JS: add boxing/unboxing to default accessors of non-simple properties

See KT-21421

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

@@ -833,6 +833,12 @@ public class BoxJsTestGenerated extends AbstractBoxJsTest {
             doTest(fileName);
         }
 
+        @TestMetadata("defaultAccessors.kt")
+        public void testDefaultAccessors() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("js/js.translator/testData/box/coercion/defaultAccessors.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("derivedFunctionReturningChar.kt")
         public void testDerivedFunctionReturningChar() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("js/js.translator/testData/box/coercion/derivedFunctionReturningChar.kt");

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

@@ -21,6 +21,7 @@ import org.jetbrains.kotlin.descriptors.impl.LocalVariableAccessorDescriptor
 import org.jetbrains.kotlin.descriptors.impl.LocalVariableDescriptor
 import org.jetbrains.kotlin.js.backend.ast.*
 import org.jetbrains.kotlin.js.backend.ast.metadata.synthetic
+import org.jetbrains.kotlin.js.backend.ast.metadata.type
 import org.jetbrains.kotlin.js.translate.callTranslator.CallTranslator
 import org.jetbrains.kotlin.js.translate.context.Namer
 import org.jetbrains.kotlin.js.translate.context.Namer.getReceiverParameterName
@@ -94,13 +95,14 @@ class DefaultPropertyTranslator(
 
         assert(!descriptor.isExtension) { "Unexpected extension property $descriptor}" }
         assert(descriptor is PropertyDescriptor) { "Property descriptor expected: $descriptor" }
-        val result = backingFieldReference(context(), descriptor as PropertyDescriptor)
+        var result: JsExpression = backingFieldReference(context(), descriptor as PropertyDescriptor)
         if (getterDescriptor is PropertyAccessorDescriptor && getterDescriptor.correspondingProperty.isLateInit) {
             val throwFunction = context().getReferenceToIntrinsic(Namer.THROW_UNINITIALIZED_PROPERTY_ACCESS_EXCEPTION)
             function.body.statements += JsIf(JsBinaryOperation(JsBinaryOperator.EQ, result, JsNullLiteral()),
                                              JsReturn(JsInvocation(throwFunction,
                                                                    JsStringLiteral(getterDescriptor.correspondingProperty.name.asString()))))
         }
+        result = TranslationUtils.coerce(context(), result, TranslationUtils.getReturnTypeForCoercion(getterDescriptor))
         function.body.statements += JsReturn(result).apply { source = descriptor.source.getPsi() }
     }
 
@@ -126,7 +128,8 @@ class DefaultPropertyTranslator(
         assert(setterDescriptor.valueParameters.size == 1) { "Setter must have 1 parameter" }
         val correspondingPropertyName = setterDescriptor.correspondingVariable.name.asString()
         val valueParameter = function.addParameter(correspondingPropertyName).name
-        val withAliased = context().innerContextWithAliased(setterDescriptor.valueParameters[0], valueParameter.makeRef())
+        val parameter = setterDescriptor.valueParameters[0]
+        val withAliased = context().innerContextWithAliased(parameter, valueParameter.makeRef())
         val delegatedCall = bindingContext()[BindingContext.DELEGATED_PROPERTY_RESOLVED_CALL, setterDescriptor]
 
         if (delegatedCall != null) {
@@ -142,7 +145,12 @@ class DefaultPropertyTranslator(
         else {
             assert(!descriptor.isExtension) { "Unexpected extension property $descriptor}" }
             assert(descriptor is PropertyDescriptor) { "Property descriptor expected: $descriptor" }
-            val assignment = assignmentToBackingField(withAliased, descriptor as PropertyDescriptor, valueParameter.makeRef())
+            var value: JsExpression = valueParameter.makeRef().apply {
+                type = TranslationUtils.getReturnTypeForCoercion(setterDescriptor.correspondingVariable)
+            }
+            value = TranslationUtils.coerce(
+                    context(), value, TranslationUtils.getReturnTypeForCoercion(setterDescriptor.correspondingVariable, true))
+            val assignment = assignmentToBackingField(withAliased, descriptor as PropertyDescriptor, value)
             function.addStatement(assignment.apply { source = descriptor.source.getPsi() }.makeStmt())
         }
     }

js/js.translator/testData/box/coercion/defaultAccessors.kt

@@ -0,0 +1,29 @@
+// EXPECTED_REACHABLE_NODES: 1140
+interface I {
+    val a: Char
+}
+
+object X : I {
+    override var a = '#'
+}
+
+var result = ""
+
+object Y : I {
+    override var a = '#'
+        get() {
+            result = jsTypeOf(field.asDynamic())
+            return field
+        }
+}
+
+fun box(): String {
+    val t = jsTypeOf(X.asDynamic().a)
+    if (t != "object") return "fail1: $t"
+
+    Y.a = '@'
+    Y.a
+    if (result != "number") return "fail2: $result"
+
+    return "OK"
+}