Note base types of coercion

compiler/rustc_middle/src/traits/mod.rs

@@ -281,9 +281,6 @@ pub enum ObligationCauseCode<'tcx> {
  /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
  ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
 
- /// Obligation incurred due to an object cast.
- ObjectCastObligation(/* Concrete type */ Ty<'tcx>, /* Object type */ Ty<'tcx>),
-
  /// Obligation incurred due to a coercion.
  Coercion {
  source: Ty<'tcx>,

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

@@ -796,9 +796,17 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
  err.span_label(span, explanation);
  }
 
- if let ObligationCauseCode::ObjectCastObligation(concrete_ty, obj_ty) = obligation.cause.code().peel_derives() &&
- Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
- self.suggest_borrowing_for_object_cast(&mut err, &root_obligation, *concrete_ty, *obj_ty);
+ if let ObligationCauseCode::Coercion { source, target } =
+ *obligation.cause.code().peel_derives()
+ {
+ if Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
+ self.suggest_borrowing_for_object_cast(
+ &mut err,
+ &root_obligation,
+ source,
+ target,
+ );
+ }
  }
 
  let UnsatisfiedConst(unsatisfied_const) = self
@@ -1505,7 +1513,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
  | ObligationCauseCode::BindingObligation(_, _)
  | ObligationCauseCode::ExprItemObligation(..)
  | ObligationCauseCode::ExprBindingObligation(..)
- | ObligationCauseCode::ObjectCastObligation(..)
+ | ObligationCauseCode::Coercion { .. }
  | ObligationCauseCode::OpaqueType
  );
 

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

@@ -1442,8 +1442,9 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
  err: &mut Diagnostic,
  obligation: &PredicateObligation<'tcx>,
  self_ty: Ty<'tcx>,
- object_ty: Ty<'tcx>,
+ target_ty: Ty<'tcx>,
  ) {
+ let ty::Ref(_, object_ty, hir::Mutability::Not) = target_ty.kind() else { return; };
  let ty::Dynamic(predicates, _, ty::Dyn) = object_ty.kind() else { return; };
  let self_ref_ty = self.tcx.mk_imm_ref(self.tcx.lifetimes.re_erased, self_ty);
 
@@ -1458,7 +1459,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
  err.span_suggestion(
  obligation.cause.span.shrink_to_lo(),
  format!(
- "consider borrowing the value, since `&{self_ty}` can be coerced into `{object_ty}`"
+ "consider borrowing the value, since `&{self_ty}` can be coerced into `{target_ty}`"
  ),
  "&",
  Applicability::MaybeIncorrect,
@@ -2851,30 +2852,27 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
  err.span_note(tcx.def_span(item_def_id), descr);
  }
  }
- ObligationCauseCode::ObjectCastObligation(concrete_ty, object_ty) => {
- let (concrete_ty, concrete_file) =
- self.tcx.short_ty_string(self.resolve_vars_if_possible(concrete_ty));
- let (object_ty, object_file) =
- self.tcx.short_ty_string(self.resolve_vars_if_possible(object_ty));
+ ObligationCauseCode::Coercion { source, target } => {
+ let (source, source_file) =
+ self.tcx.short_ty_string(self.resolve_vars_if_possible(source));
+ let (target, target_file) =
+ self.tcx.short_ty_string(self.resolve_vars_if_possible(target));
  err.note(with_forced_trimmed_paths!(format!(
- "required for the cast from `{concrete_ty}` to the object type `{object_ty}`",
+ "required for the cast from `{source}` to `{target}`",
  )));
- if let Some(file) = concrete_file {
+ if let Some(file) = source_file {
  err.note(format!(
- "the full name for the casted type has been written to '{}'",
+ "the full name for the source type has been written to '{}'",
  file.display(),
  ));
  }
- if let Some(file) = object_file {
+ if let Some(file) = target_file {
  err.note(format!(
- "the full name for the object type has been written to '{}'",
+ "the full name for the target type has been written to '{}'",
  file.display(),
  ));
  }
  }
- ObligationCauseCode::Coercion { source: _, target } => {
- err.note(format!("required by cast to type `{}`", self.ty_to_string(target)));
- }
  ObligationCauseCode::RepeatElementCopy { is_const_fn } => {
  err.note(
  "the `Copy` trait is required because this value will be copied for each element of the array",

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

@@ -28,9 +28,9 @@ use crate::traits::{
  ImplSourceAutoImplData, ImplSourceBuiltinData, ImplSourceClosureData,
  ImplSourceConstDestructData, ImplSourceFnPointerData, ImplSourceFutureData,
  ImplSourceGeneratorData, ImplSourceObjectData, ImplSourceTraitAliasData,
- ImplSourceTraitUpcastingData, ImplSourceUserDefinedData, Normalized, ObjectCastObligation,
- Obligation, ObligationCause, OutputTypeParameterMismatch, PredicateObligation, Selection,
- SelectionError, TraitNotObjectSafe, TraitObligation, Unimplemented,
+ ImplSourceTraitUpcastingData, ImplSourceUserDefinedData, Normalized, Obligation,
+ ObligationCause, OutputTypeParameterMismatch, PredicateObligation, Selection, SelectionError,
+ TraitNotObjectSafe, TraitObligation, Unimplemented,
 };
 
 use super::BuiltinImplConditions;
@@ -898,16 +898,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
  .map_err(|_| Unimplemented)?;
  nested.extend(obligations);
 
- // Register one obligation for 'a: 'b.
- let cause = ObligationCause::new(
- obligation.cause.span,
- obligation.cause.body_id,
- ObjectCastObligation(source, target),
- );
  let outlives = ty::OutlivesPredicate(r_a, r_b);
  nested.push(Obligation::with_depth(
  tcx,
- cause,
+ obligation.cause.clone(),
  obligation.recursion_depth + 1,
  obligation.param_env,
  obligation.predicate.rebind(outlives),
@@ -998,15 +992,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
  nested.extend(obligations);
 
  // Register one obligation for 'a: 'b.
- let cause = ObligationCause::new(
- obligation.cause.span,
- obligation.cause.body_id,
- ObjectCastObligation(source, target),
- );
  let outlives = ty::OutlivesPredicate(r_a, r_b);
  nested.push(Obligation::with_depth(
  tcx,
- cause,
+ obligation.cause.clone(),
  obligation.recursion_depth + 1,
  obligation.param_env,
  obligation.predicate.rebind(outlives),
@@ -1020,16 +1009,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
  return Err(TraitNotObjectSafe(did));
  }
 
- let cause = ObligationCause::new(
- obligation.cause.span,
- obligation.cause.body_id,
- ObjectCastObligation(source, target),
- );
-
  let predicate_to_obligation = |predicate| {
  Obligation::with_depth(
  tcx,
- cause.clone(),
+ obligation.cause.clone(),
  obligation.recursion_depth + 1,
  obligation.param_env,
  predicate,
@@ -1049,7 +1032,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
  );
 
  // We can only make objects from sized types.
- let tr = ty::TraitRef::from_lang_item(tcx, LangItem::Sized, cause.span, [source]);
+ let tr = ty::TraitRef::from_lang_item(
+ tcx,
+ LangItem::Sized,
+ obligation.cause.span,
+ [source],
+ );
  nested.push(predicate_to_obligation(tr.without_const().to_predicate(tcx)));
 
  // If the type is `Foo + 'a`, ensure that the type

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

@@ -2647,14 +2647,19 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
  let predicates = predicates.instantiate_own(tcx, substs);
  let mut obligations = Vec::with_capacity(predicates.len());
  for (index, (predicate, span)) in predicates.into_iter().enumerate() {
- let cause = cause.clone().derived_cause(parent_trait_pred, |derived| {
- ImplDerivedObligation(Box::new(ImplDerivedObligationCause {
- derived,
- impl_or_alias_def_id: def_id,
- impl_def_predicate_index: Some(index),
- span,
- }))
- });
+ let cause =
+ if Some(parent_trait_pred.def_id()) == tcx.lang_items().coerce_unsized_trait() {
+ cause.clone()
+ } else {
+ cause.clone().derived_cause(parent_trait_pred, |derived| {
+ ImplDerivedObligation(Box::new(ImplDerivedObligationCause {
+ derived,
+ impl_or_alias_def_id: def_id,
+ impl_def_predicate_index: Some(index),
+ span,
+ }))
+ })
+ };
  let predicate = normalize_with_depth_to(
  self,
  param_env,

tests/ui/associated-types/associated-types-eq-3.stderr

@@ -43,7 +43,7 @@ note: expected this to be `Bar`
  |
 LL | type A = usize;
  | ^^^^^
- = note: required for the cast from `isize` to the object type `dyn Foo<A = Bar>`
+ = note: required for the cast from `&isize` to `&dyn Foo<A = Bar>`
 
 error: aborting due to 3 previous errors
 

tests/ui/associated-types/associated-types-overridden-binding-2.stderr

@@ -4,7 +4,7 @@ error[E0271]: expected `IntoIter<u32>` to be an iterator that yields `i32`, but
 LL | let _: &dyn I32Iterator<Item = u32> = &vec![42].into_iter();
  | ^^^^^^^^^^^^^^^^^^^^^ expected `i32`, found `u32`
  |
- = note: required for the cast from `std::vec::IntoIter<u32>` to the object type `dyn Iterator<Item = u32, Item = i32>`
+ = note: required for the cast from `&std::vec::IntoIter<u32>` to `&dyn Iterator<Item = u32, Item = i32>`
 
 error: aborting due to previous error
 

tests/ui/associated-types/issue-65774-1.stderr

@@ -25,7 +25,7 @@ LL | impl<'a, T: MyDisplay> MyDisplay for &'a mut T { }
  | --------- ^^^^^^^^^ ^^^^^^^^^
  | |
  | unsatisfied trait bound introduced here
- = note: required for the cast from `&mut T` to the object type `dyn MyDisplay`
+ = note: required for the cast from `&&mut T` to `&dyn MyDisplay`
 
 error: aborting due to 2 previous errors
 

tests/ui/associated-types/issue-65774-2.stderr

@@ -18,7 +18,7 @@ LL | writer.my_write(valref)
  | ^^^^^^ the trait `MyDisplay` is not implemented for `T`
  |
  = help: the trait `MyDisplay` is implemented for `&'a mut T`
- = note: required for the cast from `T` to the object type `dyn MyDisplay`
+ = note: required for the cast from `&mut T` to `&dyn MyDisplay`
 
 error: aborting due to 2 previous errors
 

tests/ui/async-await/async-block-control-flow-static-semantics.stderr

@@ -35,7 +35,7 @@ error[E0271]: expected `[async block@$DIR/async-block-control-flow-static-semant
 LL | let _: &dyn Future<Output = ()> = &block;
  | ^^^^^^ expected `()`, found `u8`
  |
- = note: required for the cast from `[async block@$DIR/async-block-control-flow-static-semantics.rs:23:17: 25:6]` to the object type `dyn Future<Output = ()>`
+ = note: required for the cast from `&[async block@$DIR/async-block-control-flow-static-semantics.rs:23:17: 25:6]` to `&dyn Future<Output = ()>`
 
 error[E0308]: mismatched types
  --> $DIR/async-block-control-flow-static-semantics.rs:12:43
@@ -51,7 +51,7 @@ error[E0271]: expected `[async block@$DIR/async-block-control-flow-static-semant
 LL | let _: &dyn Future<Output = ()> = &block;
  | ^^^^^^ expected `()`, found `u8`
  |
- = note: required for the cast from `[async block@$DIR/async-block-control-flow-static-semantics.rs:14:17: 16:6]` to the object type `dyn Future<Output = ()>`
+ = note: required for the cast from `&[async block@$DIR/async-block-control-flow-static-semantics.rs:14:17: 16:6]` to `&dyn Future<Output = ()>`
 
 error[E0308]: mismatched types
  --> $DIR/async-block-control-flow-static-semantics.rs:49:44

tests/ui/async-await/issue-86507.drop_tracking.stderr

@@ -13,7 +13,7 @@ note: captured value is not `Send` because `&` references cannot be sent unless
  |
 LL | let x = x;
  | ^ has type `&T` which is not `Send`, because `T` is not `Sync`
- = note: required for the cast from `[async block@$DIR/issue-86507.rs:21:17: 23:18]` to the object type `dyn Future<Output = ()> + Send`
+ = note: required for the cast from `Pin<Box<[async block@$DIR/issue-86507.rs:21:17: 23:18]>>` to `Pin<Box<(dyn Future<Output = ()> + Send + 'async_trait)>>`
 help: consider further restricting this bound
  |
 LL | fn bar<'me, 'async_trait, T: Send + std::marker::Sync>(x: &'me T)

tests/ui/async-await/issue-86507.drop_tracking_mir.stderr

@@ -13,7 +13,7 @@ note: captured value is not `Send` because `&` references cannot be sent unless
  |
 LL | let x = x;
  | ^ has type `&T` which is not `Send`, because `T` is not `Sync`
- = note: required for the cast from `[async block@$DIR/issue-86507.rs:21:17: 23:18]` to the object type `dyn Future<Output = ()> + Send`
+ = note: required for the cast from `Pin<Box<[async block@$DIR/issue-86507.rs:21:17: 23:18]>>` to `Pin<Box<(dyn Future<Output = ()> + Send + 'async_trait)>>`
 help: consider further restricting this bound
  |
 LL | fn bar<'me, 'async_trait, T: Send + std::marker::Sync>(x: &'me T)

tests/ui/async-await/issue-86507.no_drop_tracking.stderr

@@ -13,7 +13,7 @@ note: captured value is not `Send` because `&` references cannot be sent unless
  |
 LL | let x = x;
  | ^ has type `&T` which is not `Send`, because `T` is not `Sync`
- = note: required for the cast from `[async block@$DIR/issue-86507.rs:21:17: 23:18]` to the object type `dyn Future<Output = ()> + Send`
+ = note: required for the cast from `Pin<Box<[async block@$DIR/issue-86507.rs:21:17: 23:18]>>` to `Pin<Box<(dyn Future<Output = ()> + Send + 'async_trait)>>`
 help: consider further restricting this bound
  |
 LL | fn bar<'me, 'async_trait, T: Send + std::marker::Sync>(x: &'me T)

tests/ui/closure_context/issue-26046-fn-mut.stderr

@@ -9,7 +9,7 @@ LL | num += 1;
 LL | Box::new(closure)
  | ----------------- the requirement to implement `Fn` derives from here
  |
- = note: required for the cast from `[closure@$DIR/issue-26046-fn-mut.rs:4:19: 4:21]` to the object type `dyn Fn()`
+ = note: required for the cast from `Box<[closure@$DIR/issue-26046-fn-mut.rs:4:19: 4:21]>` to `Box<(dyn Fn() + 'static)>`
 
 error: aborting due to previous error
 

tests/ui/closure_context/issue-26046-fn-once.stderr

@@ -9,7 +9,7 @@ LL | vec
 LL | Box::new(closure)
  | ----------------- the requirement to implement `Fn` derives from here
  |
- = note: required for the cast from `[closure@$DIR/issue-26046-fn-once.rs:4:19: 4:26]` to the object type `dyn Fn() -> Vec<u8>`
+ = note: required for the cast from `Box<[closure@$DIR/issue-26046-fn-once.rs:4:19: 4:26]>` to `Box<(dyn Fn() -> Vec<u8> + 'static)>`
 
 error: aborting due to previous error
 

tests/ui/coercion/coerce-issue-49593-box-never.nofallback.stderr

@@ -4,15 +4,15 @@ error[E0277]: the trait bound `(): std::error::Error` is not satisfied
 LL | /* *mut $0 is coerced to Box<dyn Error> here */ Box::<_ /* ! */>::new(x)
  | ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::error::Error` is not implemented for `()`
  |
- = note: required for the cast from `()` to the object type `dyn std::error::Error`
+ = note: required for the cast from `Box<()>` to `Box<(dyn std::error::Error + 'static)>`
 
 error[E0277]: the trait bound `(): std::error::Error` is not satisfied
  --> $DIR/coerce-issue-49593-box-never.rs:23:49
  |
 LL | /* *mut $0 is coerced to *mut Error here */ raw_ptr_box::<_ /* ! */>(x)
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::error::Error` is not implemented for `()`
  |
- = note: required for the cast from `()` to the object type `(dyn std::error::Error + 'static)`
+ = note: required for the cast from `*mut ()` to `*mut (dyn std::error::Error + 'static)`
 
 error: aborting due to 2 previous errors
 

tests/ui/const-generics/defaults/trait_objects_fail.stderr

@@ -5,7 +5,7 @@ LL | foo(&10_u32);
  | ^^^^^^^ the trait `Trait` is not implemented for `u32`
  |
  = help: the trait `Trait<2>` is implemented for `u32`
- = note: required for the cast from `u32` to the object type `dyn Trait`
+ = note: required for the cast from `&u32` to `&dyn Trait`
 
 error[E0277]: the trait bound `bool: Traitor<_>` is not satisfied
  --> $DIR/trait_objects_fail.rs:28:9
@@ -14,7 +14,7 @@ LL | bar(&true);
  | ^^^^^ the trait `Traitor<_>` is not implemented for `bool`
  |
  = help: the trait `Traitor<2, 3>` is implemented for `bool`
- = note: required for the cast from `bool` to the object type `dyn Traitor<_>`
+ = note: required for the cast from `&bool` to `&dyn Traitor<_>`
 
 error: aborting due to 2 previous errors
 

tests/ui/custom_test_frameworks/mismatch.stderr

@@ -6,7 +6,7 @@ LL | #[test]
 LL | fn wrong_kind(){}
  | ^^^^^^^^^^^^^^^^^ the trait `Testable` is not implemented for `TestDescAndFn`
  |
- = note: required for the cast from `TestDescAndFn` to the object type `dyn Testable`
+ = note: required for the cast from `&TestDescAndFn` to `&dyn Testable`
  = note: this error originates in the attribute macro `test` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error

tests/ui/diagnostic-width/E0271.stderr

@@ -15,8 +15,8 @@ note: expected this to be `Foo`
  |
 LL | type Error = E;
  | ^
- = note: required for the cast from `Result<Result<..., ...>, ...>` to the object type `dyn Future<Error = Foo>`
- = note: the full name for the casted type has been written to '$TEST_BUILD_DIR/diagnostic-width/E0271/E0271.long-type-hash.txt'
+ = note: required for the cast from `Box<Result<..., ...>>` to `Box<(dyn Future<Error = Foo> + 'static)>`
+ = note: the full name for the source type has been written to '$TEST_BUILD_DIR/diagnostic-width/E0271/E0271.long-type-hash.txt'
 
 error: aborting due to previous error
 

tests/ui/dst/dst-bad-coerce1.stderr

@@ -15,7 +15,7 @@ error[E0277]: the trait bound `Foo: Bar` is not satisfied
 LL | let f3: &Fat<dyn Bar> = f2;
  | ^^ the trait `Bar` is not implemented for `Foo`
  |
- = note: required for the cast from `Foo` to the object type `dyn Bar`
+ = note: required for the cast from `&Fat<Foo>` to `&Fat<dyn Bar>`
 
 error[E0308]: mismatched types
  --> $DIR/dst-bad-coerce1.rs:28:27
@@ -34,7 +34,7 @@ error[E0277]: the trait bound `Foo: Bar` is not satisfied
 LL | let f3: &(dyn Bar,) = f2;
  | ^^ the trait `Bar` is not implemented for `Foo`
  |
- = note: required for the cast from `Foo` to the object type `dyn Bar`
+ = note: required for the cast from `&(Foo,)` to `&(dyn Bar,)`
 
 error: aborting due to 4 previous errors