KT-3652: Char is converted to Int when used inside string interpolation

#KT-3652 Fixed

compiler/backend/src/org/jetbrains/jet/codegen/AsmUtil.java

@@ -354,8 +354,8 @@ public class AsmUtil {
         v.invokevirtual("java/lang/StringBuilder", "append", "(" + type.getDescriptor() + ")Ljava/lang/StringBuilder;");
     }
 
-    public static StackValue genToString(InstructionAdapter v, StackValue receiver) {
-        Type type = stringValueOfOrStringBuilderAppendType(receiver.type);
+    public static StackValue genToString(InstructionAdapter v, StackValue receiver, Type receiverType) {
+        Type type = stringValueOfOrStringBuilderAppendType(receiverType);
         receiver.put(type, v);
         v.invokestatic("java/lang/String", "valueOf", "(" + type.getDescriptor() + ")Ljava/lang/String;");
         return StackValue.onStack(JAVA_STRING_TYPE);

compiler/backend/src/org/jetbrains/jet/codegen/ExpressionCodegen.java

@@ -1173,7 +1173,8 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> implem
         JetStringTemplateEntry[] entries = expression.getEntries();
 
         if (entries.length == 1 && entries[0] instanceof JetStringTemplateEntryWithExpression) {
-            return genToString(v, gen(entries[0].getExpression()));
+            JetExpression expr = entries[0].getExpression();
+            return genToString(v, gen(expr), expressionType(expr));
         }
 
         for (JetStringTemplateEntry entry : entries) {

compiler/backend/src/org/jetbrains/jet/codegen/intrinsics/ToString.java

@@ -40,6 +40,6 @@ public class ToString implements IntrinsicMethod {
             StackValue receiver,
             @NotNull GenerationState state
     ) {
-        return genToString(v, receiver);
+        return genToString(v, receiver, receiver.type);
     }
 }

compiler/testData/codegen/box/strings/kt3652.kt

@@ -0,0 +1,9 @@
+fun box(): String {
+ var a = 'a'
+
+  if ("${a++}x" != "ax") return "fail1"
+
+  if ("${a++}" != "b") return "fail2"
+
+  return "OK"
+}

compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxCodegenTestGenerated.java

@@ -1546,8 +1546,8 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                 doTest("compiler/testData/codegen/box/defaultArguments/constructor/kt2852.kt");
             }
             
-        }
-        
+            }
+            
         @TestMetadata("compiler/testData/codegen/box/defaultArguments/function")
         public static class Function extends AbstractBlackBoxCodegenTest {
             public void testAllFilesPresentInFunction() throws Exception {
@@ -3686,6 +3686,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest("compiler/testData/codegen/box/strings/ea35743.kt");
         }
         
+        @TestMetadata("kt3652.kt")
+        public void testKt3652() throws Exception {
+            doTest("compiler/testData/codegen/box/strings/kt3652.kt");
+        }
+        
         @TestMetadata("kt881.kt")
         public void testKt881() throws Exception {
             doTest("compiler/testData/codegen/box/strings/kt881.kt");