JS: make string template optimization more conservative

See KT-18548

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

@@ -3175,6 +3175,12 @@ public class BoxJsTestGenerated extends AbstractBoxJsTest {
                 KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("js/js.translator/testData/box/expression/stringTemplates"), Pattern.compile("^([^_](.+))\\.kt$"), TargetBackend.JS, true);
             }
 
+            @TestMetadata("nonStrings.kt")
+            public void testNonStrings() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("js/js.translator/testData/box/expression/stringTemplates/nonStrings.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("objectWithToString.kt")
             public void testObjectWithToString() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("js/js.translator/testData/box/expression/stringTemplates/objectWithToString.kt");

js/js.translator/src/org/jetbrains/kotlin/js/translate/expression/StringTemplateTranslator.java

@@ -112,16 +112,11 @@ public final class StringTemplateTranslator extends AbstractTranslator {
 
         private boolean mustCallToString(@NotNull KotlinType type) {
             Name typeName = DescriptorUtilsKt.getNameIfStandardType(type);
-            if (typeName != null) {
+            //TODO: this is a hacky optimization, should use some generic approach
-                //TODO: this is a hacky optimization, should use some generic approach
+            if (typeName != null && NamePredicate.STRING.test(typeName)) {
-                if (NamePredicate.STRING.test(typeName)) {
+                return false;
-                    return false;
-                }
-                else if (NamePredicate.PRIMITIVE_NUMBERS.test(typeName)) {
-                    return resultingExpression == null;
-                }
             }
-            return expressionEntries.length == 1;
+            return resultingExpression == null;
         }
 
         @Override

js/js.translator/testData/box/expression/stringTemplates/nonStrings.kt

@@ -0,0 +1,23 @@
+// EXPECTED_REACHABLE_NODES: 1024
+fun box(): String {
+    val x = foo()
+    val y = bar()
+
+    var r = "$x$y"
+    if (r != "2342") return "fail: $r"
+
+    r = "$y$x"
+    if (r != "4223") return "fail: $r"
+
+    r = "$x$x"
+    if (r != "2323") return "fail: $r"
+
+    r = "$y$y"
+    if (r != "4242") return "fail: $r"
+
+    return "OK"
+}
+
+fun foo(): Any = 23
+
+fun bar() = 42