Remove the witness type from coroutine args

compiler-errors · compiler-errors · commit 8756bdc053c2 · 2025-07-25T17:47:17.000Z
diff --git a/compiler/rustc_borrowck/src/type_check/input_output.rs b/compiler/rustc_borrowck/src/type_check/input_output.rs
@@ -86,7 +86,6 @@ 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,
diff --git a/compiler/rustc_hir_analysis/src/collect/generics_of.rs b/compiler/rustc_hir_analysis/src/collect/generics_of.rs
@@ -379,20 +379,14 @@ 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>",
-                "<witness>",
-                "<upvars>",
-            ][..],
+            ClosureKind::Coroutine(_) => {
+                &["<coroutine_kind>", "<resume_ty>", "<yield_ty>", "<return_ty>", "<upvars>"][..]
+            }
             ClosureKind::CoroutineClosure(_) => &[
                 "<closure_kind>",
                 "<closure_signature_parts>",
                 "<upvars>",
                 "<bound_captures_by_ref>",
-                "<witness>",
             ][..],
         };
 
diff --git a/compiler/rustc_hir_typeck/src/closure.rs b/compiler/rustc_hir_typeck/src/closure.rs
@@ -161,8 +161,6 @@ 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
@@ -182,7 +180,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         resume_ty,
                         yield_ty,
                         return_ty: liberated_sig.output(),
-                        witness: interior,
                         tupled_upvars_ty,
                     },
                 );
@@ -210,7 +207,6 @@ 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),
@@ -243,7 +239,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         ),
                         tupled_upvars_ty,
                         coroutine_captures_by_ref_ty,
-                        coroutine_witness_ty: interior,
                     },
                 );
 
diff --git a/compiler/rustc_middle/src/ty/generic_args.rs b/compiler/rustc_middle/src/ty/generic_args.rs
@@ -96,38 +96,29 @@ 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,
-                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(),
-            },
+            [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(),
+                }
+            }
             _ => bug!("coroutine args missing synthetics"),
         }
     }
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -913,9 +913,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                         " yield_ty=",
                         print(args.as_coroutine().yield_ty()),
                         " return_ty=",
-                        print(args.as_coroutine().return_ty()),
-                        " witness=",
-                        print(args.as_coroutine().witness())
+                        print(args.as_coroutine().return_ty())
                     );
                 }
 
@@ -1035,9 +1033,7 @@ 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()),
-                        " coroutine_witness_ty=",
-                        print(args.as_coroutine_closure().coroutine_witness_ty())
+                        print(args.as_coroutine_closure().coroutine_captures_by_ref_ty())
                     );
                 }
                 p!("}}");
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
@@ -75,9 +75,16 @@ where
             Ok(ty::Binder::dummy(vec![args.as_coroutine_closure().tupled_upvars_ty()]))
         }
 
-        ty::Coroutine(_, args) => {
+        ty::Coroutine(def_id, args) => {
             let coroutine_args = args.as_coroutine();
-            Ok(ty::Binder::dummy(vec![coroutine_args.tupled_upvars_ty(), coroutine_args.witness()]))
+            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()),
+                ),
+            ]))
         }
 
         ty::CoroutineWitness(def_id, args) => Ok(ecx
@@ -245,7 +252,14 @@ where
             Movability::Movable => {
                 if ecx.cx().features().coroutine_clone() {
                     let coroutine = args.as_coroutine();
-                    Ok(ty::Binder::dummy(vec![coroutine.tupled_upvars_ty(), coroutine.witness()]))
+                    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()),
+                        ),
+                    ]))
                 } else {
                     Err(NoSolution)
                 }
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -1166,9 +1166,7 @@ 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());
-                            let resolved_witness =
-                                self.infcx.shallow_resolve(args.as_coroutine().witness());
-                            if resolved_upvars.is_ty_var() || resolved_witness.is_ty_var() {
+                            if resolved_upvars.is_ty_var() {
                                 // Not yet resolved.
                                 candidates.ambiguous = true;
                             } else {
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -2199,7 +2199,11 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
                                 args.as_coroutine()
                                     .upvar_tys()
                                     .iter()
-                                    .chain([args.as_coroutine().witness()])
+                                    .chain([Ty::new_coroutine_witness(
+                                        self.tcx(),
+                                        coroutine_def_id,
+                                        self.tcx().mk_args(args.as_coroutine().parent_args()),
+                                    )])
                                     .collect::<Vec<_>>(),
                             )
                         } else {
@@ -2330,9 +2334,13 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
                 ty::Binder::dummy(AutoImplConstituents { types: vec![ty], assumptions: vec![] })
             }
 
-            ty::Coroutine(_, args) => {
+            ty::Coroutine(def_id, args) => {
                 let ty = self.infcx.shallow_resolve(args.as_coroutine().tupled_upvars_ty());
-                let witness = args.as_coroutine().witness();
+                let witness = Ty::new_coroutine_witness(
+                    self.tcx(),
+                    def_id,
+                    self.tcx().mk_args(args.as_coroutine().parent_args()),
+                );
                 ty::Binder::dummy(AutoImplConstituents {
                     types: [ty].into_iter().chain(iter::once(witness)).collect(),
                     assumptions: vec![],
diff --git a/compiler/rustc_type_ir/src/ty_kind/closure.rs b/compiler/rustc_type_ir/src/ty_kind/closure.rs
@@ -101,7 +101,6 @@ 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> {
@@ -239,8 +238,6 @@ 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> {
@@ -251,7 +248,6 @@ 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(),
             ])),
         }
     }
@@ -292,7 +288,6 @@ 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 {
@@ -302,7 +297,6 @@ impl<I: Interner> CoroutineClosureArgs<I> {
                 panic!()
             };
             CoroutineClosureSignature {
-                interior,
                 tupled_inputs_ty,
                 resume_ty,
                 yield_ty,
@@ -318,10 +312,6 @@ 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
@@ -361,7 +351,6 @@ 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,
@@ -407,7 +396,6 @@ 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,
             },
         );
@@ -587,11 +575,6 @@ 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,
@@ -607,7 +590,6 @@ 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(),
             ])),
         }
@@ -629,15 +611,6 @@ 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.
diff --git a/tests/mir-opt/building/async_await.b-{closure#0}.coroutine_resume.0.mir b/tests/mir-opt/building/async_await.b-{closure#0}.coroutine_resume.0.mir
@@ -9,10 +9,6 @@
                     std::future::ResumeTy,
                     (),
                     (),
-                    CoroutineWitness(
-                        DefId(0:5 ~ async_await[ccf8]::a::{closure#0}),
-                        [],
-                    ),
                     (),
                 ],
             ),
@@ -30,10 +26,6 @@
                     std::future::ResumeTy,
                     (),
                     (),
-                    CoroutineWitness(
-                        DefId(0:5 ~ async_await[ccf8]::a::{closure#0}),
-                        [],
-                    ),
                     (),
                 ],
             ),
diff --git a/tests/ui/async-await/async-closures/def-path.stderr b/tests/ui/async-await/async-closures/def-path.stderr
@@ -5,11 +5,11 @@ LL |     let x = async || {};
    |                      -- the expected `async` closure body
 LL |
 LL |     let () = x();
-   |         ^^   --- this expression has type `{static main::{closure#0}::{closure#0}<?16t> upvar_tys=?15t resume_ty=ResumeTy yield_ty=() return_ty=() witness={main::{closure#0}::{closure#0}}}`
+   |         ^^   --- this expression has type `{static main::{closure#0}::{closure#0}<?15t> upvar_tys=?14t resume_ty=ResumeTy yield_ty=() return_ty=()}`
    |         |
    |         expected `async` closure body, found `()`
    |
-   = note: expected `async` closure body `{static main::{closure#0}::{closure#0}<?16t> upvar_tys=?15t resume_ty=ResumeTy yield_ty=() return_ty=() witness={main::{closure#0}::{closure#0}}}`
+   = note: expected `async` closure body `{static main::{closure#0}::{closure#0}<?15t> upvar_tys=?14t resume_ty=ResumeTy yield_ty=() return_ty=()}`
                          found unit type `()`
 
 error: aborting due to 1 previous error
diff --git a/tests/ui/async-await/higher-ranked-auto-trait-6.no_assumptions.stderr b/tests/ui/async-await/higher-ranked-auto-trait-6.no_assumptions.stderr
@@ -21,30 +21,6 @@ LL |     Box::new(async { new(|| async { f().await }).await })
    = help: consider pinning your async block and casting it to a trait object
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error[E0308]: mismatched types
-  --> $DIR/higher-ranked-auto-trait-6.rs:16:5
-   |
-LL |     Box::new(async { new(|| async { f().await }).await })
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
-   |
-   = note: expected `async` block `{async block@$DIR/higher-ranked-auto-trait-6.rs:16:29: 16:34}`
-              found `async` block `{async block@$DIR/higher-ranked-auto-trait-6.rs:16:29: 16:34}`
-   = note: no two async blocks, even if identical, have the same type
-   = help: consider pinning your async block and casting it to a trait object
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error[E0308]: mismatched types
-  --> $DIR/higher-ranked-auto-trait-6.rs:16:5
-   |
-LL |     Box::new(async { new(|| async { f().await }).await })
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
-   |
-   = note: expected `async` block `{async block@$DIR/higher-ranked-auto-trait-6.rs:16:29: 16:34}`
-              found `async` block `{async block@$DIR/higher-ranked-auto-trait-6.rs:16:29: 16:34}`
-   = note: no two async blocks, even if identical, have the same type
-   = help: consider pinning your async block and casting it to a trait object
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: aborting due to 4 previous errors
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/coroutine/print/coroutine-print-verbose-2.stderr b/tests/ui/coroutine/print/coroutine-print-verbose-2.stderr
diff --git a/tests/ui/coroutine/print/coroutine-print-verbose-3.stderr b/tests/ui/coroutine/print/coroutine-print-verbose-3.stderr
diff --git a/tests/ui/impl-trait/issues/issue-55872-2.rs b/tests/ui/impl-trait/issues/issue-55872-2.rs
diff --git a/tests/ui/impl-trait/issues/issue-55872-2.stderr b/tests/ui/impl-trait/issues/issue-55872-2.stderr
diff --git a/tests/ui/impl-trait/issues/issue-55872-3.rs b/tests/ui/impl-trait/issues/issue-55872-3.rs
diff --git a/tests/ui/impl-trait/issues/issue-55872-3.stderr b/tests/ui/impl-trait/issues/issue-55872-3.stderr

Original file line number	Diff line number	Diff line change
`@@ -86,7 +86,6 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {`
`86`	`86`	`// them with fresh ty vars.`
`87`	`87`	`resume_ty: next_ty_var(),`
`88`	`88`	`yield_ty: next_ty_var(),`
`89`		`- witness: next_ty_var(),`
`90`	`89`	`},`
`91`	`90`	`)`
`92`	`91`	`.args,`