TIM PETTERSEN • SENIOR DEVELOPER • ATLASSIAN • @KANNONBOY

Code review vs

Pull requests

Code review at Atlassian

2006

2007Atlassian acquires Cenqua, starts using Crucible

TO O L I N G T H R O W D O W N

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

T H E V E R D I C T

Agenda

n. koâla tēaQuality

CodeReview

Photo: Yogi (Flickr)

Better Code

Shared Knowledge

Team Ownership

G = 1

R+1

Developer guilt

Team Ownership

Better Code

Shared Knowledge

Team Ownership

Types of code review

Pull requests

Code review

Post-commit

Pre-commit

master

for/master

Gerrit

Criteria

Creation Iteration HistoryCollaboration

Pull requests

Post-commit

Pre-commit

master

for/master

Gerrit

Pre-commit review

dev $project-dev@example.com

mastermaintainer

// 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;

Pre-commit reviewFrom: Tim Pettersen <tim@atlassian.com> 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

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

> > > > >

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

> >

> >

> > > > > > > >

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

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Pre-commit review

dev maintainer

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

Iteration

master

Pre-commit reviewLinus Torvalds*

Module maintainers

File / driver maintainers

Contributorslinux-kernel@vger.kernel.org

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

Pre-commit review

Junio C Hamano*

Contributorsgit@vger.kernel.org

* Also an oversimplification

Pull requests

Post-commit review

Pre-commit review

master

for/master

Gerrit

Pre-commit reviewVersion control agnostic

Simple and decentralized

Easy to keep ‘000s of people in the loop

Plain text diffs

One contributor per patch

Difficult to iterate

Have to manually merge work

Flexible structure

master

master

patches & untracked files

commits

branches

specific filesmultiple repos

Iterative review in

Not an SCM

SCM host (e.g. Bitbucket)

Review host (e.g. Crucible)

Dev team

push & pull

code review

slurp

slurp

slurp

slurp

Pull requests

Post-commit review

Pre-commit review

master

for/master

Gerrit

Post-commit reviewSupports popular CVCS and DVCS

Flexible review content

Easy to iterate

Have to manually merge work

Need a separate VCS host

Hard to enforce process

Gerritand DIFFY The Kung Foo Review Cuckoo

Gerrit is very “Git-y”

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

http://localhost:8080/

for/master

master

reviewers approved?

verified (build passing)?

Dev team

fetch

push

Gerrit

From: Gerrit Code Review - A Quick Introduction

+2+10-1-2

“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://...'

“squash commits first”

for/master

push

push --force

push --force

From: Gerrit Code Review - A Quick Introduction

Pull requests

Post-commit review

Pre-commit review

master

for/master

Staging area

GerritSophisticated policy enforcement

FOSS project built in Java, on JGit

Clean commit history

Steep learning curve to use & administer

Iteration is a little awkward

Git only

One contributor per patch

Branches only

master

master

patches & untracked files

commits

branches

specific filesmultiple repos

Iterative review in

Pull requests

review before merging

> Code review

Passing build

Reviewer sign-off

Ready for deployment

Pull request == IssueIN REVIEW DONEIN PROGRESSOPEN

Branch created!

Pull request created!

Pull request merged!

Two developers about to press the “Merge” button

@kannonboy

mas

ter

Pull requests Mailing list / Gerrit

Merge Strategies

--no-ff

--ff-only

--squash --ff-only

--squash

--ff

git merge --ff

master

feature/JIRA-123

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

git merge --no-ff

master

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

git merge --ff-only

master

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

git merge --squash

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

master

feature/JIRA-123

git merge --squash \

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

master

--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

No merge commits

Verbose history

Requires rebasing

Pull requestsSophisticated policy enforcement

Choice of merge strategies

Multiple team members can author code under review

Git & Mercurial

Less flexible review content

Code Review vs. Pull requests

Need to review multiple repos at once

Not on Git

Heavily iterative workflow Literally everyone else

Dendrophobia

+

(Traditional)

bitbucket.org

Bitbucket

atlassian.com/crucible

Crucible

gerritcodereview.com

Gerrit

Lookingfor

more?

@kannonboy