[Interop][Lowering] Support constants

Previously `const val`s from metadata-based interop libraries accidentally
were linked as IrField. It is fixed, and now we should properly lower these constants.

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/lower/InteropLowering.kt

@@ -16,6 +16,7 @@ import org.jetbrains.kotlin.backend.common.push
 import org.jetbrains.kotlin.backend.konan.*
 import org.jetbrains.kotlin.backend.konan.cgen.*
 import org.jetbrains.kotlin.backend.konan.descriptors.allOverriddenFunctions
+import org.jetbrains.kotlin.backend.konan.descriptors.isFromInteropLibrary
 import org.jetbrains.kotlin.backend.konan.descriptors.synthesizedName
 import org.jetbrains.kotlin.backend.konan.ir.*
 import org.jetbrains.kotlin.backend.konan.ir.companionObject
@@ -881,6 +882,29 @@ private class InteropTransformer(val context: Context, override val irFile: IrFi
         return expression
     }
 
+    /**
+     * Handle `const val`s that come from interop libraries.
+     *
+     * We extract constant value from the backing field, and replace getter invocation with it.
+     */
+    private fun tryGenerateInteropConstantRead(expression: IrCall): IrExpression? {
+        val function = expression.symbol.owner
+
+        if (!function.descriptor.module.isFromInteropLibrary()) return null
+        if (!function.isGetter) return null
+
+        val constantProperty = (function as? IrSimpleFunction)
+                ?.correspondingPropertySymbol
+                ?.owner
+                ?.takeIf { it.isConst }
+                ?: return null
+
+        return constantProperty.backingField
+                ?.initializer
+                ?.expression
+                ?: error("Constant property ${constantProperty.name} has no initializer!")
+    }
+
     override fun visitCall(expression: IrCall): IrExpression {
 
         expression.transformChildrenVoid(this)
@@ -903,6 +927,8 @@ private class InteropTransformer(val context: Context, override val irFile: IrFi
 
         tryGenerateInteropMemberAccess(expression, symbols, builder)?.let { return it }
 
+        tryGenerateInteropConstantRead(expression)?.let { return it }
+
         val intrinsicType = tryGetIntrinsicType(expression)
 
         if (intrinsicType != null) {