Refactoring merged code - ReSharper meets SemanticMerge

No fear refactoring in the DVCS age

ReSharper + SemanticMerge

pablo santos @psluaces@semanticmerge

Agenda

• Introduce SemanticMerge• Walk through different refactor and merge cases

using ReSharper + Semantic• Q&A

What is semanticmerge?

• 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 :-)

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

I guess you all know by now ;-)

3-way merge - reminder

Theirs Yours

SSource Destination

D

Base

BaseB

ResultR

0

main

1 3

4

task001

2 5 6

7

Base

Source

Destination

Can be used with any version control• Git• Mercurial• Perforce• TFS• And Plastic SCM

(Free trial available and very affordable)

http://www.semanticmerge.com/index.html#documentation

Case0 – Add the same method twice

Case0 – What a conventional 3-way merge tool does?

• No conflict!• And two methods!!

Case0 – What will a conventional 3-way merge tool do?• No conflict!• And two methods!!

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

Case0 – What SemanticMerge does• It *knows* about the methods so…

Case 1 – Cleaned up code

• Typical case where an Open Source contributor “helps” rearranging a class with ReSharper.• While another contributor was making changes in

the original file.• Merge will be a nightmare… :-)

Case 1 – Cleaned up code (II)

Case 1 – Cleaned up code (III) – ReSharper settings

Case 2 - Split a class in subclasses

Case 2 - Splitting a class in subclasses (II)• Refactor the file with ReSharper, two developers in

parallel

Case 2 - Splitting a class in subclasses (III - merge)

Case 3 – Divergent move

Case 4 – Code format changes

Semantic is able to discard the changes made on source (method call in multiple lines) and automatically accept the new param instead of raising a conflict resolution

Case 5 – Move/delete conflict

• What happens if you move a method inside a class• That is deleted on a different branch?• How the merge deals with this scenario?

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

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.

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

Multi-file SemanticMerge