Currently we try to delete a branch normally, and if git returns an error and
its output contains the text "branch -D", then we prompt the user to force
delete, and try again using -D. Besides just being ugly, this has the
disadvantage that git's logic to decide whether a branch is merged is not very
good; it only considers a branch merged if it is either reachable from the
current head, or from its own upstream. In many cases I want to delete a branch
that has been merged to master, but I don't have master checked out, so the
current branch is really irrelevant, and it should rather (or in addition) check
whether the branch is reachable from one of the main branches. The problem is
that git doesn't know what those are.
But lazygit does, so make the check on our side, prompt the user if necessary,
and always use -D. This is both cleaner, and works better.
See this mailing list discussion for more:
https://lore.kernel.org/git/bf6308ce-3914-4b85-a04b-4a9716bac538@haller-berlin.de/
This might seem controversial; in many cases the client code gets longer,
because it needs an extra line for an explicit `return nil`. I still prefer
this, because it makes it clearer which calls can return errors.
