Fixed short span (duplicate match arms) in match_same_arms lint

clippy_lints/src/matches/match_same_arms.rs

@@ -117,10 +117,14 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, arms: &'tcx [Arm<'_>]) {
             continue;
         }
 
+        // Skip the first (original) arm and only highlight duplicates.
+        // This avoids pointing at the non-redundant arm and keeps the lint clear.
+        let spans = group.iter().skip(1).map(|(_, arm)| arm.span).collect_vec();
+
         span_lint_and_then(
             cx,
             MATCH_SAME_ARMS,
-            group.iter().map(|(_, arm)| arm.span).collect_vec(),
+            spans,
             "these match arms have identical bodies",
             |diag| {
                 diag.help("if this is unintentional make the arms return different values");

tests/ui/span_in_match_same_arm.fixed

@@ -0,0 +1,12 @@
+#![warn(clippy::match_same_arms)]
+
+fn multiple_duplicate_groups() {
+    let y = 5;
+
+    match y {
+        //~ ERROR: these match arms have identical bodies
+        3 => println!("different"),
+        1 | 2 | 4 | 5 => println!("same"),
+        _ => println!("other"),
+    }
+}

tests/ui/span_in_match_same_arm.rs

@@ -0,0 +1,14 @@
+#![warn(clippy::match_same_arms)]
+
+fn multiple_duplicate_groups() {
+    let y = 5;
+
+    match y {
+        1 => println!("same"),
+        2 => println!("same"), //~ ERROR: these match arms have identical bodies
+        3 => println!("different"),
+        4 => println!("same"),
+        5 => println!("same"),
+        _ => println!("other"),
+    }
+}

tests/ui/span_in_match_same_arm.stderr

@@ -0,0 +1,23 @@
+error: these match arms have identical bodies
+  --> tests/ui/span_in_match_same_arm.rs:8:9
+   |
+LL |         2 => println!("same"),
+   |         ^^^^^^^^^^^^^^^^^^^^^
+LL |         3 => println!("different"),
+LL |         4 => println!("same"),
+   |         ^^^^^^^^^^^^^^^^^^^^^
+LL |         5 => println!("same"),
+   |         ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: if this is unintentional make the arms return different values
+   = note: `-D clippy::match-same-arms` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::match_same_arms)]`
+help: otherwise merge the patterns into a single arm
+   |
+LL ~
+LL |         3 => println!("different"),
+LL ~         1 | 2 | 4 | 5 => println!("same"),
+   |
+
+error: aborting due to 1 previous error
+