Git merge in depth

How exactly 3-way recursive merge and rebase work.

1. git merge in depth Anton Chikin
2. test branch merge master to branch test branch merge branch to master test master
3. test branch merge master to branch test branch merge branch to master test master WAT
4. I don’t trust merge!
7. 3-way merge
8. master
9. master branch
10. master branch
11. master branch
12. master branch
13. master branch
14. master branch ?
15. master branch ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data
16. ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data master branch
17. ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data master branch ?
18. ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data master branch ? ?
19. ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data master branch ? ? ?
20. ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data master branch ? ? ? ?
21. ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data master branch ? ? ? ? Nearest common ancestor var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data
22. ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor master branch
23. ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch
24. ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo”
25. ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo”
26. ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var data = {} for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) def getData(string path)
27. ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var data = {} for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) def getData(string path)
28. def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {}
29. def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} ?????????????
30. def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} ?????????????
31. def getData(string path) <<<<<<< HEAD var data = Map() ||||||| merged common ancestors var data = {} ======= var data = Array() >>>>>>> branch
32. def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} var data = Map() for l in visit(path)
33. def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} var data = Map() for l in visit(path)
34. def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} var data = Map() for l in visit(path) data[l.id] = l.data
35. def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} var data = Map() for l in visit(path) data[l.id] = l.data
36. def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} var data = Map() for l in visit(path) data[l.id] = l.data return data.JSON()
37. def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} var data = Map() for l in visit(path) data[l.id] = l.data return data.JSON()
38. master branch ?
39. master branch
40. master branch merge master into branch
41. master branch merge master into branch
42. branch merge branch into master master
43. recursive 3-way merge
44. master Let’s take a look at a more complicated picture
45. master hotfix Let’s take a look at a more complicated picture
46. master hotfix Let’s take a look at a more complicated picture
47. master feature hotfix Let’s take a look at a more complicated picture
48. master hotfix feature Let’s take a look at a more complicated picture
49. master hotfix feature Let’s take a look at a more complicated picture
50. master M hotfix feature Let’s take a look at a more complicated picture
51. master M M hotfix feature Let’s take a look at a more complicated picture
52. master M M ? hotfix feature Let’s take a look at a more complicated picture
53. master M M ? hotfix feature Let’s take a look at a more complicated picture nearest common ancestor
54. master M M ? hotfix feature How to deal with two nearest common ancestors? nearest common ancestor nearest common ancestor
55. master M M ? hotfix nearest common ancestor Step 1: find nearest common ancestor of those ancestors
56. master M M ? hotfix Step 2: merge them into “fake” commit nearest common ancestor
57. master M M ? hotfix Step 3: Merge our commits using that “fake” ancestor nearest common ancestor
58. master M M hotfix M nearest common ancestor This process can be recursive
59. master M M hotfix feature M
60. And what about rebase?
61. master branch master A B C
62. master branch master A B C nearest common ancestor Again, find NCO
63. master branch master diff B diff C diff A A B C Create diffs between each commits starting from NCO
64. master branch master A B C diff B diff C diff A Move branch head to master
65. master branch master A B C A’ diff B diff C Apply each diff on top of latest master commit
66. master branch master A B C A’ B’ diff C Apply each diff on top of latest master commit
67. master branch master A B C A’ B’ C’ Apply each diff on top of latest master commit
68. @1,1 - A + B What does it mean to “apply diff”? Diff format is quite simple: In the first line
69. @1,1 - A + B Diff format is quite simple: In the first line replace “A” What does it mean to “apply diff”?
70. @1,1 - A + B Diff format is quite simple: In the first line replace “A” with “B” What does it mean to “apply diff”?
71. A B C @1,1 - A + B B B C What does it mean to “apply diff”?
72. D B C @1,1 - A + B ???????? B C What if first line in file is not “A” but “D”? Same as in merge - conflict! What does it mean to “apply diff”?
73. D B C @1,1 - A + B ???????? B C What if first line in file is not “A” but “D”? Same as in merge - conflict! What does it mean to “apply diff”?
74. master branch branch master A’ B’ C’ A B C M Merge and rebase give you different branch structure but the same result
75. Merge commits “train station”
76. Merge commits “subway”
77. Finally - don’t be afraid of recursive merge - merge a ->b == merge b ->a - merge == rebase - prefer merge over rebase - merge will never never let you down
78. •http://think-like-a-git.net/ •http://git-school.github.io/visualizing-git/ Resources
79. Questions?
80. git merge in depth Anton Chikin