KT-12873: add temporary variables generated by delegation expression to class initializer. Fix #KT-12873

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/DelegationTest.java

@@ -99,4 +99,8 @@ public class DelegationTest extends SingleFileTranslationTest {
     public void testOnObject() throws Exception {
         checkFooBoxIsOk();
     }
+
+    public void testComplexDelegation() throws Exception {
+        checkFooBoxIsOk();
+    }
 }

js/js.translator/src/org/jetbrains/kotlin/js/translate/declaration/DelegationTranslator.kt

@@ -73,8 +73,10 @@ class DelegationTranslator(
             val field = fields[specifier]!!
             if (field.generateField) {
                 val expression = specifier.delegateExpression!!
-                val delegateInitExpr = Translation.translateAsExpression(expression, context())
+                val context = context().innerBlock()
-                statements.add(JsAstUtils.defineSimpleProperty(field.name, delegateInitExpr))
+                val delegateInitExpr = Translation.translateAsExpression(expression, context)
+                statements += context.dynamicContext().jsBlock().statements
+                statements += JsAstUtils.defineSimpleProperty(field.name, delegateInitExpr)
             }
         }
     }

js/js.translator/testData/delegation/cases/complexDelegation.kt

@@ -0,0 +1,29 @@
+package foo
+
+interface C {
+    fun f(): String
+}
+
+class B(val value: String) : C {
+    override fun f() = value
+}
+
+val b: Any = B("O")
+
+val x = B("failure1")
+val y = B("K")
+val z = B("failure2")
+
+fun selector() = 2
+
+class A : C by (b as C)
+
+class D : C by when (selector()) {
+    1 -> x
+    2 -> y
+    else -> z
+}
+
+fun box(): String {
+    return A().f() + D().f()
+}