Reword E0277 default error message

```
error[E0277]: the trait `Copy` is not implemented for `X`
  --> $DIR/trait-impl-bound-suggestions.rs:14:52
   |
LL |     fn return_the_constrained_type(&self, x: X) -> ConstrainedStruct<X> {
   |                                                    ^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `X`
```

Author: estebank

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

@@ -4774,20 +4774,28 @@ pub(super) fn get_explanation_based_on_obligation<'tcx>(
         } else {
             String::new()
         };
-        match ty_desc {
-            Some(desc) => format!(
-                "{}the trait `{}` is not implemented for {} `{}`{post}",
-                pre_message,
-                trait_predicate.print_modifiers_and_trait_path(),
-                desc,
-                tcx.short_ty_string(trait_ref.skip_binder().self_ty(), &mut None),
-            ),
-            None => format!(
-                "{}the trait `{}` is not implemented for `{}`{post}",
-                pre_message,
-                trait_predicate.print_modifiers_and_trait_path(),
-                tcx.short_ty_string(trait_ref.skip_binder().self_ty(), &mut None),
-            ),
+        let desc = match ty_desc {
+            Some(desc) => format!(" {desc}"),
+            None => String::new(),
+        };
+
+        let pred = tcx.erase_regions(if tcx.features().non_lifetime_binders {
+            // We can't erase the lifetime bounds on their own when this feature is enabled.
+            // `instantiate_bound_regions_with_erased` expects there to be no type bounds.
+            trait_predicate.skip_binder()
+        } else {
+            tcx.instantiate_bound_regions_with_erased(*trait_predicate)
+        });
+        if let ty::ImplPolarity::Positive = pred.polarity {
+            format!(
+                "{pre_message}the trait `{}` is not implemented for{desc} `{}`{post}",
+                pred.print_modifiers_and_trait_path(),
+                tcx.short_ty_string(pred.self_ty(), &mut None),
+            )
+        } else {
+            // "the trait bound `!Send: T` is not satisfied" reads better than "`!Send` is
+            // not implemented for `T`".
+            format!("{pre_message}the trait bound `{pred}` is not satisfied{post}")
         }
     }
 }

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

@@ -2950,7 +2950,24 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 }
             })
             .unwrap_or_else(|| {
-                format!("the trait bound `{trait_predicate}` is not satisfied{post_message}")
+                let pred = self.tcx.erase_regions(if self.tcx.features().non_lifetime_binders {
+                    // We can't erase the lifetime bounds on their own when this feature is enabled.
+                    // `instantiate_bound_regions_with_erased` expects there to be no type bounds.
+                    trait_predicate.skip_binder()
+                } else {
+                    self.tcx.instantiate_bound_regions_with_erased(*trait_predicate)
+                });
+                if let ty::ImplPolarity::Positive = pred.polarity {
+                    format!(
+                        "the trait `{}` is not implemented for `{}`{post_message}",
+                        pred.print_modifiers_and_trait_path(),
+                        self.tcx.short_ty_string(pred.self_ty(), &mut None),
+                    )
+                } else {
+                    // "the trait bound `!Send: T` is not satisfied" reads better than "`!Send` is
+                    // not implemented for `T`".
+                    format!("the trait bound `{pred}` is not satisfied{post_message}")
+                }
             })
     }
 

tests/ui-fulldeps/session-diagnostic/diagnostic-derive-doc-comment-field.rs

@@ -34,7 +34,7 @@ struct Test {
     span: Span,
     /// A doc comment
     arg: NotIntoDiagnosticArg,
-    //~^ ERROR the trait bound `NotIntoDiagnosticArg: IntoDiagnosticArg` is not satisfied
+    //~^ ERROR trait `IntoDiagnosticArg` is not implemented for `NotIntoDiagnosticArg`
 }
 
 #[derive(Subdiagnostic)]
@@ -44,5 +44,5 @@ struct SubTest {
     span: Span,
     /// A doc comment
     arg: NotIntoDiagnosticArg,
-    //~^ ERROR the trait bound `NotIntoDiagnosticArg: IntoDiagnosticArg` is not satisfied
+    //~^ ERROR trait `IntoDiagnosticArg` is not implemented for `NotIntoDiagnosticArg`
 }

tests/ui-fulldeps/session-diagnostic/diagnostic-derive-doc-comment-field.stderr

@@ -1,4 +1,4 @@
-error[E0277]: the trait bound `NotIntoDiagnosticArg: IntoDiagnosticArg` is not satisfied
+error[E0277]: the trait `IntoDiagnosticArg` is not implemented for `NotIntoDiagnosticArg`
   --> $DIR/diagnostic-derive-doc-comment-field.rs:36:10
    |
 LL | #[derive(Diagnostic)]
@@ -12,7 +12,7 @@ note: required by a bound in `DiagnosticBuilder::<'a, G>::arg`
   --> $COMPILER_DIR/rustc_errors/src/diagnostic.rs:LL:CC
    = note: this error originates in the macro `with_fn` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `NotIntoDiagnosticArg: IntoDiagnosticArg` is not satisfied
+error[E0277]: the trait `IntoDiagnosticArg` is not implemented for `NotIntoDiagnosticArg`
   --> $DIR/diagnostic-derive-doc-comment-field.rs:46:10
    |
 LL | #[derive(Subdiagnostic)]

tests/ui-fulldeps/session-diagnostic/diagnostic-derive.rs

@@ -347,7 +347,7 @@ struct ArgFieldWithoutSkip {
     #[primary_span]
     span: Span,
     other: Hello,
-    //~^ ERROR the trait bound `Hello: IntoDiagnosticArg` is not satisfied
+    //~^ ERROR trait `IntoDiagnosticArg` is not implemented for `Hello`
 }
 
 #[derive(Diagnostic)]

tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr

@@ -618,7 +618,7 @@ LL | #[derive(Diagnostic)]
    |
    = note: this error originates in the derive macro `Diagnostic` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `Hello: IntoDiagnosticArg` is not satisfied
+error[E0277]: the trait `IntoDiagnosticArg` is not implemented for `Hello`
   --> $DIR/diagnostic-derive.rs:349:12
    |
 LL | #[derive(Diagnostic)]

tests/ui/allocator/not-an-allocator.stderr

@@ -1,4 +1,4 @@
-error[E0277]: the trait bound `usize: GlobalAlloc` is not satisfied
+error[E0277]: the trait `GlobalAlloc` is not implemented for `usize`
   --> $DIR/not-an-allocator.rs:2:11
    |
 LL | #[global_allocator]
@@ -9,7 +9,7 @@ LL | static A: usize = 0;
    = help: the trait `GlobalAlloc` is implemented for `System`
    = note: this error originates in the attribute macro `global_allocator` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `usize: GlobalAlloc` is not satisfied
+error[E0277]: the trait `GlobalAlloc` is not implemented for `usize`
   --> $DIR/not-an-allocator.rs:2:11
    |
 LL | #[global_allocator]
@@ -21,7 +21,7 @@ LL | static A: usize = 0;
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this error originates in the attribute macro `global_allocator` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `usize: GlobalAlloc` is not satisfied
+error[E0277]: the trait `GlobalAlloc` is not implemented for `usize`
   --> $DIR/not-an-allocator.rs:2:11
    |
 LL | #[global_allocator]
@@ -33,7 +33,7 @@ LL | static A: usize = 0;
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this error originates in the attribute macro `global_allocator` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `usize: GlobalAlloc` is not satisfied
+error[E0277]: the trait `GlobalAlloc` is not implemented for `usize`
   --> $DIR/not-an-allocator.rs:2:11
    |
 LL | #[global_allocator]

tests/ui/array-slice-vec/repeat_empty_ok.rs

@@ -6,10 +6,10 @@ pub struct Header<'a> {
 
 pub fn test() {
     let headers = [Header{value: &[]}; 128];
-    //~^ ERROR the trait bound
+    //~^ ERROR the trait
 }
 
 pub fn test2() {
     let headers = [Header{value: &[0]}; 128];
-    //~^ ERROR the trait bound
+    //~^ ERROR the trait
 }

tests/ui/array-slice-vec/repeat_empty_ok.stderr

@@ -1,4 +1,4 @@
-error[E0277]: the trait bound `Header<'_>: Copy` is not satisfied
+error[E0277]: the trait `Copy` is not implemented for `Header<'_>`
   --> $DIR/repeat_empty_ok.rs:8:20
    |
 LL |     let headers = [Header{value: &[]}; 128];
@@ -13,7 +13,7 @@ LL + #[derive(Copy)]
 LL | pub struct Header<'a> {
    |
 
-error[E0277]: the trait bound `Header<'_>: Copy` is not satisfied
+error[E0277]: the trait `Copy` is not implemented for `Header<'_>`
   --> $DIR/repeat_empty_ok.rs:13:20
    |
 LL |     let headers = [Header{value: &[0]}; 128];

tests/ui/associated-consts/associated-const-array-len.rs

@@ -3,7 +3,7 @@ trait Foo {
 }
 
 const X: [i32; <i32 as Foo>::ID] = [0, 1, 2];
-//~^ ERROR the trait bound `i32: Foo` is not satisfied
+//~^ ERROR trait `Foo` is not implemented for `i32`
 
 fn main() {
     assert_eq!(1, X);