Calling Kotlin from C++ runtime (#107)

* backend: support exporting Kotlin functions for C++ runtime

* runtime: implement several functions in Kotlin

* Throw{NullPointer,ArrayIndexOutOfBounds,ClassCast}Exception

* runtime: add literal declared in Kotlin as empty string

Also
* add corresponding test
* use empty string literal in strdedup2
  (however keep it disabled)

* fixup! runtime: add literal declared in Kotlin as empty string

* Review feedback: add more TheEmptyString() usages

Also improve string index checks in runtime

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/NameUtils.kt

@@ -4,16 +4,20 @@ import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.descriptors.ClassKind.*
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.descriptors.PropertyDescriptor
+import org.jetbrains.kotlin.descriptors.annotations.AnnotationDescriptor
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.resolve.constants.StringValue
 import org.jetbrains.kotlin.resolve.descriptorUtil.fqNameSafe
 import org.jetbrains.kotlin.resolve.findOriginalTopMostOverriddenDescriptors
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.TypeUtils
+import org.jetbrains.kotlin.utils.addToStdlib.ifNotEmpty
 
 
 private val symbolNameAnnotation = FqName("konan.SymbolName")
 
+private val exportForCppRuntimeAnnotation = FqName("konan.internal.ExportForCppRuntime")
+
 fun typeToHashString(type: KotlinType): String {
     if (TypeUtils.isTypeParameter(type)) return "GENERIC"
 
@@ -52,18 +56,32 @@ internal val FunctionDescriptor.symbolName: String
     get() {
         this.annotations.findAnnotation(symbolNameAnnotation)?.let {
             if (this.isExternal) {
-                val nameValue = it.allValueArguments.values.single() as StringValue
-                return nameValue.value
+                return getStringValue(it)!!
             } else {
                 // ignore; TODO: report compile error
             }
         }
+
+        this.annotations.findAnnotation(exportForCppRuntimeAnnotation)?.let {
+            val name = getStringValue(it) ?: this.name.asString()
+            return name // no wrapping currently required
+        }
+
         val containingDeclarationPart = containingDeclaration.fqNameSafe.let {
             if (it.isRoot) "" else "$it."
         }
         return "kfun:$containingDeclarationPart$functionName"
     }
 
+private fun getStringValue(annotation: AnnotationDescriptor): String? {
+    annotation.allValueArguments.values.ifNotEmpty {
+        val stringValue = this.single() as StringValue
+        return stringValue.value
+    }
+
+    return null
+}
+
 internal val ClassDescriptor.symbolName: String
     get() = when (this.kind) {
         CLASS -> "kclass:"

backend.native/tests/build.gradle

@@ -323,6 +323,11 @@ task tostring2(type: RunKonanTest) {
     source = "runtime/basic/tostring2.kt"
 }
 
+task empty_substring(type: RunKonanTest) {
+    goldValue = "\n"
+    source = "runtime/basic/empty_substring.kt"
+}
+
 task array0(type: RunKonanTest) {
     goldValue = "5\n6\n7\n8\n9\n10\n11\n12\n13\n"
     source = "runtime/basic/array0.kt"
@@ -395,7 +400,9 @@ task strdedup1(type: RunKonanTest) {
 }
 
 /*
-TODO: enable after supporting Unit object
+TODO: string deduplication across several components seems to require
+linking them as bitcode modules before translating to machine code.
+
 task strdedup2(type: RunKonanTest) {
     goldValue = "true\ntrue\n"
     source = "datagen/literals/strdedup2.kt"

backend.native/tests/datagen/literals/strdedup2.kt

@@ -1,6 +1,6 @@
 fun main(args : Array<String>) {
-    val str1 = "kotlin.Unit"
-    val str2 = Unit.toString()
+    val str1 = ""
+    val str2 = "hello".subSequence(2, 2)
     println(str1 == str2)
     println(str1 === str2)
 }

backend.native/tests/runtime/basic/empty_substring.kt

@@ -0,0 +1,4 @@
+fun main(args : Array<String>) {
+    val hello = "Hello world"
+    println(hello.subSequence(1, 1).toString())
+}