[SCRIPT/RFC 1/3] setup.sh

On 26/11/2017 23:35, Igor Djordjevic wrote:

This is what we end up with once "master" and topic branches are 
merged in merge commit M1 inside temporary "test" branch for further 
integration testing:

(2)        o---o---A (topicA)
          /         \
         /           M1 (test, HEAD)
        /           /||
    ---o---o---M---/ || (master)
        \   \       / |
         \   o---B-/  | (topicB)
          \           |
           o---o---C--/ (topicC)

To begin with, you can use provided "setup.sh"[*1*] script, putting 
you straight into position shown on graph (2) above, with addition of 
tag "A" and remote branch "origin/topicA" so you could try using 
these as "--onto-parent" values, too.

As seen in there, change "X" is already made and staged, so you can 
now just run something like:

	git-commit--onto-parent.sh --onto-parent topicA

... to see the logic in action.
 
Instead of "topicA", you may try providing tag "A", remote branch 
"origin/topicA" or even plain commit hash. It`s interesting to add 
"--amend" option into the mix, too, and see what happens. Also, you 
can try using "topicB" and see the commit fail (as it doesn`t merge 
cleanly).

All this while "test.txt" file doesn`t get modified on disk (nor 
would any other file) - being desired behaviour, as we didn`t 
actually change anything inside the working tree, but just amended 
history of how we got here, so recompilation isn`t needlessly 
triggered :)

p.s. Note these two lines near the end:

	sed -i '4iX1' test.txt  # works with simple patch apply
	sed -i '17iX2' test.txt # needs three-way file merge

You can play with it, commenting out one or the other and observing 
how it influences "git commit --onto-parent" in regards of the parent 
provided.

Regards, Buga

[*1*] "setup.sh", can clean previous setup run as well, but commented 
 out here for safety, not to unexpectedly delete something for unwary 
 user.

--- 8< ---

#!/bin/sh

#rm -rf ./.git
#rm -f ./test.txt

git init

touch ./test.txt
git add -- test.txt

for i in {1..10}
do
	echo $i >>test.txt	
	git commit -am "$i"
done

echo M >>test.txt
git commit -am "M"

git checkout -b topicA HEAD~2

for i in 1 2
do
	sed -i "${i}iA${i}" test.txt
	git commit -am "A$i"
done
sed -i '3iA' test.txt
git commit -am "A"
git tag A

# simulate remote branch
mkdir -p ./.git/refs/remotes/origin &&
echo $(git rev-parse HEAD^0) >$_/topicA

git checkout -b topicB master^

sed -i '4iB1' test.txt
git commit -am "B1"
sed -i '5iB' test.txt
git commit -am "B"

git checkout -b topicC master~2

for i in 1 2
do
	j=`expr "$i" + 5`
	sed -i "${j}iC${i}" test.txt
	git commit -am "C$i"
done
sed -i "8iC" test.txt
git commit -am "C"

git checkout -b test master
git merge --no-edit topicA topicB topicC

sed -i '4iX1' test.txt  # works with simple patch apply
sed -i '17iX2' test.txt # needs three-way file merge
git add -- test.txt

echo
git log --all --decorate --oneline --graph
echo
git diff --cached