Combine redundant obligation cause codes

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -1883,7 +1883,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             exp_span, exp_found.expected, exp_found.found,
         );
 
-        if let ObligationCauseCode::CompareImplMethodObligation { .. } = cause.code() {
+        if let ObligationCauseCode::CompareImplItemObligation { .. } = cause.code() {
             return;
         }
 
@@ -2351,16 +2351,12 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             GenericKind::Projection(ref p) => format!("the associated type `{}`", p),
         };
 
-        match origin {
+        if let Some(SubregionOrigin::CompareImplItemObligation {
-            Some(SubregionOrigin::CompareImplMethodObligation {
             span,
             impl_item_def_id,
             trait_item_def_id,
-            } | SubregionOrigin::CompareImplTypeObligation {
+        }) = origin
-                span,
+        {
-                impl_item_def_id,
-                trait_item_def_id,
-            }) => {
             return self.report_extra_impl_obligation(
                 span,
                 impl_item_def_id,
@@ -2368,8 +2364,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 &format!("`{}: {}`", bound_kind, sub),
             );
         }
-            _ => {}
-        }
 
         fn binding_suggestion<'tcx, S: fmt::Display>(
             err: &mut Diagnostic,
@@ -2794,8 +2788,15 @@ impl<'tcx> ObligationCauseExt<'tcx> for ObligationCause<'tcx> {
         use self::FailureCode::*;
         use crate::traits::ObligationCauseCode::*;
         match self.code() {
-            CompareImplMethodObligation { .. } => Error0308("method not compatible with trait"),
+            CompareImplItemObligation { kind: ty::AssocKind::Fn, .. } => {
-            CompareImplTypeObligation { .. } => Error0308("type not compatible with trait"),
+                Error0308("method not compatible with trait")
+            }
+            CompareImplItemObligation { kind: ty::AssocKind::Type, .. } => {
+                Error0308("type not compatible with trait")
+            }
+            CompareImplItemObligation { kind: ty::AssocKind::Const, .. } => {
+                Error0308("const not compatible with trait")
+            }
             MatchExpressionArm(box MatchExpressionArmCause { source, .. }) => {
                 Error0308(match source {
                     hir::MatchSource::TryDesugar => "`?` operator has incompatible types",
@@ -2829,8 +2830,15 @@ impl<'tcx> ObligationCauseExt<'tcx> for ObligationCause<'tcx> {
     fn as_requirement_str(&self) -> &'static str {
         use crate::traits::ObligationCauseCode::*;
         match self.code() {
-            CompareImplMethodObligation { .. } => "method type is compatible with trait",
+            CompareImplItemObligation { kind: ty::AssocKind::Fn, .. } => {
-            CompareImplTypeObligation { .. } => "associated type is compatible with trait",
+                "method type is compatible with trait"
+            }
+            CompareImplItemObligation { kind: ty::AssocKind::Type, .. } => {
+                "associated type is compatible with trait"
+            }
+            CompareImplItemObligation { kind: ty::AssocKind::Const, .. } => {
+                "const is compatible with trait"
+            }
             ExprAssignable => "expression is assignable",
             IfExpression { .. } => "`if` and `else` have incompatible types",
             IfExpressionWithNoElse => "`if` missing an `else` returns `()`",

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/trait_impl_difference.rs

@@ -3,7 +3,7 @@
 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
 use crate::infer::lexical_region_resolve::RegionResolutionError;
 use crate::infer::Subtype;
-use crate::traits::ObligationCauseCode::{CompareImplMethodObligation, CompareImplTypeObligation};
+use crate::traits::ObligationCauseCode::CompareImplItemObligation;
 use rustc_errors::{ErrorGuaranteed, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def::Res;
@@ -33,8 +33,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             && let (Subtype(sup_trace), Subtype(sub_trace)) = (&sup_origin, &sub_origin)
             && let sub_expected_found @ Some((sub_expected, sub_found)) = sub_trace.values.ty()
             && let sup_expected_found @ Some(_) = sup_trace.values.ty()
-            && let CompareImplMethodObligation { trait_item_def_id, .. }
+            && let CompareImplItemObligation { trait_item_def_id, .. } = sub_trace.cause.code()
-                 | CompareImplTypeObligation { trait_item_def_id, .. } = sub_trace.cause.code()
             && sup_expected_found == sub_expected_found
         {
             let guar =

compiler/rustc_infer/src/infer/error_reporting/note.rs

@@ -86,13 +86,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     "...so that the declared lifetime parameter bounds are satisfied",
                 );
             }
-            infer::CompareImplMethodObligation { span, .. } => {
+            infer::CompareImplItemObligation { span, .. } => {
-                label_or_note(
-                    span,
-                    "...so that the definition in impl matches the definition from the trait",
-                );
-            }
-            infer::CompareImplTypeObligation { span, .. } => {
                 label_or_note(
                     span,
                     "...so that the definition in impl matches the definition from the trait",
@@ -329,15 +323,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 );
                 err
             }
-            infer::CompareImplMethodObligation { span, impl_item_def_id, trait_item_def_id } => {
+            infer::CompareImplItemObligation { span, impl_item_def_id, trait_item_def_id } => self
-                self.report_extra_impl_obligation(
-                    span,
-                    impl_item_def_id,
-                    trait_item_def_id,
-                    &format!("`{}: {}`", sup, sub),
-                )
-            }
-            infer::CompareImplTypeObligation { span, impl_item_def_id, trait_item_def_id } => self
                 .report_extra_impl_obligation(
                     span,
                     impl_item_def_id,

compiler/rustc_infer/src/infer/mod.rs

@@ -405,15 +405,7 @@ pub enum SubregionOrigin<'tcx> {
 
     /// Comparing the signature and requirements of an impl method against
     /// the containing trait.
-    CompareImplMethodObligation {
+    CompareImplItemObligation { span: Span, impl_item_def_id: LocalDefId, trait_item_def_id: DefId },
-        span: Span,
-        impl_item_def_id: LocalDefId,
-        trait_item_def_id: DefId,
-    },
-
-    /// Comparing the signature and requirements of an impl associated type
-    /// against the containing trait
-    CompareImplTypeObligation { span: Span, impl_item_def_id: LocalDefId, trait_item_def_id: DefId },
 
     /// Checking that the bounds of a trait's associated type hold for a given impl
     CheckAssociatedTypeBounds {
@@ -1945,8 +1937,7 @@ impl<'tcx> SubregionOrigin<'tcx> {
             ReborrowUpvar(a, _) => a,
             DataBorrowed(_, a) => a,
             ReferenceOutlivesReferent(_, a) => a,
-            CompareImplMethodObligation { span, .. } => span,
+            CompareImplItemObligation { span, .. } => span,
-            CompareImplTypeObligation { span, .. } => span,
             CheckAssociatedTypeBounds { ref parent, .. } => parent.span(),
         }
     }
@@ -1960,19 +1951,11 @@ impl<'tcx> SubregionOrigin<'tcx> {
                 SubregionOrigin::ReferenceOutlivesReferent(ref_type, cause.span)
             }
 
-            traits::ObligationCauseCode::CompareImplMethodObligation {
+            traits::ObligationCauseCode::CompareImplItemObligation {
                 impl_item_def_id,
                 trait_item_def_id,
-            } => SubregionOrigin::CompareImplMethodObligation {
+                kind: _,
-                span: cause.span,
+            } => SubregionOrigin::CompareImplItemObligation {
-                impl_item_def_id,
-                trait_item_def_id,
-            },
-
-            traits::ObligationCauseCode::CompareImplTypeObligation {
-                impl_item_def_id,
-                trait_item_def_id,
-            } => SubregionOrigin::CompareImplTypeObligation {
                 span: cause.span,
                 impl_item_def_id,
                 trait_item_def_id,

compiler/rustc_middle/src/traits/mod.rs

@@ -311,18 +311,10 @@ pub enum ObligationCauseCode<'tcx> {
     },
 
     /// Error derived when matching traits/impls; see ObligationCause for more details
-    CompareImplConstObligation,
+    CompareImplItemObligation {
-
-    /// Error derived when matching traits/impls; see ObligationCause for more details
-    CompareImplMethodObligation {
-        impl_item_def_id: LocalDefId,
-        trait_item_def_id: DefId,
-    },
-
-    /// Error derived when matching traits/impls; see ObligationCause for more details
-    CompareImplTypeObligation {
         impl_item_def_id: LocalDefId,
         trait_item_def_id: DefId,
+        kind: ty::AssocKind,
     },
 
     /// Checking that the bounds of a trait's associated type hold for a given impl

compiler/rustc_middle/src/ty/assoc.rs

@@ -105,6 +105,16 @@ impl AssocKind {
     }
 }
 
+impl std::fmt::Display for AssocKind {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            AssocKind::Fn => write!(f, "method"),
+            AssocKind::Const => write!(f, "associated const"),
+            AssocKind::Type => write!(f, "associated type"),
+        }
+    }
+}
+
 /// A list of `ty::AssocItem`s in definition order that allows for efficient lookup by name.
 ///
 /// When doing lookup by name, we try to postpone hygienic comparison for as long as possible since

compiler/rustc_middle/src/ty/error.rs

@@ -660,12 +660,8 @@ impl<T> Trait<T> for X {
                     | hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }),
             )
         );
-        let impl_comparison = matches!(
+        let impl_comparison =
-            cause_code,
+            matches!(cause_code, ObligationCauseCode::CompareImplItemObligation { .. });
-            ObligationCauseCode::CompareImplMethodObligation { .. }
-                | ObligationCauseCode::CompareImplTypeObligation { .. }
-                | ObligationCauseCode::CompareImplConstObligation
-        );
         let assoc = self.associated_item(proj_ty.item_def_id);
         if !callable_scope || impl_comparison {
             // We do not want to suggest calling functions when the reason of the

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -224,6 +224,7 @@ TrivialTypeTraversalAndLiftImpls! {
     // general `Region`.
     crate::ty::BoundRegionKind,
     crate::ty::AssocItem,
+    crate::ty::AssocKind,
     crate::ty::Placeholder<crate::ty::BoundRegionKind>,
     crate::ty::ClosureKind,
     crate::ty::FreeRegion,

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

@@ -301,13 +301,10 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         span = obligation.cause.span;
                     }
                 }
-                if let ObligationCauseCode::CompareImplMethodObligation {
+                if let ObligationCauseCode::CompareImplItemObligation {
-                    impl_item_def_id,
-                    trait_item_def_id,
-                }
-                | ObligationCauseCode::CompareImplTypeObligation {
                     impl_item_def_id,
                     trait_item_def_id,
+                    kind: _,
                 } = *obligation.cause.code()
                 {
                     self.report_extra_impl_obligation(

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

@@ -2682,11 +2682,11 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     )
                 });
             }
-            ObligationCauseCode::CompareImplMethodObligation { trait_item_def_id, .. } => {
+            ObligationCauseCode::CompareImplItemObligation { trait_item_def_id, kind, .. } => {
                 let item_name = self.tcx.item_name(trait_item_def_id);
                 let msg = format!(
-                    "the requirement `{}` appears on the impl method `{}` but not on the \
+                    "the requirement `{}` appears on the `impl`'s {kind} `{}` but not on the \
-                     corresponding trait method",
+                     corresponding trait's {kind}",
                     predicate, item_name,
                 );
                 let sp = self
@@ -2697,7 +2697,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 let mut assoc_span: MultiSpan = sp.into();
                 assoc_span.push_span_label(
                     sp,
-                    format!("this trait method doesn't have the requirement `{}`", predicate),
+                    format!("this trait's {kind} doesn't have the requirement `{}`", predicate),
                 );
                 if let Some(ident) = self
                     .tcx
@@ -2708,38 +2708,6 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 }
                 err.span_note(assoc_span, &msg);
             }
-            ObligationCauseCode::CompareImplTypeObligation { trait_item_def_id, .. } => {
-                let item_name = self.tcx.item_name(trait_item_def_id);
-                let msg = format!(
-                    "the requirement `{}` appears on the associated impl type `{}` but not on the \
-                     corresponding associated trait type",
-                    predicate, item_name,
-                );
-                let sp = self.tcx.def_span(trait_item_def_id);
-                let mut assoc_span: MultiSpan = sp.into();
-                assoc_span.push_span_label(
-                    sp,
-                    format!(
-                        "this trait associated type doesn't have the requirement `{}`",
-                        predicate,
-                    ),
-                );
-                if let Some(ident) = self
-                    .tcx
-                    .opt_associated_item(trait_item_def_id)
-                    .and_then(|i| self.tcx.opt_item_ident(i.container.id()))
-                {
-                    assoc_span.push_span_label(ident.span, "in this trait");
-                }
-                err.span_note(assoc_span, &msg);
-            }
-            ObligationCauseCode::CompareImplConstObligation => {
-                err.note(&format!(
-                    "the requirement `{}` appears on the associated impl constant \
-                     but not on the corresponding associated trait constant",
-                    predicate
-                ));
-            }
             ObligationCauseCode::TrivialBound => {
                 err.help("see issue #48214");
                 if tcx.sess.opts.unstable_features.is_nightly_build() {

compiler/rustc_typeck/src/astconv/mod.rs

@@ -1150,17 +1150,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             .expect("missing associated type");
 
         if !assoc_item.vis.is_accessible_from(def_scope, tcx) {
-            let kind = match assoc_item.kind {
-                ty::AssocKind::Type => "type",
-                ty::AssocKind::Const => "const",
-                _ => unreachable!(),
-            };
             tcx.sess
                 .struct_span_err(
                     binding.span,
-                    &format!("associated {kind} `{}` is private", binding.item_name),
+                    &format!("{} `{}` is private", assoc_item.kind, binding.item_name),
                 )
-                .span_label(binding.span, &format!("private associated {kind}"))
+                .span_label(binding.span, &format!("private {}", assoc_item.kind))
                 .emit();
         }
         tcx.check_stability(assoc_item.def_id, Some(hir_ref_id), binding.span, None);

compiler/rustc_typeck/src/check/compare_method.rs

@@ -90,9 +90,10 @@ fn compare_predicate_entailment<'tcx>(
     let mut cause = ObligationCause::new(
         impl_m_span,
         impl_m_hir_id,
-        ObligationCauseCode::CompareImplMethodObligation {
+        ObligationCauseCode::CompareImplItemObligation {
             impl_item_def_id: impl_m.def_id.expect_local(),
             trait_item_def_id: trait_m.def_id,
+            kind: impl_m.kind,
         },
     );
 
@@ -223,9 +224,10 @@ fn compare_predicate_entailment<'tcx>(
             let cause = ObligationCause::new(
                 span,
                 impl_m_hir_id,
-                ObligationCauseCode::CompareImplMethodObligation {
+                ObligationCauseCode::CompareImplItemObligation {
                     impl_item_def_id: impl_m.def_id.expect_local(),
                     trait_item_def_id: trait_m.def_id,
+                    kind: impl_m.kind,
                 },
             );
             ocx.register_obligation(traits::Obligation::new(cause, param_env, predicate));
@@ -1079,7 +1081,11 @@ pub(crate) fn compare_const_impl<'tcx>(
         let mut cause = ObligationCause::new(
             impl_c_span,
             impl_c_hir_id,
-            ObligationCauseCode::CompareImplConstObligation,
+            ObligationCauseCode::CompareImplItemObligation {
+                impl_item_def_id: impl_c.def_id.expect_local(),
+                trait_item_def_id: trait_c.def_id,
+                kind: impl_c.kind,
+            },
         );
 
         // There is no "body" here, so just pass dummy id.
@@ -1249,9 +1255,10 @@ fn compare_type_predicate_entailment<'tcx>(
             let cause = ObligationCause::new(
                 span,
                 impl_ty_hir_id,
-                ObligationCauseCode::CompareImplTypeObligation {
+                ObligationCauseCode::CompareImplItemObligation {
                     impl_item_def_id: impl_ty.def_id.expect_local(),
                     trait_item_def_id: trait_ty.def_id,
+                    kind: impl_ty.kind,
                 },
             );
             ocx.register_obligations(obligations);

src/test/ui/associated-consts/associated-const-impl-wrong-lifetime.rs

@@ -5,7 +5,7 @@ trait Foo {
 
 impl<'a> Foo for &'a () {
     const NAME: &'a str = "unit";
-    //~^ ERROR mismatched types [E0308]
+    //~^ ERROR const not compatible with trait
 }
 
 fn main() {}

src/test/ui/associated-consts/associated-const-impl-wrong-lifetime.stderr

@@ -1,4 +1,4 @@
-error[E0308]: mismatched types
+error[E0308]: const not compatible with trait
   --> $DIR/associated-const-impl-wrong-lifetime.rs:7:5
    |
 LL |     const NAME: &'a str = "unit";

src/test/ui/generic-associated-types/impl_bounds.stderr

@@ -47,14 +47,14 @@ note: required because of the requirements on the impl of `Copy` for `Fooy<T>`
    |
 LL | #[derive(Copy, Clone)]
    |          ^^^^
-note: the requirement `Fooy<T>: Copy` appears on the associated impl type `C` but not on the corresponding associated trait type
+note: the requirement `Fooy<T>: Copy` appears on the `impl`'s associated type `C` but not on the corresponding trait's associated type
-  --> $DIR/impl_bounds.rs:7:5
+  --> $DIR/impl_bounds.rs:7:10
    |
 LL | trait Foo {
    |       --- in this trait
 ...
 LL |     type C where Self: Clone;
-   |     ^^^^^^ this trait associated type doesn't have the requirement `Fooy<T>: Copy`
+   |          ^ this trait's associated type doesn't have the requirement `Fooy<T>: Copy`
    = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider restricting type parameter `T`
    |
@@ -72,14 +72,14 @@ note: required because of the requirements on the impl of `Copy` for `Fooy<T>`
    |
 LL | #[derive(Copy, Clone)]
    |          ^^^^
-note: the requirement `Fooy<T>: Copy` appears on the impl method `d` but not on the corresponding trait method
+note: the requirement `Fooy<T>: Copy` appears on the `impl`'s method `d` but not on the corresponding trait's method
   --> $DIR/impl_bounds.rs:8:8
    |
 LL | trait Foo {
    |       --- in this trait
 ...
 LL |     fn d() where Self: Clone;
-   |        ^ this trait method doesn't have the requirement `Fooy<T>: Copy`
+   |        ^ this trait's method doesn't have the requirement `Fooy<T>: Copy`
    = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider restricting type parameter `T`
    |

src/test/ui/nll/trait-associated-constant.rs

@@ -19,7 +19,7 @@ struct FailStruct { }
 
 impl<'a: 'b, 'b, 'c> Anything<'a, 'b> for FailStruct {
     const AC: Option<&'c str> = None;
-    //~^ ERROR: mismatched types
+    //~^ ERROR: const not compatible with trait
 }
 
 struct OKStruct2 { }

src/test/ui/nll/trait-associated-constant.stderr

@@ -1,4 +1,4 @@
-error[E0308]: mismatched types
+error[E0308]: const not compatible with trait
   --> $DIR/trait-associated-constant.rs:21:5
    |
 LL |     const AC: Option<&'c str> = None;