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

ANTIPATTERN DANGER

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

Server

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

folder

commit

branch

For more details, refer to book Git Internals by Scott Chacon

folder

commit

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

folder

commit

branch

folder

commit

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

folder

commit

folder

commit

branch

Server

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

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

commit

folder

commit

folder

commit

branch

folder

commit

folder

commit

folder

commit

branch

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 ?

ANTIPATTERN DANGER

5CHERRY-PICK OBSSESSION ANTI-PATTERN

merge and unmergedo you o!en need to

just before releases ?

master

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

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

ORIGIN/master

always pull with rebase

$ git pull --rebase origin master

to get forced pushes securely to rebase your commits

master

STEP 2

ORIGIN/master

and do it o!en!

master

STEP 2

ORIGIN/master

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

and do it o!en!

master

STEP 2

ORIGIN/master

if you branch is pushed already$ git push -f

and do it o!en!

master

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

STEP 3

ORIGIN/master

tests are passing app is working code is reviewed (*)

master

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

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

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

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

ANTIPATTERN DANGER

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

F*CKING COMMIT MESSAGES ANTI-PATTERN9

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

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10ZOMBIE REBASE ANTI-PATTERN

Rebase ConflictsDeath by

master

c1 c2 c3 c4 c7

c5 c6c5 c6

git:(topic) $ git rebase masterrebase how

really workscommand

master

c1 c2 c3 c4 c7

c5 c6c5 c6

really workscommand

master

c1 c2 c3 c4 c7

c5 c6c5 c6

really workscommand

master

c1 c2 c3 c4 c7

c5 c6c5 c6 c5'

REPLAY #1

git:(topic) $ git rebase master

orig_HEAD

rebase how

really workscommand

master

c1 c2 c3 c4 c7

c5 c6c5 c6 c5' c6c6'

REPLAY #2

orig_HEAD

rebase how

really workscommand

master

c1 c2 c3 c4 c7

c5 c6c5 c6 c5' c6c6'

REWIND

orig_HEAD

rebase how

really workscommand

master

c1 c2 c3 c4 c7

c5' c6c6'

REWIND

rebase how

really workscommand

master

YOU STILL WANT TO REBASE, RIGHT?

master

$ 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

what was reallyhappened at that time?

LET’S

master

TAG/v1.1

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

DETACHED HEAD STATE

$ git rebase (and conflicts happen)

$ git checkout HEAD~2

$ git checkout 43e3ab01

$ git checkout tags/v1.1

WHEN IT HAPPENS

master

TAG/v1.1

poor little developer...

master

TAG/v1.1

$ git checkout master

master

TAG/v1.1

$ 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

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

$ git branch typofix 630ddad6e

master

typofix

TAG/v1.1

$ git branch typofix 630ddad6e

KEEP CALM, NOTHING WILL BE LOST

LEMi ORHAN ERGiN

LEMi ORHAN ERGiNagile software craftsman @ iyzico

/lemiorhan lemiorhanergin.com @lemiorhan

ANTIPATTERN DANGER

thank you all!Feedback: bit.ly/lemiorhan

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