Cabal run leaves children running when killed

[robx]

Describe the bug

When cabal run receives SIGTERM, it exits, but leaves its children running.

I'm not entirely sure whether this is buggy behaviour, but I was surprised by this,
in the context of running a Haskell tool via cabal run and withProcessTerm.

If I run cabal run target from the shell, and run
kill <cabal-run-pid>, I would have expected both cabal and target
to stop. Instead, cabal exits but target keeps running.

Note that when run interactively, Ctrl-C sends SIGINT to the whole
process group, which is how cabal run interrupts nicely on Ctrl-C.

To Reproduce

$ cat x.hs
{- cabal:
build-depends: base
-}

module Main where

import Control.Concurrent (threadDelay)
import Control.Exception
import Control.Monad (when)

main = loop `catch` logInterrupt
  where
    loop = do
      putStrLn "yo"
      threadDelay 1000000
      loop
    logInterrupt e = do
      when (e == UserInterrupt) $ putStrLn "ouch"
      throwIO e

Then call cabal run x.hs, in a different terminal:

$ ps | grep cabal
77565 ttys002    0:04.09 cabal run x.hs
77726 ttys002    0:00.01 /s/cabal/dist-newstyle/build/x86_64-osx/ghc-8.10.7/fake-package-0/x/script/build/script/script
$ kill 77565

Then the child keeps running although cabal exits:

yo
yo
yo
yo
Terminated: 15
$ yo
yo
yo

Expected behavior

I'd like the child process to be killed, too.

System information

• Operating system: macos
• cabal-install version 3.4.0.0, compiled using version 3.4.0.0 of the Cabal library
• ghc 8.10.7

[Mikolaj]

I seem to remember an old ticket about that.

[robx]

I think in some sense the right/expected thing would be for cabal run to exec() instead of forking.

[Mikolaj]

Oh, yes, I know some of these words. The related issue might have been one of these: #7757 or #7309.

[robx]

Ah, yes, #7757 seems to address this issue explicitly. Thanks! I'd looked through issues but not PRs.

[robx]

I'm convinced this is a bug by now. cabal should stop and wait for all its children when killed.

As a work-around, I'm using this shell script to replace cabal run:

#!/usr/bin/env bash

#   cabal-run.sh target args
#
# is equivalent to
#
#   cabal run target -- args
#
# except that killing it will also kill the target.
#
# https://github.com/haskell/cabal/issues/7914

set -euo pipefail

target="$1"
shift

echo "building target: ${target}"
cabal build "$target"

executable=$(cabal list-bin "$target")

exec "$executable" "$@"