fix: match_ref_pats FP on unimplement!() in match scrutinee

Author: profetia

clippy_lints/src/matches/match_ref_pats.rs

@@ -1,6 +1,7 @@
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::source::{snippet, walk_span_to_context};
 use clippy_utils::sugg::Sugg;
+use clippy_utils::usage::is_todo_unimplemented_stub;
 use core::iter::once;
 use rustc_errors::Applicability;
 use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability, Pat, PatKind};
@@ -17,6 +18,11 @@ where
         return;
     }
 
+    // `todo!()` and `unimplemented!()` stub cannot deref
+    if is_todo_unimplemented_stub(cx, scrutinee) {
+        return;
+    }
+
     let (first_sugg, msg, title);
     let ctxt = expr.span.ctxt();
     let mut app = Applicability::Unspecified;

tests/ui/match_ref_pats.fixed

@@ -120,4 +120,16 @@ mod issue_7740 {
     }
 }
 
+mod issue15378 {
+    fn unimplemented_in_match() {
+        match unimplemented!() {
+            &_ => {},
+            &&&42 => {
+                todo!()
+            },
+            _ => {},
+        }
+    }
+}
+
 fn main() {}

tests/ui/match_ref_pats.rs

@@ -120,4 +120,16 @@ mod issue_7740 {
     }
 }
 
+mod issue15378 {
+    fn unimplemented_in_match() {
+        match unimplemented!() {
+            &_ => {},
+            &&&42 => {
+                todo!()
+            },
+            _ => {},
+        }
+    }
+}
+
 fn main() {}