Git Anti Patterns - XP Days Ukraine 2017

1. $ git anti-patterns how to mess up with git and love it again LEMi ORHAN ERGiN Agile Software Craftsman, iyzico /lemiorhan @lemiorhan lemiorhanergin.com bit.ly/lemiorhan

2. /lemiorhan lemiorhanergin.com @lemiorhan LEMi ORHAN ERGiN agile software craftsman @ iyzico ex-Sony, ex-eBay founder of Turkish Software Craftsmanship Community

3. git is powerful but you have to know using it properly because of its internal structure

4. Are you using git if all you do is commit-push-pull use dropbox instead ANTIPATTERN DANGER as if it is dropbox ? 1DROPBOX-ISH GIT ANTI-PATTERN

5. learn no worries, I will cover how git behaves in 5 minutes git works how

6. the way it keeps FILES & FOLDERS .git folder, aka repository working copy staging area objects database the way it keeps REFERENCES directed acyclic graph keeping snapshots traversing graph branches, tags, heads git has 2 mechanisms

7. Source Code Working Copy you want to version changes

8. Source Code Working Copy $ git init Object Database .git Folder / Object Database Cache Staging Area / The Index initializing repo

9. Source Code Working Copy $ git init --bare Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server initializing bare repo

10. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy $ git add . preparing commits

11. folder folder folder file file file $ git add . preparing commits

12. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy $ git add . preparing commits

13. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy $ git commit -m “initial commit” commi!ing

14. $ git commit -m “initial commit” commi!ing folder folder folder file file file commit branch HEAD For more details, refer to book Git Internals by Scott Chacon

15. folder folder folder file file file commit $ git commit -m “second commit” commi!ing folder commit branch HEAD folder file folder For more details, refer to book Git Internals by Scott Chacon

16. folder folder folder file file file commit $ git commit -m “third commit” commi!ing folder commit folder file folder folder commit branch HEAD file For more details, refer to book Git Internals by Scott Chacon

17. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy $ git commit -m “initial commit” commi!ing

18. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy $ git remote add origin http://upstream.repo $ git push -u origin master pushing to remote

19. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy new changes from others are pushed

20. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy $ git fetch fetching changes

21. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy $ git merge FETCHED_HEAD updating working copy

22. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy $ git pull git fetch + git merge ge!ing changes to source code

23. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy want to update last commit

24. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy $ git reset --soft $ git commit --amend/ so" reseting cannot be reached Only the cache for the commit you reseted is removed from staging area for your current branch

25. folder folder folder file file file commit folder commit folder file folder folder commit branch HEAD file For more details, refer to book Git Internals by Scott Chacon $ git reset --soft $ git commit --amend/ so" reseting

26. folder folder folder file file file commit folder commit folder file folder folder commit branch HEAD file For more details, refer to book Git Internals by Scott Chacon $ git reset --soft $ git commit --amend/ so" reseting

27. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy want to squash or change last commits

28. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy $ git reset --mixed mixed reseting cannot be reached entries for commits, files and folders are removed from staging area

29. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy want to get rid of last commits

30. Object Database .git Folder / Object Database Cache Staging Area / The Index Remote Upstream Repo / Remote Repo Server Source Code Working Copy $ git reset --hard hard reseting cannot be reached removed from staging area removed from working copy

31. are you brave enough to jump to any commit ? jump to a branch create a branch from a commit create a branch from a tag ANTIPATTERN DANGER $ git checkout feature/PA-121 $ git checkout -b fix/missing-sign-parameter 2449be8 $ git checkout -b hotfix/v1.1 tags/v1 2BROKEN TIME MACHINE ANTI-PATTERN

32. are you sure? are you brave enough to jump to any commit ?

33. do you have loooooong living topic branches ? ANTIPATTERN DANGER 3LONG LIVING BRANCHES ANTI-PATTERN

34. do you have loooooong living topic branches ? welcome to merge hell

35. before merging do you validate commits back to source ? ANTIPATTERN DANGER code review, continuous integration, automated testing… 4TOO LATE TO VALIDATE ANTI-PATTERN

36. before merging do you validate commits back to source ? areyou sure?

37. merge and unmerge do you o!en need to just before releases ? ANTIPATTERN DANGER 5CHERRY-PICK OBSSESSION ANTI-PATTERN

38. merge and unmerge do you o!en need to just before releases ? master HEAD TAG/v13 version 14 $ git cherry-pick Every-Single-Commit-We-Want-To-Deploy

39. the commit graph ? do you fully understand ANTIPATTERN DANGER 6DEATH ON COMMIT GRAPH ANTI-PATTERN

40. the commit graph ? do you fully understand topic and shared branches, tracking branches, tags, HEADs, merge commits, reverted commits…

41. Cure?

42. Commit Early, Commit O"en Perfect Later, Publish Once

43. STEP 0 split your big feature into mini shippable tasks master HEAD TOPIC ORIGIN/master refactorings tasks, like rest endpoints red-green-refactor each task will have a branch, not a feature

44. STEP 1 commit early commit o!en no need to compile no need for CI it’s only for versioning do not push master HEAD TOPIC ORIGIN/master

45. always pull with rebase $ git pull --rebase origin master to get forced pushes securely to rebase your commits master HEAD TOPIC STEP 2 ORIGIN/master and do it o!en!

46. $ git pull --rebase origin master master HEAD TOPIC STEP 2 ORIGIN/master always pull with rebase to get forced pushes securely to rebase your commits and do it o!en!

47. $ git pull --rebase origin master master HEAD TOPIC STEP 2 ORIGIN/master if you branch is pushed already $ git push -f always pull with rebase to get forced pushes securely to rebase your commits and do it o!en!

48. $ git pull --rebase origin master master HEAD TOPIC STEP 2 ORIGIN/master if you branch is pushed already $ git push -f Sync source branch a!erwards $ git fetch origin master:master always pull with rebase to get forced pushes securely to rebase your commits and do it o!en!

49. perfect later make it single commit $ git reset HEAD~3 $ git rebase -i HEAD~3 $ git merge --squash HEAD TOPIC STEP 3 ORIGIN/master tests are passing app is working code is reviewed (*) master

50. HEAD TOPIC STEP 3 ORIGIN/master perfect later make it single commit tests are passing app is working code is reviewed (*) master $ git reset HEAD~3 $ git rebase -i HEAD~3 $ git merge --squash

51. Use feature ﬂags/toggles HEAD TOPIC STEP 4 ORIGIN/master if feature should be disabled merge back to source $ git checkout master $ git merge topic master

52. Use feature ﬂags/toggles master HEAD TOPIC STEP 4 ORIGIN/master if feature should be disabled merge back to source $ git checkout master $ git merge topic

53. Continuous Integration validates master branch continuouslymaster HEAD TOPIC ORIGIN/master Pull requests can be used to review code and to validate before merging back to master Scrum tasks are mapped to commits, not stories Github Flow can be used to govern overall TRUNK-BASED DEVELOPMENT let's make git great again Feature ﬂags should be used whenever possible Commit early & o"en perfect later, publish once philosophy Deliver frequently be prepared to send every single commit Deleting branches a"er merge will make your commit graph readable

54. use terminal GUIs are prison balls of developers it’s ok to use GUIs while checking diﬀs, resolving conﬂicts and viewing commit graph BUTTON ADDICT ANTI-PATTERN 7 ANTIPATTERN DANGER

55. stop adding prevent commits from being big ball of muds every change OMNIBUS BILL ANTI-PATTERN 8 ANTIPATTERN DANGER

56. stop adding prevent commits from being big ball of muds every change local change sets at JetBrains IDEs

57. stop adding every change partial add

58. messages are read! # WHAT # <issue id> (this commit will...) <subject> # WHY and HOW # Explain why this change is being made # RELATED # Provide links or keys to any relevant issues or other resources # REMEMBER # use lower case in the subject line # start with a verb in imperative tone in the subject line # do not end the subject line with a period # separate subject from body with a blank line # use the body to explain what and why vs. how # can use multiple lines with "-" for bullet points in body $ git config --global commit.template ~/.git-commit-template.txt $ git config --global commit.cleanup strip use git commit templates to create be"er commit messages comtmi F*CKING COMMIT MESSAGES ANTI-PATTERN 9 ANTIPATTERN DANGER

59. messages are read! use git commit templates to create be"er commit messages comtmi

60. ANTIPATTERN DANGER 10ZOMBIE REBASE ANTI-PATTERN Rebase Conﬂicts Death by master HEAD TOPIC

61. TOPIC master c1 c2 c3 c4 c7 HEAD c5 c6c5 c6 git:(topic) $ git rebase master rebase how really works command

64. TOPIC master c1 c2 c3 c4 c7 HEAD c5 c6c5 c6 c5' REPLAY #1 git:(topic) $ git rebase master orig_HEAD rebase how really works command

65. TOPIC master c1 c2 c3 c4 c7 c5 c6c5 c6 c5' c6c6' git:(topic) $ git rebase master HEAD REPLAY #2 orig_HEAD rebase how really works command

66. TOPIC master c1 c2 c3 c4 c7 HEAD c5 c6c5 c6 c5' c6c6' git:(topic) $ git rebase master REWIND orig_HEAD rebase how really works command

67. master c1 c2 c3 c4 c7 c5' c6c6' git:(topic) $ git rebase master TOPIC HEAD REWIND rebase how really works command

68. master HEAD TOPIC YOU STILL WANT TO REBASE, RIGHT?

69. master HEAD TOPIC $ git merge topicmerge to branches: merge with squash: squash and rebase: $ git merge topic --squash $ git reset HEAD~8 $ git commit $ git rebase master

70. 1. DROPBOX-ISH GIT 2. BROKEN TIME MACHINE 3. LONG LIVING BRANCHES 4. TOO LATE TO VALIDATE 5. CHERRY-PICK OBSSESSION 6. DEATH ON COMMIT GRAPH 7. BUTTON ADDICT 8. TRASH HOUSE 9. OMNIBUS BILL 10. F*CKING COMMIT MESSAGES 11. ZOMBIE REBASE 12. CODE LOSING SYNDROME 13. MESS UP WITH THE ROLLBACK 14. CENTRALIZED GIT 15. MERGE FANATIC 16. BRANCH CEMETERY 17. UNCONTROLLED POWER 18. WEB OF REPOSITORIES 19. ORACLE SYNDROME 20. WAITING FOR HACKERS 21. EVIL MERGE 22. BRANCH OVERDOSE 23. CHUCKY THE COMMAND 24. NO HERO TO SAVE LIVES 25. DUPLICATE COMMITS 26. BIG FAT COMMIT 27. CONFLICT-FOBIA 28. LIVING AT DETACHED HEAD STATE

71. RECAP what was really happened at that time? LET’S

72. master TAG/v1.1 login HEAD DETACHED HEAD STATE $ git checkout cecd95914 Note: checking out 'cecd95914'. You are in 'detached HEAD' state. You can look around, make experimental changes and commit them, and you can discard any commits you make in this state without impacting any branches by performing another checkout. LIVING AT DETACHED HEAD STATE ANTI-PATTERN 11 ANTIPATTERN DANGER

73. master TAG/v1.1 login DETACHED HEAD STATE $ git rebase (and conflicts happen) $ git checkout HEAD~2 $ git checkout 43e3ab01 $ git checkout tags/v1.1 WHEN IT HAPPENS HEAD

74. master TAG/v1.1 login HEAD poor little developer...

75. master TAG/v1.1 login HEAD $ git checkout master

76. master TAG/v1.1 login HEAD $ git reflog aa67e3a2c HEAD@{0}: rebase finished: returning to refs/heads/fix/java-sql-Date-violates-LSR aa67e3a2c HEAD@{1}: rebase: fixes UnsupportedOperationException while calling toIstant() method of java.sql.Date a45f3c4e5 HEAD@{2}: rebase: checkout develop 630ddad6e HEAD@{3}: checkout: moving from develop to fix/java-sql-Date-violates-LSR b26cf7a1a HEAD@{4}: rebase: checkout develop 630ddad6e HEAD@{5}: checkout: moving from develop to fix/java-sql-Date-violates-LSR b26cf7a1a HEAD@{6}: pull: Fast-forward 8b59f8f50 HEAD@{7}: checkout: moving from fix/java-sql-Date-violates-LSR to develop

77. $ git reflog 630ddad6e the one we are searching for master TAG/v1.1 login HEAD aa67e3a2c HEAD@{0}: rebase finished: returning to refs/heads/fix/java-sql-Date-violates-LSR aa67e3a2c HEAD@{1}: rebase: fixes UnsupportedOperationException while calling toIstant() method of java.sql.Date a45f3c4e5 HEAD@{2}: rebase: checkout develop 630ddad6e HEAD@{3}: checkout: moving from develop to fix/java-sql-Date-violates-LSR b26cf7a1a HEAD@{4}: rebase: checkout develop 630ddad6e HEAD@{5}: checkout: moving from develop to fix/java-sql-Date-violates-LSR b26cf7a1a HEAD@{6}: pull: Fast-forward 8b59f8f50 HEAD@{7}: checkout: moving from fix/java-sql-Date-violates-LSR to develop

78. master typofix TAG/v1.1 login HEAD $ git branch typofix 630ddad6e

79. master typofix TAG/v1.1 login HEAD $ git branch typofix 630ddad6e KEEP CALM, NOTHING WILL BE LOST

80. LEMi ORHAN ERGiN agile software craftsman @ iyzico /lemiorhan lemiorhanergin.com @lemiorhan ANTIPATTERN DANGER thank you all! Feedback: bit.ly/lemiorhan

Git Anti Patterns - XP Days Ukraine 2017

Lemi Orhan Ergin

Git Anti Patterns - XP Days Ukraine 2017