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History of a Thriving Codebase
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Peter Brown
September 21, 2013
Technology
2
420
History of a Thriving Codebase
Given at VT Code Camp 2013
Peter Brown
September 21, 2013
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Transcript
History of a Thriving Codebase VT Code Camp 2013
into the great wide open
my inspiration
Why version control?
collaborate • Work asynchronously • Reduce friction in teams •
Github was built around collaboration
Communicate • Poor communication causes project failure • Git helps
reduce effort to share ideas and build features
experiment • Experimentation is part of developer happiness • Git
encourages us to experiment via branches
gain Confidence • We need to be confident that things
will work far into the future • Git allows us to adapt to changing requirements
safety net • We make lots of mistakes • Git
allows us to gracefully recover
What is code history?
code History • A series of changes • Story about
how the code evolved • Lasts forever • Searchable • Never outdated
a series of Changes
a series of commits Last Commit
a series of commits
• SHA (unique identifier) • Snapshot / Set of changes
• Description • Date and time • Author • Other details (parents, etc) What is a commit
fixing typos
refactoring code
documentation
a new feature
Clean history
recording history
recording history
why record history? Learn from the past Adapt to the
future
but first a story...
FFFFFuuuuuuuuuu
What is clean history? • Production commits • Every commit
has meaning • Every commit adds value • Most commits are complete features, bug fixes, or refactors
reducing complexity KISS YAGNI DRY
why clean history? • Easier to track down why changes
were made • Easier to track down bugs and revert changes • Required in some OSS projects • Easier to backport changes
three types of commits • Progress commits • Merge commits
• Production commits
three types of commits • Progress commits • Merge commits
• Production commits History Not History
Progress commits • Used to develop a feature • Always
in a new branch • Track progress • Short-term safety net • Mutable and not permanent • Ok if tests are failing
Merge commits • Represent when a branch is merged •
Can be useful • Not required (fast forward merges)
Production Commits • Master branch • Tagged (sometimes) • “Immutable”
and “permanent” • These are your history • Tests should not be failing
crafting a commit message • git commit -v (verbose) •
Start with a short summary • Follow with a description of why the commit exists
short summary (<= 50 chars) describe “why” (72 column wrap)
tools for a clean history
branching
“we need a feature”
“Let’s branch first!”
“pick a descriptive name”
git branch git branch my_branch git checkout my_branch or... git
checkout -b my_branch
“now what?”
merge, delete, repeat git checkout master git merge my_branch git
branch -d my_branch (delete)
Branching protips • Always Be Branching • Use a descriptive
name • Reduce longevity of branches • Clean up when you’re done • Keep changes to a minimum
how do i maintain clean history with branches?
Rewriting history
ways to rewrite history • Amending commits • Rebasing •
Interactive Rebasing • Resetting
types of rebasing • git rebase master my_branch • git
rebase --onto master br1 br2 • git pull --rebase origin master • git rebase -i origin/master
rebasing Master Feature Branch
rebasing Master Feature Branch
rebasing Feature Branch Master
Squashing Commits Master Squashed Commits
squashing commits • Understand why you are squashing the commits
(is it a single feature, bug fix, etc?) • git fetch (to get master from origin) • git rebase -i origin/master
git log --oneline master..convert-hashes
git rebase -i origin/master
reword & fixup
None
None
After Before git log --oneline master..convert-hashes
rebasing protips • Always fetch before rebasing • Never rebase
a branch someone has based work off • Prolong squashing as long as possible • Don’t be discouraged
isn’t that dangerous?
how does it all fit together?
My workflows • Years of changing workflows • Started centralized
(subversion style) • Evolved to feature and release focus
general workflow • Create branch • Write code and commit
it • Open pull request (code review) • Squash commits (if needed) • Merge & tag • Ship it™
two types of workflows • Feature branch centric • Release
centric
feature workflow • Focused on branches for development • Master
== Production • Ideal for small projects, early development • Easy to introduce to new teams
feature workflow cont. •Branch from master • Write code •
Open pull request (code review) •Merge to master • Test in staging environment • Ship it™
feature workflow cont. Master
feature workflow cont. Master Feature Branch
feature workflow cont. Master Feature Branch
feature workflow cont. Master
release workflow • Also called “gitflow” • Centralized around tagged
releases • Ideal for larger projects, enterprise development • More complicated than feature branch workflow
release workflow Cont. • Introduces “development” and “release” branches •
Branch from development branch • Merge into development branch • Merge development into release • Tag it
release workflow cont. courtesy atlassian.com
clean history workflow • Every merge/tag has meaning • Every
merge/tag adds value • All merges/tags are complete features, bug fixes, or refactors
what can we do with a clean history?
Search commits
Search by message git log -p --grep "wtf"
Search by message
search by content git log -p -S 'wtf'
search by author git log -p --author='beerlington'
search by author
Search by date git log -p --since=2013-01-01 git log -p
--until=2013-09-01 or... Combine them!
track down bugs
git bisect Broken X
git bisect Bad Good ✓ X
git bisect Bad Good ? X ✓
git bisect Bad Good X ✓
git bisect Bad Good X ✓ ?
git bisect Bad Good X ✓ X
git bisect X X ✓ ✓ ✓ ✓ ✓
git bisect • Determine how to verify the bug •
Find commit before bug was introduced • Find commit after bug was introduced • git bisect
git bisect
git bisect
git bisect
git bisect
git bisect protips • Automate with “run” option • The
cleaner the history, the easier and faster it is to bisect • git bisect visualize can show where you are in the process
who broke the build?
who broke the build?
How can I fix the code?
git blame git blame path/to/file git blame -L start,stop path/to/file
git blame
github blame
Gitk gitk path/to/file
git blame protips • Focus on why, not who •
Blame doesn’t fix bugs or ship code
what if something goes wrong?
amending commits
a wild typo appears :(
git commit --amend
reverting commits
which commit?
git revert xxxxx
git revert protips • Always write a good commit message
describing why the commit is being reverted. • Better for public commits than rebasing
restoring commits
git reflog • Records when tip of branches are updated
• Reset to, checkout or cherry-pick a commit to recover it
git reflog --date=relative Rebase began here
my commits! git cherry-pick acb1ffc (individual commits) or git reset
--hard af12217 (full recovery)
reflog protips • Git periodically purges the reflog • Only
available on local system (not distributed) • Commit early and often
"Clean history always looks like it was written by someone
who cares."
Resources https://www.atlassian.com/git/ http://try.github.io http://git-scm.com/docs/gittutorial
Thanks! @beerlington beerlington.com