I have a minor issue where less gets suspended/backgrounded unexpectedly when using two pipes and the last one is a grep (with some caveats, see below). It's easy to work around, so not a big priority but I wanted to raise it if other people stumble upon it.

How to reproduce the issue

# Make a file called "minimal_example.txt" that contains 50 empty lines
# (it has to be more lines than can fit in your terminal vertically)
> string repeat -n 50 \n > minimal_example.txt
> cat minimal_example.txt | grep '.*' | less
:fish: Job 1, 'cat minimal_example.txt | grep…' has stopped
# less is suspended/backgrounded immediately as the command is run

I can reliably reproduce the issue both using fish --no-config and sh -c 'env HOME=$(mktemp -d) fish'.

Interestingly, replacing cat minimal_example.txt with string repeat -n 50 \n or replacing grep '.*' with cat "fixes" the issue. Also the pipeline must have two pipes, e.g. grep '.*' minimal_example.txt | less works perfectly fine.
Furthermore, it seems related to terminal height. If I resize the terminal window to be tall enough for all the lines to fit the window the issue also does not occur.

The issue happens both when fish is run in Terminal.app and iTerm2. It does not occur in bash and zsh (not that fish should emulate any of those -- but this feels like bug).

In this asciinema video of the issue, the issue only happens on the second invocation, so it might be some kind race-condition. I currently hit the bug 95% of the time I run the test command, but it's been a bit lower previously.

fish version

> fish --version
fish, version 3.3.1
> echo $version
3.3.1
> echo $TERM
xterm-256color
> uname -a
Darwin Malthes-MBP.lan 21.3.0 Darwin Kernel Version 21.3.0: Wed Jan  5 21:37:58 PST 2022; root:xnu-8019.80.24~20/RELEASE_ARM64_T6000 arm64

I'm on a Macbook Pro (Apple M1 Pro) with macOS 12.2.