Optimize top level class searching in LazyJavaPackageScope

Do not try to search something, that is known not to exist

compiler/frontend.java/src/org/jetbrains/kotlin/load/java/JavaClassFinderImpl.java

@@ -36,6 +36,7 @@ import org.jetbrains.kotlin.resolve.jvm.KotlinJavaPsiFacade;
 
 import javax.annotation.PostConstruct;
 import javax.inject.Inject;
+import java.util.Set;
 
 public class JavaClassFinderImpl implements JavaClassFinder {
     private Project project;
@@ -108,4 +109,10 @@ public class JavaClassFinderImpl implements JavaClassFinder {
         PsiPackage psiPackage = javaFacade.findPackage(fqName.asString(), javaSearchScope);
         return psiPackage == null ? null : new JavaPackageImpl(psiPackage, javaSearchScope);
     }
+
+    @Nullable
+    @Override
+    public Set<String> knownClassNamesInPackage(@NotNull FqName packageFqName) {
+        return javaFacade.knownClassNamesInPackage(packageFqName);
+    }
 }

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/KotlinCliJavaFileManager.kt

@@ -20,7 +20,10 @@ import com.intellij.psi.PsiClass
 import com.intellij.psi.impl.file.impl.JavaFileManager
 import com.intellij.psi.search.GlobalSearchScope
 import org.jetbrains.kotlin.name.ClassId
+import org.jetbrains.kotlin.name.FqName
 
 interface KotlinCliJavaFileManager : JavaFileManager {
     fun findClass(classId: ClassId, searchScope: GlobalSearchScope): PsiClass?
+
+    fun knownClassNamesInPackage(packageFqName: FqName): Set<String>?
 }

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/KotlinJavaPsiFacade.java

@@ -40,12 +40,15 @@ import kotlin.collections.ArraysKt;
 import kotlin.collections.CollectionsKt;
 import kotlin.jvm.functions.Function1;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+import org.jetbrains.kotlin.name.FqName;
 import org.jetbrains.kotlin.progress.ProgressIndicatorAndCompilationCanceledStatus;
 import org.jetbrains.kotlin.name.ClassId;
 
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Set;
 import java.util.concurrent.ConcurrentMap;
 
 public class KotlinJavaPsiFacade {
@@ -112,6 +115,17 @@ public class KotlinJavaPsiFacade {
         return null;
     }
 
+    @Nullable
+    public Set<String> knownClassNamesInPackage(@NotNull FqName packageFqName) {
+        KotlinPsiElementFinderWrapper[] finders = finders();
+
+        if (finders.length == 1) {
+            return ((KotlinPsiElementFinderImpl) finders[0]).knownClassNamesInPackage(packageFqName);
+        }
+
+        return null;
+    }
+
     @NotNull
     private PsiClass[] findClassesInDumbMode(@NotNull String qualifiedName, @NotNull GlobalSearchScope scope) {
         String packageName = StringUtil.getPackageName(qualifiedName);
@@ -328,6 +342,15 @@ public class KotlinJavaPsiFacade {
             return findClass(classId.asSingleFqName().asString(), scope);
         }
 
+        @Nullable
+        public Set<String> knownClassNamesInPackage(@NotNull FqName packageFqName) {
+            if (isCliFileManager) {
+                return ((KotlinCliJavaFileManager) javaFileManager).knownClassNamesInPackage(packageFqName);
+            }
+
+            return null;
+        }
+
         @Override
         public PsiPackage findPackage(@NotNull String qualifiedName, @NotNull GlobalSearchScope scope) {
             if (isCliFileManager) {