Auto merge of #117703 - compiler-errors:recursive-async, r=<try>

Support async recursive calls (as long as they have indirection)

TL;DR: This code should work

```
async fn foo() {
  Box::pin(foo()).await;
}
```

r? `@ghost` while I write up a description, etc.

Author: bors

compiler/rustc_ast_lowering/src/expr.rs

@@ -792,8 +792,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // debuggers and debugger extensions expect it to be called `__awaitee`. They use
         // this name to identify what is being awaited by a suspended async functions.
         let awaitee_ident = Ident::with_dummy_span(sym::__awaitee);
-        let (awaitee_pat, awaitee_pat_hid) =
-            self.pat_ident_binding_mode(span, awaitee_ident, hir::BindingAnnotation::MUT);
+        let (awaitee_pat, awaitee_pat_hid) = self.pat_ident_binding_mode(
+            gen_future_span,
+            awaitee_ident,
+            hir::BindingAnnotation::MUT,
+        );
 
         let task_context_ident = Ident::with_dummy_span(sym::_task_context);
 

compiler/rustc_hir/src/hir.rs

@@ -1529,6 +1529,15 @@ pub enum CoroutineKind {
     Coroutine,
 }
 
+impl CoroutineKind {
+    pub fn is_fn_like(self) -> bool {
+        matches!(
+            self,
+            CoroutineKind::Async(CoroutineSource::Fn) | CoroutineKind::Gen(CoroutineSource::Fn)
+        )
+    }
+}
+
 impl fmt::Display for CoroutineKind {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {

compiler/rustc_hir_analysis/src/check/check.rs

@@ -216,13 +216,12 @@ fn check_opaque(tcx: TyCtxt<'_>, id: hir::ItemId) {
         return;
     }
 
-    let args = GenericArgs::identity_for_item(tcx, item.owner_id);
     let span = tcx.def_span(item.owner_id.def_id);
 
     if tcx.type_of(item.owner_id.def_id).instantiate_identity().references_error() {
         return;
     }
-    if check_opaque_for_cycles(tcx, item.owner_id.def_id, args, span, &origin).is_err() {
+    if check_opaque_for_cycles(tcx, item.owner_id.def_id, span).is_err() {
         return;
     }
 
@@ -233,16 +232,16 @@ fn check_opaque(tcx: TyCtxt<'_>, id: hir::ItemId) {
 pub(super) fn check_opaque_for_cycles<'tcx>(
     tcx: TyCtxt<'tcx>,
     def_id: LocalDefId,
-    args: GenericArgsRef<'tcx>,
     span: Span,
-    origin: &hir::OpaqueTyOrigin,
 ) -> Result<(), ErrorGuaranteed> {
+    let args = GenericArgs::identity_for_item(tcx, def_id);
     if tcx.try_expand_impl_trait_type(def_id.to_def_id(), args).is_err() {
-        let reported = match origin {
-            hir::OpaqueTyOrigin::AsyncFn(..) => async_opaque_type_cycle_error(tcx, span),
-            _ => opaque_type_cycle_error(tcx, def_id, span),
-        };
+        let reported = opaque_type_cycle_error(tcx, def_id, span);
         Err(reported)
+    } else if let Err(&LayoutError::Cycle(guar)) =
+        tcx.layout_of(tcx.param_env(def_id).and(Ty::new_opaque(tcx, def_id.to_def_id(), args)))
+    {
+        Err(guar)
     } else {
         Ok(())
     }
@@ -1324,16 +1323,6 @@ pub(super) fn check_mod_item_types(tcx: TyCtxt<'_>, module_def_id: LocalModDefId
     }
 }
 
-fn async_opaque_type_cycle_error(tcx: TyCtxt<'_>, span: Span) -> ErrorGuaranteed {
-    struct_span_err!(tcx.sess, span, E0733, "recursion in an `async fn` requires boxing")
-        .span_label(span, "recursive `async fn`")
-        .note("a recursive `async fn` must be rewritten to return a boxed `dyn Future`")
-        .note(
-            "consider using the `async_recursion` crate: https://crates.io/crates/async_recursion",
-        )
-        .emit()
-}
-
 /// Emit an error for recursive opaque types.
 ///
 /// If this is a return `impl Trait`, find the item's return expressions and point at them. For

compiler/rustc_middle/src/query/keys.rs

@@ -40,7 +40,7 @@ pub trait Key: Sized {
         None
     }
 
-    fn ty_adt_id(&self) -> Option<DefId> {
+    fn ty_def_id(&self) -> Option<DefId> {
         None
     }
 }
@@ -406,9 +406,10 @@ impl<'tcx> Key for Ty<'tcx> {
         DUMMY_SP
     }
 
-    fn ty_adt_id(&self) -> Option<DefId> {
-        match self.kind() {
+    fn ty_def_id(&self) -> Option<DefId> {
+        match *self.kind() {
             ty::Adt(adt, _) => Some(adt.did()),
+            ty::Coroutine(def_id, ..) => Some(def_id),
             _ => None,
         }
     }
@@ -452,6 +453,10 @@ impl<'tcx, T: Key> Key for ty::ParamEnvAnd<'tcx, T> {
     fn default_span(&self, tcx: TyCtxt<'_>) -> Span {
         self.value.default_span(tcx)
     }
+
+    fn ty_def_id(&self) -> Option<DefId> {
+        self.value.ty_def_id()
+    }
 }
 
 impl Key for Symbol {
@@ -550,7 +555,7 @@ impl<'tcx> Key for (ValidityRequirement, ty::ParamEnvAnd<'tcx, Ty<'tcx>>) {
         DUMMY_SP
     }
 
-    fn ty_adt_id(&self) -> Option<DefId> {
+    fn ty_def_id(&self) -> Option<DefId> {
         match self.1.value.kind() {
             ty::Adt(adt, _) => Some(adt.did()),
             _ => None,

compiler/rustc_middle/src/query/mod.rs

@@ -1390,6 +1390,8 @@ rustc_queries! {
     ) -> Result<ty::layout::TyAndLayout<'tcx>, &'tcx ty::layout::LayoutError<'tcx>> {
         depth_limit
         desc { "computing layout of `{}`", key.value }
+        // we emit our own error during query cycle handling
+        cycle_delay_bug
     }
 
     /// Compute a `FnAbi` suitable for indirect calls, i.e. to `fn` pointers.

compiler/rustc_middle/src/query/plumbing.rs

@@ -53,7 +53,7 @@ pub struct DynamicQuery<'tcx, C: QueryCache> {
         fn(tcx: TyCtxt<'tcx>, key: &C::Key, index: SerializedDepNodeIndex) -> bool,
     pub hash_result: HashResult<C::Value>,
     pub value_from_cycle_error:
-        fn(tcx: TyCtxt<'tcx>, cycle: &[QueryInfo], guar: ErrorGuaranteed) -> C::Value,
+        fn(tcx: TyCtxt<'tcx>, cycle_error: &CycleError, guar: ErrorGuaranteed) -> C::Value,
     pub format_value: fn(&C::Value) -> String,
 }
 

compiler/rustc_middle/src/ty/layout.rs

@@ -215,7 +215,7 @@ pub enum LayoutError<'tcx> {
     SizeOverflow(Ty<'tcx>),
     NormalizationFailure(Ty<'tcx>, NormalizationError<'tcx>),
     ReferencesError(ErrorGuaranteed),
-    Cycle,
+    Cycle(ErrorGuaranteed),
 }
 
 impl<'tcx> LayoutError<'tcx> {
@@ -226,7 +226,7 @@ impl<'tcx> LayoutError<'tcx> {
             Unknown(_) => middle_unknown_layout,
             SizeOverflow(_) => middle_values_too_big,
             NormalizationFailure(_, _) => middle_cannot_be_normalized,
-            Cycle => middle_cycle,
+            Cycle(_) => middle_cycle,
             ReferencesError(_) => middle_layout_references_error,
         }
     }
@@ -240,7 +240,7 @@ impl<'tcx> LayoutError<'tcx> {
             NormalizationFailure(ty, e) => {
                 E::NormalizationFailure { ty, failure_ty: e.get_type_for_failure() }
             }
-            Cycle => E::Cycle,
+            Cycle(_) => E::Cycle,
             ReferencesError(_) => E::ReferencesError,
         }
     }
@@ -261,7 +261,7 @@ impl<'tcx> fmt::Display for LayoutError<'tcx> {
                 t,
                 e.get_type_for_failure()
             ),
-            LayoutError::Cycle => write!(f, "a cycle occurred during layout computation"),
+            LayoutError::Cycle(_) => write!(f, "a cycle occurred during layout computation"),
             LayoutError::ReferencesError(_) => write!(f, "the type has an unknown layout"),
         }
     }
@@ -333,7 +333,7 @@ impl<'tcx> SizeSkeleton<'tcx> {
             Err(err @ LayoutError::Unknown(_)) => err,
             // We can't extract SizeSkeleton info from other layout errors
             Err(
-                e @ LayoutError::Cycle
+                e @ LayoutError::Cycle(_)
                 | e @ LayoutError::SizeOverflow(_)
                 | e @ LayoutError::NormalizationFailure(..)
                 | e @ LayoutError::ReferencesError(_),

compiler/rustc_middle/src/ty/util.rs

@@ -747,9 +747,13 @@ impl<'tcx> TyCtxt<'tcx> {
         match def_kind {
             DefKind::AssocFn if self.associated_item(def_id).fn_has_self_parameter => "method",
             DefKind::Coroutine => match self.coroutine_kind(def_id).unwrap() {
-                rustc_hir::CoroutineKind::Async(..) => "async closure",
-                rustc_hir::CoroutineKind::Coroutine => "coroutine",
-                rustc_hir::CoroutineKind::Gen(..) => "gen closure",
+                hir::CoroutineKind::Async(hir::CoroutineSource::Fn) => "async fn",
+                hir::CoroutineKind::Async(hir::CoroutineSource::Block) => "async block",
+                hir::CoroutineKind::Async(hir::CoroutineSource::Closure) => "async closure",
+                hir::CoroutineKind::Gen(hir::CoroutineSource::Fn) => "gen fn",
+                hir::CoroutineKind::Gen(hir::CoroutineSource::Block) => "gen block",
+                hir::CoroutineKind::Gen(hir::CoroutineSource::Closure) => "gen closure",
+                hir::CoroutineKind::Coroutine => "coroutine",
             },
             _ => def_kind.descr(def_id),
         }
@@ -765,9 +769,9 @@ impl<'tcx> TyCtxt<'tcx> {
         match def_kind {
             DefKind::AssocFn if self.associated_item(def_id).fn_has_self_parameter => "a",
             DefKind::Coroutine => match self.coroutine_kind(def_id).unwrap() {
-                rustc_hir::CoroutineKind::Async(..) => "an",
-                rustc_hir::CoroutineKind::Coroutine => "a",
-                rustc_hir::CoroutineKind::Gen(..) => "a",
+                hir::CoroutineKind::Async(..) => "an",
+                hir::CoroutineKind::Coroutine => "a",
+                hir::CoroutineKind::Gen(..) => "a",
             },
             _ => def_kind.article(),
         }
@@ -850,18 +854,7 @@ impl<'tcx> OpaqueTypeExpander<'tcx> {
         }
         let args = args.fold_with(self);
         if !self.check_recursion || self.seen_opaque_tys.insert(def_id) {
-            let expanded_ty = match self.expanded_cache.get(&(def_id, args)) {
-                Some(expanded_ty) => *expanded_ty,
-                None => {
-                    for bty in self.tcx.coroutine_hidden_types(def_id) {
-                        let hidden_ty = bty.instantiate(self.tcx, args);
-                        self.fold_ty(hidden_ty);
-                    }
-                    let expanded_ty = Ty::new_coroutine_witness(self.tcx, def_id, args);
-                    self.expanded_cache.insert((def_id, args), expanded_ty);
-                    expanded_ty
-                }
-            };
+            let expanded_ty = Ty::new_coroutine_witness(self.tcx, def_id, args);
             if self.check_recursion {
                 self.seen_opaque_tys.remove(&def_id);
             }