EnhancedSwitchMigrationInspection: suppress, when used value from another branch

java/java-impl/src/com/intellij/codeInspection/EnhancedSwitchMigrationInspection.java

@@ -442,6 +442,15 @@ public class EnhancedSwitchMigrationInspection extends AbstractBaseJavaLocalInsp
       for (SwitchBranch branch : branches) {
         if (branch.myIsFallthrough) return null;
       }
+      for (SwitchBranch branch : branches) {
+        boolean allBranchRefsWillBeValid = StreamEx.of(branch.myStatements)
+          .flatMap((PsiElement stmt) -> StreamEx.ofTree(stmt, el -> StreamEx.of(el.getChildren())))
+          .select(PsiReferenceExpression.class)
+          .map(PsiReference::resolve)
+          .select(PsiLocalVariable.class)
+          .allMatch(variable -> isInBranchOrOutside(switchStmt, branch, variable));
+        if (!allBranchRefsWillBeValid) return null;
+      }
       List<SwitchExpressionBranch> switchRules = new ArrayList<>();
       for (SwitchBranch branch : branches) {
         PsiStatement[] statements = branch.getStatements();
@@ -449,6 +458,12 @@ public class EnhancedSwitchMigrationInspection extends AbstractBaseJavaLocalInsp
       }
       return new SwitchStatementReplacer(switchStmt, expression, switchRules);
     }
+
+    private static boolean isInBranchOrOutside(@NotNull PsiSwitchStatement switchStmt,
+                                               SwitchBranch branch, PsiLocalVariable variable) {
+      return !PsiTreeUtil.isAncestor(switchStmt, variable, false)
+             || StreamEx.of(branch.myStatements).anyMatch(stmt -> PsiTreeUtil.isAncestor(stmt, variable, false));
+    }
   }
 
   private static class SwitchStatementBranch implements SwitchRuleResult {

java/java-tests/testData/inspection/switchExpressionMigration/beforeSwitchStatementsDuplicatingBranch.java

@@ -0,0 +1,17 @@
+// "Replace with enhanced 'switch' statement" "false"
+import java.util.*;
+
+class SwitchExpressionMigration {
+  private static String m(int n) {
+    switch<caret> (n) {
+      case 1:
+        int x = 0;
+        System.out.println("a");
+        break;
+      case 2:
+        x = 3;
+        System.out.println(x);
+        break;
+    }
+  }
+}