Git Anti Patterns - XP Days Ukraine 2017
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Transcript of 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
Source CodeWorking Copy
$ git init
Object Database.git Folder / Object Database
CacheStaging Area / The Index
initializing repo
Source CodeWorking Copy
$ git init --bare
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
initializing bare repo
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
$ git add . preparing commits
folder
folder
folder
file
file
file
$ git add . preparing commits
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
$ git add . preparing commits
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
$ git commit -m “initial commit” commi!ing
$ 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
For more details, refer to book Git Internals by Scott Chacon
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
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
$ git commit -m “initial commit” commi!ing
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
$ git remote add origin http://upstream.repo$ git push -u origin master pushing to remote
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
new changes from others are pushed
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
$ git fetch fetching changes
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
$ git merge FETCHED_HEAD updating working copy
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
$ git pullgit fetch + git merge
ge!ing changes to source code
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
want to update last commit
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking 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
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
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
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
want to squash or change last commits
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
$ git reset --mixed mixed reseting
cannot be reached
entries for commits, files
and folders are removed from staging area
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
want to get rid of last commits
Object Database.git Folder / Object Database
CacheStaging Area / The Index
RemoteUpstream Repo / Remote Repo
Server
Source CodeWorking Copy
$ 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
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
are you sure?
are you brave enough tojump to any commit ?
do you haveloooooong living
topic branches ?
ANTIPATTERN DANGER
3LONG LIVING BRANCHES ANTI-PATTERN
do you haveloooooong living
topic branches ?
welcome tomerge hell
before mergingdo you validate commits
back to source ?
ANTIPATTERN DANGER
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
HEAD
TAG/v13
version 14
$ git cherry-pick Every-Single-Commit-We-Want-To-Deploy
the commit graph ?do you fully understand
ANTIPATTERN DANGER
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…
Cure?
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!
$ git pull --rebase origin master
master
HEAD
TOPIC
STEP 2
ORIGIN/master
always pull with rebaseto get forced pushes securely to rebase your commits
and do it o!en!
$ git pull --rebase origin master
master
HEAD
TOPIC
STEP 2
ORIGIN/master
if you branch is pushed already$ git push -f
always pull with rebaseto get forced pushes securely to rebase your commits
and do it o!en!
$ 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 rebaseto get forced pushes securely to rebase your commits
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
ANTIPATTERN DANGER
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
comt
mi
F*CKING COMMIT MESSAGES ANTI-PATTERN9
ANTIPATTERN DANGER
messages areread!use git commit templates to create be"er commit messages
comt
mi
ANTIPATTERN DANGER
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
git:(topic) $ git rebase masterrebase how
really workscommand
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'
git:(topic) $ git rebase master
HEAD
REPLAY #2
orig_HEAD
rebase how
really workscommand
TOPIC
master
c1 c2 c3 c4 c7
HEAD
c5 c6c5 c6 c5' c6c6'
git:(topic) $ git rebase master
REWIND
orig_HEAD
rebase how
really workscommand
master
c1 c2 c3 c4 c7
c5' c6c6'
git:(topic) $ git rebase master
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
ANTIPATTERN DANGER
thank you all!Feedback: bit.ly/lemiorhan