Always take java source before class files.

Also when searching for inner classes.

^Fixes KT-51025

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/KotlinCliJavaFileManagerImpl.kt

@@ -174,6 +174,15 @@ class KotlinCliJavaFileManagerImpl(private val myPsiManager: PsiManager) : CoreJ
         val result = ArrayList<PsiClass>(1)
         forEachClassId(qName) { classId ->
             val relativeClassName = classId.relativeClassName.asString()
+
+            // Search java sources first. For build tools, it makes sense to build new files passing all the
+            // class files for the previous build on the class path.
+            result.addIfNotNull(
+                singleJavaFileRootsIndex.findJavaSourceClass(classId)
+                    ?.takeIf { it in scope }
+                    ?.findPsiClassInVirtualFile(relativeClassName)
+            )
+
             index.traverseDirectoriesInPackage(classId.packageFqName) { dir, rootType ->
                 val psiClass =
                     findVirtualFileGivenPackage(dir, relativeClassName, rootType)
@@ -186,12 +195,6 @@ class KotlinCliJavaFileManagerImpl(private val myPsiManager: PsiManager) : CoreJ
                 true
             }
 
-            result.addIfNotNull(
-                singleJavaFileRootsIndex.findJavaSourceClass(classId)
-                    ?.takeIf { it in scope }
-                    ?.findPsiClassInVirtualFile(relativeClassName)
-            )
-
             if (result.isNotEmpty()) {
                 return@time result.toTypedArray()
             }

compiler/tests/org/jetbrains/kotlin/cli/JavaSourceInnerClassInClassPathTest.kt

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.cli
+
+import org.jetbrains.kotlin.cli.common.ExitCode
+import org.jetbrains.kotlin.cli.jvm.K2JVMCompiler
+import org.jetbrains.kotlin.test.TestCaseWithTmpdir
+
+class JavaSourceInnerClassInClassPathTest : TestCaseWithTmpdir() {
+
+    // Test that a java source file for a class is taken before a class file for the same
+    // class on the class path.
+    fun test() {
+        val aJava = tmpdir.resolve("A.java").also {
+            it.writeText("class A { interface AInner { int foo(); } }")
+        }
+        val bJava = tmpdir.resolve("B.java").also {
+            it.writeText("class B implements A.AInner { public int foo() { return 42; } }")
+        }
+        val cKt = tmpdir.resolve("C.kt").also {
+            it.writeText("fun main() { B().foo() }")
+        }
+        val (output, exit) = AbstractCliTest.executeCompilerGrabOutput(
+            K2JVMCompiler(),
+            listOf(aJava.path, bJava.path, cKt.path, "-d", tmpdir.path, "-Xcompile-java", "-Xuse-javac")
+        )
+        assert(exit == ExitCode.OK) { output }
+        val (output2, exit2) = AbstractCliTest.executeCompilerGrabOutput(
+            K2JVMCompiler(),
+            listOf(aJava.path, bJava.path, cKt.path, "-cp", tmpdir.path)
+        )
+        assert(exit2 == ExitCode.OK) { output2 }
+    }
+}