The document provides expert tips on using git features such as rebase, squash, and fixup to enhance commit messages and maintain a clean commit history. It emphasizes the importance of structured commits that are logically themed and offers various solutions for common issues encountered during version control. The author also encourages the use of interactive rebase to refine commit messages and organize changes more effectively.

1. Git Pro Tips
Rebase, squash, and fixup, for tomorrow we may merge

2. Provide as much context on your change
as you can. Derek Prior asks for two
paragraphs in your commit message
A big ask, but its probably only going to
take you 5 minutes to write, and save the
reader 30 minutes of researching
Give The Reader a Break

3. Good or Bad Commit Message?
Fix rake db:migrate from scratch
This commit fixes a bug reported by Bindu's team. Currently, since the
Rake task `db:create_di_sql_views` is not versioned, it refers to the
_latest_ state of the database.
This can break stuff if you've dropped your database and are migrating
back up from scratch. A field referenced in the Rake task may not yet
exist.
The solution we've come up with until we upgrade to Rails 4 is to
comment out earlier migrations, leaving only the most recent one.

4. “Cleaning”
Good or Bad Commit Message?

5. [#92611712] CP06 executed_at is now Time.zone.now
We had a purchase that initiated a few minutes before midnight, yet
settled after midnight on the following day. This resulted in a CP06
with a transaction value from the previous day (creation date) and was
omitted from the finance_r2 export for the following day range
When a purchase record settles, DiFinanceTransaction.
create_from_flubit_purchase
is called for the CP06 generation, effectively the settled at date.
The executed at time is only modified for CP06 purchases, and is not
used on SH01 records. For SH01, the dispatched date is used instead
Good or Bad Commit Message?

6. “Merge branch 'echo'”
Good or Bad Commit Message?

7. “Turn it to 11 (fix stores.longitude
encrypted column precision)”
Good or Bad Commit Message?
diff --git a/db/migrate/20150413183503_add_encryption_fields_to_store.rb
b/db/migrate/20150413183503_add_encryption_fields_to_store.rb
index 6e5aacc..498a25f 100644
--- a/db/migrate/20150413183503_add_encryption_fields_to_store.rb
+++ b/db/migrate/20150413183503_add_encryption_fields_to_store.rb
@@ -13,7 +13,7 @@ class AddEncryptionFieldsToStore < ActiveRecord::Migration
add_column table, :encryption_migration_latitude, :string
- add_column table, :encrypted_longitude, :decimal, :precision => 10, :scale => 8
+ add_column table, :encrypted_longitude, :decimal, :precision => 11, :scale => 8
add_column table, :encryption_migration_longitude, :string

8. Single Responsibility Principle (SRP)
Commits are free! Make lots of smaller
commits instead of one big ball of mud
Try to structure a commit around one
logical theme, e.g. new model, bug fix
What Makes a Good Commit?

9. Presentation is important. The way that
you categorize and present your changes is
as important as the changes themselves.
Would you rather have 10 smaller commits
under cognitive load, or one commit with
+312 -592 line changes?
Food For Thought

10. Problem: How many times have you made
edits to an email, term paper, long
message, or other before you sent it?
Did your recipient need to know about all
of your in between edits, or just the final
message?
Keeping A Clean History

11. Solution: Git allows you to change the past
(admit it - you’ve always wanted to have
this power)
Rebasing interactively allows you to
introduce in between commits, delete,
even combine/split separate commits
Git Rebase for a Clean History

12. git log -p
git add -p
git diff --staged
git commit --amend
git stash --save
Yeah yeah, I already know this...
Quick Review of the Basics

13. git reset <target> (unstage file)
git reset --hard HEAD@{#} (revert branch)
git commit -m “squash! <SHA>”
git push origin -f (careful!)
git reflog
git rebase <target> -i
Advanced Concepts In This Talk

14. We will be using rebase to tackle (almost) all of the
following scenarios
e, edit = use commit, but stop for amending
r, reword = use commit, but edit the commit message
s, squash = use commit, but meld into previous commit
f, fixup = like "squash", but discard this commit's log
message
Lets Change History

16. Shameless Plug
I could demonstrate these scenarios
anywhere, but I’m going to plug a pet
project called Routastic.
http://routastic.herokuapp.com

17. Problem: The order of my commits should
be rearranged so they make more sense
Possible solution: git rebase, reorder
commits
Scenario #1 (Order)

18. Problem: Your commit message isn’t
descriptive enough and you want to
improve it
Possible Solution: git commit --amend
Possible Solution: git rebase, mark commit
as reword
Scenario #2 (Description)

19. Problem: You have made a change to a file
in one commit that you are now modifying
again
Possible Solution: git add -p, git commit -m
“fixup! <SHA>, git rebase
Note autosquash can help here
Scenario #3 (Multiple Revisions)

20. Problem: Your commit is too big and you
want to break it down
Possible Solution: git rebase, mark commit
as edit, git reset HEAD~1, git add -p, git
commit, git add -p, git commit, etc, git
rebase --continue
Scenario #4 (Decomposing)

21. To automagically position fixup, squash
messages, put this in your gitconfig
# ~/.gitconfig
[rebase]
autosquash = true
Git Autosquash

22. Problem: You’ve committed a change to
the wrong commit
Possible Solution: git rebase, mark commit
as edit, git reset HEAD~1, git add -p, git
commit -m “fixup <SHA>, git commit -a, git
rebase --continue, git rebase
Scenario #5 (Conflation)

23. Interactive rebase can be used in
conjunction with basic git commands to
completely alter the way your feature
branch looks
Use it with the objective of improving
comprehensibility for those after you
Reviewing What We’ve Learned

24. Don’t merge your commits like this guy

25. Rebase before you merge
Tag with annotation (git tag -a)
Merge with --log
Minimize merge commits
Always review your commit structure
before sharing a PR
More Git Tips

26. Ben Simpson
thehoagie@gmail.com
@mrfrosti
http://mrfrosti.com
Questions?