Handle lambda argument of staticCFunction

INTEROP.md

@@ -275,7 +275,9 @@ methods available:
 ### Callbacks ###
 
 To convert Kotlin function to pointer to C function,
-`staticCFunction(::kotlinFunction)` can be used.
+`staticCFunction(::kotlinFunction)` can be used. It is also allowed to provide
+the lambda instead of function reference. The function or lambda must not
+capture any values.
 
 Note that some function types are not supported currently. For example,
 it is not possible to get pointer to function that receives or returns structs

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

@@ -277,16 +277,17 @@ private class InteropTransformer(val context: Context, val irFile: IrFile) : IrB
             }
 
             in interop.staticCFunction -> {
-                val argument = expression.getValueArgument(0)!!
-                if (argument !is IrCallableReference || argument.getArguments().isNotEmpty()) {
+                val irCallableReference = unwrapStaticFunctionArgument(expression.getValueArgument(0)!!)
+
+                if (irCallableReference == null || irCallableReference.getArguments().isNotEmpty()) {
                     context.reportCompilationError(
-                            "${descriptor.fqNameSafe} must take an unbound, non-capturing function",
+                            "${descriptor.fqNameSafe} must take an unbound, non-capturing function or lambda",
                             irFile, expression
                     )
                     // TODO: should probably be reported during analysis.
                 }
 
-                val target = argument.descriptor.original
+                val target = irCallableReference.descriptor.original
                 val signatureTypes = target.allParameters.map { it.type } + target.returnType!!
 
                 signatureTypes.forEachIndexed { index, type ->
@@ -385,6 +386,35 @@ private class InteropTransformer(val context: Context, val irFile: IrFile) : IrB
         reportError("Type $this is not supported in callback signature")
     }
 
+    private fun unwrapStaticFunctionArgument(argument: IrExpression): IrCallableReference? {
+        if (argument is IrCallableReference) {
+            return argument
+        }
+
+        // Otherwise check whether it is a lambda:
+
+        // 1. It is a container with two statements and expected origin:
+
+        if (argument !is IrContainerExpression || argument.statements.size != 2) {
+            return null
+        }
+        if (argument.origin != IrStatementOrigin.LAMBDA && argument.origin != IrStatementOrigin.ANONYMOUS_FUNCTION) {
+            return null
+        }
+
+        // 2. First statement is an empty container (created during local functions lowering):
+
+        val firstStatement = argument.statements.first()
+
+        if (firstStatement !is IrContainerExpression || firstStatement.statements.size != 0) {
+            return null
+        }
+
+        // 3. Second statement is IrCallableReference:
+
+        return argument.statements.last() as? IrCallableReference
+    }
+
     private fun IrCall.getSingleTypeArgument(): KotlinType {
         val typeParameter = descriptor.original.typeParameters.single()
         return getTypeArgument(typeParameter)!!

backend.native/tests/interop/basics/3.kt

@@ -11,7 +11,12 @@ fun main(args: Array<String>) {
         values[3] = 13
         values[4] = 8
 
-        cstdlib.qsort(values, count.toLong(), IntVar.size, staticCFunction(::comparator))
+        cstdlib.qsort(values, count.toLong(), IntVar.size, staticCFunction { a, b ->
+            val aValue = a!!.reinterpret<IntVar>()[0]
+            val bValue = b!!.reinterpret<IntVar>()[0]
+
+            (aValue - bValue)
+        })
 
         for (i in 0 .. count - 1) {
             print(values[i])
@@ -20,10 +25,3 @@ fun main(args: Array<String>) {
         println()
     }
 }
-
-private fun comparator(a: COpaquePointer?, b: COpaquePointer?): Int {
-    val aValue = a!!.reinterpret<IntVar>()[0]
-    val bValue = b!!.reinterpret<IntVar>()[0]
-
-    return (aValue - bValue)
-}