Rust does not correctly handle async recursion with nice errors in certain cases

[cheesycod]

I tried this code (its too big for a example and I don't have a MVP as it relies on a slew of things going wrong): https://github.com/Anti-Raid/khronos/blob/c67dbc8c1f3e4eb3bbfdd103d6ddb3fc3a877da0/crates/runtime/src/plugins/antiraid/discord/mod.rs#L194

I expected to see this happen: A error telling me to use async recursion/infinitely sized future error

Instead, this happened:

error[E0391]: cycle detected when computing layout of `core::mem::maybe_uninit::MaybeUninit<{async fn body of khronos_runtime::plugins::antiraid::discord::DiscordActionExecutor<templatingrt::primitives::dummyctx::DummyProvider>::check_channel_permissions()}>`
    |
    = note: ...which requires computing layout of `core::mem::manually_drop::ManuallyDrop<{async fn body of khronos_runtime::plugins::antiraid::discord::DiscordActionExecutor<templatingrt::primitives::dummyctx::DummyProvider>::check_channel_permissions()}>`...
note: ...which requires computing layout of `{async fn body of khronos_runtime::plugins::antiraid::discord::DiscordActionExecutor<templatingrt::primitives::dummyctx::DummyProvider>::check_channel_permissions()}`...
   --> /home/antiraid/.cargo/git/checkouts/khronos-a39d166da77a1483/c67dbc8/crates/runtime/src/plugins/antiraid/discord/mod.rs:242:63
    |
242 | ...d(gt) => return self.check_channel_permissions(gt.owner_id, gt.parent_id.widen(), needed_permissions).await,
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: ...which again requires computing layout of `core::mem::maybe_uninit::MaybeUninit<{async fn body of khronos_runtime::plugins::antiraid::discord::DiscordActionExecutor<templatingrt::primitives::dummyctx::DummyProvider>::check_channel_permissions()}>`, completing the cycle
note: cycle used when computing layout of `{async closure body@<khronos_runtime::plugins::antiraid::discord::DiscordActionExecutor<templatingrt::primitives::dummyctx::DummyProvider> as mluau::userdata::UserData>::add_methods<mluau::userdata::registry::UserDataRegistry<khronos_runtime::plugins::antiraid::discord::DiscordActionExecutor<templatingrt::primitives::dummyctx::DummyProvider>>>::{closure#6}::{closure#0}<templatingrt::primitives::dummyctx::DummyProvider>}`
   --> /home/antiraid/.cargo/git/checkouts/khronos-a39d166da77a1483/c67dbc8/crates/runtime/src/plugins/antiraid/discord/mod.rs:379:65
    |
379 |   ...   let (partial_guild, member, channel, permissions) = this.check_channel_permissions(data.user_id, data.channel_id, data...
    |  ___________________________________________________________^
380 | | ...       .await
    | |________________^
    = 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

error[E0391]: cycle detected when computing layout of `core::mem::maybe_uninit::MaybeUninit<{async fn body of khronos_runtime::plugins::antiraid::discord::DiscordActionExecutor<templatingrt::primitives::ctxprovider::TemplateContextProvider>::check_channel_permissions()}>`
    |
    = note: ...which requires computing layout of `core::mem::manually_drop::ManuallyDrop<{async fn body of khronos_runtime::plugins::antiraid::discord::DiscordActionExecutor<templatingrt::primitives::ctxprovider::TemplateContextProvider>::check_channel_permissions()}>`...
note: ...which requires computing layout of `{async fn body of khronos_runtime::plugins::antiraid::discord::DiscordActionExecutor<templatingrt::primitives::ctxprovider::TemplateContextProvider>::check_channel_permissions()}`...
   --> /home/antiraid/.cargo/git/checkouts/khronos-a39d166da77a1483/c67dbc8/crates/runtime/src/plugins/antiraid/discord/mod.rs:242:63
    |
242 | ...d(gt) => return self.check_channel_permissions(gt.owner_id, gt.parent_id.widen(), needed_permissions).await,
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: ...which again requires computing layout of `core::mem::maybe_uninit::MaybeUninit<{async fn body of khronos_runtime::plugins::antiraid::discord::DiscordActionExecutor<templatingrt::primitives::ctxprovider::TemplateContextProvider>::check_channel_permissions()}>`, completing the cycle
note: cycle used when computing layout of `{async closure body@<khronos_runtime::plugins::antiraid::discord::DiscordActionExecutor<templatingrt::primitives::ctxprovider::TemplateContextProvider> as mluau::userdata::UserData>::add_methods<mluau::userdata::registry::UserDataRegistry<khronos_runtime::plugins::antiraid::discord::DiscordActionExecutor<templatingrt::primitives::ctxprovider::TemplateContextProvider>>>::{closure#6}::{closure#0}<templatingrt::primitives::ctxprovider::TemplateContextProvider>}`
   --> /home/antiraid/.cargo/git/checkouts/khronos-a39d166da77a1483/c67dbc8/crates/runtime/src/plugins/antiraid/discord/mod.rs:379:65
    |
379 |   ...   let (partial_guild, member, channel, permissions) = this.check_channel_permissions(data.user_id, data.channel_id, data...
    |  ___________________________________________________________^
380 | | ...       .await
    | |________________^
    = 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

For more information about this error, try `rustc --explain E0391`.
error: could not compile `template-worker` (bin "template-worker") due to 2 previous errors

The error points to rustc-dev-guide and doesn't mention the recursion whatsoever.

While I'm not sure what the error is, it seems to be related to using a trait that contains a async function that recurses

Meta

rustc --version --verbose:

rustc 1.89.0-nightly (1677d46cb 2025-06-10)
binary: rustc
commit-hash: 1677d46cb128cc8f285dbd32b0dc4d7a46437050
commit-date: 2025-06-10
host: x86_64-unknown-linux-gnu
release: 1.89.0-nightly
LLVM version: 20.1.5

[compiler-errors]

It would be really nice if you could minimize this into something self-contained that reproduces this issue. We do have some support for nice errors that explain that async recursion must be Box'ed, e.g.

async fn foo() {
    foo().await;
}

error[E0733]: recursion in an async fn requires boxing
 --> src/lib.rs:1:1
  |
1 | async fn foo() {
  | ^^^^^^^^^^^^^^
2 |     foo().await;
  |     ----------- recursive call here
  |
  = note: a recursive `async fn` call must introduce indirection such as `Box::pin` to avoid an infinitely sized future

But presumably this is breaking down somewhere in your code.

[cheesycod]

It would be really nice if you could minimize this into something self-contained that reproduces this issue. We do have some support for nice errors that explain that async recursion must be Box'ed, e.g.

async fn foo() {
foo().await;
}

error[E0733]: recursion in an async fn requires boxing
 --> src/lib.rs:1:1
  |
1 | async fn foo() {
  | ^^^^^^^^^^^^^^
2 |     foo().await;
  |     ----------- recursive call here
  |
  = note: a recursive `async fn` call must introduce indirection such as `Box::pin` to avoid an infinitely sized future

But presumably this is breaking down somewhere in your code.

Thats the annoying part, I haven't been able to shrink down the example yet (though I'm still trying to)