replace "cast" with "coercion" where applicable

This changes the remaining span for the cast, because the new `Cast`
category has a higher priority (lower `Ord`) than the old `Coercion`
category, so we no longer report the region error for the "unsizing"
coercion from `*const Trait` to itself.

3 files changed, 20 insertions, 13 deletions

diff --git a/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs b/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
index 7077d78f459..63b653bc9f4 100644
--- a/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
@@ -333,7 +333,9 @@ impl<'tcx> BorrowExplanation<'tcx> {
                     }
                 }
 
-                if let ConstraintCategory::Cast { unsize_to: Some(unsize_ty) } = category {
+                if let ConstraintCategory::Cast { is_coercion: true, unsize_to: Some(unsize_ty) } =
+                    category
+                {
                     self.add_object_lifetime_default_note(tcx, err, unsize_ty);
                 }
                 self.add_lifetime_bound_suggestion_to_diagnostic(err, &category, span, region_name);
diff --git a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
index ca0a3c66130..a4a9734de3f 100644
--- a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
@@ -47,7 +47,8 @@ impl<'tcx> ConstraintDescription for ConstraintCategory<'tcx> {
             ConstraintCategory::Yield => "yielding this value ",
             ConstraintCategory::UseAsConst => "using this value as a constant ",
             ConstraintCategory::UseAsStatic => "using this value as a static ",
-            ConstraintCategory::Cast { .. } => "cast ",
+            ConstraintCategory::Cast { is_coercion: false, .. } => "cast ",
+            ConstraintCategory::Cast { is_coercion: true, .. } => "coercion ",
             ConstraintCategory::CallArgument(_) => "argument ",
             ConstraintCategory::TypeAnnotation => "type annotation ",
             ConstraintCategory::ClosureBounds => "closure body ",
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index 29a0c5bdf57..db69f48e515 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -2007,7 +2007,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                             self.prove_predicate(
                                 ty::ClauseKind::WellFormed(src_ty.into()),
                                 location.to_locations(),
-                                ConstraintCategory::Cast { unsize_to: None },
+                                ConstraintCategory::Cast { is_coercion: true, unsize_to: None },
                             );
 
                             let src_ty = self.normalize(src_ty, location);
@@ -2015,7 +2015,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                                 src_ty,
                                 *ty,
                                 location.to_locations(),
-                                ConstraintCategory::Cast { unsize_to: None },
+                                ConstraintCategory::Cast { is_coercion: true, unsize_to: None },
                             ) {
                                 span_mirbug!(
                                     self,
@@ -2036,7 +2036,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         self.prove_predicate(
                             ty::ClauseKind::WellFormed(src_ty.into()),
                             location.to_locations(),
-                            ConstraintCategory::Cast { unsize_to: None },
+                            ConstraintCategory::Cast { is_coercion: true, unsize_to: None },
                         );
 
                         // The type that we see in the fcx is like
@@ -2049,7 +2049,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                             src_ty,
                             *ty,
                             location.to_locations(),
-                            ConstraintCategory::Cast { unsize_to: None },
+                            ConstraintCategory::Cast { is_coercion: true, unsize_to: None },
                         ) {
                             span_mirbug!(
                                 self,
@@ -2074,7 +2074,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                             ty_fn_ptr_from,
                             *ty,
                             location.to_locations(),
-                            ConstraintCategory::Cast { unsize_to: None },
+                            ConstraintCategory::Cast { is_coercion: true, unsize_to: None },
                         ) {
                             span_mirbug!(
                                 self,
@@ -2103,7 +2103,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                             ty_fn_ptr_from,
                             *ty,
                             location.to_locations(),
-                            ConstraintCategory::Cast { unsize_to: None },
+                            ConstraintCategory::Cast { is_coercion: true, unsize_to: None },
                         ) {
                             span_mirbug!(
                                 self,
@@ -2128,6 +2128,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                             trait_ref,
                             location.to_locations(),
                             ConstraintCategory::Cast {
+                                is_coercion: true,
                                 unsize_to: Some(tcx.fold_regions(ty, |r, _| {
                                     if let ty::ReVar(_) = r.kind() {
                                         tcx.lifetimes.re_erased
@@ -2155,7 +2156,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                                 .iter()
                                 .map(|predicate| predicate.with_self_ty(tcx, self_ty)),
                             location.to_locations(),
-                            ConstraintCategory::Cast { unsize_to: None },
+                            ConstraintCategory::Cast { is_coercion: true, unsize_to: None },
                         );
 
                         let outlives_predicate = tcx.mk_predicate(Binder::dummy(
@@ -2166,7 +2167,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         self.prove_predicate(
                             outlives_predicate,
                             location.to_locations(),
-                            ConstraintCategory::Cast { unsize_to: None },
+                            ConstraintCategory::Cast { is_coercion: true, unsize_to: None },
                         );
                     }
 
@@ -2184,7 +2185,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                             *ty_from,
                             *ty_to,
                             location.to_locations(),
-                            ConstraintCategory::Cast { unsize_to: None },
+                            ConstraintCategory::Cast { is_coercion: true, unsize_to: None },
                         ) {
                             span_mirbug!(
                                 self,
@@ -2246,7 +2247,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                             *ty_elem,
                             *ty_to,
                             location.to_locations(),
-                            ConstraintCategory::Cast { unsize_to: None },
+                            ConstraintCategory::Cast { is_coercion: true, unsize_to: None },
                         ) {
                             span_mirbug!(
                                 self,
@@ -2427,7 +2428,10 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                                         src_obj,
                                         dst_obj,
                                         location.to_locations(),
-                                        ConstraintCategory::Cast { unsize_to: None },
+                                        ConstraintCategory::Cast {
+                                            is_coercion: false,
+                                            unsize_to: None,
+                                        },
                                     )
                                     .unwrap();
                                 }