when started from python's subprocess.call(), fish does not handle ctrl-c properly.

[etoombs-encircle]

Version, etc:

$ pacman -Qi fish python3 | egrep 'Name|Version'
Name            : fish
Version         : 3.0.2-2
Name            : python
Version         : 3.7.4-2
$ uname -s -r -v -m -o
Linux 5.3.7-arch1-1-ARCH #1 SMP PREEMPT Fri Oct 18 00:17:03 UTC 2019 x86_64 GNU/Linux

So, first, you start fish using subprocess.call(). Then, you try a ^C at the prompt. It's supposed to just reset the prompt state. This is what it does instead:

env -i HOME=(mktemp -d) TERM=xterm-256color python3 -c 'from subprocess import *; call(["fish"])'
Welcome to fish, the friendly interactive shell
eric@<hostname> /h/eric> Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python3.7/subprocess.py", line 325, in call
    return p.wait(timeout=timeout)
  File "/usr/lib/python3.7/subprocess.py", line 990, in wait
    return self._wait(timeout=timeout)
  File "/usr/lib/python3.7/subprocess.py", line 1624, in _wait
    (pid, sts) = self._try_wait(0)
  File "/usr/lib/python3.7/subprocess.py", line 1582, in _try_wait
    (pid, sts) = os.waitpid(self.pid, wait_flags)
KeyboardInterrupt

I'd normally blame python, but this only seems to happen when using fish. Here's what happens when you use bash, for example:

env -i HOME=(mktemp -d) TERM=xterm-256color python3 -c 'from subprocess import *; call(["bash"])'
[eric@<hostname> eric]$ ^C
[eric@<hostname> eric]$ ^C
[eric@<hostname> eric]$ ^C
[eric@<hostname> eric]$ exit

If you swap the subprocess.call() function for an os.execvp(), it works fine. I tested it in xfce4-terminal and the linux terminal and saw the same behaviour in both places.
I guess this might still be a problem with python. IDK, what do you think?

[zanchey]

bash starts a new process group, where fish doesn't:

USER    PID  PPID  PGID   SESS JOBC STAT   TT       TIME COMMAND
david 23932 23836 23932      0    1 S+   s007    0:00.07 /usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3
david 23933 23932 23932      0    1 S+   s007    0:00.11 /usr/local/bin/fish
david 23959 23940 23959      0    1 S    s008    0:00.08 /usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3
david 23960 23959 23960      0    1 S+   s008    0:00.01 bash

This is a duplicate of #5909.