JS: fix char to string convertion in string templates (#KT-17966 fixed)

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

@@ -422,6 +422,12 @@ public class BoxJsTestGenerated extends AbstractBoxJsTest {
             doTest(fileName);
         }
 
+        @TestMetadata("charInStringTemplate.kt")
+        public void testCharInStringTemplate() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("js/js.translator/testData/box/char/charInStringTemplate.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("charIsCheck.kt")
         public void testCharIsCheck() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("js/js.translator/testData/box/char/charIsCheck.kt");

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

@@ -16,16 +16,14 @@
 
 package org.jetbrains.kotlin.js.translate.expression;
 
-import org.jetbrains.kotlin.js.backend.ast.JsExpression;
-import org.jetbrains.kotlin.js.backend.ast.JsInvocation;
-import org.jetbrains.kotlin.js.backend.ast.JsNameRef;
-import org.jetbrains.kotlin.js.backend.ast.JsNumberLiteral;
+import org.jetbrains.kotlin.js.backend.ast.*;
 import com.intellij.util.SmartList;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns;
 import org.jetbrains.kotlin.js.descriptorUtils.DescriptorUtilsKt;
 import org.jetbrains.kotlin.js.patterns.NamePredicate;
+import org.jetbrains.kotlin.js.translate.context.TemporaryVariable;
 import org.jetbrains.kotlin.js.translate.context.TranslationContext;
 import org.jetbrains.kotlin.js.translate.general.AbstractTranslator;
 import org.jetbrains.kotlin.js.translate.general.Translation;
@@ -87,17 +85,23 @@ public final class StringTemplateTranslator extends AbstractTranslator {
 
             KotlinType type = context().bindingContext().getType(entryExpression);
 
-            if (translatedExpression instanceof JsNumberLiteral) {
+            if (type != null && KotlinBuiltIns.isCharOrNullableChar(type)) {
+                if (type.isMarkedNullable()) {
+                    TemporaryVariable tmp = context().declareTemporary(translatedExpression);
+                    append(new JsConditional(JsAstUtils.equality(tmp.assignmentExpression(), JsLiteral.NULL),
+                                             JsLiteral.NULL,
+                                             JsAstUtils.charToString(tmp.reference())));
+                }
+                else {
+                    append(JsAstUtils.charToString(translatedExpression));
+                }
+            }
+            else if (translatedExpression instanceof JsNumberLiteral) {
                 append(context().program().getStringLiteral(translatedExpression.toString()));
-                return;
             }
-
-            if (type == null || type.isMarkedNullable()) {
+            else if (type == null || type.isMarkedNullable()) {
                 append(TopLevelFIF.TO_STRING.apply((JsExpression) null, new SmartList<>(translatedExpression), context()));
             }
-            else if (KotlinBuiltIns.isChar(type)) {
-                append(JsAstUtils.charToString(translatedExpression));
-            }
             else if (mustCallToString(type)) {
                 append(new JsInvocation(new JsNameRef("toString", translatedExpression)));
             }

js/js.translator/testData/box/char/charInStringTemplate.kt

@@ -0,0 +1,24 @@
+package foo
+
+var log = ""
+
+fun sideEffects(c: Char?, msg: String): Char? {
+    log += msg
+    return c
+}
+
+fun box(): String {
+    val name = run { "John" }        // Force compiler to actually do some concatenation
+    assertEquals("${'$'}name = $name", "\$name = John")
+
+    val ch1: Char? = null
+    assertEquals("${ch1}name = $name", "nullname = John")
+
+    val ch2: Char? = '$'
+    assertEquals("${ch2}name = $name", "\$name = John")
+
+    assertEquals("${sideEffects('$', "1")!!}${sideEffects('n', "2")}ame = $name", "\$name = John")
+    assertEquals(log, "12")
+
+    return "OK"
+}