[java] IDEA-376793 Fix 'Duplicate class' error check to highlight each duplicate class exactly once

Merge-request: IJ-MR-171426
Merged-by: Marcin Mikosik <marcin.mikosik@jetbrains.com>

GitOrigin-RevId: 882e7e6b7ee66083be0376bbc84b23bd60903977

java/codeserver/highlighting/src/com/intellij/java/codeserver/highlighting/ClassChecker.java

@@ -159,16 +159,10 @@ final class ClassChecker {
     PsiElement parent = aClass.getParent();
     boolean checkSiblings;
     if (parent instanceof PsiClass psiClass && !PsiUtil.isLocalOrAnonymousClass(psiClass) && !PsiUtil.isLocalOrAnonymousClass(aClass)) {
-      // optimization: instead of iterating PsiClass children manually, we can get them all from caches
-      PsiClass innerClass = psiClass.findInnerClassByName(name, false);
-      if (innerClass != null && innerClass != aClass) {
-        if (innerClass.getTextOffset() > aClass.getTextOffset()) {
-          // report duplicate lower in text
-          PsiClass c = innerClass;
-          innerClass = aClass;
-          aClass = c;
-        }
-        myVisitor.report(JavaErrorKinds.CLASS_DUPLICATE.create(aClass, innerClass));
+      var duplicates = ContainerUtil.filter(psiClass.getInnerClasses(), c -> Objects.equals(c.getName(), name));
+      var duplicatesWithoutMe = ContainerUtil.filter(duplicates, c -> c != aClass);
+      if (!duplicatesWithoutMe.isEmpty()) {
+        myVisitor.report(JavaErrorKinds.CLASS_DUPLICATE.create(aClass, duplicatesWithoutMe.get(0)));
         return;
       }
       checkSiblings = false; // there still might be duplicates in parents
@@ -204,6 +198,7 @@ final class ClassChecker {
 
       if (element instanceof PsiClass psiClass && name.equals(psiClass.getName())) {
         myVisitor.report(JavaErrorKinds.CLASS_DUPLICATE.create(aClass, psiClass));
+        return;
       }
     }
   }

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/advHighlighting/DuplicateClassMethod.java

@@ -20,6 +20,20 @@ interface ii {
 class <error descr="Duplicate class: 'a'">a</error> {
 }
 
+class DuplicateNestedClassesTest {
+  public class <error descr="Duplicate class: 'C'">C</error> {}
+  public class <error descr="Duplicate class: 'C'">C</error> {}
+  public class <error descr="Duplicate class: 'C'">C</error> {}
+}
+
+class DuplicateLocalClassesTest {
+  public void foo() {
+    class D {}
+    class <error descr="Duplicate class: 'D'">D</error> {}
+    class <error descr="Duplicate class: 'D'">D</error> {}
+  }
+}
+
 class Foo {
     void f() {
         class Bar {
@@ -41,7 +55,7 @@ class c2 {
 
 
 class cont {
-        class B {
+        class <error descr="Duplicate class: 'B'">B</error> {
         }
         {
             class B {

java/java-tests/testData/ig/com/siyeh/igtest/inheritance/abstract_method_with_missing_implementations/DuplicateClass.java

@@ -5,7 +5,7 @@ class Temp35 {
     @Override public void work() { }
   }; }
 
-  public interface Workable { void work(); }
+  public interface <error descr="Duplicate class: 'Workable'">Workable</error> { void work(); }
   public interface <error descr="Duplicate class: 'Workable'">Workable</error> { void work(); }
 
   public static void main(String[] args) {