JS: fix unit materialization in case of null check and elvis operator

See KT-20287

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

@@ -893,6 +893,12 @@ public class BoxJsTestGenerated extends AbstractBoxJsTest {
             doTest(fileName);
         }
 
+        @TestMetadata("unitNullCheck.kt")
+        public void testUnitNullCheck() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("js/js.translator/testData/box/coercion/unitNullCheck.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("unitSafeCall.kt")
         public void testUnitSafeCall() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("js/js.translator/testData/box/coercion/unitSafeCall.kt");

js/js.translator/src/org/jetbrains/kotlin/js/translate/intrinsic/operation/EqualsBOIF.kt

@@ -39,6 +39,7 @@ import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.TypeUtils
 import org.jetbrains.kotlin.types.expressions.OperatorConventions
 import org.jetbrains.kotlin.types.isDynamic
+import org.jetbrains.kotlin.types.typeUtil.makeNullable
 import java.util.*
 
 object EqualsBOIF : BinaryOperationIntrinsicFactory {
@@ -50,8 +51,12 @@ object EqualsBOIF : BinaryOperationIntrinsicFactory {
 
         override fun apply(expression: KtBinaryExpression, left: JsExpression, right: JsExpression, context: TranslationContext): JsExpression {
             val isNegated = expression.isNegated()
+            val anyType = context.currentModule.builtIns.anyType
             if (right is JsNullLiteral || left is JsNullLiteral) {
-                return TranslationUtils.nullCheck(if (right is JsNullLiteral) left else right, isNegated)
+                val (subject, ktSubject) = if (right is JsNullLiteral) Pair(left, expression.left!!) else Pair(right, expression.right!!)
+                val type = context.bindingContext().getType(ktSubject) ?: anyType
+                val coercedSubject = TranslationUtils.coerce(context, subject, type.makeNullable())
+                return TranslationUtils.nullCheck(coercedSubject, isNegated)
             }
 
             val ktLeft = checkNotNull(expression.left) { "No left-hand side: " + expression.text }
@@ -78,7 +83,6 @@ object EqualsBOIF : BinaryOperationIntrinsicFactory {
                 return JsBinaryOperation(if (isNegated) JsBinaryOperator.NEQ else JsBinaryOperator.EQ, left, right)
             }
 
-            val anyType = context.currentModule.builtIns.anyType
             val coercedLeft = TranslationUtils.coerce(context, left, anyType)
             val coercedRight = TranslationUtils.coerce(context, right, anyType)
             val result = TopLevelFIF.KOTLIN_EQUALS.apply(coercedLeft, listOf(coercedRight), context)

js/js.translator/src/org/jetbrains/kotlin/js/translate/operation/BinaryOperationTranslator.java

@@ -41,6 +41,7 @@ import org.jetbrains.kotlin.resolve.calls.model.ResolvedCall;
 import org.jetbrains.kotlin.types.KotlinType;
 import org.jetbrains.kotlin.types.TypeUtils;
 import org.jetbrains.kotlin.types.expressions.OperatorConventions;
+import org.jetbrains.kotlin.types.typeUtil.TypeUtilsKt;
 
 import java.util.Collections;
 
@@ -129,7 +130,7 @@ public final class BinaryOperationTranslator extends AbstractTranslator {
         assert expressionType != null;
 
         JsExpression leftExpression = TranslationUtils.coerce(
-                context(), Translation.translateAsExpression(leftKtExpression, context()), expressionType);
+                context(), Translation.translateAsExpression(leftKtExpression, context()), TypeUtilsKt.makeNullable(expressionType));
 
         JsBlock rightBlock = new JsBlock();
         JsExpression rightExpression = TranslationUtils.coerce(

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

@@ -0,0 +1,18 @@
+// EXPECTED_REACHABLE_NODES: 1027
+var log = ""
+
+fun box(): String {
+    foo() ?: bar()
+    if (foo() == null) bar()
+
+    if (log != "foo;foo;") return "fail: $log"
+    return "OK"
+}
+
+fun foo() {
+    log += "foo;"
+}
+
+fun bar() {
+    log += "bar;"
+}