Make async closures directly lower to ClosureKind::CoroutineClosure

compiler/rustc_ast_lowering/messages.ftl

@@ -117,9 +117,6 @@ ast_lowering_never_pattern_with_guard =
     a guard on a never pattern will never be run
     .suggestion = remove this guard
 
-ast_lowering_not_supported_for_lifetime_binder_async_closure =
-    `for<...>` binders on `async` closures are not currently supported
-
 ast_lowering_previously_used_here = previously used here
 
 ast_lowering_register1 = register `{$reg1_name}`

compiler/rustc_ast_lowering/src/errors.rs

@@ -326,13 +326,6 @@ pub struct MisplacedRelaxTraitBound {
     pub span: Span,
 }
 
-#[derive(Diagnostic, Clone, Copy)]
-#[diag(ast_lowering_not_supported_for_lifetime_binder_async_closure)]
-pub struct NotSupportedForLifetimeBinderAsyncClosure {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag(ast_lowering_match_arm_with_no_body)]
 pub struct MatchArmWithNoBody {

compiler/rustc_ast_lowering/src/expr.rs

@@ -2,8 +2,7 @@ use super::errors::{
     AsyncCoroutinesNotSupported, AwaitOnlyInAsyncFnAndBlocks, BaseExpressionDoubleDot,
     ClosureCannotBeStatic, CoroutineTooManyParameters,
     FunctionalRecordUpdateDestructuringAssignment, InclusiveRangeWithNoEnd, MatchArmWithNoBody,
-    NeverPatternWithBody, NeverPatternWithGuard, NotSupportedForLifetimeBinderAsyncClosure,
+    NeverPatternWithBody, NeverPatternWithGuard, UnderscoreExprLhsAssign,
-    UnderscoreExprLhsAssign,
 };
 use super::ResolverAstLoweringExt;
 use super::{ImplTraitContext, LoweringContext, ParamMode, ParenthesizedGenericArgs};
@@ -1026,30 +1025,21 @@ impl<'hir> LoweringContext<'_, 'hir> {
         fn_decl_span: Span,
         fn_arg_span: Span,
     ) -> hir::ExprKind<'hir> {
-        if let &ClosureBinder::For { span, .. } = binder {
-            self.dcx().emit_err(NotSupportedForLifetimeBinderAsyncClosure { span });
-        }
-
         let (binder_clause, generic_params) = self.lower_closure_binder(binder);
 
         let body = self.with_new_scopes(fn_decl_span, |this| {
+            let inner_decl =
+                FnDecl { inputs: decl.inputs.clone(), output: FnRetTy::Default(fn_decl_span) };
+
             // Transform `async |x: u8| -> X { ... }` into
             // `|x: u8| || -> X { ... }`.
             let body_id = this.lower_body(|this| {
-                let async_ret_ty = if let FnRetTy::Ty(ty) = &decl.output {
-                    let itctx = ImplTraitContext::Disallowed(ImplTraitPosition::AsyncBlock);
-                    Some(hir::FnRetTy::Return(this.lower_ty(ty, &itctx)))
-                } else {
-                    None
-                };
-
                 let (parameters, expr) = this.lower_coroutine_body_with_moved_arguments(
-                    decl,
+                    &inner_decl,
                     |this| this.with_new_scopes(fn_decl_span, |this| this.lower_expr_mut(body)),
                     body.span,
                     coroutine_kind,
                     hir::CoroutineSource::Closure,
-                    async_ret_ty,
                 );
 
                 let hir_id = this.lower_node_id(coroutine_kind.closure_id());
@@ -1060,15 +1050,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
             body_id
         });
 
-        let outer_decl =
-            FnDecl { inputs: decl.inputs.clone(), output: FnRetTy::Default(fn_decl_span) };
-
         let bound_generic_params = self.lower_lifetime_binder(closure_id, generic_params);
         // We need to lower the declaration outside the new scope, because we
         // have to conserve the state of being inside a loop condition for the
         // closure argument types.
         let fn_decl =
-            self.lower_fn_decl(&outer_decl, closure_id, fn_decl_span, FnDeclKind::Closure, None);
+            self.lower_fn_decl(&decl, closure_id, fn_decl_span, FnDeclKind::Closure, None);
 
         let c = self.arena.alloc(hir::Closure {
             def_id: self.local_def_id(closure_id),
@@ -1079,7 +1066,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             body,
             fn_decl_span: self.lower_span(fn_decl_span),
             fn_arg_span: Some(self.lower_span(fn_arg_span)),
-            kind: hir::ClosureKind::Closure,
+            kind: hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Async),
             constness: hir::Constness::NotConst,
         });
         hir::ExprKind::Closure(c)

compiler/rustc_ast_lowering/src/item.rs

@@ -1086,7 +1086,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 body.span,
                 coroutine_kind,
                 hir::CoroutineSource::Fn,
-                None,
             );
 
             // FIXME(async_fn_track_caller): Can this be moved above?
@@ -1108,7 +1107,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
         body_span: Span,
         coroutine_kind: CoroutineKind,
         coroutine_source: hir::CoroutineSource,
-        return_type_hint: Option<hir::FnRetTy<'hir>>,
     ) -> (&'hir [hir::Param<'hir>], hir::Expr<'hir>) {
         let mut parameters: Vec<hir::Param<'_>> = Vec::new();
         let mut statements: Vec<hir::Stmt<'_>> = Vec::new();
@@ -1284,7 +1282,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             // all async closures would default to `FnOnce` as their calling mode.
             CaptureBy::Ref,
             closure_id,
-            return_type_hint,
+            None,
             body_span,
             desugaring_kind,
             coroutine_source,

compiler/rustc_ast_lowering/src/lib.rs

@@ -33,6 +33,7 @@
 #![allow(internal_features)]
 #![feature(rustdoc_internals)]
 #![doc(rust_logo)]
+#![feature(assert_matches)]
 #![feature(box_patterns)]
 #![feature(let_chains)]
 #![deny(rustc::untranslatable_diagnostic)]
@@ -296,7 +297,6 @@ enum ImplTraitPosition {
     Path,
     Variable,
     Trait,
-    AsyncBlock,
     Bound,
     Generic,
     ExternFnParam,
@@ -323,7 +323,6 @@ impl std::fmt::Display for ImplTraitPosition {
             ImplTraitPosition::Path => "paths",
             ImplTraitPosition::Variable => "the type of variable bindings",
             ImplTraitPosition::Trait => "traits",
-            ImplTraitPosition::AsyncBlock => "async blocks",
             ImplTraitPosition::Bound => "bounds",
             ImplTraitPosition::Generic => "generics",
             ImplTraitPosition::ExternFnParam => "`extern fn` parameters",

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -858,7 +858,9 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             use crate::session_diagnostics::CaptureVarCause::*;
             match kind {
                 hir::ClosureKind::Coroutine(_) => MoveUseInCoroutine { var_span },
-                hir::ClosureKind::Closure => MoveUseInClosure { var_span },
+                hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
+                    MoveUseInClosure { var_span }
+                }
             }
         });
 
@@ -905,7 +907,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 hir::ClosureKind::Coroutine(_) => {
                     BorrowUsePlaceCoroutine { place: desc_place, var_span, is_single_var: true }
                 }
-                hir::ClosureKind::Closure => {
+                hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
                     BorrowUsePlaceClosure { place: desc_place, var_span, is_single_var: true }
                 }
             }
@@ -1056,7 +1058,8 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                                     var_span,
                                     is_single_var: true,
                                 },
-                                hir::ClosureKind::Closure => BorrowUsePlaceClosure {
+                                hir::ClosureKind::Closure
+                                | hir::ClosureKind::CoroutineClosure(_) => BorrowUsePlaceClosure {
                                     place: desc_place,
                                     var_span,
                                     is_single_var: true,
@@ -1140,7 +1143,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         var_span,
                         is_single_var: false,
                     },
-                    hir::ClosureKind::Closure => {
+                    hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
                         BorrowUsePlaceClosure { place: desc_place, var_span, is_single_var: false }
                     }
                 }
@@ -1158,7 +1161,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         hir::ClosureKind::Coroutine(_) => {
                             FirstBorrowUsePlaceCoroutine { place: borrow_place_desc, var_span }
                         }
-                        hir::ClosureKind::Closure => {
+                        hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
                             FirstBorrowUsePlaceClosure { place: borrow_place_desc, var_span }
                         }
                     }
@@ -1175,7 +1178,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         hir::ClosureKind::Coroutine(_) => {
                             SecondBorrowUsePlaceCoroutine { place: desc_place, var_span }
                         }
-                        hir::ClosureKind::Closure => {
+                        hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
                             SecondBorrowUsePlaceClosure { place: desc_place, var_span }
                         }
                     }
@@ -2942,7 +2945,9 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     use crate::session_diagnostics::CaptureVarCause::*;
                     match kind {
                         hir::ClosureKind::Coroutine(_) => BorrowUseInCoroutine { var_span },
-                        hir::ClosureKind::Closure => BorrowUseInClosure { var_span },
+                        hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
+                            BorrowUseInClosure { var_span }
+                        }
                     }
                 });
 
@@ -2958,7 +2963,9 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             use crate::session_diagnostics::CaptureVarCause::*;
             match kind {
                 hir::ClosureKind::Coroutine(_) => BorrowUseInCoroutine { var_span },
-                hir::ClosureKind::Closure => BorrowUseInClosure { var_span },
+                hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
+                    BorrowUseInClosure { var_span }
+                }
             }
         });
 

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -614,7 +614,7 @@ impl UseSpans<'_> {
                         PartialAssignment => AssignPartInCoroutine { path_span },
                     });
                 }
-                hir::ClosureKind::Closure => {
+                hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
                     err.subdiagnostic(match action {
                         Borrow => BorrowInClosure { path_span },
                         MatchOn | Use => UseInClosure { path_span },
@@ -1253,7 +1253,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     hir::ClosureKind::Coroutine(_) => {
                         CaptureVarCause::PartialMoveUseInCoroutine { var_span, is_partial }
                     }
-                    hir::ClosureKind::Closure => {
+                    hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
                         CaptureVarCause::PartialMoveUseInClosure { var_span, is_partial }
                     }
                 })

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -692,7 +692,10 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                     hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
                         hir::CoroutineDesugaring::Async,
                         hir::CoroutineSource::Closure,
-                    )) => " of async closure",
+                    ))
+                    | hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Async) => {
+                        " of async closure"
+                    }
 
                     hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
                         hir::CoroutineDesugaring::Async,
@@ -719,7 +722,10 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                     hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
                         hir::CoroutineDesugaring::Gen,
                         hir::CoroutineSource::Closure,
-                    )) => " of gen closure",
+                    ))
+                    | hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Gen) => {
+                        " of gen closure"
+                    }
 
                     hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
                         hir::CoroutineDesugaring::Gen,
@@ -743,7 +749,10 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                     hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
                         hir::CoroutineDesugaring::AsyncGen,
                         hir::CoroutineSource::Closure,
-                    )) => " of async gen closure",
+                    ))
+                    | hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::AsyncGen) => {
+                        " of async gen closure"
+                    }
 
                     hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
                         hir::CoroutineDesugaring::AsyncGen,

compiler/rustc_hir/src/hir.rs

@@ -952,6 +952,11 @@ pub enum ClosureKind {
     ///  usage (e.g. `let x = || { yield (); }`) or from a desugared expression
     /// (e.g. `async` and `gen` blocks).
     Coroutine(CoroutineKind),
+    /// This is a coroutine-closure, which is a special sugared closure that
+    /// returns one of the sugared coroutine (`async`/`gen`/`async gen`). It
+    /// additionally allows capturing the coroutine's upvars by ref, and therefore
+    /// needs to be specially treated during analysis and borrowck.
+    CoroutineClosure(CoroutineDesugaring),
 }
 
 /// A block of statements `{ .. }`, which may have a label (in this case the

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -349,6 +349,7 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
             ClosureKind::Coroutine(_) => {
                 &["<resume_ty>", "<yield_ty>", "<return_ty>", "<witness>", "<upvars>"][..]
             }
+            ClosureKind::CoroutineClosure(_) => todo!(),
         };
 
         params.extend(dummy_args.iter().map(|&arg| ty::GenericParamDef {

compiler/rustc_hir_typeck/src/closure.rs

@@ -192,6 +192,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     Some(CoroutineTypes { resume_ty, yield_ty }),
                 )
             }
+            hir::ClosureKind::CoroutineClosure(_) => todo!(),
         };
 
         check_fn(
@@ -690,7 +691,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     _,
                 ))
                 | hir::ClosureKind::Coroutine(hir::CoroutineKind::Coroutine(_))
-                | hir::ClosureKind::Closure => astconv.ty_infer(None, decl.output.span()),
+                | hir::ClosureKind::Closure
+                | hir::ClosureKind::CoroutineClosure(_) => {
+                    astconv.ty_infer(None, decl.output.span())
+                }
             },
         };
 

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -1924,45 +1924,50 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     fn describe_closure(&self, kind: hir::ClosureKind) -> &'static str {
         match kind {
             hir::ClosureKind::Closure => "a closure",
-            hir::ClosureKind::Coroutine(kind) => match kind {
+            hir::ClosureKind::Coroutine(hir::CoroutineKind::Coroutine(_)) => "a coroutine",
-                hir::CoroutineKind::Coroutine(_) => "a coroutine",
+            hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
-                hir::CoroutineKind::Desugared(
+                hir::CoroutineDesugaring::Async,
-                    hir::CoroutineDesugaring::Async,
+                hir::CoroutineSource::Block,
-                    hir::CoroutineSource::Block,
+            )) => "an async block",
-                ) => "an async block",
+            hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
-                hir::CoroutineKind::Desugared(
+                hir::CoroutineDesugaring::Async,
-                    hir::CoroutineDesugaring::Async,
+                hir::CoroutineSource::Fn,
-                    hir::CoroutineSource::Fn,
+            )) => "an async function",
-                ) => "an async function",
+            hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
-                hir::CoroutineKind::Desugared(
+                hir::CoroutineDesugaring::Async,
-                    hir::CoroutineDesugaring::Async,
+                hir::CoroutineSource::Closure,
-                    hir::CoroutineSource::Closure,
+            ))
-                ) => "an async closure",
+            | hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Async) => {
-                hir::CoroutineKind::Desugared(
+                "an async closure"
-                    hir::CoroutineDesugaring::AsyncGen,
+            }
-                    hir::CoroutineSource::Block,
+            hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
-                ) => "an async gen block",
+                hir::CoroutineDesugaring::AsyncGen,
-                hir::CoroutineKind::Desugared(
+                hir::CoroutineSource::Block,
-                    hir::CoroutineDesugaring::AsyncGen,
+            )) => "an async gen block",
-                    hir::CoroutineSource::Fn,
+            hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
-                ) => "an async gen function",
+                hir::CoroutineDesugaring::AsyncGen,
-                hir::CoroutineKind::Desugared(
+                hir::CoroutineSource::Fn,
-                    hir::CoroutineDesugaring::AsyncGen,
+            )) => "an async gen function",
-                    hir::CoroutineSource::Closure,
+            hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
-                ) => "an async gen closure",
+                hir::CoroutineDesugaring::AsyncGen,
-                hir::CoroutineKind::Desugared(
+                hir::CoroutineSource::Closure,
-                    hir::CoroutineDesugaring::Gen,
+            ))
-                    hir::CoroutineSource::Block,
+            | hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::AsyncGen) => {
-                ) => "a gen block",
+                "an async gen closure"
-                hir::CoroutineKind::Desugared(
+            }
-                    hir::CoroutineDesugaring::Gen,
+            hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
-                    hir::CoroutineSource::Fn,
+                hir::CoroutineDesugaring::Gen,
-                ) => "a gen function",
+                hir::CoroutineSource::Block,
-                hir::CoroutineKind::Desugared(
+            )) => "a gen block",
-                    hir::CoroutineDesugaring::Gen,
+            hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
-                    hir::CoroutineSource::Closure,
+                hir::CoroutineDesugaring::Gen,
-                ) => "a gen closure",
+                hir::CoroutineSource::Fn,
-            },
+            )) => "a gen function",
+            hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
+                hir::CoroutineDesugaring::Gen,
+                hir::CoroutineSource::Closure,
+            ))
+            | hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Gen) => "a gen closure",
         }
     }