Added tests for Kotlin top-level functions

utbot-framework-api/src/main/kotlin/org/utbot/framework/plugin/api/util/IdUtil.kt

@@ -498,6 +498,7 @@ val Method.displayName: String
 
 val KCallable<*>.declaringClazz: Class<*>
     get() = when (this) {
+        is KFunction<*> -> javaMethod?.declaringClass?.kotlin
         is CallableReference -> owner as? KClass<*>
         else -> instanceParameter?.type?.classifier as? KClass<*>
     }?.java ?: tryConstructor(this) ?: error("Can't get parent class for $this")

utbot-framework-test/src/test/kotlin/org/utbot/examples/codegen/FileWithTopLevelFunctionsTest.kt

@@ -0,0 +1,38 @@
+package org.utbot.examples.codegen
+
+import org.junit.jupiter.api.Test
+import org.utbot.testcheckers.eq
+import org.utbot.tests.infrastructure.UtValueTestCaseChecker
+
+internal class FileWithTopLevelFunctionsTest : UtValueTestCaseChecker(testClass = FileWithTopLevelFunctionsReflectHelper.clazz.kotlin) {
+    @Test
+    fun topLevelSumTest() {
+        check(
+            ::topLevelSum,
+            eq(1),
+        )
+    }
+
+    @Test
+    fun extensionOnBasicTypeTest() {
+        check(
+            Int::extensionOnBasicType,
+            eq(1),
+        )
+    }
+
+    @Test
+    fun extensionOnCustomClassTest() {
+        check(
+            CustomClass::extensionOnCustomClass,
+            eq(3),
+            additionalDependencies = dependenciesForClassExtensions
+        )
+    }
+
+    companion object {
+        // Compilation of extension methods for ref objects produces call to
+        // `kotlin.jvm.internal.Intrinsics::checkNotNullParameter`, so we need to add it to dependencies
+        val dependenciesForClassExtensions = arrayOf<Class<*>>(kotlin.jvm.internal.Intrinsics::class.java)
+    }
+}

utbot-intellij/src/main/kotlin/org/utbot/intellij/plugin/process/EngineProcess.kt

@@ -238,7 +238,16 @@ class EngineProcess(parent: Lifetime, val project: Project) {
         }
 
     private fun MemberInfo.paramNames(): List<String> =
-        (this.member as PsiMethod).parameterList.parameters.map { it.name }
+        (this.member as PsiMethod).parameterList.parameters.map {
+            if (it.name.startsWith("\$this"))
+                // If member is Kotlin extension function, name of first argument isn't good for further usage,
+                // so we better choose name based on type of receiver.
+                //
+                // There seems no API to check whether parameter is an extension receiver by PSI
+                it.type.presentableText
+            else
+                it.name
+        }
 
     fun generate(
         mockInstalled: Boolean,

utbot-sample/src/main/java/org/utbot/examples/codegen/FileWithTopLevelFunctionsReflectHelper.java

@@ -0,0 +1,6 @@
+package org.utbot.examples.codegen;
+
+// We can't access FileWithTopLevelFunctionsKt::class from Kotlin, so we use this class to get reflection from Java
+public class FileWithTopLevelFunctionsReflectHelper {
+    static Class<FileWithTopLevelFunctionsKt> clazz = FileWithTopLevelFunctionsKt.class;
+}

utbot-sample/src/main/kotlin/org/utbot/examples/codegen/FileWithTopLevelFunctions.kt

@@ -0,0 +1,23 @@
+package org.utbot.examples.codegen
+
+// TODO: currently we can't properly handle properties in constructors, change CustomClass to data class after that is fixed
+class CustomClass {
+    var x: Int = 0
+    var y: Int = 0
+
+    fun f(): Int {
+       return 0
+    }
+}
+
+fun topLevelSum(a: Int, b: Int): Int {
+    return a + b
+}
+
+fun Int.extensionOnBasicType(other: Int): Int {
+    return this + other
+}
+
+fun CustomClass.extensionOnCustomClass(other: CustomClass): Boolean {
+    return x >= other.x && y >= other.y
+}