Incremental compilation OOM

[TapGhoul]

This comes from the bug report DioxusLabs/dioxus#3903 with DioxusLabs/dioxus#3903 (comment) being especially relevant.

I have no idea how to diagnose this, and there is no real crash - just an OOM that requires the linux OOM killer step in. It feels like the borrow checker freaking out? Probably an incorrect guess
This does not appear to be related to macro expansion, which is what the original report's title says - this seems to occur well after expansion. While the sample code does still contain a macro, expanding beyond this still reproduces the issue.

This occurs both on stable (1.85.1) and latest nightly (920d95eaf 2025-03-28) as of my most recent test.

I'm happy to rewrite this bug report, I just have no idea where to start in actually trying to diagnose this (I lack knowledge on tooling etc for bugs like this) - it eats about 1GB/s if you let it, and ate all 96GB of RAM I have installed, but I'm not sure how to instrument it.
The linked issue has a sample project that reproduces this, with reproduction instructions in the initial bug report.

[saethlin]

I have followed the directions and cannot reproduce an OOM on nightly or stable.

[TapGhoul]

Strange... Is there anything I can do on my end to maybe help get a dump to investigate what may be going on? I tried some heap profiling tools before but I could never get it to actually capture a majority of the data (likely my own inexperience with such tools), so I'm not sure what's going wrong in capturing said dump, so if there's anything I can do to provide something useful let me know.

[TapGhoul]

If it helps too - there is also a hilariously deep backtrace I can get with a debugger that's at least 600,000 entries deep.

A lot of the lines are just this repeating

0x00007ffff4e46d73 librustc_driver-fdfc7fb14758cf9e.so`rustc_query_impl::query_impl::coroutine_kind::try_collect_active_jobs + 35
0x00007ffff4e2e68c librustc_driver-fdfc7fb14758cf9e.so`<rustc_query_impl::plumbing::QueryCtxt as rustc_query_system::query::QueryContext>::collect_active_jobs + 76
0x00007ffff4d7ec1e librustc_driver-fdfc7fb14758cf9e.so`rustc_query_system::query::plumbing::cycle_error::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt> + 46
0x00007ffff5e30ce6 librustc_driver-fdfc7fb14758cf9e.so`rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, true> + 14886
0x00007ffff5e2c5ee librustc_driver-fdfc7fb14758cf9e.so`rustc_query_impl::query_impl::def_span::get_query_incr::__rust_end_short_backtrace + 218
0x00007ffff5d8cbe4 librustc_driver-fdfc7fb14758cf9e.so`rustc_middle::query::plumbing::query_get_at::<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>> (.llvm.5519915731637686349) + 528
0x00007ffff4e30ea8 librustc_driver-fdfc7fb14758cf9e.so`rustc_query_impl::plumbing::create_query_frame::<rustc_span::def_id::DefId> + 424
0x00007ffff4e085d5 librustc_driver-fdfc7fb14758cf9e.so`<rustc_query_impl::query_impl::coroutine_kind::try_collect_active_jobs::{closure#0} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::DefId)>>::call_once + 37
0x00007ffff4d6682a librustc_driver-fdfc7fb14758cf9e.so`<rustc_query_system::query::plumbing::QueryState<rustc_span::def_id::DefId>>::try_collect_active_jobs::<rustc_middle::ty::context::TyCtxt> + 890

[cyrgani]

I can reproduce this on the latest nightly, will try to minimize it

[cyrgani]

reduction, reproducible with cargo clean && cargo build && cargo rustc -- --cfg=a:

fn main() {
    #[cfg(a)]
    || ();

    || {
        Some(())
            .map(|_| ())
            .map(|y| y);
    };

    async || {};
}

@rustbot label S-has-mcve A-closures A-async-closures

[cyrgani]

reducing further to leave only closures removes the hang, but generates a nonsensical cycle error (only with incr comp too):

fn main() {
    #[cfg(a)]
    || ();

    || {
        || ();
        || ();
    };

    async || {};
}

error[E0391]: cycle detected when type-checking `main`
 --> src/main.rs:1:1
  |
1 | fn main() {
  | ^^^^^^^^^
  |
  = note: ...which requires looking up span for `main::{closure#1}::{closure#1}`...
  = note: ...which again requires type-checking `main`, completing the cycle
note: cycle used when checking that `main` is well-formed
 --> src/main.rs:1:1
  |
1 | fn main() {
  | ^^^^^^^^^
  = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information