[Exercise Discussion] T6L2/merge-undo

[damithc]

Existing exercise check

• I have verified that this exercise is not yet already in discussion, in progress, or exists

Lesson

https://nus-cs2103-ay2526s1.github.io/website/book/gitAndGithub/merge/index.html (see detour: Undoing a Merge)

Exercise learning outcomes

Able to undo a merge

Exercise setup

Inputs to the new.sh:

Exercise name: merge-undo
Tags (space separated): git-branch git-merge git-reset
Requires Git? (defaults to y)  [y/N]: y
Requires Github? (defaults to y)  [y/N]: N
Exercise repo type (local, remote, or ignore) (defaults to 'local'): local
Exercise repo name (defaults to ...): play-characters
Git-Mastery Github repository title (defaults to ''): 
Initialize exercise repo as Git repository? (defaults to y)  [y/N]: Y

Equivalent steps to populate the repo

echo -e "Scientist" >> rick.txt
git add .
git commit -m "Add Rick"

echo -e "Boy" >> morty.txt
git add .
git commit -m "Add morty"

git switch -c daughter
echo -e "Vet" >> beth.txt
git add .
git commit -m "Add Beth"

git switch -c son-in-law main
echo -e "Salesman" >> jerry.txt
git add .
git commit -m "Add Jerry"

git switch main
echo -e "Grandson" >> morty.txt
git commit -am "Mention Morty is grandson"

git switch main
git merge daughter -m "Introduce Beth"
git merge son-in-law -m "introduce Jerry"

Instructions for students

Scenario: You are keeping notes on the characters of a play that you are writing. In the main story line (which is in the main branch), you introduced two characters, Rick and Morty. You had two other characters in two separate branches daughter and son-in-law. Just now, you introduced these two characters to the main story line by merging the two branches to the main branch.

// insert the current revision graph here

However, now you realise this is premature, and wish to undo that change.

Task:

Undo the merging of branches son-in-law and daughter.

The result should be as follows:

// insert the expected revision graph here

Exercise grading

Verify that,

• both merges have been undone
• main is pointing to the correct commit

Requires remote repository?

No response

Additional remarks

No response

[woojiahao]

@damithc for the fifth block, we don't need git commit -am because we already used git add . for a new file.

Do we care about whether the merges happen as fast forwards or not?

[damithc]

@damithc for the fifth block, we don't need git commit -am because we already used git add . for a new file.

@woojiahao removed a

Do we care about whether the merges happen as fast forwards or not?

In this specific case, the merges will not be fast-forward because the main branch has a new commit.
But this made me realise that we can add a separate exercise for undoing a fast-forwarded merge.

[woojiahao]

Sounds good! Curious but wouldn't undoing a fast-forwarded merge just be git reset --hard? Not sure if there's any alternatives to it

[damithc]

Curious but wouldn't undoing a fast-forwarded merge just be git reset --hard?

It is, but it is something students need to realise too.
Also, you need to be specific which commit to reset to (can't just use HEAD~1 as is the case if there is a merge commit).

[kea-S]

Hi! If no one's been assigned this exercise, can I ask to be assigned?