JS IR: materialize Unit in lambdas

^KT-52010 fixed

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/InteropCallableReferenceLowering.kt

@@ -24,6 +24,7 @@ import org.jetbrains.kotlin.ir.expressions.impl.*
 import org.jetbrains.kotlin.ir.symbols.*
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.classifierOrNull
+import org.jetbrains.kotlin.ir.types.isUnit
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
 import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
@@ -185,6 +186,11 @@ class InteropCallableReferenceLowering(val context: JsIrBackendContext) : BodyLo
         // Fix parents of declarations inside body
         body.patchDeclarationParents(lambdaDeclaration)
 
+        if (invokeFun.returnType.isUnit()) {
+            val unitValue = JsIrBuilder.buildGetObjectValue(context.irBuiltIns.unitType, context.irBuiltIns.unitClass)
+            (body as IrBlockBody).statements.add(IrReturnImpl(UNDEFINED_OFFSET, UNDEFINED_OFFSET, context.irBuiltIns.nothingType, lambdaDeclaration.symbol, unitValue))
+        }
+
         return body as IrBlockBody
     }
 

js/js.translator/testData/box/expression/function/lambdaReturnValue.kt

@@ -0,0 +1,35 @@
+// EXPECTED_REACHABLE_NODES: 1285
+
+fun <T> rawReturnValue(fn: () -> T): Any {
+    return fn() as Any
+}
+
+fun unitFun() {}
+
+fun charFun(): Char = 'a'
+
+value class VC(val v: Int)
+
+fun vcFun(): VC = VC(1)
+
+
+
+fun box(): String {
+    if (rawReturnValue { unitFun() } != Unit) return "fail1.1"
+    if (rawReturnValue<Unit> { unitFun() } != Unit) return "fail1.2"
+    if (rawReturnValue<Any> { unitFun() } != Unit) return "fail1.3"
+
+    val boxedA: Any = 'a'
+
+    if (rawReturnValue { charFun() } != boxedA) return "fail2.1"
+    if (rawReturnValue<Char> { charFun() } != boxedA) return "fail2.2"
+    if (rawReturnValue<Any> { charFun() } != boxedA) return "fail2.3"
+
+    val boxed1: Any = VC(1)
+
+    if (rawReturnValue { vcFun() } != boxed1) return "fail3.1"
+    if (rawReturnValue<VC> { vcFun() } != boxed1) return "fail3.2"
+    if (rawReturnValue<Any> { vcFun() } != boxed1) return "fail3.3"
+
+    return "OK"
+}

js/js.translator/testData/box/regression/kt52010.kt

@@ -0,0 +1,22 @@
+// EXPECTED_REACHABLE_NODES: 1274
+
+fun box(): String {
+    instance = Holder()
+    instance?.applyAndRet<Unit> { sideEffect("left") } ?: sideEffect("right")
+
+    if (log == "left") return "OK" else return "fail: $log"
+}
+
+var log = ""
+
+fun sideEffect(msg: String) {
+    log += msg
+}
+
+var instance: Holder? = null
+
+class Holder() {
+    fun <T> applyAndRet(block: () -> T): T {
+        return block()
+    }
+}