Bad `+ use<>` suggestion in nested macro_rules

Failure in migrating rocket 0.5.1 to 2024 due to the _typed_stream macro getting modified to:

macro_rules! _typed_stream {
    ($S:ident, $($t:tt)*) => (
        $crate::__typed_stream! {
            $crate::response::stream::$S,
            $crate::response::stream::stream,
            $crate::futures::stream::Stream,
            $($t)*
        } + use<'b>
    )
}

where that is invalid syntax. Just removing the + use<'b> seems to make things work?

Unraveling this to a minimal example seems to be quite a bit of work since there are many layers of macros involved. This could also just be an issue with the rocket_codegen proc-macro respanning, but I did not unravel it that far.

Meta

rustc 1.85.0-nightly (5e1440ae5 2024-12-01)
binary: rustc
commit-hash: 5e1440ae514d98ddfcbf1607acb64d41e07ef616
commit-date: 2024-12-01
host: aarch64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.4

Start by reproducing the report with rustc 1.85.0-nightly and Rocket's _typed_stream macro in core/lib/src/response/stream/mod.rs:292-301. Trace the nested macro expansion and the rocket_codegen proc-macro respanning to determine why + use<'b> is suggested; done means the expansion no longer produces invalid syntax.