From 8c7352e6686381f59101408fd1dce71a5f71f39b Mon Sep 17 00:00:00 2001
From: Dmitry Petrov <dmitry.petrov@jetbrains.com>
Date: Fri, 14 Jul 2017 18:27:31 +0300
Subject: [PATCH] Generate constant "" for effectively empty string

---
 .../kotlin/codegen/ExpressionCodegen.java     | 25 +++++++++++--------
 .../bytecodeText/stringOperations/kt19037.kt  |  7 ++++++
 .../codegen/BytecodeTextTestGenerated.java    |  6 +++++
 3 files changed, 28 insertions(+), 10 deletions(-)
 create mode 100644 compiler/testData/codegen/bytecodeText/stringOperations/kt19037.kt

diff --git a/compiler/backend/src/org/jetbrains/kotlin/codegen/ExpressionCodegen.java b/compiler/backend/src/org/jetbrains/kotlin/codegen/ExpressionCodegen.java
index b4a19cf0953..91faa53d558 100644
--- a/compiler/backend/src/org/jetbrains/kotlin/codegen/ExpressionCodegen.java
+++ b/compiler/backend/src/org/jetbrains/kotlin/codegen/ExpressionCodegen.java
@@ -831,24 +831,29 @@ public class ExpressionCodegen extends KtVisitor<StackValue, StackValue> impleme
     public StackValue visitStringTemplateExpression(@NotNull KtStringTemplateExpression expression, StackValue receiver) {
         List<StringTemplateEntry> entries = preprocessStringTemplate(expression);
 
-        if (entries.size() == 1) {
+        Type type = expressionType(expression);
+
+        if (entries.size() == 0) {
+            return StackValue.constant("", type);
+        }
+        else if (entries.size() == 1) {
             StringTemplateEntry entry = entries.get(0);
             if (entry instanceof StringTemplateEntry.Expression) {
                 KtExpression expr = ((StringTemplateEntry.Expression) entry).expression;
-                return genToString(gen(expr), expressionType(expr));
+                return genToString(gen(expr), type);
             }
             else {
-                Type type = expressionType(expression);
                 return StackValue.constant(((StringTemplateEntry.Constant) entry).value, type);
             }
         }
-
-        return StackValue.operation(JAVA_STRING_TYPE, v -> {
-            genStringBuilderConstructor(v);
-            invokeAppendForEntries(v, entries);
-            v.invokevirtual("java/lang/StringBuilder", "toString", "()Ljava/lang/String;", false);
-            return Unit.INSTANCE;
-        });
+        else {
+            return StackValue.operation(type, v -> {
+                genStringBuilderConstructor(v);
+                invokeAppendForEntries(v, entries);
+                v.invokevirtual("java/lang/StringBuilder", "toString", "()Ljava/lang/String;", false);
+                return Unit.INSTANCE;
+            });
+        }
     }
 
     private void invokeAppendForEntries(InstructionAdapter v, List<StringTemplateEntry> entries) {
diff --git a/compiler/testData/codegen/bytecodeText/stringOperations/kt19037.kt b/compiler/testData/codegen/bytecodeText/stringOperations/kt19037.kt
new file mode 100644
index 00000000000..76b370bdc93
--- /dev/null
+++ b/compiler/testData/codegen/bytecodeText/stringOperations/kt19037.kt
@@ -0,0 +1,7 @@
+const val empty = ""
+
+val test1 = ""
+val test2 = "abc$empty"
+val test3 = "$empty$empty$empty"
+
+// 0 StringBuilder
\ No newline at end of file
diff --git a/compiler/tests/org/jetbrains/kotlin/codegen/BytecodeTextTestGenerated.java b/compiler/tests/org/jetbrains/kotlin/codegen/BytecodeTextTestGenerated.java
index a263a49029c..e0d7161dd8f 100644
--- a/compiler/tests/org/jetbrains/kotlin/codegen/BytecodeTextTestGenerated.java
+++ b/compiler/tests/org/jetbrains/kotlin/codegen/BytecodeTextTestGenerated.java
@@ -2090,6 +2090,12 @@ public class BytecodeTextTestGenerated extends AbstractBytecodeTextTest {
             doTest(fileName);
         }
 
+        @TestMetadata("kt19037.kt")
+        public void testKt19037() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeText/stringOperations/kt19037.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("nestedConcat.kt")
         public void testNestedConcat() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeText/stringOperations/nestedConcat.kt");