Auto merge of #145395 - lcnr:review-coroutine-witness, r=petrochenkov

[BETA] Revert "Remove the witness type from coroutine args"

fixes #145151 and #145288

we do not revert on nightly as its instead fixed by #145194 and #145338.

See the discussion in https://rust-lang.zulipchat.com/#narrow/channel/238009-t-compiler.2Fmeetings/topic/.5Bweekly.5D.202025-08-14/near/534490313

Author: bors

compiler/rustc_borrowck/src/type_check/input_output.rs

@@ -86,6 +86,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         // them with fresh ty vars.
                         resume_ty: next_ty_var(),
                         yield_ty: next_ty_var(),
+                        witness: next_ty_var(),
                     },
                 )
                 .args,

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -379,14 +379,20 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
         // for info on the usage of each of these fields.
         let dummy_args = match kind {
             ClosureKind::Closure => &["<closure_kind>", "<closure_signature>", "<upvars>"][..],
-            ClosureKind::Coroutine(_) => {
-                &["<coroutine_kind>", "<resume_ty>", "<yield_ty>", "<return_ty>", "<upvars>"][..]
-            }
+            ClosureKind::Coroutine(_) => &[
+                "<coroutine_kind>",
+                "<resume_ty>",
+                "<yield_ty>",
+                "<return_ty>",
+                "<witness>",
+                "<upvars>",
+            ][..],
             ClosureKind::CoroutineClosure(_) => &[
                 "<closure_kind>",
                 "<closure_signature_parts>",
                 "<upvars>",
                 "<bound_captures_by_ref>",
+                "<witness>",
             ][..],
         };
 

compiler/rustc_hir_typeck/src/closure.rs

@@ -161,6 +161,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // Resume type defaults to `()` if the coroutine has no argument.
                 let resume_ty = liberated_sig.inputs().get(0).copied().unwrap_or(tcx.types.unit);
 
+                let interior = Ty::new_coroutine_witness(tcx, expr_def_id.to_def_id(), parent_args);
+
                 // Coroutines that come from coroutine closures have not yet determined
                 // their kind ty, so make a fresh infer var which will be constrained
                 // later during upvar analysis. Regular coroutines always have the kind
@@ -180,6 +182,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         resume_ty,
                         yield_ty,
                         return_ty: liberated_sig.output(),
+                        witness: interior,
                         tupled_upvars_ty,
                     },
                 );
@@ -207,6 +210,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 };
                 // Compute all of the variables that will be used to populate the coroutine.
                 let resume_ty = self.next_ty_var(expr_span);
+                let interior = self.next_ty_var(expr_span);
 
                 let closure_kind_ty = match expected_kind {
                     Some(kind) => Ty::from_closure_kind(tcx, kind),
@@ -239,6 +243,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         ),
                         tupled_upvars_ty,
                         coroutine_captures_by_ref_ty,
+                        coroutine_witness_ty: interior,
                     },
                 );
 

compiler/rustc_middle/src/ty/generic_args.rs

@@ -96,29 +96,38 @@ impl<'tcx> rustc_type_ir::inherent::GenericArgs<TyCtxt<'tcx>> for ty::GenericArg
                 signature_parts_ty,
                 tupled_upvars_ty,
                 coroutine_captures_by_ref_ty,
+                coroutine_witness_ty,
             ] => ty::CoroutineClosureArgsParts {
                 parent_args,
                 closure_kind_ty: closure_kind_ty.expect_ty(),
                 signature_parts_ty: signature_parts_ty.expect_ty(),
                 tupled_upvars_ty: tupled_upvars_ty.expect_ty(),
                 coroutine_captures_by_ref_ty: coroutine_captures_by_ref_ty.expect_ty(),
+                coroutine_witness_ty: coroutine_witness_ty.expect_ty(),
             },
             _ => bug!("closure args missing synthetics"),
         }
     }
 
     fn split_coroutine_args(self) -> ty::CoroutineArgsParts<TyCtxt<'tcx>> {
         match self[..] {
-            [ref parent_args @ .., kind_ty, resume_ty, yield_ty, return_ty, tupled_upvars_ty] => {
-                ty::CoroutineArgsParts {
-                    parent_args,
-                    kind_ty: kind_ty.expect_ty(),
-                    resume_ty: resume_ty.expect_ty(),
-                    yield_ty: yield_ty.expect_ty(),
-                    return_ty: return_ty.expect_ty(),
-                    tupled_upvars_ty: tupled_upvars_ty.expect_ty(),
-                }
-            }
+            [
+                ref parent_args @ ..,
+                kind_ty,
+                resume_ty,
+                yield_ty,
+                return_ty,
+                witness,
+                tupled_upvars_ty,
+            ] => ty::CoroutineArgsParts {
+                parent_args,
+                kind_ty: kind_ty.expect_ty(),
+                resume_ty: resume_ty.expect_ty(),
+                yield_ty: yield_ty.expect_ty(),
+                return_ty: return_ty.expect_ty(),
+                witness: witness.expect_ty(),
+                tupled_upvars_ty: tupled_upvars_ty.expect_ty(),
+            },
             _ => bug!("coroutine args missing synthetics"),
         }
     }

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -913,7 +913,9 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                         " yield_ty=",
                         print(args.as_coroutine().yield_ty()),
                         " return_ty=",
-                        print(args.as_coroutine().return_ty())
+                        print(args.as_coroutine().return_ty()),
+                        " witness=",
+                        print(args.as_coroutine().witness())
                     );
                 }
 
@@ -1033,7 +1035,9 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                         " upvar_tys=",
                         print(args.as_coroutine_closure().tupled_upvars_ty()),
                         " coroutine_captures_by_ref_ty=",
-                        print(args.as_coroutine_closure().coroutine_captures_by_ref_ty())
+                        print(args.as_coroutine_closure().coroutine_captures_by_ref_ty()),
+                        " coroutine_witness_ty=",
+                        print(args.as_coroutine_closure().coroutine_witness_ty())
                     );
                 }
                 p!("}}");

compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs

@@ -75,16 +75,9 @@ where
             Ok(ty::Binder::dummy(vec![args.as_coroutine_closure().tupled_upvars_ty()]))
         }
 
-        ty::Coroutine(def_id, args) => {
+        ty::Coroutine(_, args) => {
             let coroutine_args = args.as_coroutine();
-            Ok(ty::Binder::dummy(vec![
-                coroutine_args.tupled_upvars_ty(),
-                Ty::new_coroutine_witness(
-                    ecx.cx(),
-                    def_id,
-                    ecx.cx().mk_args(coroutine_args.parent_args().as_slice()),
-                ),
-            ]))
+            Ok(ty::Binder::dummy(vec![coroutine_args.tupled_upvars_ty(), coroutine_args.witness()]))
         }
 
         ty::CoroutineWitness(def_id, args) => Ok(ecx
@@ -252,14 +245,7 @@ where
             Movability::Movable => {
                 if ecx.cx().features().coroutine_clone() {
                     let coroutine = args.as_coroutine();
-                    Ok(ty::Binder::dummy(vec![
-                        coroutine.tupled_upvars_ty(),
-                        Ty::new_coroutine_witness(
-                            ecx.cx(),
-                            def_id,
-                            ecx.cx().mk_args(coroutine.parent_args().as_slice()),
-                        ),
-                    ]))
+                    Ok(ty::Binder::dummy(vec![coroutine.tupled_upvars_ty(), coroutine.witness()]))
                 } else {
                     Err(NoSolution)
                 }

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -1166,7 +1166,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         if self.tcx().features().coroutine_clone() {
                             let resolved_upvars =
                                 self.infcx.shallow_resolve(args.as_coroutine().tupled_upvars_ty());
-                            if resolved_upvars.is_ty_var() {
+                            let resolved_witness =
+                                self.infcx.shallow_resolve(args.as_coroutine().witness());
+                            if resolved_upvars.is_ty_var() || resolved_witness.is_ty_var() {
                                 // Not yet resolved.
                                 candidates.ambiguous = true;
                             } else {

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -2196,11 +2196,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
                                 args.as_coroutine()
                                     .upvar_tys()
                                     .iter()
-                                    .chain([Ty::new_coroutine_witness(
-                                        self.tcx(),
-                                        coroutine_def_id,
-                                        self.tcx().mk_args(args.as_coroutine().parent_args()),
-                                    )])
+                                    .chain([args.as_coroutine().witness()])
                                     .collect::<Vec<_>>(),
                             )
                         } else {
@@ -2331,13 +2327,9 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
                 ty::Binder::dummy(AutoImplConstituents { types: vec![ty], assumptions: vec![] })
             }
 
-            ty::Coroutine(def_id, args) => {
+            ty::Coroutine(_, args) => {
                 let ty = self.infcx.shallow_resolve(args.as_coroutine().tupled_upvars_ty());
-                let witness = Ty::new_coroutine_witness(
-                    self.tcx(),
-                    def_id,
-                    self.tcx().mk_args(args.as_coroutine().parent_args()),
-                );
+                let witness = args.as_coroutine().witness();
                 ty::Binder::dummy(AutoImplConstituents {
                     types: [ty].into_iter().chain(iter::once(witness)).collect(),
                     assumptions: vec![],

compiler/rustc_type_ir/src/ty_kind/closure.rs

@@ -101,6 +101,7 @@ use crate::{self as ty, Interner};
 ///   `yield` inside the coroutine.
 /// * `GR`: The "return type", which is the type of value returned upon
 ///   completion of the coroutine.
+/// * `GW`: The "coroutine witness".
 #[derive_where(Clone, Copy, PartialEq, Eq, Hash, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 pub struct ClosureArgs<I: Interner> {
@@ -238,6 +239,8 @@ pub struct CoroutineClosureArgsParts<I: Interner> {
     /// while the `tupled_upvars_ty`, representing the by-move version of the same
     /// captures, will be `(String,)`.
     pub coroutine_captures_by_ref_ty: I::Ty,
+    /// Witness type returned by the generator produced by this coroutine-closure.
+    pub coroutine_witness_ty: I::Ty,
 }
 
 impl<I: Interner> CoroutineClosureArgs<I> {
@@ -248,6 +251,7 @@ impl<I: Interner> CoroutineClosureArgs<I> {
                 parts.signature_parts_ty.into(),
                 parts.tupled_upvars_ty.into(),
                 parts.coroutine_captures_by_ref_ty.into(),
+                parts.coroutine_witness_ty.into(),
             ])),
         }
     }
@@ -288,6 +292,7 @@ impl<I: Interner> CoroutineClosureArgs<I> {
     }
 
     pub fn coroutine_closure_sig(self) -> ty::Binder<I, CoroutineClosureSignature<I>> {
+        let interior = self.coroutine_witness_ty();
         let ty::FnPtr(sig_tys, hdr) = self.signature_parts_ty().kind() else { panic!() };
         sig_tys.map_bound(|sig_tys| {
             let [resume_ty, tupled_inputs_ty] = *sig_tys.inputs().as_slice() else {
@@ -297,6 +302,7 @@ impl<I: Interner> CoroutineClosureArgs<I> {
                 panic!()
             };
             CoroutineClosureSignature {
+                interior,
                 tupled_inputs_ty,
                 resume_ty,
                 yield_ty,
@@ -312,6 +318,10 @@ impl<I: Interner> CoroutineClosureArgs<I> {
         self.split().coroutine_captures_by_ref_ty
     }
 
+    pub fn coroutine_witness_ty(self) -> I::Ty {
+        self.split().coroutine_witness_ty
+    }
+
     pub fn has_self_borrows(&self) -> bool {
         match self.coroutine_captures_by_ref_ty().kind() {
             ty::FnPtr(sig_tys, _) => sig_tys
@@ -351,6 +361,7 @@ impl<I: Interner> TypeVisitor<I> for HasRegionsBoundAt {
 #[derive_where(Clone, Copy, PartialEq, Eq, Hash, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 pub struct CoroutineClosureSignature<I: Interner> {
+    pub interior: I::Ty,
     pub tupled_inputs_ty: I::Ty,
     pub resume_ty: I::Ty,
     pub yield_ty: I::Ty,
@@ -396,6 +407,7 @@ impl<I: Interner> CoroutineClosureSignature<I> {
                 resume_ty: self.resume_ty,
                 yield_ty: self.yield_ty,
                 return_ty: self.return_ty,
+                witness: self.interior,
                 tupled_upvars_ty,
             },
         );
@@ -575,6 +587,11 @@ pub struct CoroutineArgsParts<I: Interner> {
     pub yield_ty: I::Ty,
     pub return_ty: I::Ty,
 
+    /// The interior type of the coroutine.
+    /// Represents all types that are stored in locals
+    /// in the coroutine's body.
+    pub witness: I::Ty,
+
     /// The upvars captured by the closure. Remains an inference variable
     /// until the upvar analysis, which happens late in HIR typeck.
     pub tupled_upvars_ty: I::Ty,
@@ -590,6 +607,7 @@ impl<I: Interner> CoroutineArgs<I> {
                 parts.resume_ty.into(),
                 parts.yield_ty.into(),
                 parts.return_ty.into(),
+                parts.witness.into(),
                 parts.tupled_upvars_ty.into(),
             ])),
         }
@@ -611,6 +629,15 @@ impl<I: Interner> CoroutineArgs<I> {
         self.split().kind_ty
     }
 
+    /// This describes the types that can be contained in a coroutine.
+    /// It will be a type variable initially and unified in the last stages of typeck of a body.
+    /// It contains a tuple of all the types that could end up on a coroutine frame.
+    /// The state transformation MIR pass may only produce layouts which mention types
+    /// in this tuple. Upvars are not counted here.
+    pub fn witness(self) -> I::Ty {
+        self.split().witness
+    }
+
     /// Returns an iterator over the list of types of captured paths by the coroutine.
     /// In case there was a type error in figuring out the types of the captured path, an
     /// empty iterator is returned.

tests/mir-opt/building/async_await.b-{closure#0}.coroutine_resume.0.mir

@@ -9,6 +9,10 @@
                     std::future::ResumeTy,
                     (),
                     (),
+                    CoroutineWitness(
+                        DefId(0:5 ~ async_await[ccf8]::a::{closure#0}),
+                        [],
+                    ),
                     (),
                 ],
             ),
@@ -26,6 +30,10 @@
                     std::future::ResumeTy,
                     (),
                     (),
+                    CoroutineWitness(
+                        DefId(0:5 ~ async_await[ccf8]::a::{closure#0}),
+                        [],
+                    ),
                     (),
                 ],
             ),