Improve the pretty print of UnstableFeature clause

Author: tiif

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -3177,8 +3177,9 @@ define_print! {
                 write!(p, "` can be evaluated")?;
             }
             ty::ClauseKind::UnstableFeature(symbol) => {
-                write!(p, "unstable feature: ")?;
+                write!(p, "unstable feature ")?;
                 write!(p, "`{symbol}`")?;
+                write!(p, " is enabled")?;
             }
         }
     }

tests/ui/const-generics/adt_const_params/unsized_field-1.stderr

@@ -7,7 +7,7 @@ LL |
 LL | struct A([u8]);
    |          ---- this field does not implement `ConstParamTy_`
    |
-note: the `ConstParamTy_` impl for `[u8]` requires that `unstable feature: `unsized_const_params``
+note: the `ConstParamTy_` impl for `[u8]` requires that `unstable feature `unsized_const_params` is enabled`
   --> $DIR/unsized_field-1.rs:10:10
    |
 LL | struct A([u8]);
@@ -22,7 +22,7 @@ LL |
 LL | struct B(&'static [u8]);
    |          ------------- this field does not implement `ConstParamTy_`
    |
-note: the `ConstParamTy_` impl for `&'static [u8]` requires that `unstable feature: `unsized_const_params``
+note: the `ConstParamTy_` impl for `&'static [u8]` requires that `unstable feature `unsized_const_params` is enabled`
   --> $DIR/unsized_field-1.rs:14:10
    |
 LL | struct B(&'static [u8]);
@@ -37,7 +37,7 @@ LL |
 LL | struct D(unsized_const_param::GenericNotUnsizedParam<&'static [u8]>);
    |          ---------------------------------------------------------- this field does not implement `ConstParamTy_`
    |
-note: the `ConstParamTy_` impl for `GenericNotUnsizedParam<&'static [u8]>` requires that `unstable feature: `unsized_const_params``
+note: the `ConstParamTy_` impl for `GenericNotUnsizedParam<&'static [u8]>` requires that `unstable feature `unsized_const_params` is enabled`
   --> $DIR/unsized_field-1.rs:21:10
    |
 LL | struct D(unsized_const_param::GenericNotUnsizedParam<&'static [u8]>);

tests/ui/unstable-feature-bound/unstable_impl_coherence.disabled.stderr

@@ -6,7 +6,7 @@ LL | impl aux::Trait for LocalTy {}
    |
    = note: conflicting implementation in crate `unstable_impl_coherence_aux`:
            - impl<T> Trait for T
-             where unstable feature: `foo`;
+             where unstable feature `foo` is enabled;
 
 error: aborting due to 1 previous error
 

tests/ui/unstable-feature-bound/unstable_impl_coherence.enabled.stderr

@@ -6,7 +6,7 @@ LL | impl aux::Trait for LocalTy {}
    |
    = note: conflicting implementation in crate `unstable_impl_coherence_aux`:
            - impl<T> Trait for T
-             where unstable feature: `foo`;
+             where unstable feature `foo` is enabled;
 
 error: aborting due to 1 previous error
 

tests/ui/unstable-feature-bound/unstable_impl_method_selection.stderr

@@ -7,7 +7,7 @@ LL |     vec![].foo();
    = note: multiple `impl`s satisfying `Vec<_>: Trait` found in the `unstable_impl_method_selection_aux` crate:
            - impl Trait for Vec<u32>;
            - impl Trait for Vec<u64>
-             where unstable feature: `bar`;
+             where unstable feature `bar` is enabled;
 
 error: aborting due to 1 previous error