Java: fix "Duplicate branches in 'switch'" inspection false positive on method reference (IDEA-355483)

GitOrigin-RevId: 0d5e06632a349494f05b79dab40d37988fdd7412

java/java-impl-inspections/src/com/intellij/codeInspection/DuplicateBranchesInSwitchInspection.java

@@ -779,16 +779,11 @@ public final class DuplicateBranchesInSwitchInspection extends LocalInspectionTo
       }
       int hash = 0;
       if (depth > 0) {
-        int count = 0;
         for (PsiElement child = element.getFirstChild(); child != null; child = child.getNextSibling()) {
           if (child instanceof PsiWhiteSpace || child instanceof PsiComment || child instanceof PsiJavaToken) {
             continue;
           }
           hash = hash * 31 + hashElement(child, depth - 1);
-          count++;
-        }
-        if (count != 0) {
-          hash = hash * 31 + count;
         }
       }
       IElementType type = PsiUtilCore.getElementType(element);
@@ -806,6 +801,9 @@ public final class DuplicateBranchesInSwitchInspection extends LocalInspectionTo
         return hashExpression(parenthesizedExpression.getExpression());
       }
       short index = expression.getNode().getElementType().getIndex();
+      if (expression instanceof PsiMethodReferenceExpression methodReferenceExpression) {
+        return hashReference(methodReferenceExpression, index) * 31 + hashElement(methodReferenceExpression.getQualifier(), 1);
+      }
       if (expression instanceof PsiReferenceExpression referenceExpression) {
         return hashReference(referenceExpression, index);
       }

java/java-tests/testData/inspection/duplicateBranchesInSwitch/MethodReferences.java

@@ -0,0 +1,50 @@
+package com.example;
+
+class Foo {
+
+  public static void main(String[] args) {
+    new Foo(Mode.A).run();
+    new Foo(Mode.B).run();
+  }
+
+  public interface Supplier<T> {
+      T get();
+  }
+  private final Supplier<MyInterface> supplier;
+
+  public Foo(Mode mode) {
+    supplier = switch (mode) {
+      case A -> A::new;
+      case B -> B::new; // incorrect warning happening here
+    };
+  }
+
+  public void run() {
+    supplier.get().doSomething();
+  }
+
+  public enum Mode {
+    A,
+    B
+  }
+
+  private interface MyInterface {
+    void doSomething();
+  }
+
+  private static class A implements MyInterface {
+
+    @Override
+    public void doSomething() {
+      System.out.println("A");
+    }
+  }
+
+  private static class B implements MyInterface {
+
+    @Override
+    public void doSomething() {
+      System.out.println("B");
+    }
+  }
+}

java/java-tests/testSrc/com/intellij/java/codeInspection/DuplicateBranchesInSwitchSuite.java

@@ -1,4 +1,4 @@
-// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package com.intellij.java.codeInspection;
 
 import org.junit.runner.RunWith;
@@ -12,7 +12,8 @@ import org.junit.runners.Suite;
   DuplicateBranchesInEnhancedSwitchFixTest.class,
   DuplicateBranchesInEnhancedSwitchTest.class,
   DuplicateBranchesInSwitchFixTest.class,
-  DuplicateBranchesInSwitchTest.class
+  DuplicateBranchesInSwitchTest.class,
+  DuplicateBranchesInEnhancedSwitchFix21PreviewTest.class,
 })
 public class DuplicateBranchesInSwitchSuite {
 }

java/java-tests/testSrc/com/intellij/java/codeInspection/DuplicateBranchesInSwitchTest.kt

@@ -1,4 +1,4 @@
-// Copyright 2000-2023 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package com.intellij.java.codeInspection
 
 import com.intellij.JavaTestUtil
@@ -40,6 +40,7 @@ class DuplicateBranchesInSwitchTest : LightJavaCodeInsightFixtureTestCase() {
   fun testManySimilarBranches() = doTest()
   fun testParentheses() = doTest()
   fun testAssignment() = doTest()
+  fun testMethodReferences() = doTest()
   fun testNoExceptionWhenFirstLabelIsMissing() = doTest()
   fun testUnresolvedQualifier() = doTest()
   fun testCatchTypeReference() = doTest()