branch dependency.md

# branch1 comes from master's head.
# branch1 is not integrated on master yet but we need to create branch2 that depends on branch1.
# this gist shows how to work on branch2 and then integrate it on master.

# initial situation:
# 
# 1 - 2 - 3 - 4 master
#          \
#           5 - 6 branch1

git checkout branch1
git checkout -b branch2
# add your commits

# 1 - 2 - 3 - 4 master
#          \
#           5 - 6
#                \
#                 7 - 8 branch2

# branch1 may change after branch2 was created, for example if a fix is needed

# 1 - 2 - 3 - 4 master
#          \
#           5 - 6 - 9 branch1
#                \
#                 7 - 8 branch2

# apply these changes on branch2

git checkout branch2
git rebase branch1 branch2

# 1 - 2 - 3 - 4 master
#          \
#           5 - 6 - 9 branch1
#                    \
#                     7'- 8' branch2

# branch1 must be merged on master before branch2 since the latter depends on the former.
# before merging, rebase branch1 on master.

git rebase master branch1

# 1 - 2 - 3 -------------------- 4 master
#          \                      \
#           5 - 6 - 9 (detached)   5'- 6'- 9' branch1
#                    \
#                     7'- 8' branch2

git checkout master
git merge branch1

# 1 - 2 - 3 -------------------- 4 --------- 10 master
#          \                      \         /
#           5 - 6 - 9 (detached)   5'- 6'- 9' branch1
#                    \
#                     7'- 8' branch2

# rebase branch2 on master.
# note that 5 - 6 - 9 are part of branch2 and not master, which means these commits will be kept when rebasing the branch.
# 5 - 6 - 9 are duplicates of 5'- 6'- 9', so you don't want them on the rebased version of branch2.
# In order to avoid such behaviour, specify a commit to start with rather than a branch.
# Specify 8+ rather than branch2 (5 - 6 - 9 - 7'- 8').

git checkout branch2
git rebase --onto master <commit>

# commit is the commit before 7'. It can be HEAD~2, the commit code for 9, the commit code for 7' with ~ appended to it.
# everything after this commit will be used

#                                              7"- 8" branch2
#                                             /
# 1 - 2 - 3 -------------------- 4 --------- 10 master
#          \                      \         /
#           5 - 6 - 9 (detached)   5'- 6'- 9' branch1
#                    \
#                     7' - 8' (detached)

git checkout master
git merge branch2

#                                              7"- 8" branch2
#                                             /     \
# 1 - 2 - 3 -------------------- 4 --------- 10 ---- 11 master
#          \                      \         /
#           5 - 6 - 9 (detached)   5'- 6'- 9' branch1
#                    \
#                     7'- 8' (detached)

# master history looks like this: 1 - 2 - 3 - 4 - 5'- 6'- 9'- 10- 7"- 8"- 11

# note that if there is no conflict when merging, changes will be fast-forwarded

#                                              7"- 8" branch2
#                                             / \   \
# 1 - 2 - 3 -------------------- 4 - 5'- 6'- 9'- 7"- 8" - master
#          \                      \ /   /   /
#           5 - 6 - 9 (detached)   5'- 6'- 9' branch1
#                    \
#                     7'- 8' (detached)