Java: disallow introduce variable in interface field initializers (IDEA-369318)

GitOrigin-RevId: 9581036bab179eb78d908aff92da0517ccaaa328

java/java-impl-refactorings/src/com/intellij/refactoring/introduceVariable/IntroduceVariableBase.java

@@ -1,4 +1,4 @@
-// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+// Copyright 2000-2025 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package com.intellij.refactoring.introduceVariable;
 
 import com.intellij.codeInsight.CodeInsightUtil;
@@ -55,6 +55,7 @@ import com.intellij.util.IncorrectOperationException;
 import com.intellij.util.Processor;
 import com.intellij.util.containers.ContainerUtil;
 import com.intellij.util.containers.MultiMap;
+import com.siyeh.ig.psiutils.ExpressionUtils;
 import com.siyeh.ig.psiutils.VariableAccessUtils;
 import one.util.streamex.EntryStream;
 import one.util.streamex.StreamEx;
@@ -293,6 +294,15 @@ public abstract class IntroduceVariableBase extends IntroduceHandlerBase {
         showErrorMessage(project, editor, RefactoringBundle.getCannotRefactorMessage(errorMessage));
         return false;
       }
+      PsiExpression topLevelExpression = ExpressionUtils.getTopLevelExpression(expr);
+      if (topLevelExpression.getParent() instanceof PsiField f) {
+        PsiClass containingClass = f.getContainingClass();
+        if (containingClass != null && containingClass.isInterface()) {
+          String message = JavaRefactoringBundle.message("introduce.variable.message.cannot.extract.variable.in.interface");
+          showErrorMessage(project, editor, RefactoringBundle.getCannotRefactorMessage(message));
+          return false;
+        }
+      }
     }
 
     if (expr != null && expr.getParent() instanceof PsiExpressionStatement) {

java/java-tests/testData/refactoring/introduceVariable/DisallowInInterface.java

@@ -0,0 +1,4 @@
+interface DisallowInInterface {
+
+  int i = <selection>10</selection>;
+}

java/java-tests/testSrc/com/intellij/java/refactoring/IntroduceVariableTest.java

@@ -393,6 +393,10 @@ public class IntroduceVariableTest extends LightJavaCodeInsightTestCase {
     doTestWithFailure("input", "Object", "The selected expression refers to pattern variable 's', which will be out of scope.");
   }
 
+  public void testDisallowInInterface() {
+    doTestWithFailure("", "", "Cannot extract variable in an interface.");
+  }
+
   public void testOneLineLambdaVoidCompatible() {UiInterceptors.register(new ChooserInterceptor(null, Pattern.quote("Runnable: () -> {...}"))); doTest("c", false, false, false, JAVA_LANG_STRING); }
   public void testOneLineLambdaValueCompatible() { doTest("c", false, false, false, "int"); }
   public void testStatementsBeforeSuper() {

java/openapi/resources/messages/JavaRefactoringBundle.properties

@@ -821,6 +821,7 @@ progress.title.collect.hierarchy=Collect ''{0}'' hierarchy
 introduce.variable.message.change.semantics.warning=Extracting the selected expression changes the semantics of the surrounding expression.
 introduce.variable.message.expression.refers.to.pattern.variable.declared.outside=The selected expression refers to pattern variable ''{0}'', which will be out of scope.
 introduce.variable.message.cannot.extract.in.implicit.class=Cannot extract in implicitly declared class.
+introduce.variable.message.cannot.extract.variable.in.interface=Cannot extract variable in an interface.
 tooltip.cannot.inline.pattern.variable=Cannot inline pattern variable
 inline.popup.highlight=Highlight {0} conflicting {0, choice, 1#write|2#writes}
 inline.popup.ignore.conflicts=Ignore writes and continue