darwin: use vim, not vi, to avoid data-loss inducing posix behavior Apple's version of vim, available at opensource.apple.com/release/macos-1015.html (for Catalina, but this behavior has been there for a while) has several tweaks from the version of vim from vim.org. Most of these tweaks appear to be for "Unix2003" compatibility. One of the tweaks is that if any ex command raises an error, the entire process will (when you exit, possibly minutes/hours later) also exit non-zero. Ex commands are things like `:foo`. Luckily, they only enabled this if vim was executed (via a symlink or copying the binary) as `vi` or `ex`. If you start it as `vim`, it doesn't have this behavior, so let's do that. To see this in action, run the following two commands on macOS: ``` $ vi -c ':unknown' -c ':qa' ; echo $? 1 $ vim -c ':unknown' -c ':qa' ; echo $? 0 ``` We don't want to start ignoring non-zero return types from the editor because that will mean you can't use `:cquit` to intentionally exit 1 (which, shows up as 2 if you combine an ex command error and a cquit, but only a 1 if you just use cquit, so we can't differentiate between the two statuses). Since we can't differentiate, we have to assume that all non-zero exit codes are intentional and an indication of the user's desire to not continue with whatever we're doing. If this was a complicated `hg split` or `hg histedit`, this is especially disastrous :( Differential Revision: https://phab.mercurial-scm.org/D8321