git anti patterns - xp days ukraine 2017

$ git anti-patterns

how to mess up with git and love it again

LEMi ORHAN ERGiNAgile Software Craftsman, iyzico

/lemiorhan @lemiorhan lemiorhanergin.com bit.ly/lemiorhan

/lemiorhan lemiorhanergin.com @lemiorhan

LEMi ORHAN ERGiNagile software craftsman @ iyzico ex-Sony, ex-eBay founder of Turkish Software Craftsmanship Community

git is powerfulbut you have to know using it properly

because of its internal structure

Are you using git

if all you do is commit-push-pulluse dropbox instead

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as if it is dropbox ?

1DROPBOX-ISH GIT ANTI-PATTERN

learnno worries, I will cover how git behaves in 5 minutes

git workshow

the way it keeps FILES & FOLDERS.git folder, aka repository

working copy staging area

objects database

the way it keeps REFERENCESdirected acyclic graph keeping snapshots traversing graph branches, tags, heads

git has 2 mechanisms

Source CodeWorking Copy

you want to version changes


$ git init

Object Database.git Folder / Object Database

CacheStaging Area / The Index

initializing repo


$ git init --bare



RemoteUpstream Repo / Remote Repo

Server

initializing bare repo




Server


$ git add . preparing commits

folder

folder

folder

file

file

file





Server






Server


$ 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

folder

folder

folder

file

file

file

commit

$ git commit -m “second commit” commi!ing

folder

commit

branch

HEAD

folder

file

folder


folder

folder

folder

file

file

file

commit

$ git commit -m “third commit” commi!ing

folder

commit

folder

file

folder

folder

commit

branch

HEAD

file





Server






Server


$ git remote add origin http://upstream.repo$ git push -u origin master pushing to remote




Server


new changes from others are pushed




Server


$ git fetch fetching changes




Server


$ git merge FETCHED_HEAD updating working copy




Server


$ git pullgit fetch + git merge

ge!ing changes to source code




Server


want to update last commit




Server


$ 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

folder

folder

folder

file

file

file

commit

folder

commit

folder

file

folder

folder

commit

branch

HEAD

file


$ git reset --soft $ git commit --amend/ so" reseting




Server


want to squash or change last commits




Server


$ git reset --mixed mixed reseting

cannot be reached

entries for commits, files

and folders are removed from staging area




Server


want to get rid of last commits




Server


$ git reset --hard hard reseting

cannot be reached

removed from staging area

removed from working copy

are you brave enough tojump to any commit ?

jump to a branch

create a branch from a commit

create a branch from a tag

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$ 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

are you sure?

are you brave enough tojump to any commit ?

do you haveloooooong living

topic branches ?

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3LONG LIVING BRANCHES ANTI-PATTERN

do you haveloooooong living

topic branches ?

welcome tomerge hell

before mergingdo you validate commits

back to source ?

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code review, continuous integration, automated testing…

4TOO LATE TO VALIDATE ANTI-PATTERN

before mergingdo you validate commits

back to source ? are you sure?

merge and unmergedo you o!en need to

just before releases ?

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5CHERRY-PICK OBSSESSION ANTI-PATTERN

merge and unmergedo you o!en need to

just before releases ?

master

HEAD

TAG/v13

version 14

$ git cherry-pick Every-Single-Commit-We-Want-To-Deploy

the commit graph ?do you fully understand

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6DEATH ON COMMIT GRAPH ANTI-PATTERN

the commit graph ?do you fully understand

topic and shared branches, tracking branches, tags, HEADs, merge commits, reverted commits…

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

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

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

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!


master

HEAD

TOPIC

STEP 2

ORIGIN/master

always pull with rebaseto get forced pushes securely to rebase your commits

and do it o!en!


master

HEAD

TOPIC

STEP 2

ORIGIN/master

if you branch is pushed already$ git push -f


and do it o!en!


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


and do it o!en!

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

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

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

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

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

use terminalGUIs are prison balls of developers

it’s ok to use GUIs while checking diffs, resolving conflicts and viewing commit graph

BUTTON ADDICT ANTI-PATTERN7

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stop adding

prevent commits from being big ball of mudsevery change

OMNIBUS BILL ANTI-PATTERN8

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stop adding

prevent commits from being big ball of mudsevery change

local change sets at JetBrains IDEs

stop adding every changepartial add

messages areread!

# 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

comt

mi

F*CKING COMMIT MESSAGES ANTI-PATTERN9

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messages areread!use git commit templates to create be"er commit messages

comt

mi

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10ZOMBIE REBASE ANTI-PATTERN

Rebase ConflictsDeath by

master

HEAD

TOPIC

TOPIC

master

c1 c2 c3 c4 c7

HEAD

c5 c6c5 c6

git:(topic) $ git rebase masterrebase how

really workscommand

TOPIC

master

c1 c2 c3 c4 c7

HEAD

c5 c6c5 c6 c5'

REPLAY #1

git:(topic) $ git rebase master

orig_HEAD

rebase how

really workscommand

TOPIC

master

c1 c2 c3 c4 c7

c5 c6c5 c6 c5' c6c6'


HEAD

REPLAY #2

orig_HEAD

rebase how

really workscommand

TOPIC

master

c1 c2 c3 c4 c7

HEAD

c5 c6c5 c6 c5' c6c6'


REWIND

orig_HEAD

rebase how

really workscommand

master

c1 c2 c3 c4 c7

c5' c6c6'


TOPIC

HEAD

REWIND

rebase how

really workscommand

master

HEAD

TOPIC

YOU STILL WANT TO REBASE, RIGHT?

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

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

RECAP

what was reallyhappened at that time?

LET’S

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-PATTERN11

ANTIPATTERN DANGER

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

master

TAG/v1.1

login

HEAD

poor little developer...

master

TAG/v1.1

login

HEAD

$ git checkout master

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 630ddad6e HEAD@{8}: rebase: updating HEAD

$ 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 630ddad6e HEAD@{8}: rebase: updating HEAD

master

typofix

TAG/v1.1

login

HEAD

$ git branch typofix 630ddad6e

master

typofix

TAG/v1.1

login

HEAD

$ git branch typofix 630ddad6e

KEEP CALM, NOTHING WILL BE LOST

LEMi ORHAN ERGiN

LEMi ORHAN ERGiNagile software craftsman @ iyzico

/lemiorhan lemiorhanergin.com @lemiorhan

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thank you all!Feedback: bit.ly/lemiorhan