When finding a match expr with multiple arms that requires more, suggest it

Given

```rust
match Some(42) {
    Some(0) => {}
    Some(1) => {}
}
```

suggest

```rust
match Some(42) {
    Some(0) => {}
    Some(1) => {}
    None | Some(_) => todo!(),
}
```

1 files changed, 15 insertions, 0 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 f1c2ec08c3c..a0325101c41 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -604,6 +604,21 @@ fn non_exhaustive_match<'p, 'tcx>(
                 format!("{}{}{} => todo!()", comma, pre_indentation, pattern),
             ));
         }
+        [.., prev, last] if prev.span.ctxt() == last.span.ctxt() => {
+            if let Ok(snippet) = sm.span_to_snippet(prev.span.between(last.span)) {
+                let comma =
+                    if matches!(last.body.kind, hir::ExprKind::Block(..)) { "" } else { "," };
+                suggestion = Some((
+                    last.span.shrink_to_hi(),
+                    format!(
+                        "{}{}{} => todo!()",
+                        comma,
+                        snippet.strip_prefix(",").unwrap_or(&snippet),
+                        pattern
+                    ),
+                ));
+            }
+        }
         _ => {}
     }