compilation stuck while resolving futures_async_stream

[xxchan]

Code

INFO rustc_trait_selection::traits::query::normalize normalize::<rustc_middle::mir::ConstantKind>: result=Ok(Val(ZeroSized, for<'a, 'b, 'c> fn(std::pin::Pin<&'a mut futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:760:5: 760:61]>>, &'b mut std::task::Context<'c>) -> std::task::Poll<std::option::Option<<futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:760:5: 760:61]> as tokio_stream::Stream>::Item>> {<futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:760:5: 760:61]> as tokio_stream::Stream>::poll_next})) with 4052 obligations
INFO rustc_trait_selection::traits::query::normalize normalize::<rustc_middle::ty::subst::GenericArg>: result=Ok(unsafe fn(&mut futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:760:5: 760:61]>) -> std::pin::Pin<&mut futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:760:5: 760:61]>> {std::pin::Pin::<&mut futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:760:5: 760:61]>>::new_unchecked}) with 4052 obligations
INFO rustc_trait_selection::traits::query::normalize normalize::<rustc_middle::mir::ConstantKind>: result=Ok(Val(ZeroSized, unsafe fn(&mut futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:760:5: 760:61]>) -> std::pin::Pin<&mut futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:760:5: 760:61]>> {std::pin::Pin::<&mut futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:760:5: 760:61]>>::new_unchecked})) with 4052 obligations

It seems that Rust is very slow with resolving futures_async_stream. It took about 1sec for each resolving. As a comparison, previous builds only have 0 obligations for all these things.

Originally posted by @skyzh in risingwavelabs/risingwave#5119 (comment)

And we have located the problem occurs on this function: https://github.com/risingwavelabs/risingwave/blob/2c5bc306cb063376e3497bc27f14f80ed15a6a97/src/stream/src/executor/hash_join.rs#L604-L605

After removing the #[for_await] in the function body, it will compiles quickly.

I expected to see this happen: it compiles.

Instead, this happened: it got stuck.

Version it worked on

It most recently worked on: nightly-2022-07-29

Version with regression

rustc --version --verbose:

rustc 1.66.0-nightly (b8c35ca26 2022-10-15)
binary: rustc
commit-hash: b8c35ca26b191bb9a9ac669a4b3f4d3d52d97fb1
commit-date: 2022-10-15
host: aarch64-apple-darwin
release: 1.66.0-nightly
LLVM version: 15.0.2

Backtrace

Backtrace

<backtrace>

[skyzh]

Probably I'll get some easy-to-reproduce examples...

[skyzh]

The difference:

INFO rustc_trait_selection::traits::query::normalize normalize::<rustc_middle::ty::subst::GenericArg>: result=Ok(fn(futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:604:5: 604:61]>) -> std::pin::Pin<std::boxed::Box<dyn tokio_stream::Stream<Item = <futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:604:5: 604:61]> as tokio_stream::Stream>::Item> + std::marker::Send>> {<futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:604:5: 604:61]> as futures::StreamExt>::boxed::<'_>}) with 4052 obligations

where in nightly-07-29

INFO rustc_trait_selection::traits::query::normalize normalize::<rustc_middle::ty::subst::GenericArg>: result=Ok(fn(futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:604:5: 604:61]>) -> std::pin::Pin<std::boxed::Box<dyn tokio_stream::Stream<Item = <futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:604:5: 604:61]> as tokio_stream::Stream>::Item> + std::marker::Send>> {<futures_async_stream::try_stream::from_generator::GenTryStream<[static generator@src/stream/src/executor/hash_join.rs:604:5: 604:61]> as futures::StreamExt>::boxed}) with 0 obligations

Note that the latest nightly has an extra ::<'_> after boxed. Not sure if this is the contributing factor of so many obligations... still working on a minimum reproducible example.

[skyzh]

Not related to futures_async_stream. Need investigate where are the 4000+ obligations from. cc @xxchan let's close for now until we find the root cause and submit another issue?

[skyzh]

Probably has fixed by #102945? Let's try again. Nope 🤣