Teach Ui's writing functions to write to a pager without touching the
process's file descriptors. This is done by introducing UiOutput::Paged,
which spawns a pager that Ui's functions can write to.
The pager program can be chosen via `ui.pager`. (defaults to Defaults to
$PAGER, and 'less' if that is unset (falling back to 'less' also makes
the tests pass).
Currently, commands are paginated if:
- they have "long" output (as defined by jj developers)
- jj is invoked in a terminal
The next commit will allow pagination to be turned off via a CLI option.
More complex pagination toggling (e.g. showing a pager even if the
output doesn't look like a terminal, using a pager for shorter ouput) is
left for a future PR.
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.
It's now pretty easy to add a custom command. Let's have an example to
show how to do it, and to protect against regressions.
It would be nice to also have some tests of the custom command, to
check that the command works, that other commands can be run, and that
`jj debug completion` includes the custom command. I'm not sure how to
do that, however.
