This command uses an external merge tool to resolve conflicts
simple enough that they can be resolved with a 3-way merge.
This commit provides a very basic version of `jj resolve` that
is hardcoded to use vimdiff.
This also slightly changes the errors of the Diff Editor, so that
both the diff editor and `jj resolve can share an error type.
Let's acknowledge everyone's contributions by replacing "Google LLC"
in the copyright header by "The Jujutsu Authors". If I understand
correctly, it won't have any legal effect, but maybe it still helps
reduce concerns from contributors (though I haven't heard any
concerns).
Google employees can read about Google's policy at
go/releasing/contributions#copyright.
In the test case `test_branch_mutually_exclusive_actions`, we weren't actually testing anything useful, because the interface has since changed to use subcommands instead of options. The test has been deleted in this commit, and `TestEnvironment::jj_cmd_cli_error` has been changed to return a `#[must_use]` `String` representing stderr. I also added `#[must_use]` to `TestEnvironment::jj_cmd_failure` while I was here.
It can be confusing that some commits (typically the working copy)
don't have a description. Let's show a placeholder text in such cases.
I chose the format to match the "(no email configured)" message we
already have.
We didn't have any testing of exit codes on failure, other than
checking that they were not 0. This patch changes that so we always
check. Since we have the special exit code 2 (set by `clap`) for
incorrect command line, I've replaced some testing of error messages
by testing of just the exit code.
As part of this, I also fixed `jj branch --allow-backwards` to
actually require `-r` (it didn't before because having a default value
means the argument is considered always provided).
