Re: [RFC] Rebasing merges: a jorney to the ultimate solution (Road Clear)

[Igor Djordjevic <igor.d.djordjevic@gmail.com>]

On 28/02/2018 02:33, Igor Djordjevic wrote:
> 
> This seems to be working inside my (too trivial?) test case, for 
> interactive adding, dropping, and amending of rebased commits, 
> resulting "rebased" merge containing all the added/modified/dropped 
> changes, plus the original merge amendment, all as expected :P

In case anyone has a wish to examine my (now pretty messy) test 
script, here it is - sorry for not having time to clean it up! :(

What I get when I diff original and "rebased" merge is this:

    diff --git a/test.txt b/test.txt
    index a82470b..d458032 100644
    --- a/test.txt
    +++ b/test.txt
    @@ -1,10 +1,14 @@
    +A21
    +A22
    +A23
    +A24
    +A25
     A1
     A2
    -B11
    +B1111
     A3
     A4
     A5
    -B12
     A6
     A7
     A8
    @@ -14,6 +18,7 @@ A10
     A11
     A12
     A13
    +BX
     A14
     B2
     A15


... where A21 to A25 are additions due to new base, B11 was 
interactively amended to B1111, B12 was interactively dropped, and BX 
interactively added :)

We don`t see line X here, being an "evil merge" amendment being 
correctly preserved from original merge commit (thus not a 
difference). If we do `git show` of the "rebased" merge, we get this, 
as expected:

    diff --cc test.txt
    index b173cef,fad39a8..d458032
    --- a/test.txt
    +++ b/test.txt
    @@@ -13,6 -13,6 +13,7 @@@ A
      A7
      A8
      A9
    ++X
      A10
      A11
      A12


Regards, Buga

-- 8< --
#!/bin/sh

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

git init

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

for i in {1..20}
do
	echo A$i >>test.txt
	git commit -am "A$i"
done

git checkout -b b1
sed -i '3iB11' test.txt
git commit -am "B11"
sed -i '7iB12' test.txt
git commit -am "B12"

git checkout -b b2 HEAD^
sed -i '16iB2' test.txt
git commit -am "B2"

git checkout -b merge b1
git merge --no-commit b2
sed -i '12iX' test.txt # amend merge commit
git commit -am "M"
git tag original-merge

git checkout master
for i in {1..5}
do
	j=`expr "$i" + 20`
	sed -i "${i}iA${j}" test.txt
	git commit -am "A$j"
done

# simple/naive demonstration of proposed merge rebasing logic
# using described "Trivial Merge" (TM, or "Angel Merge"),
# preserving merge commit manual amendments, but still respecting
# interactively rebased added/modified/dropped commits :)

# read -p "Press enter to continue"
git checkout b1
git cherry-pick -m1 original-merge && git tag U1
git reset --hard HEAD^^ # drop U1 and last b1 commit
sed -i '/B11/c\B1111' test.txt
git commit -a --amend --no-edit
git rebase master
git cherry-pick U1 && git tag U1-prime

# read -p "Press enter to continue"
git checkout b2
git cherry-pick -m2 original-merge && git tag U2
git reset --hard HEAD^ # drop U2
git rebase master
sed -i '20iBX' test.txt
git commit -am "BX" # add new commit
git cherry-pick U2 && git tag U2-prime

git diff U1 U1-prime | git apply --3way && git commit -m "U2-second" && git tag U2-second
git checkout b1
git diff U2 U2-prime | git apply --3way && git commit -m "U1-second" && git tag U1-second

# read -p "Press enter to continue"
git branch -f merge b1
git checkout merge
git merge b2 --no-commit
git commit -a --reuse-message original-merge
git tag angel-merge

# read -p "Press enter to continue"
git reset --hard b1^
git read-tree --reset angel-merge
git update-ref refs/heads/merge "$(git show -s --format=%B original-merge | git commit-tree "$(git write-tree)" -p "$(git rev-parse b1^^)" -p "$(git rev-parse b2^^)")"
git tag -f angel-merge
git checkout angel-merge .
git branch -f b1 b1^^
git branch -f b2 b2^^

# show resulting graph
echo
git log --all --decorate --oneline --graph

# comparison between original merge and rebased merge,
# showing merge commit amendment "X" being preserved during rebase
# (not shown in diff)
echo
echo 'diff original-merge angel-merge:'
git diff original-merge angel-merge