How to merge safely

Stream: general

[Etienne Marion]

Hello!
When I want to merge master into a branch, I do git merge origin/master, which does the merging fine, and allows me to resolve potential merge conflicts. However in tricky cases (file splitting for instance) it might not behave as I intended, and in such cases I wish I had not done the merge. It is always possible to cancel it, but the question I wanted to ask is:
Is there a way to see what the merging will do to the files I modified on my branch before merging?

I'm using VSCode.

[Kevin Buzzard]

The naive approach is just to make a new branch based on your current branch and merge to that instead :-) (that's the sort of thing I'd do, precisely because I'm not a git guru)

[Etienne Marion]

Indeed that would work, thanks :sweat_smile:

[Damiano Testa]

Does git merge take a -n flag that skips the committing step?

[Etienne Marion]

Hmm in fact -n does not do that but there is a --no-commit option indeed. I'll try it next time. Thanks!

[Damiano Testa]

I only used the -n flag with cherry-pick and I find it very useful, especially when I am cherry-picking something and then I want to see what else to cherry-pick, without passing all hashes at once.

[Eric Wieser]

Another good option is

git tag -f hold-my-oleans
lake exe cache pack

git merge whatever
lake exe cache get
# open some files in vscode and check if they are ok

# if things go wrong
git reset --hard hold-my-oleans
lake exe cache unpack

[Julian Berman]

Another thing worth at least being passingly familiar with is the existence of rerere which is not enabled by default. In short (to see if you care to read that page) it can occasionally save you some time performing the same merge multiple times.

[Etienne Marion]

Thank you!