Code reviews vs Pull requests

TIM PETTERSEN • SENIOR DEVELOPER • ATLASSIAN • @KANNONBOY

Code review vs

Pull requests

@kannonboy

Code review at Atlassian

2006

2007Atlassian acquires Cenqua, starts using Crucible @kannonboy

@kannonboy

2006

2007Atlassian acquires Cenqua, starts using Crucible

2010 Atlassian acquires Bitbucket

@kannonboy

@kannonboy

2007Atlassian acquires Cenqua, starts using Crucible


2011 Work starts on “Caviar”!@kannonboy

@kannonboy


2011 Work starts on “Caviar”

2012 Stash 1.0 ships

!

Stash 2.0 ships with

@kannonboy

@kannonboy

2011 Work starts on “Caviar”


!

Stash 2.0 ships with pull requests

Comment drift

Unread status@kannonboy

@kannonboy

2011


!

Stash 2.0 ships with pull requests

Merge checks

Comment drift

Unread status

Conflict markers

Build status integration

Branch permissions

@kannonboy

@kannonboy

Stash renamed to Bitbucket Server2015

Merge checks

Comment drift

Conflict markers

Build status integration

Reviewer suggestions

Branch permissions

Comment likes

Enhanced branch permissions

Iterative review

Merge strategies

Reviewer statuses

Today@kannonboy

@kannonboy

Stash renamed to Bitbucket Server2015

Comment likes

Enhanced branch permissions

Iterative review

Merge strategies

Reviewer statuses

Today

@kannonboy

@kannonboy

T Y P E S O F R E V I E W

Y O U N E E D C O D E R E V I E W

C O D E R E V I E W @ AT L A S S I A N

T I P S F O R T E A M S

Agenda

Automated tests

@kannonboy

Automated tests

@kannonboy

human judgement needed

?

“what-evs”

bad API decision

O(n!) algorithm

technical debt

Automated tests

@kannonboy

CodeReview

Photo: Yogi (Flickr)

@kannonboy

Better Code

Shared Knowledge

Team Ownership

@kannonboy

G = 1

R+1

Developer guilt

@kannonboy

Team Ownership

@kannonboy

Team Ownership

@kannonboy

Better Code

Shared Knowledge

Team Ownership

@kannonboy

Code reviews take negative time

@kannonboy

Reviews and releases

10

20

30

40

Daily Weekly Monthly Quarterly Yearly

Code Review No Code Review

Source: Atlassian Git Survey 2013

@kannonboy

Types of code review

@kannonboy

Pull requests

Code review

Post-commit review

Pre-commit review

master

for/master

Staging area @kannonboy

Post-commit review

Pre-commit review

master@kannonboy

Pre-commit review

dev [email protected]

mastermaintainer @kannonboy

// flat fees and taxes final float customsFee = 5.5f; final float immigrationFee = 7f; final float federalTransportTax = .025f;

public float calculateAirfare(float baseFare) { float fare = baseFare; fare += immigrationFee + customsFee; fare *= return fare; }

AirfareCalculator.java

federalTransportTax;

@kannonboy

// flat fees and taxes final float customsFee = 5.5f; final float immigrationFee = 7f; final float federalTransportTax = .025f;

public float calculateAirfare(float baseFare) { float fare = baseFare; fare += immigrationFee + customsFee; fare *= return fare; }

(1 + )

AirfareCalculator.java

federalTransportTax ;

@kannonboy

Pre-commit reviewFrom: Tim Pettersen <[email protected]> Date: Mon, 12 Sep 2016 10:24:10 +1000 Subject: [PATCH] Calculate federal transport tax correctly

--- a/com/atlassian/airfare/AirfareCalculator.java +++ b/com/atlassian/airfare/AirfareCalculator.java @@ -10,7 +10,7 @@ public float calculateAirfare(float baseFare) { float fare = baseFare; fare += immigrationFee + customsFee; - fare *= federalTransportTax; + fare *= (1 + federalTransportTax); return fare; }

$ git format-patch HEAD~1 --stdout

@kannonboy

Pre-commit review

dev maintainer

public float calculateAirfare(float baseFare) { float fare = baseFare; fare += immigrationFee + customsFee;- fare *= federalTransportTax;+ fare *= (1 + federalTransportTax); return fare;}

Subject: [PATCH] Calculate federal transport tax correctly

@kannonboy

> > > > >

The braces are unnecessary.

Pre-commit review

dev maintainer

public float calculateAirfare(float baseFare) { float fare = baseFare; fare += immigrationFee + customsFee;- fare *= federalTransportTax;+ fare *= (1 + federalTransportTax);

return fare;}

Subject: Re: [PATCH] Calculate federal transport tax correctly

> >

@kannonboy

> >

> > > > > > > >

Technically true, but I think they add clarity.

> >

> > > > >

The braces are unnecessary.

Pre-commit review

dev maintainer

public float calculateAirfare(float baseFare) { float fare = baseFare; fare += immigrationFee + customsFee;- fare *= federalTransportTax;+ fare *= (1 + federalTransportTax);

return fare;}

Subject: Re: Re: [PATCH] Calculate federal transport tax correctly

@kannonboy

> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >

Pre-commit review

dev maintainer

Subject: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re:

@kannonboy

Iteration

master

@kannonboy

Pre-commit reviewLinus Torvalds*

Module maintainers

File / driver maintainers

[email protected]

* Gross oversimplification, check out: bit.ly/linux-dev

@kannonboy

mailto:[email protected]?subject=

Pre-commit review

Junio C Hamano*

[email protected]

* Also an oversimplification

@kannonboy

mailto:[email protected]?subject=

Pull requests

Post-commit review

Pre-commit review

master

for/master

Staging area

Pre-commit reviewVersion control agnostic

Difficult to read

High barrier to submit patches

Simple and decentralized

Difficult to iterate

Easy to keep ‘000s of people in the loop

Have to manually merge work@kannonboy

Pull requests

Post-commit review

@kannonboy

Flexible structure

master

master

patches & untracked files

commits

branches

specific filesmultiple repos

@kannonboy

Iterative review

Branch diff

Merge diff

Pull request diffs

@kannonboy

Iterative review

Branch diff

Post-commit review diffs

Arbitrary commit diffs

@kannonboy

Iterative review in

@kannonboy

Iterative review in

@kannonboy

Not an SCM

SCM host (e.g. Bitbucket)

Review host (e.g. Crucible)

Dev team

push & pull

code review

slurp

slurp

slurp

slurp

@kannonboy

Pull requests

Post-commit review

Post-commit reviewSupports popular CVCS and DVCS

Have to manually merge work

Flexible review content

Need a separate VCS host

Easy to iterate

Hard to enforce process

@kannonboy

Pull requests

Post-commit review

master

for/master

Staging area@kannonboy

Gerritand DIFFYThe Kung FooReview Cuckoo

@kannonboy

Gerrit is very “Git-y”

$ git config -f ~/gerrit/etc/gerrit.config gerrit.canonicalWebUrl

http://localhost:8080/

@kannonboy

Staging area review

for/master

master

reviewers approved?

verified (build passing)?

Dev team

fetchpush

@kannonboy

From: Gerrit Code Review - A Quick Introduction

@kannonboy


+2+10-1-2

@kannonboy

“squash commits first”

$ git push origin HEAD:refs/for/master

# typey type type

$ git commit -am “Review feedback”

Counting objects: 2108776, done.Delta compression using up to 8 threads.Compressing objects: 100% (59/59), done.Writing objects: 100% (86/86), 893.21 KiB, done.Total 86 (delta 0), reused 0 (delta 0)

! [remote rejected] HEAD -> refs/for/master (squash commits first)error: failed to push some refs to ‘ssh://...'

@kannonboy


for/master

@kannonboy


for/master

push

@kannonboy


for/master

push

push --force

@kannonboy


for/master

push

push --force

push --force

@kannonboy


@kannonboy

Pull requests

Post-commit review

Pre-commit review

master

for/master

Staging area

Staging area reviewSophisticated policy enforcement

Steep learning curve to use & administer

Iteration is a little awkward

FOSS project built in Java, on JGit

Git only

Clean commit history

@kannonboy

Pull requests

Post-commit review

@kannonboy

Branches only

master

master

patches & untracked files

commits

branches

specific filesmultiple repos

@kannonboy

Pull requests

review before merging

> Code review

@kannonboy

Pull requests > Code review

Passing build

Reviewer sign-off

Ready for deployment

@kannonboy

Pull requests > Code review

Passing build

Reviewer sign-off

Ready for deployment

@kannonboy

Two developers about to press the “Merge” button

@kannonboy

Merge Strategies

@kannonboy

@kannonboy

--no-ff

--ff-only

--squash --ff-only

--squash

--ff

@kannonboy

git merge --no-ff

@kannonboy

master

feature/JIRA-123“Always create a merge commit.”

git merge --no-ff

@kannonboy

master

feature/JIRA-123“Always create a merge commit.”

git merge --ff

@kannonboy

master

feature/JIRA-123

“Fast forward if you can, otherwise create a merge commit.”

git merge --ff

@kannonboym

aster

feature/JIRA-123


git merge --ff

@kannonboy

mast

er


git merge --ff

@kannonboy

mast

er


git merge --ff-only

@kannonboy

master

feature/JIRA-123“Only allow fast forwards.”

git merge --ff-only

@kannonboy

master

feature/JIRA-123

“Only allow fast forwards.”

git merge --ff-only

@kannonboy

mast

er


git merge --ff-only

@kannonboy

mast

er


git merge --ff-only

@kannonboy

mast

er


git merge --ff-only

@kannonboy

mast

er


git merge --squash

@kannonboy“Combine commits on branch into a new commit on master.”

master

feature/JIRA-123

git merge --squash

@kannonboy“Combine commits on branch into a new commit on master.”

master

git merge --squash \

@kannonboy“Combine commits on branch into a new commit on master. Fail if master has any commits that branch doesn’t.”

master

--ff-only



master

--ff-only



mast

er

--ff-only

Merge Commit Fast forward Squash

Concise history

Lose context of how features evolved

Which should I use?

“Ugly” history

Full traceability

Hard to screw up

mostly some

--no-ff --ff-only --squash

@kannonboy

No merge commits

Verbose history

Requires rebasing

Pull requests

bit.ly/git-lfs

Sophisticated policy enforcement

Less flexible review content

DVCS had some limitations around file size

Choice of merge strategies

Multiple team members can author code under review

Git & Mercurial

@kannonboy

pull requests@kannonboy

Tim’s

tips fortop ten

1. One issue, one pull request

= @kannonboy

1. One issue, one pull request

# what’s shipping? $ git branch --merged

# what’s left to ship? $ git branch --no-merged

@kannonboy

master

IN REVIEW DONEIN PROGRESSOPEN

@kannonboy

Automatic Transitions

feature/JIRA-30

master


Branch created!

@kannonboy


feature/JIRA-30

master


Pull Request Created!

@kannonboy


feature/JIRA-30

master


Pull Request Merged!

@kannonboy


2. Minimum TWO approvals before merge

@kannonboy

2. Minimum TWO approvals before merge

3. Have 1.5x - 2.5x that number reviewers@kannonboy

Fewer reviewers find more defects

0

7.5

15

22.5

30

1 2 3 4 5 6 7 8 9

Def

ects

/ k

LoC

Number of Reviewers @kannonboysource: bit.ly/review-stats

More reviewers spend less time

0

7

14

21

28

1 2 3 4 5 6

Min

utes

spe

nt /

revi

ewer

Number of Reviewers @kannonboysource: bit.ly/review-stats

4. Use blame to pick reviewers@kannonboy

4. Use blame to pick reviewers

$ npm install -g git-guilt

# find blame delta for current branch $ git guilt `git merge-base master HEAD` HEAD

Alice Foo ++++++++++++++++++++++++(239) Bob Bar ++++++++ Eve Baz ------- Mira Ted ---------------- Bec Opal ------------------------(-159)

@kannonboy


bit.ly/suggest-reviewers @kannonboy





5. @mention specialists

@kannonboy

6. Stuck in review?

Make Tuesday & Thursday inbox zero days

@kannonboy

betterCode;

7. Move comments into code

reviewcomments

// comments// in code

@kannonboy

8. Build a team policy, as a team…

…and enforce it! @kannonboy

9. Add screenshots for UI/UX changes

(gifs / videos are even better) @kannonboy

9. Add screenshots for UI/UX changes

(gifs / videos are even better) @kannonboy

Monosnap GIPHY ScreenFlow

@kannonboy

Ask a programmer to review 10 lines of code, they'll find 10 issues. Ask them to do 500 lines and they'll say it looks good.@ G I R AY O Z I L

“”

10. Keep it concise

10. Keep it concise Se

cond

s pe

r lin

e

Lines of Code

1 line per second

100 lines per second

@kannonboysource: bit.ly/review-stats

Code Review vs. Pull requests

Need to review multiple repos at once

Not on Git

Heavily iterative workflow Literally everyone else

Dendrophobia

+

@kannonboy

(Traditional)

@kannonboy

bitbucket.orgBitbucket

atlassian.com/crucibleCrucible

gerritcodereview.comGerrit

Lookingfor

more?

Follow me for occasional Git &Bitbucket trivia

Code reviews vs Pull requests

Software