when calling function stored in local variable as unary operation, don't forget to push function instance (KT-1953)

I'm sure that there are similar cases that still don't work;  please let me know if you find any
#KT-1953 fixed

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

@@ -1023,19 +1023,7 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> {
 
         int index = lookupLocal(descriptor);
         if (index >= 0) {
-            if(descriptor instanceof VariableDescriptor) {
+            return stackValueForLocal(descriptor, index);
-                Type sharedVarType = typeMapper.getSharedVarType(descriptor);
-                final JetType outType = ((VariableDescriptor) descriptor).getType();
-                if(sharedVarType != null) {
-                    return StackValue.shared(index, asmType(outType));
-                }
-                else {
-                    return StackValue.local(index, asmType(outType));
-                }
-            }
-            else {
-                return StackValue.local(index, TYPE_OBJECT);
-            }
         }
 
         if (descriptor instanceof PropertyDescriptor) {
@@ -1157,6 +1145,22 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> {
         return value;
     }
 
+    private StackValue stackValueForLocal(DeclarationDescriptor descriptor, int index) {
+        if(descriptor instanceof VariableDescriptor) {
+            Type sharedVarType = typeMapper.getSharedVarType(descriptor);
+            final JetType outType = ((VariableDescriptor) descriptor).getType();
+            if(sharedVarType != null) {
+                return StackValue.shared(index, asmType(outType));
+            }
+            else {
+                return StackValue.local(index, asmType(outType));
+            }
+        }
+        else {
+            return StackValue.local(index, TYPE_OBJECT);
+        }
+    }
+
     public int lookupLocal(DeclarationDescriptor descriptor) {
         return myFrameMap.getIndex(descriptor);
     }
@@ -2198,6 +2202,10 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> {
     }
 
     private StackValue invokeOperation(JetOperationExpression expression, FunctionDescriptor op, CallableMethod callable) {
+        int functionLocalIndex = myFrameMap.getIndex(op);
+        if (functionLocalIndex >= 0) {
+            stackValueForLocal(op, functionLocalIndex).put(ClosureCodegen.getInternalClassName(op).getAsmType(), v);
+        }
         ResolvedCall<? extends CallableDescriptor> resolvedCall = bindingContext.get(BindingContext.RESOLVED_CALL, expression.getOperationReference());
         assert resolvedCall != null;
         genThisAndReceiverFromResolvedCall(StackValue.none(), resolvedCall, callable);

compiler/testData/codegen/regressions/kt1953.kt

@@ -0,0 +1,9 @@
+fun box(): String {
+    val sb = StringBuilder()
+    fun String.plus() {
+        sb.append(this)
+    }
+
+    +"OK"
+    return sb.toString()!!
+}

compiler/testData/codegen/regressions/kt1953_class.kt

@@ -0,0 +1,14 @@
+class A {
+    private val sb: StringBuilder = StringBuilder()
+
+    fun String.plus {
+        sb.append(this)
+    }
+
+    fun foo(): String {
+        +"OK"
+        return sb.toString()!!
+    }
+}
+
+fun box(): String = A().foo()

compiler/tests/org/jetbrains/jet/codegen/ExtensionFunctionsTest.java

@@ -96,4 +96,14 @@ public class ExtensionFunctionsTest extends CodegenTestCase {
         createEnvironmentWithMockJdkAndIdeaAnnotations(CompilerSpecialMode.BUILTINS);
         blackBoxFile("regressions/kt1290.kt");
     }
+
+    public void testKt1953() throws Exception {
+        createEnvironmentWithMockJdkAndIdeaAnnotations(CompilerSpecialMode.JDK_HEADERS);
+        blackBoxFile("regressions/kt1953.kt");
+    }
+
+    public void testKt1953Class() throws Exception {
+        createEnvironmentWithMockJdkAndIdeaAnnotations(CompilerSpecialMode.JDK_HEADERS);
+        blackBoxFile("regressions/kt1953_class.kt");
+    }
 }