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.

12 files changed, 38 insertions, 29 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();
                                 }
diff --git a/compiler/rustc_middle/src/mir/query.rs b/compiler/rustc_middle/src/mir/query.rs
index 1002f64f849..47fea6f6d90 100644
--- a/compiler/rustc_middle/src/mir/query.rs
+++ b/compiler/rustc_middle/src/mir/query.rs
@@ -234,7 +234,9 @@ pub enum ConstraintCategory<'tcx> {
     UseAsStatic,
     TypeAnnotation,
     Cast {
-        /// Whether this is an unsizing cast and if yes, this contains the target type.
+        /// Whether this cast is a coercion.
+        is_coercion: bool,
+        /// Whether this is an unsizing coercion and if yes, this contains the target type.
         /// Region variables are erased to ReErased.
         #[derive_where(skip)]
         unsize_to: Option<Ty<'tcx>>,
diff --git a/tests/ui/borrowck/two-phase-surprise-no-conflict.stderr b/tests/ui/borrowck/two-phase-surprise-no-conflict.stderr
index b3bf2f924fc..89b15a7a659 100644
--- a/tests/ui/borrowck/two-phase-surprise-no-conflict.stderr
+++ b/tests/ui/borrowck/two-phase-surprise-no-conflict.stderr
@@ -75,7 +75,7 @@ LL |     reg.register_univ(Box::new(CapturePass::new(&reg.sess_mut)));
    |     ^^^^^^^^^^^^^^^^^^-----------------------------------------^
    |     |                 |                         |
    |     |                 |                         immutable borrow occurs here
-   |     |                 cast requires that `reg.sess_mut` is borrowed for `'a`
+   |     |                 coercion requires that `reg.sess_mut` is borrowed for `'a`
    |     mutable borrow occurs here
    |
    = note: due to object lifetime defaults, `Box<dyn for<'b> LateLintPass<'b>>` actually means `Box<(dyn for<'b> LateLintPass<'b> + 'static)>`
@@ -119,7 +119,7 @@ LL |     reg.register_univ(Box::new(CapturePass::new_mut(&mut reg.sess_mut)));
    |     ^^^^^^^^^^^^^^^^^^-------------------------------------------------^
    |     |                 |                             |
    |     |                 |                             first mutable borrow occurs here
-   |     |                 cast requires that `reg.sess_mut` is borrowed for `'a`
+   |     |                 coercion requires that `reg.sess_mut` is borrowed for `'a`
    |     second mutable borrow occurs here
    |
    = note: due to object lifetime defaults, `Box<dyn for<'b> LateLintPass<'b>>` actually means `Box<(dyn for<'b> LateLintPass<'b> + 'static)>`
diff --git a/tests/ui/cast/ptr-to-trait-obj-different-regions-misc.stderr b/tests/ui/cast/ptr-to-trait-obj-different-regions-misc.stderr
index 4a699780c64..6069f4f3b55 100644
--- a/tests/ui/cast/ptr-to-trait-obj-different-regions-misc.stderr
+++ b/tests/ui/cast/ptr-to-trait-obj-different-regions-misc.stderr
@@ -138,7 +138,7 @@ error: lifetime may not live long enough
 LL | fn extend_to_static<'a>(ptr: *const dyn Trait<'a>) {
    |                     -- lifetime `'a` defined here
 LL |     require_static(ptr as _)
-   |                    ^^^ cast requires that `'a` must outlive `'static`
+   |                    ^^^^^^^^ cast requires that `'a` must outlive `'static`
 
 error: aborting due to 9 previous errors
 
diff --git a/tests/ui/dropck/dropck_trait_cycle_checked.stderr b/tests/ui/dropck/dropck_trait_cycle_checked.stderr
index 63fd07a9163..f32736f1a67 100644
--- a/tests/ui/dropck/dropck_trait_cycle_checked.stderr
+++ b/tests/ui/dropck/dropck_trait_cycle_checked.stderr
@@ -2,7 +2,7 @@ error[E0597]: `o2` does not live long enough
   --> $DIR/dropck_trait_cycle_checked.rs:111:13
    |
 LL |     let (o1, o2, o3): (Box<dyn Obj>, Box<dyn Obj>, Box<dyn Obj>) = (O::new(), O::new(), O::new());
-   |              -- binding `o2` declared here                          -------- cast requires that `o2` is borrowed for `'static`
+   |              -- binding `o2` declared here                          -------- coercion requires that `o2` is borrowed for `'static`
 LL |     o1.set0(&o2);
    |             ^^^ borrowed value does not live long enough
 ...
@@ -15,7 +15,7 @@ error[E0597]: `o3` does not live long enough
   --> $DIR/dropck_trait_cycle_checked.rs:112:13
    |
 LL |     let (o1, o2, o3): (Box<dyn Obj>, Box<dyn Obj>, Box<dyn Obj>) = (O::new(), O::new(), O::new());
-   |                  -- binding `o3` declared here                      -------- cast requires that `o3` is borrowed for `'static`
+   |                  -- binding `o3` declared here                      -------- coercion requires that `o3` is borrowed for `'static`
 LL |     o1.set0(&o2);
 LL |     o1.set1(&o3);
    |             ^^^ borrowed value does not live long enough
@@ -29,7 +29,7 @@ error[E0597]: `o2` does not live long enough
   --> $DIR/dropck_trait_cycle_checked.rs:113:13
    |
 LL |     let (o1, o2, o3): (Box<dyn Obj>, Box<dyn Obj>, Box<dyn Obj>) = (O::new(), O::new(), O::new());
-   |              -- binding `o2` declared here                                    -------- cast requires that `o2` is borrowed for `'static`
+   |              -- binding `o2` declared here                                    -------- coercion requires that `o2` is borrowed for `'static`
 ...
 LL |     o2.set0(&o2);
    |             ^^^ borrowed value does not live long enough
@@ -43,7 +43,7 @@ error[E0597]: `o3` does not live long enough
   --> $DIR/dropck_trait_cycle_checked.rs:114:13
    |
 LL |     let (o1, o2, o3): (Box<dyn Obj>, Box<dyn Obj>, Box<dyn Obj>) = (O::new(), O::new(), O::new());
-   |                  -- binding `o3` declared here                                -------- cast requires that `o3` is borrowed for `'static`
+   |                  -- binding `o3` declared here                                -------- coercion requires that `o3` is borrowed for `'static`
 ...
 LL |     o2.set1(&o3);
    |             ^^^ borrowed value does not live long enough
@@ -57,7 +57,7 @@ error[E0597]: `o1` does not live long enough
   --> $DIR/dropck_trait_cycle_checked.rs:115:13
    |
 LL |     let (o1, o2, o3): (Box<dyn Obj>, Box<dyn Obj>, Box<dyn Obj>) = (O::new(), O::new(), O::new());
-   |          -- binding `o1` declared here                                                  -------- cast requires that `o1` is borrowed for `'static`
+   |          -- binding `o1` declared here                                                  -------- coercion requires that `o1` is borrowed for `'static`
 ...
 LL |     o3.set0(&o1);
    |             ^^^ borrowed value does not live long enough
@@ -71,7 +71,7 @@ error[E0597]: `o2` does not live long enough
   --> $DIR/dropck_trait_cycle_checked.rs:116:13
    |
 LL |     let (o1, o2, o3): (Box<dyn Obj>, Box<dyn Obj>, Box<dyn Obj>) = (O::new(), O::new(), O::new());
-   |              -- binding `o2` declared here                                              -------- cast requires that `o2` is borrowed for `'static`
+   |              -- binding `o2` declared here                                              -------- coercion requires that `o2` is borrowed for `'static`
 ...
 LL |     o3.set1(&o2);
    |             ^^^ borrowed value does not live long enough
diff --git a/tests/ui/lifetimes/issue-90600-expected-return-static-indirect.stderr b/tests/ui/lifetimes/issue-90600-expected-return-static-indirect.stderr
index 598f1424191..6bd6a0584c9 100644
--- a/tests/ui/lifetimes/issue-90600-expected-return-static-indirect.stderr
+++ b/tests/ui/lifetimes/issue-90600-expected-return-static-indirect.stderr
@@ -7,7 +7,7 @@ LL |     let refcell = RefCell::new(&mut foo);
    |                                ^^^^^^^^ borrowed value does not live long enough
 LL |
 LL |     let read = &refcell as &RefCell<dyn Read>;
-   |                -------- cast requires that `foo` is borrowed for `'static`
+   |                -------- coercion requires that `foo` is borrowed for `'static`
 ...
 LL | }
    |  - `foo` dropped here while still borrowed
@@ -19,7 +19,7 @@ LL | fn inner(mut foo: &[u8]) {
    |                   - let's call the lifetime of this reference `'1`
 ...
 LL |     let read = &refcell as &RefCell<dyn Read>;
-   |                ^^^^^^^^ cast requires that `'1` must outlive `'static`
+   |                ^^^^^^^^ coercion requires that `'1` must outlive `'static`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/nll/issue-54779-anon-static-lifetime.stderr b/tests/ui/nll/issue-54779-anon-static-lifetime.stderr
index 92298c6617f..a454ed26568 100644
--- a/tests/ui/nll/issue-54779-anon-static-lifetime.stderr
+++ b/tests/ui/nll/issue-54779-anon-static-lifetime.stderr
@@ -5,7 +5,7 @@ LL |         cx: &dyn DebugContext,
    |             - let's call the lifetime of this reference `'1`
 ...
 LL |         bar.debug_with(cx);
-   |                        ^^ cast requires that `'1` must outlive `'static`
+   |                        ^^ coercion requires that `'1` must outlive `'static`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/suggestions/lifetimes/suggest-using-tick-underscore-lifetime-in-return-trait-object.stderr b/tests/ui/suggestions/lifetimes/suggest-using-tick-underscore-lifetime-in-return-trait-object.stderr
index 73fa5ddb146..050ef7da9b9 100644
--- a/tests/ui/suggestions/lifetimes/suggest-using-tick-underscore-lifetime-in-return-trait-object.stderr
+++ b/tests/ui/suggestions/lifetimes/suggest-using-tick-underscore-lifetime-in-return-trait-object.stderr
@@ -4,7 +4,7 @@ error: lifetime may not live long enough
 LL | fn foo<T: Any>(value: &T) -> Box<dyn Any> {
    |                       - let's call the lifetime of this reference `'1`
 LL |     Box::new(value) as Box<dyn Any>
-   |     ^^^^^^^^^^^^^^^ cast requires that `'1` must outlive `'static`
+   |     ^^^^^^^^^^^^^^^ coercion requires that `'1` must outlive `'static`
    |
 help: to declare that the trait object captures data from argument `value`, you can add an explicit `'_` lifetime bound
    |
diff --git a/tests/ui/traits/trait-object-lifetime-default-note.rs b/tests/ui/traits/trait-object-lifetime-default-note.rs
index 31e3eb4ba41..275411ff61c 100644
--- a/tests/ui/traits/trait-object-lifetime-default-note.rs
+++ b/tests/ui/traits/trait-object-lifetime-default-note.rs
@@ -8,7 +8,7 @@ fn main() {
     //~| NOTE borrowed value does not live long enough
     //~| NOTE due to object lifetime defaults, `Box<dyn A>` actually means `Box<(dyn A + 'static)>`
     require_box(Box::new(r));
-    //~^ NOTE cast requires that `local` is borrowed for `'static`
+    //~^ NOTE coercion requires that `local` is borrowed for `'static`
 
     let _ = 0;
 } //~ NOTE `local` dropped here while still borrowed
diff --git a/tests/ui/traits/trait-object-lifetime-default-note.stderr b/tests/ui/traits/trait-object-lifetime-default-note.stderr
index 4244e34873a..8cb9bc0d800 100644
--- a/tests/ui/traits/trait-object-lifetime-default-note.stderr
+++ b/tests/ui/traits/trait-object-lifetime-default-note.stderr
@@ -7,7 +7,7 @@ LL |     let r = &local;
    |             ^^^^^^ borrowed value does not live long enough
 ...
 LL |     require_box(Box::new(r));
-   |                 ----------- cast requires that `local` is borrowed for `'static`
+   |                 ----------- coercion requires that `local` is borrowed for `'static`
 ...
 LL | }
    | - `local` dropped here while still borrowed