Stack overflow from closure TAIT in a method on the opaque type itself in debug mode

[theemathas]

Code

#![feature(type_alias_impl_trait)]

type Opaque = impl Sized;

trait Trait {
    fn foo();
}

impl Trait for Opaque {
    #[define_opaque(Opaque)]
    fn foo() {
        let _: Opaque = || {};
    }
}

fn main() {
    Opaque::foo();
}

@rustbot labels +F-type_alias_impl_trait +I-crash

Crash only occurs when compiling in debug mode

Possibly related to #136390

Meta

Reproducible on the playground with version version: 1.90.0-nightly (2025-08-01 4b55fe199cfe9c710555)

Error output

error: rustc interrupted by SIGSEGV, printing backtrace

Backtrace

/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/librustc_driver-2a52e13f9d86ed3d.so(+0x3c8efcf)[0x7e5504e8efcf]
/lib/x86_64-linux-gnu/libc.so.6(+0x45330)[0x7e550102e330]
/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/librustc_driver-2a52e13f9d86ed3d.so(+0x67e3c7c)[0x7e55079e3c7c]
/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/librustc_driver-2a52e13f9d86ed3d.so(+0x5e2959d)[0x7e550702959d]

### cycle encountered after 4 frames with period 6
/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/librustc_driver-2a52e13f9d86ed3d.so(+0x5e256f8)[0x7e55070256f8]
/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/librustc_driver-2a52e13f9d86ed3d.so(+0x5e256f8)[0x7e55070256f8]
/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/librustc_driver-2a52e13f9d86ed3d.so(+0x5e29171)[0x7e5507029171]
/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/librustc_driver-2a52e13f9d86ed3d.so(+0x5e256f8)[0x7e55070256f8]
/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/librustc_driver-2a52e13f9d86ed3d.so(+0x5e256f8)[0x7e55070256f8]
/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/librustc_driver-2a52e13f9d86ed3d.so(+0x5e29171)[0x7e5507029171]
### recursed 42 times


note: rustc unexpectedly overflowed its stack! this is a bug
note: maximum backtrace depth reached, frames may have been lost
note: we would appreciate a report at https://github.com/rust-lang/rust
help: you can increase rustc's stack size by setting RUST_MIN_STACK=16777216
error: could not compile `playground` (bin "playground")