -- --check CI step panics when formatting crates/bevy_reflect/derive/src/from_reflect.rs due to the pattern quote!(Self(#__this)).

Upstream issue: rust-lang/rustfmt#6779

Fixes #22704.

Solution

Pre-construct Self as a separate token stream before using it in the quote! macro:

let self_ty = quote!(Self);
quote!(#self_ty(#__this))  // instead of quote!(Self(#__this))

This produces identical output but avoids the rustfmt parser bug.

Testing

• cargo fmt --all no longer panics
• cargo build -p bevy_reflect_derive succeeds
• cargo nextest run -p bevy_reflect passes all 212 tests

[natepiano]

I created an issue rust-lang/rustfmt/issues/6779. The issue was updated that it is fixed with rust-lang/rust#150590 which I believe is in nightly now and is targeted for 1.94.0 milestone so if we just want to wait for that, then there won't be any need to merge this. If you want CI fixed now, you can merge this - if not, feel free to close this PR.

[mockersf]

this is not causing a CI failure, cargo is not exiting in error after the ICE and correctly continue to format