Point at const when intended binding fall-through pattern is a const

```
error[E0004]: non-exhaustive patterns: `i32::MIN..=3_i32` and `5_i32..=i32::MAX` not covered
  --> $DIR/intended-binding-pattern-is-const.rs:2:11
   |
LL |     match 1 {
   |           ^ patterns `i32::MIN..=3_i32` and `5_i32..=i32::MAX` not covered
LL |         x => {}
   |         - this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `x`
   |
   = note: the matched value is of type `i32`
note: constant `x` defined here
  --> $DIR/intended-binding-pattern-is-const.rs:7:5
   |
LL |     const x: i32 = 4;
   |     ^^^^^^^^^^^^
help: if you meant to introduce a binding, use a different name
   |
LL |         x_var => {}
   |          ++++
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern, a match arm with multiple or-patterns as shown, or multiple match arms
   |
LL |         x => {}, i32::MIN..=3_i32 | 5_i32..=i32::MAX => todo!()
   |                ++++++++++++++++++++++++++++++++++++++++++++++++
```

1 files changed, 25 insertions, 4 deletions

diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
index a8830b346ae..edd51b521fa 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -1116,13 +1116,13 @@ fn report_non_exhaustive_match<'p, 'tcx>(
             if ty.is_ptr_sized_integral() {
                 if ty.inner() == cx.tcx.types.usize {
                     err.note(format!(
-                        "`{ty}` does not have a fixed maximum value, so half-open ranges are necessary to match \
-                             exhaustively",
+                        "`{ty}` does not have a fixed maximum value, so half-open ranges are \
+                         necessary to match exhaustively",
                     ));
                 } else if ty.inner() == cx.tcx.types.isize {
                     err.note(format!(
-                        "`{ty}` does not have fixed minimum and maximum values, so half-open ranges are necessary to match \
-                             exhaustively",
+                        "`{ty}` does not have fixed minimum and maximum values, so half-open \
+                         ranges are necessary to match exhaustively",
                     ));
                 }
             } else if ty.inner() == cx.tcx.types.str_ {
@@ -1143,6 +1143,27 @@ fn report_non_exhaustive_match<'p, 'tcx>(
         }
     }
 
+    for &arm in arms {
+        let arm = &thir.arms[arm];
+        if let PatKind::Constant { opt_def: Some(def_id), .. } = arm.pattern.kind {
+            let const_name = cx.tcx.item_name(def_id);
+            err.span_label(
+                arm.pattern.span,
+                format!(
+                    "this pattern doesn't introduce a new catch-all binding, but rather pattern \
+                     matches against the value of constant `{const_name}`",
+                ),
+            );
+            err.span_note(cx.tcx.def_span(def_id), format!("constant `{const_name}` defined here"));
+            err.span_suggestion_verbose(
+                arm.pattern.span.shrink_to_hi(),
+                "if you meant to introduce a binding, use a different name",
+                "_var".to_string(),
+                Applicability::MaybeIncorrect,
+            );
+        }
+    }
+
     // Whether we suggest the actual missing patterns or `_`.
     let suggest_the_witnesses = witnesses.len() < 4;
     let suggested_arm = if suggest_the_witnesses {