This concerns the behavior when running an external command from a key
binding. The history is:
Prior to 5f16a299a7, fish would run these external commands in shell
modes. This meant that fish would pick up any tty changes from external
commands (see #2114).
After 5f16a299a7, fish would save and restore its shell modes around
these external commands. This introduced a regression where anything the
user typed while a bound external command was executing would be echoed,
because external command mode has ECHO set in c_lflag. (This can be
reproed easily with `bind -q 'sleep 1'` and then pressing q and typing).
So 5f16a299a7 was reverted in fd9355966.
This commit partially reverts fd9355966. It has it both ways: external
commands are launched with shell modes, but/and shell modes are restored
after the external command completes. This allows commands to muck with
the tty, as long as they can handle getting shell modes; but it does not
enable ECHO mode so it fixes the regression found in #7770.
Fixes#7770. Fixes#2114 (for the third time!)
This partially reverts commit fd9355966e.
Unfortunately this causes input coming in while bind functions are
running to show up on screen.
Since the cure is worse than the disease let's just stop doing it.
My guess is this needs to *only* be done while running an external
command.
Fixes#7770
Reintroduces #2114
Partially reverts 5f16a299a7
NetBSD's sleep quits when foregrounded sometimes. I'm not entirely
sure *why*, but this is reproducible with the default /bin/sh, so it's
not our fault.
Because this fails our tests, go back to using cat *there*, because we
can't use it on macOS - 4c9d01cab0.
Apparently on macOS SIGTSTP (from control-Z) causes `read()` to return
EINTR.
This means `cat | cat` will exit as soon as it's backgrounded and
brought back.
So instead we use `sleep`, which won't read(), and therefore is
impervious to these puny attacks.
See discussion in #7447.
