git-merge-file functionality for bare repos (generate merge file in memory)

[mhodgson]

It isn't currently possible to generate a merge-file when working with bare repos. This makes it impossible to determine the conflicting parts of a given file when trying resolve a conflict during a merge. It would be lovely if there were a mechanism by which to generate a diff (or something like it) that only shows the conflicting parts of the file. This would enable the creation of user friendly merge tools without relying on parsing the merge-file from the filesystem (especially in cases where you're using bare repos and alternate ODB backends).

I don't have a proposal for the API for this feature, but I suspect it should look something like a diff.

Would anyone else find this useful? Happy to help work on it if we can rough out an API. At the very least I promise to update the Rugged bindings.

cc/ @ethomson

[arthurschreiber]

Yes, I'd also love to see this implemented. 👍

[ethomson]

@arthurschreiber how would you want the data back? Is a git_buf okay?

[vmg]

@ethomson: Like most APIs, ideally we'd have a callback-based writer so we can write directly to a buffer, or somewhere else. :)

[carlosmn]

The work to introduce this from #2140 was merged as part of #2183.