[java, fix] support creating static methods for inner classes IDEA-310703

GitOrigin-RevId: bcb0a09fd5d3e92957b4543880c5ef4640eb4d8f

java/java-impl/src/com/intellij/codeInsight/intention/impl/JavaElementActionsFactory.kt

@@ -135,10 +135,12 @@ class JavaElementActionsFactory : JvmElementActionsFactory() {
     val staticMethodRequested = JvmModifier.STATIC in requestedModifiers
 
     if (staticMethodRequested) {
-      // static method in interfaces are allowed starting with Java 8
+      // static methods in interfaces are allowed starting with Java 8
       if (javaClass.isInterface && !PsiUtil.isLanguageLevel8OrHigher(javaClass)) return emptyList()
-      // static methods in inner classes are disallowed: see JLS 8.1.3
-      if (javaClass.containingClass != null && !javaClass.hasModifierProperty(PsiModifier.STATIC)) return emptyList()
+      // static methods in inner classes are disallowed before Java 16: see JLS 8.1.3
+      if (javaClass.containingClass != null &&
+          !javaClass.hasModifierProperty(PsiModifier.STATIC) &&
+          !PsiUtil.isLanguageLevel16OrHigher(javaClass)) return emptyList()
     }
 
     val result = ArrayList<IntentionAction>()

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/createMethodFromUsage/afterCreatePropertyInNonStaticInnerClass.java

@@ -0,0 +1,19 @@
+// "Create property 'next' in 'InnerClass in MainClass'" "true-preview"
+public class MainClass {
+  void foo() {
+    int counter = InnerClass.getNext();
+  }
+
+  private class InnerClass {
+
+      private static int next;
+
+      public static int getNext() {
+          return next;
+      }
+
+      public static void setNext(int next) {
+          InnerClass.next = next;
+      }
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/createMethodFromUsage/afterCreateReadOnlyPropertyInNonStaticInnerClass.java

@@ -0,0 +1,15 @@
+// "Create read-only property 'next' in 'InnerClass in MainClass'" "true-preview"
+public class MainClass {
+  void foo() {
+    int counter = InnerClass.getNext();
+  }
+
+  private class InnerClass {
+
+      private static int next;
+
+      public static int getNext() {
+          return next;
+      }
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/createMethodFromUsage/afterCreateStaticMethodInNonStaticInnerClass.java

@@ -0,0 +1,13 @@
+// "Create method 'getNext' in 'InnerClass in MainClass'" "true-preview"
+public class MainClass {
+  void foo() {
+    int counter = InnerClass.getNext();
+  }
+
+  private class InnerClass {
+
+      public static int getNext() {
+          return 0;
+      }
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/createMethodFromUsage/beforeCreatePropertyInNonStaticInnerClass.java

@@ -0,0 +1,10 @@
+// "Create property 'next' in 'InnerClass in MainClass'" "true-preview"
+public class MainClass {
+  void foo() {
+    int counter = InnerClass.<caret>getNext();
+  }
+
+  private class InnerClass {
+
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/createMethodFromUsage/beforeCreateReadOnlyPropertyInNonStaticInnerClass.java

@@ -0,0 +1,10 @@
+// "Create read-only property 'next' in 'InnerClass in MainClass'" "true-preview"
+public class MainClass {
+  void foo() {
+    int counter = InnerClass.<caret>getNext();
+  }
+
+  private class InnerClass {
+
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/createMethodFromUsage/beforeCreateStaticMethodInNonStaticInnerClass.java

@@ -0,0 +1,10 @@
+// "Create method 'getNext' in 'InnerClass in MainClass'" "true-preview"
+public class MainClass {
+  void foo() {
+    int counter = InnerClass.<caret>getNext();
+  }
+
+  private class InnerClass {
+
+  }
+}

java/java-tests/testSrc/com/intellij/codeInsight/daemon/impl/quickfix/CreateMethodFromUsageTest.java

@@ -5,7 +5,10 @@ import com.intellij.codeInsight.daemon.quickFix.ActionHint;
 import com.intellij.codeInsight.daemon.quickFix.LightQuickFixParameterizedTestCase;
 import com.intellij.codeInsight.intention.IntentionAction;
 import com.intellij.codeInsight.intention.impl.preview.IntentionPreviewPopupUpdateProcessor;
+import com.intellij.openapi.projectRoots.Sdk;
+import com.intellij.pom.java.LanguageLevel;
 import com.intellij.psi.PsiFile;
+import com.intellij.testFramework.IdeaTestUtil;
 import com.intellij.testFramework.fixtures.LightJavaCodeInsightFixtureTestCase;
 import org.jetbrains.annotations.NotNull;
 
@@ -16,6 +19,16 @@ public class CreateMethodFromUsageTest extends LightQuickFixParameterizedTestCas
     return "/codeInsight/daemonCodeAnalyzer/quickFix/createMethodFromUsage";
   }
 
+  @Override
+  protected LanguageLevel getLanguageLevel() {
+    return LanguageLevel.JDK_21_PREVIEW;
+  }
+
+  @Override
+  protected Sdk getProjectJDK() {
+    return IdeaTestUtil.getMockJdk21();
+  }
+
   @Override
   protected ActionHint parseActionHintImpl(@NotNull PsiFile file, @NotNull String contents) {
     return ActionHint.parse(file, contents, false);