semantic merge - no fear refactoring

No fear refactoring in the DVCS age

Enter SemanticMerge

pablo santos @psluaces@semanticmerge

meet us at booth #14

Agenda

• How to diff and merge refactored code with SemanticMerge• Under the hood: the inner workings of the tool• Next step: multi-file SemanticMerge• Towards Semantic version control

Tech from the 80’s

• Git and the DVCS pack came in 2005• They went mainstream (GitHub)• They all can do awesome merges• But they rely on old-fashioned diff and merge tools

You can do amazing things with DVCS

You can do amazing things with DVCS• It has greatly improved merge tracking• It does a great job finding the contributors for the

3-way merge

• But at the end of the day… it invokes an external 3-way merge tool to solve the merge

Simple example

Simple example

Simple example

What will a conventional 3-way merge tool do?• No conflict!• And two methods!!

What will a conventional 3-way merge tool do?• No conflict!• And two methods!!

• It simply finds two blocks of text being added and the original block being deleted… Doesn’t care about the code structure

What SemanticMerge does• It *knows* about the methods so…

What is semanticmerge?

• It is a 3-way merge tool (handles src, dst and base).

• It is refactor-aware and programming language-aware.

• Handles merging at the structure level and not textblock level.

• It means: • It first parses the code – creates intermediate

trees.• Then calculates diff pairs: base-src, base-dst.• Then looks for conflicts between pairs.

• Enabling eXtreme Refactoring was always the goal :-)

I guess you all know by now ;-)

How can semanticmerge affect development?We were always motivated by “the cost of change” and how refactoring can greatly help keeping code quality high and reducing maintenance costs.

SemanticMerge is all about helping teams to clean up the code, keep it readable and simple, without restrictions: do it in parallel, fine!

How can semanticmerge affect development?

1) It helps simplifying the merges TODAY already.

2) But more importantly it enables new scenarios that you’re not doing today: clean up the code, move methods, split classes… and just be able to merge it back.

A SemanticMerge scenario

A divergent move case

Detect conflicts that regular tools can’t• What if the same method is modified concurrently

at different lines?• Semantic detects the case and can force the

conflict resolution to be manual – a regular text based merge tool can’t do that because it doesn’t have the context

Under the hood

Creating a tree-like view of the code

namespace Sample [4-26]

int Add(int a, int b) [8-12]

int Mul(int a, int b) [14-18]

int Subst(int a, int b) [20-24]

using System [1]

using System.Text [2]

class Math [6-25]

Processbase

base tree

source destination

Parser

source tree destination tree

Diff er Diff er

Merger

src-base diff s dst-base diff s

result

automatic confl icts

manual confl icts

source ops to apply

Some complex cases – cyclic move

namespace Testnamespace Test

namespace Test

class Socket

class Socket

class DNS

class DNS

class Socket

base

source destination

class Utils

class Utils

class DNSclass Utils

Evil twinnamespace Test

class Socket

base

source

method Connect

namespace Test

class Socket

method Connect

namespace Test

class Socket

method Connect

destination

method Send method Send

Two methods with exactly the same signature can’t be added on the same

location -> conflict

Integrations

• IntelliJ (and Android Studio)• Git, Mercurial, TFS, Plastic SCM, Perforce, SVN…

everything!

Next steps

• JavaScript is the top request• C/C++ - Objective-C• XML• Ruby, Scala…•Mac OS X support• External Parsers (Delphi

already there)

Check UserVoice - http://plasticscm.uservoice.com

Next steps

• Semantic code review – each time you review code you would like to go straight to the point…

• Semantic blame/annotate – calculate the blame considering methods

• Semantic Method History• Semantic repository stats

Multi-file SemanticMerge