broken MIR in let_else statements

[Eugeny]

I'm getting broken MIR errors in about each 10th of my let-else usages. I think it's related to incremental compilation since if never happens on a fresh first-time Clippy run.

Unfortunately, I'm unable to reproduce it in an isolated project, but the code is OSS - here are a few snippets:

Code: https://github.com/warp-tech/warpgate/blob/main/warpgate-protocol-mysql/src/client.rs#L149-L151

warning: Error finalizing incremental compilation session directory `/Users/eugene/Work/warpgate/target/debug/incremental/warpgate_protocol_mysql-2e3tgexhc7x8e/s-gf31whx4hw-1ja190i-working`: No such file or directory (os error 2)

error: internal compiler error: no errors encountered even though `delay_span_bug` issued

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:68 ~ warpgate_protocol_mysql[9d48]::client::{impl#1}::connect::{closure#0}), const_param_did: None }) (after pass PhaseChange-Runtime(Optimized)) at bb1145[0]:
                                use of local _1023, which has no storage here
   --> warpgate-protocol-mysql/src/client.rs:151:10
    |
151 |         };
    |          ^
    |
    = note: delayed at compiler/rustc_const_eval/src/transform/validate.rs:128:36

Code: https://github.com/warp-tech/warpgate/blob/main/warpgate-protocol-mysql/src/session.rs#L418-L420

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:263 ~ warpgate_protocol_mysql[9d48]::session::{impl#0}::passthrough_until_result::{closure#0}), const_param_did: None }) (after pass PhaseChange-Runtime(Optimized)) at bb257[0]:
                                use of local _11, which has no storage here
   --> warpgate-protocol-mysql/src/session.rs:420:14
    |
420 |             };
    |              ^
    |
    = note: delayed at compiler/rustc_const_eval/src/transform/validate.rs:128:36

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1530:13
stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: std::panic::panic_any::<rustc_errors::ExplicitBug>
   2: <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop
   3: core::ptr::drop_in_place::<rustc_session::parse::ParseSess>
   4: <alloc::rc::Rc<rustc_session::session::Session> as core::ops::drop::Drop>::drop
   5: core::ptr::drop_in_place::<rustc_interface::interface::Compiler>
   6: rustc_span::with_source_map::<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_interface::interface::create_compiler_and_run<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#1}>
   7: rustc_interface::interface::create_compiler_and_run::<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>
   8: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust-clippy/issues/new

note: Clippy version: clippy 0.1.65 (8ce3204a 2022-09-30)

query stack during panic:
end of query stack

[est31]

@Eugeny can you still reproduce it with latest master?

Your bug looks a lot like rust-lang/rust#102317 which was fixed Oct 6 in rustc master, and in the rustup after that in clippy. Your toolchain is from end of September so doesn't have the fix yet.

[Eugeny]

Thanks - I can confirm it's fixed in the nightly!