generate chained append calls for chained string concatenations

idea/src/org/jetbrains/jet/codegen/ExpressionCodegen.java

@@ -723,6 +723,14 @@ public class ExpressionCodegen extends JetVisitor {
     }
 
     private void invokeAppend(final JetExpression expr) {
+        if (expr instanceof JetBinaryExpression) {
+            final JetBinaryExpression binaryExpression = (JetBinaryExpression) expr;
+            if (binaryExpression.getOperationToken() == JetTokens.PLUS) {
+                invokeAppend(binaryExpression.getLeft());
+                invokeAppend(binaryExpression.getRight());
+                return;
+            }
+        }
         Type exprType = expressionType(expr);
         gen(expr, exprType);
         Method appendDescriptor = new Method("append", Type.getObjectType(CLASS_STRING_BUILDER),

idea/src/org/jetbrains/jet/lang/psi/JetBinaryExpression.java

@@ -2,6 +2,7 @@ package org.jetbrains.jet.lang.psi;
 
 import com.intellij.lang.ASTNode;
 import com.intellij.psi.PsiElement;
+import com.intellij.psi.tree.IElementType;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.jet.JetNodeTypes;
@@ -45,4 +46,8 @@ public class JetBinaryExpression extends JetExpression {
         return (JetSimpleNameExpression) findChildByType(JetNodeTypes.OPERATION_REFERENCE);
     }
 
+    public IElementType getOperationToken() {
+        return getOperationReference().getReferencedNameElementType();
+    }
+
 }

idea/tests/org/jetbrains/jet/codegen/NamespaceGenTest.java

@@ -568,6 +568,15 @@ public class NamespaceGenTest extends LightCodeInsightFixtureTestCase {
         assertEquals("jetLang", main.invoke(null, "jet", "Lang"));
     }
 
+    public void testStringPlusChained() throws Exception {
+        loadText("fun foo(s1: String, s2: String, s3: String) = s1 + s2 + s3");
+        final String text = generateToText();
+        final int firstStringBuilderCreation = text.indexOf("NEW java/lang/StringBuilder");
+        assertEquals(-1, text.indexOf("NEW java/lang/StringBuilder", firstStringBuilderCreation+1));
+        final Method main = generateFunction();
+        assertEquals("jet Lang", main.invoke(null, "jet", " ", "Lang"));
+    }
+
     private void binOpTest(final String text, final Object arg1, final Object arg2, final Object expected) throws Exception {
         loadText(text);
         System.out.println(generateToText());