Is there a git-merge --dry-run option?

I'm merging in a remote branch that may have a lot of conflicts. How can I tell if it will have conflicts or not?

I don't see anything like a --dry-run on git-merge.

Solution 1:

As noted previously, pass in the --no-commit flag, but to avoid a fast-forward commit, also pass in --no-ff, like so:

$ git merge --no-commit --no-ff $BRANCH

To examine the staged changes:

$ git diff --cached

And you can undo the merge, even if it is a fast-forward merge:

$ git merge --abort

Solution 2:

I just had to implement a method that automatically finds conflicts between a repository and its remote. This solution does the merge in memory so it won't touch the index, nor the working tree. I think this is the safest possible way you can solve this problem. Here's how it works:

1. Fetch the remote to your repository. For example: git fetch origin master
2. Run git merge-base: git merge-base FETCH_HEAD master
3. Run git merge-tree: git merge-tree mergebase master FETCH_HEAD (mergebase is the hexadecimal id that merge-base printed in the previous step)

Now suppose that you want to merge the remote master with your local master, but you can use any branches. git merge-tree will execute the merge in memory and print the result to the standard output. Grep for the pattern << or >>. Or you can print the output to a file and check that. If you find a line starting with 'changed in both' then most probably there will be a conflict.