find the parent of merge commits to have manual branch-aware bisecting

command.sh

git log master..HEAD --merges --format="%h" | tr '\n' '\0' | xargs -0 -n1 git rev-list --parents -n 1 | awk '{print $(NF)}' | tr '\n' '\0' | xargs -0 -n1 git log --pretty=oneline -n 1

explanation.sh

# find all merges, and only print out the hash of the commit
git log master..HEAD --merges --format="%h"

# translate all \n's into \0's for `xargs`
# with gnu xargs, you can get rid of this command and pass in `-d '\n'` instead of having to convert and pass in `-0` to xargs
tr '\n' '\0'

# for every merge commit, find the most recent parents that were responsible for the merge
xargs -0 -n1 git rev-list --parents -n 1  

# get the last column, which is the hash of the parent on the branch being merged in
awk '{print $(NF)}'

# technially we could stop here, since we have a list of the last commit of each branch before it was merged in
# but lets keep going to get better output

# translate all \n's into \0's for `xargs` (again, since we have one more commit)
tr '\n' '\0'

# get a git log of each commit, in the format of '#{hash} #{commit message}'
xargs -0 -n1 git log --pretty=oneline -n 1

what?

given:

 ------feature-x--bugfix-y--bugfix-z
      /          /         / 
 ---C1          /         /
      --------C2         /
 -----C3----------------C4
 
 this command finds and prints:
 #{C1-hash} #{C1-commit message}
 #{C2-hash} #{C2-commit message}
 #{C4-hash} #{C4-commit message}