Prefer package with class files to class with the same name

See comments in JvmDependenciesIndexImpl and in the test

 #KT-15464 Fixed

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/index/JvmDependenciesIndexImpl.kt

@@ -16,6 +16,9 @@
 
 package org.jetbrains.kotlin.cli.jvm.index
 
+import com.intellij.ide.highlighter.JavaClassFileType
+import com.intellij.ide.highlighter.JavaFileType
+import com.intellij.openapi.vfs.VfsUtilCore
 import com.intellij.openapi.vfs.VirtualFile
 import com.intellij.util.containers.IntArrayList
 import org.jetbrains.kotlin.name.ClassId
@@ -236,15 +239,19 @@ class JvmDependenciesIndexImpl(_roots: List<JavaRoot>): JvmDependenciesIndex {
     private fun VirtualFile.findChildPackage(subPackageName: String, rootType: JavaRoot.RootType): VirtualFile? {
         val childDirectory = findChild(subPackageName) ?: return null
 
-        // Resolve conflicts between files and packages with the same qualified name in favor of files
         val fileExtension = when (rootType) {
-            JavaRoot.RootType.BINARY -> ".class"
-            JavaRoot.RootType.SOURCE -> ".java"
+            JavaRoot.RootType.BINARY -> JavaClassFileType.INSTANCE.defaultExtension
+            JavaRoot.RootType.SOURCE -> JavaFileType.INSTANCE.defaultExtension
         }
 
-        if (findChild(subPackageName + fileExtension)?.isDirectory == false) {
-            return null
+        // If in addition to a directory "foo" there's a class file "foo.class" AND there are no classes anywhere in the directory "foo",
+        // then we ignore the directory and let the resolution choose the class "foo" instead.
+        if (findChild("$subPackageName.$fileExtension")?.isDirectory == false) {
+            if (VfsUtilCore.processFilesRecursively(childDirectory) { file -> file.extension != fileExtension }) {
+                return null
+            }
         }
+
         return childDirectory
     }
 

compiler/testData/compileKotlinAgainstCustomBinaries/innerClassPackageConflict2/library1/test/Boo.java

@@ -0,0 +1,5 @@
+package test;
+
+public class Boo {
+    public interface Nested {}
+}

compiler/testData/compileKotlinAgainstCustomBinaries/innerClassPackageConflict2/library1/test/Foo.java

@@ -0,0 +1,6 @@
+package test;
+
+public class Foo {
+    public interface Nested {
+    }
+}

compiler/testData/compileKotlinAgainstCustomBinaries/innerClassPackageConflict2/library2/test/Boo/SubBoo/C.java

@@ -0,0 +1,5 @@
+package test.Boo.SubBoo;
+
+public class C {
+    public interface Nested {}
+}

compiler/testData/compileKotlinAgainstCustomBinaries/innerClassPackageConflict2/library2/test/Foo/Bar.java

@@ -0,0 +1,4 @@
+package test.Foo;
+
+public class Bar {
+}

compiler/testData/compileKotlinAgainstCustomBinaries/innerClassPackageConflict2/output.txt

@@ -0,0 +1,10 @@
+compiler/testData/compileKotlinAgainstCustomBinaries/innerClassPackageConflict2/source.kt:10:9: error: unresolved reference: Nested
+val v3: Nested? = null
+        ^
+compiler/testData/compileKotlinAgainstCustomBinaries/innerClassPackageConflict2/source.kt:11:18: error: unresolved reference: Nested
+val v4: test.Foo.Nested? = null
+                 ^
+compiler/testData/compileKotlinAgainstCustomBinaries/innerClassPackageConflict2/source.kt:14:18: error: unresolved reference: Nested
+val v6: test.Boo.Nested? = null
+                 ^
+COMPILATION_ERROR

compiler/testData/compileKotlinAgainstCustomBinaries/innerClassPackageConflict2/source.kt

@@ -0,0 +1,14 @@
+import test.Foo.*
+
+// Note that unlike in Java, in Kotlin we currently mostly prefer package to class in qualified name resolution.
+// So here, for example, we see both the package and the class with the name test.Foo, and prefer the former.
+// So 'Bar' should be resolved, 'Nested' should be unresolved.
+// For javac, the opposite is true: 'Bar' would be unresolved in a similar situation, 'Nested' would be resolved.
+
+val v1: Bar? = null
+val v2: test.Foo.Bar? = null
+val v3: Nested? = null
+val v4: test.Foo.Nested? = null
+
+val v5: test.Boo.SubBoo.C.Nested? = null
+val v6: test.Boo.Nested? = null

compiler/tests/org/jetbrains/kotlin/jvm/compiler/CompileKotlinAgainstCustomBinariesTest.java

@@ -20,6 +20,7 @@ import com.google.common.collect.Iterables;
 import com.intellij.openapi.util.Ref;
 import com.intellij.openapi.util.io.FileUtil;
 import com.intellij.util.ArrayUtil;
+import com.intellij.util.Processor;
 import kotlin.Pair;
 import kotlin.collections.SetsKt;
 import kotlin.io.FilesKt;
@@ -565,4 +566,27 @@ public class CompileKotlinAgainstCustomBinariesTest extends TestCaseWithTmpdir {
         Pair<String, ExitCode> output = compileKotlin("source.kt", tmpdir, jarPath);
         KotlinTestUtils.assertEqualsToFile(new File(getTestDataDirectory(), "output.txt"), normalizeOutput(output));
     }
+
+    public void testInnerClassPackageConflict2() throws Exception {
+        final File library1 = compileJava("library1");
+        final File library2 = compileJava("library2");
+
+        // Copy everything from library2 to library1
+        FileUtil.visitFiles(library2, new Processor<File>() {
+            @Override
+            public boolean process(File file) {
+                if (!file.isDirectory()) {
+                    File newFile = new File(library1, FilesKt.relativeTo(file, library2).getPath());
+                    if (!newFile.getParentFile().exists()) {
+                        assert newFile.getParentFile().mkdirs();
+                    }
+                    assert file.renameTo(newFile);
+                }
+                return true;
+            }
+        });
+
+        Pair<String, ExitCode> output = compileKotlin("source.kt", tmpdir, library1);
+        KotlinTestUtils.assertEqualsToFile(new File(getTestDataDirectory(), "output.txt"), normalizeOutput(output));
+    }
 }