assertion `left == right` failed at `src/rt/async_support/waitable.rs:201`

[badeend]

I'm hitting this assertion.

I ran into this while working on a branch that uses wit_bindgen::block_on to drive stream I/O synchronously from within an async export.

With some LLM help I was able to reduce it to: https://github.com/badeend/wasmtime/blob/waitable-panic-repro/crates/test-programs/src/bin/p3_tls_sample_application.rs

Noet that the assertion only fires if the two write futures are allocated at different heap addresses. If the allocator happens to reuse the same slot (ptr == prev) then the assert passes by coincidence, possibly causing memory corruption (?)

I have no idea what the correct behavior should be here. On the surface I'd expect this to work. Or, if block_on is not intended to be used like this, I don't think comparing memory addresses is the correct line of defense.

---

Stack trace:

thread '<unnamed>' (1) panicked at /home/dave/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/wit-bindgen-0.57.0/src/rt/async_support/waitable.rs:201:17:
assertion `left == right` failed
  left: 0x104fd0
 right: 0x104e50
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
test p3::rustls::p3_tls_sample_application ... FAILED

failures:

---- p3::rustls::p3_tls_sample_application stdout ----
Error: error while executing at wasm backtrace:
    0:  0x1a3c7 - p3_tls_sample_application-57673490efd69ec5.wasm!abort
    1:  0x155ed - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN3std3sys3pal6wasip17helpers14abort_internal17h74119267dbd11beeE
    2:  0x140af - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN3std7process5abort17h49844fb4bec76201E
    3:  0x1412b - p3_tls_sample_application-57673490efd69ec5.wasm!_RNvCsdBezzDwma51_7___rustc12___rust_abort
    4:  0x13ecf - p3_tls_sample_application-57673490efd69ec5.wasm!_RNvCsdBezzDwma51_7___rustc18___rust_start_panic
    5:  0x13ef2 - p3_tls_sample_application-57673490efd69ec5.wasm!_RNvCsdBezzDwma51_7___rustc10rust_panic
    6:  0x163c1 - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN3std9panicking15panic_with_hook17h7a3e5eaee7fad80cE
    7:  0x158b9 - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN3std9panicking13panic_handler28_$u7b$$u7b$closure$u7d$$u7d$17h36465fe3c8c216bdE
    8:  0x1421a - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN3std3sys9backtrace26__rust_end_short_backtrace17hfc6d834ad5c88707E
    9:  0x1420e - p3_tls_sample_application-57673490efd69ec5.wasm!_RNvCsdBezzDwma51_7___rustc17rust_begin_unwind
   10:  0x1ba41 - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN4core9panicking9panic_fmt17h2b55671c70ea4e21E
   11:  0x1d0ce - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN4core9panicking19assert_failed_inner17h413a92926c49224dE
   12:   0x731a - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN4core9panicking13assert_failed17ha9e7c539c84bc32eE
   13:   0xb3a7 - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN11wit_bindgen2rt13async_support8waitable26WaitableOperation$LT$S$GT$14register_waker17h24054f043d98c2e5E
   14:   0xa812 - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN11wit_bindgen2rt13async_support8waitable26WaitableOperation$LT$S$GT$23poll_complete_with_code17h52b4388adf3a6c5fE
   15:   0xa35f - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN11wit_bindgen2rt13async_support8waitable26WaitableOperation$LT$S$GT$13poll_complete17h574be3c29c8fe313E
   16:   0x85a7 - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN120_$LT$wit_bindgen..rt..async_support..stream_support..RawStreamWrite$LT$O$GT$$u20$as$u20$core..future..future..Future$GT$4poll17hdff73afdb24c0bbdE
   17:   0x2123 - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN106_$LT$p3_tls_sample_application..Component$u20$as$u20$test_programs..p3..exports..wasi..cli..run..Guest$GT$3run28_$u7b$$u7b$closure$u7d$$u7d$28_$u7b$$u7b$closure$u7d$$u7d$17h458754691bc5ca2bE
   18:   0x1b4f - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN106_$LT$p3_tls_sample_application..Component$u20$as$u20$test_programs..p3..exports..wasi..cli..run..Guest$GT$3run28_$u7b$$u7b$closure$u7d$$u7d$17h6c6098462d6d7272E
   19:   0x349d - p3_tls_sample_application-57673490efd69ec5.wasm!_ZN13test_programs2p37exports4wasi3cli3run16_export_run_cabi28_$u7b$$u7b$closure$u7d$$u7d$17h808d1ee9b878ecc9E

Caused by:
    wasm trap: wasm `unreachable` instruction executed