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Merge and Rebase: Advanced Cases

Table of contents​

  1. Recap of the basics
  2. Advanced interactive rebase
  3. Merge strategies
  4. Resolving complex conflicts
  5. Advanced workflows
  6. Recovery commands

1 - Recap of the basics​


Merge vs Rebase​

AspectMergeRebase
HistoryPreservedRewritten
CommitsMerge commitLinear
Safety✅ Always safe⚠️ Local branch only

The golden rule of Rebase​

⚠️ NEVER rebase a branch that has been shared (pushed).

If others have based their work on it, use merge.

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2 - Advanced interactive rebase​


Start an interactive rebase​

git rebase -i HEAD~5
# ou
git rebase -i abc1234

The available commands​

pick   = utiliser le commit
reword = modifier le message
edit   = s'arrêter pour modifier
squash = fusionner avec le précédent
fixup  = fusionner, ignorer le message
drop   = supprimer le commit

Example: Reorganize commits​

Initial state:

pick abc1234 feat: add login
pick def5678 fix: typo
pick ghi9012 feat: add logout
pick jkl3456 fix: another typo

Reorganized:

pick abc1234 feat: add login
pick ghi9012 feat: add logout
squash def5678 fix: typo
squash jkl3456 fix: another typo

Modify an old commit​

git rebase -i HEAD~3
# Marquer le commit comme "edit"

After saving:

# Modifier les fichiers
git add .
git commit --amend

# Continuer le rebase
git rebase --continue

Split a commit​

git rebase -i HEAD~3
# Marquer le commit comme "edit"

Then:

# Annuler le commit mais garder les modifications
git reset HEAD~1

# Commiter en plusieurs fois
git add file1.js
git commit -m "feat: part 1"

git add file2.js
git commit -m "feat: part 2"

git rebase --continue

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3 - Merge strategies​


Fast-forward (default when possible)​

git merge feature
Avant:
D---E  main
     \
      A---B  feature

Après:
D---E---A---B  main

No fast-forward (force a merge commit)​

git merge --no-ff feature
Avant:
D---E  main
     \
      A---B  feature

Après:
      A---B
     /     \
D---E-------M  main

Advantage: The history clearly shows where the feature was integrated.

Squash merge​

git merge --squash feature
git commit -m "feat: complete feature"
Avant:
D---E  main
     \
      A---B---C  feature

Après:
D---E---F  main
        │
        └── Contient tous les changements de A+B+C

Ours and Theirs​

# En cas de conflit, prendre notre version
git merge -X ours feature

# Prendre leur version
git merge -X theirs feature

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4 - Resolving complex conflicts​


Understanding the markers​

<<<<<<< HEAD
Votre code (branche actuelle)
=======
Leur code (branche à merger)
>>>>>>> feature/xyz

Conflicts with 3 sections​

<<<<<<< HEAD
Votre version
||||||| parent
Version commune originale
=======
Leur version
>>>>>>> feature

Enable this mode:

git config --global merge.conflictStyle diff3

Resolution tools​

# Utiliser un outil graphique
git mergetool

# Voir les versions
git checkout --ours file.txt    # Votre version
git checkout --theirs file.txt  # Leur version
git checkout --merge file.txt   # Revenir au conflit

See the remaining conflicts​

git diff --check

Abort if there's a problem​

# Annuler le merge
git merge --abort

# Annuler le rebase
git rebase --abort

Resolve without marking as resolved​

# Marquer manuellement comme résolu
git add file.txt

# Continuer
git merge --continue
# ou
git rebase --continue

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5 - Advanced workflows​


"Rebase before merge" workflow​

The cleanest for feature branches:

# 1. Mettre à jour main
git checkout main
git pull origin main

# 2. Rebaser la feature sur main
git checkout feature/login
git rebase main

# 3. Résoudre les conflits si nécessaire
# (pour chaque commit)
git rebase --continue

# 4. Forcer le push (branche privée!)
git push --force-with-lease origin feature/login

# 5. Merger dans main (fast-forward)
git checkout main
git merge feature/login

"Squash and merge" workflow (GitHub style)​

# Sur GitHub : Squash and merge
# Localement :
git checkout main
git merge --squash feature/login
git commit -m "feat: implement login (#123)"

Rebase --onto​

Change the base of a branch:

# Situation : feature basée sur develop, mais doit être basée sur main
#
#       A---B---C  feature
#      /
# D---E---F  develop
#    /
# G---H  main

git rebase --onto main develop feature

# Résultat :
#           A'--B'--C'  feature
#          /
# G---H  main
#    \
#     E---F  develop

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6 - Recovery commands​


Undo a merge​

# Si pas encore commité
git merge --abort

# Si déjà commité
git reset --hard HEAD~1

Undo a rebase​

# Pendant le rebase
git rebase --abort

# Après le rebase (avec reflog)
git reflog
git reset --hard HEAD@{5}

Return to the state before a rebase​

# Trouver le point avant rebase
git reflog
# Chercher "rebase (start)" ou le dernier état de votre branche

# Revenir
git reset --hard HEAD@{n}

Recover lost commits​

# Voir tous les commits (même orphelins)
git reflog

# Créer une branche pour les sauver
git branch recovered HEAD@{5}

Summary of advanced commands​

CommandUsage
git rebase -iInteractive rebase
git merge --no-ffForce a merge commit
git merge --squashMerge into a single commit
git rebase --ontoChange the base
git checkout --oursTake our version
git checkout --theirsTake their version
git reflogHistory of operations

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