Specify type kind of constant that can't be used in patterns

```
error: trait object `dyn Send` cannot be used in patterns
  --> $DIR/issue-70972-dyn-trait.rs:6:9
   |
LL | const F: &'static dyn Send = &7u32;
   | -------------------------- constant defined here
...
LL |         F => panic!(),
   |         ^ trait object can't be used in patterns
```

Author: estebank

compiler/rustc_mir_build/messages.ftl

@@ -142,7 +142,8 @@ mir_build_inline_assembly_requires_unsafe_unsafe_op_in_unsafe_fn_allowed =
 
 mir_build_interpreted_as_const = introduce a variable instead
 
-mir_build_invalid_pattern = `{$non_sm_ty}` cannot be used in patterns
+mir_build_invalid_pattern = {$prefix} `{$non_sm_ty}` cannot be used in patterns
+    .label = {$prefix} can't be used in patterns
 
 mir_build_irrefutable_let_patterns_if_let = irrefutable `if let` {$count ->
         [one] pattern

compiler/rustc_mir_build/src/errors.rs

@@ -814,8 +814,10 @@ pub(crate) struct TypeNotPartialEq<'tcx> {
 #[diag(mir_build_invalid_pattern)]
 pub(crate) struct InvalidPattern<'tcx> {
     #[primary_span]
+    #[label]
     pub(crate) span: Span,
     pub(crate) non_sm_ty: Ty<'tcx>,
+    pub(crate) prefix: String,
 }
 
 #[derive(Diagnostic)]

compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs

@@ -191,10 +191,11 @@ impl<'tcx> ConstToPat<'tcx> {
                     ty::FnPtr(..) | ty::RawPtr(..) => {
                         self.tcx().dcx().create_err(PointerPattern { span: self.span })
                     }
-                    _ => self
-                        .tcx()
-                        .dcx()
-                        .create_err(InvalidPattern { span: self.span, non_sm_ty: bad_ty }),
+                    _ => self.tcx().dcx().create_err(InvalidPattern {
+                        span: self.span,
+                        non_sm_ty: bad_ty,
+                        prefix: bad_ty.prefix_string(self.tcx()).to_string(),
+                    }),
                 };
                 return self.mk_err(e, ty);
             }
@@ -399,7 +400,11 @@ impl<'tcx> ConstToPat<'tcx> {
                 )
             }
             _ => {
-                let err = InvalidPattern { span, non_sm_ty: ty };
+                let err = InvalidPattern {
+                    span,
+                    non_sm_ty: ty,
+                    prefix: ty.prefix_string(self.tcx()).to_string(),
+                };
                 return Err(tcx.dcx().create_err(err));
             }
         };

tests/ui/inline-const/pat-match-fndef.stderr

@@ -1,8 +1,8 @@
-error: `fn() {uwu}` cannot be used in patterns
+error: fn item `fn() {uwu}` cannot be used in patterns
   --> $DIR/pat-match-fndef.rs:8:9
    |
 LL |         const { uwu } => {}
-   |         ^^^^^^^^^^^^^
+   |         ^^^^^^^^^^^^^ fn item can't be used in patterns
 
 error: aborting due to 1 previous error
 

tests/ui/match/issue-70972-dyn-trait.stderr

@@ -1,11 +1,11 @@
-error: `dyn Send` cannot be used in patterns
+error: trait object `dyn Send` cannot be used in patterns
   --> $DIR/issue-70972-dyn-trait.rs:6:9
    |
 LL | const F: &'static dyn Send = &7u32;
    | -------------------------- constant defined here
 ...
 LL |         F => panic!(),
-   |         ^
+   |         ^ trait object can't be used in patterns
 
 error: aborting due to 1 previous error
 

tests/ui/pattern/issue-72565.stderr

@@ -1,11 +1,11 @@
-error: `dyn PartialEq<u32>` cannot be used in patterns
+error: trait object `dyn PartialEq<u32>` cannot be used in patterns
   --> $DIR/issue-72565.rs:6:9
    |
 LL | const F: &'static dyn PartialEq<u32> = &7u32;
    | ------------------------------------ constant defined here
 ...
 LL |         F => panic!(),
-   |         ^
+   |         ^ trait object can't be used in patterns
 
 error: aborting due to 1 previous error
 

tests/ui/pattern/non-structural-match-types.stderr

@@ -1,14 +1,14 @@
-error: `{closure@$DIR/non-structural-match-types.rs:9:17: 9:19}` cannot be used in patterns
+error: closure `{closure@$DIR/non-structural-match-types.rs:9:17: 9:19}` cannot be used in patterns
   --> $DIR/non-structural-match-types.rs:9:9
    |
 LL |         const { || {} } => {}
-   |         ^^^^^^^^^^^^^^^
+   |         ^^^^^^^^^^^^^^^ closure can't be used in patterns
 
-error: `{async block@$DIR/non-structural-match-types.rs:12:17: 12:22}` cannot be used in patterns
+error: `async` block `{async block@$DIR/non-structural-match-types.rs:12:17: 12:22}` cannot be used in patterns
   --> $DIR/non-structural-match-types.rs:12:9
    |
 LL |         const { async {} } => {}
-   |         ^^^^^^^^^^^^^^^^^^
+   |         ^^^^^^^^^^^^^^^^^^ `async` block can't be used in patterns
 
 error: aborting due to 2 previous errors
 

tests/ui/type-alias-impl-trait/structural-match-no-leak.stderr

@@ -1,11 +1,11 @@
-error: `Bar` cannot be used in patterns
+error: opaque type `Bar` cannot be used in patterns
   --> $DIR/structural-match-no-leak.rs:16:9
    |
 LL | const LEAK_FREE: bar::Bar = bar::leak_free();
    | ------------------------- constant defined here
 ...
 LL |         LEAK_FREE => (),
-   |         ^^^^^^^^^
+   |         ^^^^^^^^^ opaque type can't be used in patterns
 
 error: aborting due to 1 previous error
 

tests/ui/type-alias-impl-trait/structural-match.stderr

@@ -1,11 +1,11 @@
-error: `foo::Foo` cannot be used in patterns
+error: opaque type `foo::Foo` cannot be used in patterns
   --> $DIR/structural-match.rs:18:9
    |
 LL | const VALUE: Foo = value();
    | ---------------- constant defined here
 ...
 LL |         VALUE => (),
-   |         ^^^^^
+   |         ^^^^^ opaque type can't be used in patterns
 
 error: aborting due to 1 previous error