DealingwithConflictingUpdatesinGit

CS5010ProgramDesignParadigms“Bootcamp”Lesson0.6

©MitchellWand,2012-2014ThisworkislicensedunderaCreative Commons Attribution-NonCommercial 4.0 International License. 1

LearningObjectives

• Attheendofthislessonyoushouldbeableto:– explainwhathappenswhenyoupullchangesfromanupstreamrepository

– understandwhataconflictis– resolveasimplemergeconflictinatextfile(includinga.rkt file)

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ACommit

my-project docs manual.docx

user_docs.docx

srcmain.rkt

module1.rkt

module2.rkt

module3.rkt

.git

commit

Whenyoudoa“commit”,yourecordallyourlocalchangesintothemini-fs.

Themini-fs is“append-only”.Nothing iseverover-writtenthere,soeverythingyouevercommitcanberecovered.

Rememberthebasicstoryfromthepreceding

lesson

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Synchronizingwiththeserver(1)

my-project docs manual.docx

user_docs.docx

srcmain.rkt

module1.rkt

module2.rkt

module3.rkt

.git push

Attheendofeachworksession,youneedtosaveyourchangesontheserver.Thisiscalleda“push”.

Nowallyourdataisbackedup.• Youcanretrieveit,onyourmachineor

someothermachine.• Wecanretrieveit(that’showwecollect

homework)

yourlocalmachine aserver,somewhereontheinternet,eg.github.com

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Synchronizingwiththeserver(2)

my-project docs manual.docx

user_docs.docx

srcmain.rkt

module1.rkt

module2.rkt

module3.rkt

.git pull

Toretrieveyourdatafromtheserver,youdoa“pull”.A“pull”takesthedatafromtheserverandputsitboth inyour localmini-fsandinyourordinary files.

Ifyourlocalfilehaschanged,git willmergethechangesifpossible.Ifitcan’tfigureouthowtothemerge,youwillgetanerrormessage.Dealingwiththisisbeyond thescopeofthistutorialL

yourlocalmachine aserver,somewhereontheinternet,eg.github.com

pull

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Q:Whenmightyouneedtomerge?

A:Whenyourpartnercommittedsomechangestotheserver,whichyoudon'thave.

Yourpartner'swork(onthe

server)

Yourwork(onyourlocalmachine)

Yourlastpull

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ResultofSyncing

Yourpartner'swork(onthe

server)

Yourwork(onyourlocalmachine)

Yourchangesareappliedtothelatestversionontheserver.Thisiscalled"rebasing"

Combinedworknowlivesonboththeserverandyourlocalmachine.

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Mostofthetime,thisworkswell

• Solongasyouandyourpartnerareworkingonseparatepartsofthefile,thisworksfine.

• Bothsetsofchangesgetmade,andthehistoryontheserverstayslinear

• Butwhathappensifyouandyourpartnercommitincompatiblechanges?

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Here'swhatyou'llsee

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So,clickontoolsandopenashell

Don'tpanic!First,lookatthefilein

aneditor

Here'swhatwe'regoing to

do

10

Here'swhatthe

conflictedfilelookslike(inemacs)

what'sontheserver

what'sonthelocalmachine

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Next:editthefilethewayyouwantit

nomore>>>'s

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addthefixed-upfiletothecommit

tellgit tocontinue tothenextchange

ok!wearereadytosync

ifthereweremoreconflicts,we'dhavetodothisprocess

foreachofthem. 13

Andwe'rereadytogetbacktowork

Observethatbothcommitsarenowin

yourhistory

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Isthisapain?• Yes,butitshouldn'thappentoooften.• Yourinteractionwiththeshellmightlooksomewhatdifferent.

• Buttheworkflowisthesame:– identifythefilesthatareconflicted– identifyandresolvetheconflictsineachfile

• theconflictedregionwillbemarkedwith>>>'s.• Useyourfavoritetexteditorforthis.

– Whenyougetthefilethewayyouwantit,addittoyourcommit.

– Commitallthefixed-upfiles.

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Summary

• Inthislessonyouhavelearned– whathappenswhenyoupullchangesfromanupstreamrepository

– whataconflictis– howtoresolveasimplemergeconflictinatextfile(includinga.rkt file)

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