Refactoring-aware Configuration Management for Object-Oriented

Programs

Written by: Danny Dig, Kashif Manzoor, Ralph Johnson, and Tien NguyenACM International Conference on Software Engineering, May 2007

Presented by: Bennie Lewis and Volodymyr PryymaSchool of Electrical Engineering and Computer Science

University of Central Florida

Overview

• Introduction• Motivation• Background and Terminology• Merging Algorithm• Implementation• Case Study• Related Work• Conclusions and Future Work

Introduction

• What is refactoring?• Automated refactoring tools– Become very popular– Help change source code quicker

• Demands on SCM systems– Refactoring cuts across module boundaries– Problems with merging refactorings

Introduction

• Refactoring process– Developers check in code– Senior designer makes global changes

• SCM Systems– Unreliable– Method overriding

Introduction

• MolhadoRef– Better merging– Better preservation of program history– Better understanding of program evolution– Operation-based approach– Eclipse as front end– Performs better than CVS

Introduction

• Paper contributions– Refactorings as strongest link in SCM– Algorithm for merging refactorings and edits– Describes the implementation– Evaluates the effectiveness

Motivation

• Text-based SCM systems– No understanding of semantics of changes– No understanding of syntax/semantics of

language– Compile-time errors– Lose the history if refactorings

Background and Terminology

• Operation-based approach– Sequence of operations– Distinguish between operations

• MolhadoRef operations– API refactorings– API edits– Code edits

Background and Terminology

• API refactorings– Rename package/class/method– Move class/method– Change method signature

• API edits– Added package/class/method/field– Deleted package/class/method/field

Background and Terminology

• Code edits– No well defined semantics– Merged textually

• However, API edits/refactorings are merged semantically

Background and Terminology

• Operations– Usually have preconditions• Adding a method• Changing method name

– Inappropriate use

Background and Terminology

• Some definitions– Commute– Conflict– Ordering dependence

Merging Algorithm

• High-level overview– Step 1: detect API and code edits– Step 2: search for conflicts– Step 3: invert each refactoring– Step 4: merge edits textually– Step 5: replay the refactorings

Merging Algorithm

• Detecting Operations– Three-way textual differencer– Construct higher level API edits– Removes edits due to refactorings

Merging Algorithm

• Detecting/Solving of conflicts– Matrix of predicates– Dependencies– User assistance

Merging Algorithm

• Inverting refactoring– Executes inverse refactoring operation– Preconditions• Name collisions

– Worst case scenarios• Treated as text-based merging

Merging Algorithm

• Textual merging– Three-way merging– Same as most text-based SCM systems– Due to inverted refactorings all conflicts are

eliminated– Merging is automatic– MolhadoRef outperforms text-based merging

when multiple refactorigns occur

Implementation

• MolhadoRef acts as Eclipse plugin• It is an object-oriented infrustructure• Java code is translated into Molhado structure• Can be retrofitted on CVS

Case Study• MolhadoRef compared with text-based CVS• MolhadoRef itself for used for analysis• CVS– Many same-line conflicts– Had 48 compile and run-time errors– Took 105 minutes

• MolhadoRef– Much fewer conflicts– Automatically merged all same-line conflicts– Did not introduce any compile or run-time errors– Took less than a minute

Related Work

• SCM Systems– Long history– Provide powerful configuration management

services

• Software Merging– Text-based tool– Lines are as considered indivisible units

Related Work

• Operation-Based Merging– A type of semantic-based merging– Better conflict detection/solving– A few previous operation-based merging systems

were presented

Conclusions and Future Work

• Refactoring creates problems for modern Software Configuration Management systems

• MolhadoRef is aware of refactorings• MolhadoRef is implemented as Eclipse plugin• Future work = empirical study on a group that

uses MolhadoRef

Paper Critique

• Advantages– Novel algorithm– Outperforms CVS– Implemented as Eclipse plugin– Can be added to CVS

• Disadvantages– Only one case study– No performance results with real users

Questions?