These are the slides used for the ReSharper + SemanticMerge webinar run with JetBrains on June 17th 2014. http://info.jetbrains.com/Webinar_ReSharper-SemanticMerge-Registration.html

2. No fear refactoring in the DVCS age
ReSharper + SemanticMerge
pablo santos @psluaces
@semanticmerge

3. Agenda
• Introduce SemanticMerge
• Walk through different refactor and merge cases using ReSharper +
Semantic
• Q&A

4. 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 ;-)

5. 3-way merge - reminder
Theirs Yours
S
Source Destination
D
Base
Base
B
Result
R
0
main
1 3
4
task001
2 5 6
7
Base
Source
Destination

6. 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

7. Case0 – Add the same method twice

8. Case0 –What a conventional 3-way merge tool
does?
• No conflict!
• And two methods!!

9. 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

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

11. 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… :-)

12. Case 1 – Cleaned up code (II)

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

14. Case 2 - Split a class in subclasses

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

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

17. Case 3 – Divergent move

18. 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

19. 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?

20. 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

21. How can
semanticmerge affect
development?
1) It helps simplifying the mergesTODAY
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.

22. 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]

23. Process
base
base tree
source destination
Parser
source tree destination tree
Differ Differ
Merger
src-base diffs dst-base diffs
result
automatic conflicts
manual conflicts
source ops to apply

24. 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

25. Evil twin namespace 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

26. Multi-file
SemanticMerge