Refactor dyn-compatibility error and suggestions

This CL makes a number of small changes to dyn compatibility errors:
- "object safety" has been renamed to "dyn-compatibility" throughout
- "Convert to enum" suggestions are no longer generated when there
  exists a type-generic impl of the trait or an impl for `dyn OtherTrait`
- Several error messages are reorganized for user readability

Additionally, the dyn compatibility error creation code has been
split out into functions.

cc #132713
cc #133267

4 files changed, 13 insertions, 11 deletions

diff --git a/tests/rustdoc-ui/invalid_const_in_lifetime_position.rs b/tests/rustdoc-ui/invalid_const_in_lifetime_position.rs
index 07fc239a8f8..427c84679ba 100644
--- a/tests/rustdoc-ui/invalid_const_in_lifetime_position.rs
+++ b/tests/rustdoc-ui/invalid_const_in_lifetime_position.rs
@@ -8,4 +8,4 @@ fn f<'a>(arg : Box<dyn X<Y<1> = &'a ()>>) {}
 //~| ERROR associated type takes 0 generic arguments but 1 generic argument
 //~| ERROR associated type takes 1 lifetime argument but 0 lifetime arguments
 //~| ERROR associated type takes 0 generic arguments but 1 generic argument
-//~| ERROR trait `X` cannot be made into an object
+//~| ERROR trait `X` is not dyn compatible
diff --git a/tests/rustdoc-ui/invalid_const_in_lifetime_position.stderr b/tests/rustdoc-ui/invalid_const_in_lifetime_position.stderr
index 0c3826c5665..180ba63927b 100644
--- a/tests/rustdoc-ui/invalid_const_in_lifetime_position.stderr
+++ b/tests/rustdoc-ui/invalid_const_in_lifetime_position.stderr
@@ -92,17 +92,18 @@ LL |     type Y<'a>;
    |          ^
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error[E0038]: the trait `X` cannot be made into an object
+error[E0038]: the trait `X` is not dyn compatible
   --> $DIR/invalid_const_in_lifetime_position.rs:4:20
    |
 LL | fn f<'a>(arg : Box<dyn X<Y<1> = &'a ()>>) {}
-   |                    ^^^^^^^^^^^^^^^^^^^^ `X` cannot be made into an object
+   |                    ^^^^^^^^^^^^^^^^^^^^ `X` is not dyn compatible
    |
-note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+note: for a trait to be dyn compatible it needs to allow building a vtable
+      for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/invalid_const_in_lifetime_position.rs:2:10
    |
 LL | trait X {
-   |       - this trait cannot be made into an object...
+   |       - this trait is not dyn compatible...
 LL |     type Y<'a>;
    |          ^ ...because it contains the generic associated type `Y`
    = help: consider moving `Y` to another trait
diff --git a/tests/rustdoc-ui/issues/ice-generic-type-alias-105742.rs b/tests/rustdoc-ui/issues/ice-generic-type-alias-105742.rs
index 027574923c7..89b55beaea1 100644
--- a/tests/rustdoc-ui/issues/ice-generic-type-alias-105742.rs
+++ b/tests/rustdoc-ui/issues/ice-generic-type-alias-105742.rs
@@ -5,8 +5,8 @@ use std::ops::Index;
 pub fn next<'a, T>(s: &'a mut dyn SVec<Item = T, Output = T>) {
     //~^ expected 1 lifetime argument
     //~| expected 1 generic argument
-    //~| the trait `SVec` cannot be made into an object
-    //~| `SVec` cannot be made into an object
+    //~| the trait `SVec` is not dyn compatible
+    //~| `SVec` is not dyn compatible
     //~| missing generics for associated type `SVec::Item`
     //~| missing generics for associated type `SVec::Item`
     let _ = s;
diff --git a/tests/rustdoc-ui/issues/ice-generic-type-alias-105742.stderr b/tests/rustdoc-ui/issues/ice-generic-type-alias-105742.stderr
index 97bd44244f3..72d1a52f710 100644
--- a/tests/rustdoc-ui/issues/ice-generic-type-alias-105742.stderr
+++ b/tests/rustdoc-ui/issues/ice-generic-type-alias-105742.stderr
@@ -294,19 +294,20 @@ help: add missing generic argument
 LL |     Output = <Self as SVec>::Item> as SVec>::Item<T>,
    |                                                  +++
 
-error[E0038]: the trait `SVec` cannot be made into an object
+error[E0038]: the trait `SVec` is not dyn compatible
   --> $DIR/ice-generic-type-alias-105742.rs:5:35
    |
 LL | pub fn next<'a, T>(s: &'a mut dyn SVec<Item = T, Output = T>) {
-   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^ `SVec` cannot be made into an object
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^ `SVec` is not dyn compatible
    |
-note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+note: for a trait to be dyn compatible it needs to allow building a vtable
+      for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/ice-generic-type-alias-105742.rs:15:17
    |
 LL |    pub trait SVec: Index<
    |  ____________----__^
    | |            |
-   | |            this trait cannot be made into an object...
+   | |            this trait is not dyn compatible...
 LL | |      <Self as SVec>::Item,
 ...  |
 LL | |/     Output = <Index<<Self as SVec>::Item,