[java-completion] JavaNoVariantsDelegator: avoid redundant chains of nested classes

Fixes IDEA-334398 Code completion of nested types suggests confusing levels of nesting

GitOrigin-RevId: 206fc2b9f4a6501720b7bc95e79d981b20450823

java/java-impl/src/com/intellij/codeInsight/completion/JavaChainLookupElement.java

@@ -28,6 +28,7 @@ public class JavaChainLookupElement extends LookupElementDecorator<LookupElement
   public JavaChainLookupElement(LookupElement qualifier, LookupElement main) {
     this(qualifier, main, ".");
   }
+  
   public JavaChainLookupElement(LookupElement qualifier, LookupElement main, String separator) {
     super(main);
     myQualifier = qualifier;
@@ -186,4 +187,22 @@ public class JavaChainLookupElement extends LookupElementDecorator<LookupElement
     }
     return ((PsiVariable) object).getType();
   }
+
+  /**
+   * @param base base item to create a chain
+   * @param item nested item
+   * @return false if the chain looks redundant, and it's better not to suggest it.
+   */
+  static boolean isReasonableChain(LookupElement base, LookupElement item) {
+    PsiElement baseElement = base.getPsiElement();
+    PsiElement itemElement = item.getPsiElement();
+    if (baseElement == null || itemElement == null) return true;
+    if (baseElement.equals(itemElement)) return false;
+    if (itemElement instanceof PsiMember member) {
+      PsiClass itemClass = member.getContainingClass();
+      if (itemClass == null || itemClass.equals(baseElement)) return true;
+      if (PsiTreeUtil.isAncestor(itemClass, baseElement, true)) return false;
+    }
+    return true;
+  }
 }

java/java-impl/src/com/intellij/codeInsight/completion/JavaNoVariantsDelegator.java

@@ -203,7 +203,9 @@ public class JavaNoVariantsDelegator extends CompletionContributor implements Du
         if (ref != null) {
           for (LookupElement item : JavaSmartCompletionContributor.completeReference(position, ref, filter, true, true, parameters,
                                                                                      result.getPrefixMatcher())) {
-            LookupElement chain = highlighter.highlightIfNeeded(null, new JavaChainLookupElement(base, item, separator), item.getObject());
+            if (!JavaChainLookupElement.isReasonableChain(base, item)) continue;
+            JavaChainLookupElement chainedElement = new JavaChainLookupElement(base, item, separator);
+            LookupElement chain = highlighter.highlightIfNeeded(null, chainedElement, item.getObject());
             if (JavaCompletionContributor.shouldInsertSemicolon(position)) {
               chain = TailTypeDecorator.withTail(chain, TailTypes.semicolonType());
             }

java/java-tests/testData/codeInsight/completion/normal/NestedClassCompletion.java

@@ -0,0 +1,13 @@
+sealed interface AddUserError {
+
+  final class NameIsEmpty implements AddUserError {}
+
+  final class NameIsTooLong implements AddUserError {}
+}
+
+class Test {
+
+  public static AddUserError TryAddUser() {
+    return new AUE.<caret>
+  }
+}

java/java-tests/testSrc/com/intellij/java/codeInsight/completion/NormalSealedCompletionTest.java

@@ -36,4 +36,11 @@ public class NormalSealedCompletionTest extends NormalCompletionTestCase {
 
   @NeedsIndex.Full(reason = "AllClassesGetter.processJavaClasses uses indices, see 0a72bf3a7baa7dc1550e8e4308431d78eb753eb6 commit")
   public void testSealedPermitsInner() { doTest("\n"); }
+
+  @NeedsIndex.Full
+  public void testNestedClassCompletion() {
+    configure();
+    myFixture.completeBasic();
+    myFixture.assertPreferredCompletionItems(0, "AddUserError.NameIsEmpty", "AddUserError.NameIsTooLong");
+  }
 }