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
```

3 files changed, 14 insertions, 6 deletions

diff --git a/compiler/rustc_mir_build/messages.ftl b/compiler/rustc_mir_build/messages.ftl
index 28011833e58..1e6b32bf605 100644
--- a/compiler/rustc_mir_build/messages.ftl
+++ b/compiler/rustc_mir_build/messages.ftl
@@ -152,7 +152,8 @@ 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
diff --git a/compiler/rustc_mir_build/src/errors.rs b/compiler/rustc_mir_build/src/errors.rs
index 1c4de5c07a1..2741830c62d 100644
--- a/compiler/rustc_mir_build/src/errors.rs
+++ b/compiler/rustc_mir_build/src/errors.rs
@@ -903,8 +903,10 @@ 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)]
diff --git a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
index b625c655fac..71cef18e316 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
@@ -171,10 +171,11 @@ 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);
             }
@@ -373,7 +374,11 @@ 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));
             }
         };