Merge like it's 2099:

Every developer working in a team of more than 2 person has experienced conflicts when merging, rebasing or cherry picking a commit. Resolving those conflicts is a tedious task and it's time for a change. This talk will propose a solution to merge smarter and not harder.

Transcript

1. MERGING LIKE IT’S 2099 ! INTRODUCING THE AUTOMERGETOOL Droidcon London 2017 1
2. ABOUT… XAVIER F. GOUCHET ANDROID ARCHITECT AT DEEZER FLUENT IN ANDROID SINCE CUPCAKE ON ALL SOCIAL NETWORKS @XGOUCHET 2
6. OUR FIRST COMMIT commit 1e7dfd3e0c6715f3e611975892d8618afb7c33a6 Author: _alex <_alex@...> Date: Tue Jan 6 14:56:57 2009 +0000 Created folder git-svn-id: file:///opt/svn-android/trunk@2 966f65aa-2a5b-49e2-8ec6-7a0f9cdf547d 6
7. SINCE THEN… 8 years 12’000+ commits 4 main repositories 30+ different committers 750’000+ lines of code 100’000+ lines of comments 10’000+ source files 7
8. WHAT'S THE PROBLEM HERE ? CVS IS TEXT BASED ! 8
9. TEXT BASED VERSIONNING Diff / Merge is based on a stream of characters Easy (and fast-ish) to compute Recognizes newlines / whitespace Doesn’t understand any syntax¹ 9
10. COMMON CONFLICTS The `imports` section Same change on both sides Additions at the same place Changes in different lines in same block Unrelated changes on same line … ? 10
11. “Most of those are fairly easy to solve, but usually tedious.” 11
12. AUTOMERGETOOL 12
13. BASIC PRINCIPLE Integrate with Integrate with 3rd party tools Many simple automatic solvers Language agnostic Manual solving as a “last resort” solution 13
14. EXAMPLE 1 : EASY CASE $ git merge master 14
15. EXAMPLE 1 : EASY CASE $ git mergetool [AMT] → Trying merge with abc 15
16. EXAMPLE 1 : EASY CASE [AMT] ✗ abc didn’t solve all conflicts [AMT] → Trying merge with jkl 16
17. EXAMPLE 1 : EASY CASE [AMT] ✗ jkl didn’t solve all conflicts [AMT] → Trying merge with xyz 17
18. EXAMPLE 1 : EASY CASE [AMT] ✓ xyz merged successfully … 18
19. EXAMPLE 2 : HARDER CASE $ git merge master 19
20. EXAMPLE 2 : HARDER CASE $ git mergetool [AMT] → Trying merge with abc 20
21. EXAMPLE 2 : HARDER CASE [AMT] ✗ abc didn’t solve all conflicts [AMT] → Trying merge with jkl 21
22. EXAMPLE 2 : HARDER CASE [AMT] ✗ jkl didn’t solve all conflicts [AMT] → Trying merge with xyz 22
23. EXAMPLE 2 : HARDER CASE [AMT] ✗ xyz didn’t solve all conflicts [AMT] → Trying merge with manualToolX 23
24. EXAMPLE 2 : HARDER CASE 24
25. CONFIGURATION ~/.gitconfig OR {project}/.git/config 25
26. [merge] tool = amt conflictstyle = diff3 [mergetool "amt"] cmd = amt.py -l $LOCAL -r $REMOTE -b $BASE -m $MERGED 26
27. [amt] tools = java_imports;gen_additions;custom;meld [mergetool "java_imports"] order = android [mergetool "custom"] cmd = custom.sh "$LOCAL" "$REMOTE" "$MERGED" extensions = html;xml 27
28. AUTOMATIC SOLVERS 28
29. LANGUAGE AGNOSTIC Addition at the same line Deleting the same block Woven conflicts Conflict simplification … 29
30. LANGUAGE SPECIFICS Java Imports Kotlin Imports (WIP) XML/Json Structural edits (WIP) … 30
31. EARLY RESULTS 31
32. FIRST TRY : REBASED A HUUUGE COMMIT (+1537/-3250) Number of conflicted files : 37 Number of conflicts : 62 Number of conflicts solved manually : 3 Time spent : 2 minutes plus time to write AutoMergeTool 32
33. DAILY USE SINCE DECEMBER 2016 Number of manual conflicts down by 75% Mood increased by 200% 33
34. WHERE CAN I GET IT ? Github : Pip / Easyinstall github.com/xgouchet/AutoMergeTool $ pip install automergetool 34
35. GOING FURTHER 35
36. GOING FURTHER 36
37. GOING FURTHER 37
38. ¹ GOING EVEN FURTHER ($6.90/month) (XML only) Semantic Merge Delta XML Why doesn’t this exist yet: Syntax-aware merge 38
39. F.A.Q. Does it work with `.xyz` files ? Even with binary formats ? Can I write a custom solver? Can it break my code ? How to write a solver ? Template 39
40. THANKS FOR YOUR ATTENTION ANY QUESTION ? https://github.com/xgouchet/AutoMergeTool 40