Ask HN: How often does Git merge make mistakes?

1 pointsiceman_w10y ago5 comments

I was working on an express app with a friend and git auto merged a file after I ran 'git pull'. There were no merge conflicts, but git added duplicate functions to a file after merge. I spent an hour trying to figure our what the problem was before realizing that git had made a mistake while merging.

I had never seen such a thing before. How often does something like this happen?

5 comments

gknoy10y ago

I've never noticed that before, but it's possible that you both had added functions in different places:

    foo() ... ; original

    bar() ...  ; added by alice
    foo() ...

    foo() ...
    bar() ...  ; added by bob

I haven't tried it, but I could imagine that being seen as separate text additions, and ending up with duplicates if git thinks it needs to merge them:

    bar() ... ; alice
    foo() ... ; original
    bar() ... ; bob

You mentioned using `git pull`, which will actually merge things if it thinks it's necessary -- which can lead to tree differences. In practice, I've found it helpful to NEVER USE `git pull`. Rather, I advise using:

    git checkout master
    git fetch origin
    git merge origin/master --ff-only

This will ensure that git only does "fast-forward" merges, and does not end up accidentally merging things - and keeps 'origin' as the system-of-record for what's been merged.

sold10y ago

I recommend

git config --global pull.ff only

instead, then you can use "git pull" without worries. Or,

git pull --ff-only

sova10y ago

Anyone wondering what a "fast-forward" merge is? https://sandofsky.com/images/fast_forward.pdf

iceman_wOP10y ago

In the following scenario:

origin: A-B-C local: A-B-D

What is the recommended action? git pull --ff-only will fail, right? So should I be using git pull --rebase?

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