KT-57207 Implement JavaClassFinder.findClasses

- This change is a prerequisite for allowing combined Java symbol
  providers (in LL FIR) to correctly disambiguate classpath order after
  getting classes with a combined scope, as the index access of the
  combined Java symbol provider is not guaranteed to return the class
  that should be first based on the original dependency order. To be
  able to disambiguate, a combined Java symbol provider needs access to
  all class candidates the index can find.

compiler/resolution.common.jvm/src/org/jetbrains/kotlin/resolve/jvm/KotlinJavaPsiFacade.java

@@ -39,6 +39,7 @@ import com.intellij.psi.util.PsiModificationTracker;
 import com.intellij.util.CommonProcessors;
 import com.intellij.util.ConcurrencyUtil;
 import com.intellij.util.Query;
+import com.intellij.util.SmartList;
 import com.intellij.util.messages.MessageBusConnection;
 import kotlin.collections.CollectionsKt;
 import org.jetbrains.annotations.NotNull;
@@ -196,6 +197,31 @@ public class KotlinJavaPsiFacade implements Disposable {
         return null;
     }
 
+    @NotNull
+    public List<JavaClass> findClasses(@NotNull JavaClassFinder.Request request, @NotNull GlobalSearchScope scope) {
+        if (scope == GlobalSearchScope.EMPTY_SCOPE) return Collections.emptyList();
+
+        // We hope this method is being called often enough to cancel daemon processes smoothly
+        ProgressIndicatorAndCompilationCanceledStatus.checkCanceled();
+
+        assert !shouldUseSlowResolve() : "`findClasses` should not be called from dumb mode, as results may be incomplete.";
+
+        ClassId classId = request.getClassId();
+        String qualifiedName = classId.asSingleFqName().asString();
+
+        List<JavaClass> javaClasses = new SmartList<>();
+
+        for (KotlinPsiElementFinderWrapper finder : finders()) {
+            ProgressIndicatorAndCompilationCanceledStatus.checkCanceled();
+
+            for (PsiClass psiClass : finder.findClasses(qualifiedName, scope)) {
+                javaClasses.add(createJavaClass(classId, psiClass));
+            }
+        }
+
+        return javaClasses;
+    }
+
     @NotNull
     private static JavaClass createJavaClass(@NotNull ClassId classId, @NotNull PsiClass psiClass) {
         JavaClassImpl javaClass = new JavaClassImpl(psiClass);
@@ -442,6 +468,7 @@ public class KotlinJavaPsiFacade implements Disposable {
 
     interface KotlinPsiElementFinderWrapper {
         PsiClass findClass(@NotNull String qualifiedName, @NotNull GlobalSearchScope scope);
+        PsiClass[] findClasses(@NotNull String qualifiedName, @NotNull GlobalSearchScope scope);
         PsiPackage findPackage(@NotNull String qualifiedName, @NotNull GlobalSearchScope scope);
         boolean isSameResultForAnyScope();
     }
@@ -458,6 +485,11 @@ public class KotlinJavaPsiFacade implements Disposable {
             return finder.findClass(qualifiedName, scope);
         }
 
+        @Override
+        public PsiClass[] findClasses(@NotNull String qualifiedName, @NotNull GlobalSearchScope scope) {
+            return finder.findClasses(qualifiedName, scope);
+        }
+
         @Override
         public PsiPackage findPackage(@NotNull String qualifiedName, @NotNull GlobalSearchScope scope) {
             // Original element finder can't search packages with scope
@@ -497,6 +529,11 @@ public class KotlinJavaPsiFacade implements Disposable {
             return javaFileManager.findClass(request, scope);
         }
 
+        @Override
+        public PsiClass[] findClasses(@NotNull String qualifiedName, @NotNull GlobalSearchScope scope) {
+            return javaFileManager.findClasses(qualifiedName, scope);
+        }
+
         @Nullable
         public Set<String> knownClassNamesInPackage(@NotNull FqName packageFqName) {
             return javaFileManager.knownClassNamesInPackage(packageFqName);
@@ -529,6 +566,11 @@ public class KotlinJavaPsiFacade implements Disposable {
             return javaFileManager.findClass(qualifiedName, scope);
         }
 
+        @Override
+        public PsiClass[] findClasses(@NotNull String qualifiedName, @NotNull GlobalSearchScope scope) {
+            return javaFileManager.findClasses(qualifiedName, scope);
+        }
+
         @Override
         public PsiPackage findPackage(@NotNull String qualifiedName, @NotNull GlobalSearchScope scope) {
             Query<VirtualFile> dirs = packageIndex.getDirsByPackageName(qualifiedName, true);