Fix dead code removal when multiple cases share a body.

Fixes #56485.

Bug: #56485
Change-Id: Idea150d9b00bdf90ecff184da14ecbdbe5902a30
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/380901
Commit-Queue: Paul Berry <[email protected]>
Reviewed-by: Samuel Rawlins <[email protected]>

Author: stereotype441

pkg/analysis_server/lib/src/services/correction/dart/remove_dead_code.dart

@@ -102,9 +102,19 @@ class RemoveDeadCode extends ResolvedCorrectionProducer {
       if (forStatement is! ForStatement) return;
 
       await _computeForStatementParts(builder, forStatement, coveringNode);
-    } else if (coveringNode is SwitchPatternCase) {
+    } else if (coveringNode is SwitchMember) {
+      var parent = coveringNode.parent as SwitchStatement;
+      var memberIndex = parent.members.indexOf(coveringNode);
+      Token? overrideEnd;
+      if (memberIndex > 0 &&
+          parent.members[memberIndex - 1].statements.isEmpty) {
+        // Previous member "falls through" to the one being removed, so don't
+        // remove the statements.
+        overrideEnd = coveringNode.colon;
+      }
       await builder.addDartFileEdit(file, (builder) {
-        builder.addDeletion(range.deletionRange(coveringNode));
+        builder.addDeletion(
+            range.deletionRange(coveringNode, overrideEnd: overrideEnd));
       });
     }
   }

pkg/analysis_server/test/src/services/correction/fix/remove_dead_code_test.dart

@@ -493,6 +493,30 @@ void f() {
 ''');
   }
 
+  Future<void> test_switchCase_sharedStatements_last() async {
+    await resolveTestCode('''
+void f() {
+  var m = 5;
+  switch(m) {
+    case 5:
+    case 3:
+    case 5:
+      break;
+  }
+}
+''');
+    await assertHasFix('''
+void f() {
+  var m = 5;
+  switch(m) {
+    case 5:
+    case 3:
+    break;
+  }
+}
+''');
+  }
+
   Future<void> test_switchCase_uniqueStatements() async {
     await resolveTestCode('''
 void f() {

pkg/analyzer_plugin/lib/utilities/range_factory.dart

@@ -63,11 +63,15 @@ class RangeFactory {
 
   /// Return the deletion range of the [node], considering the spaces and
   /// comments before and after it.
-  SourceRange deletionRange(AstNode node) {
+  ///
+  /// If a non-`null` [overrideEnd] is supplied, it will be used in place of
+  /// [AstNode.endToken] to determine the range of tokens to delete.
+  SourceRange deletionRange(AstNode node, {Token? overrideEnd}) {
     var begin = node.beginToken;
     begin = begin.precedingComments ?? begin;
 
-    var end = node.endToken.next!;
+    var initialEndToken = overrideEnd ?? node.endToken;
+    var end = initialEndToken.next!;
     end = end.precedingComments ?? end;
 
     int startOffset;
@@ -84,7 +88,7 @@ class RangeFactory {
       } else {
         startOffset = begin.previous!.end;
       }
-      endOffset = node.endToken.end;
+      endOffset = initialEndToken.end;
     } else {
       startOffset = begin.offset;
       endOffset = end.offset;