ob run: Child processes are orphaned on SIGHUP

[plt-amy]

(On Linux,) when terminating ob run with SIGHUP - e.g. because your terminal is being closed - the child ghcid process stays alive, and keeps the port occupied. Repro is essentially:

$ ob run # in basically any obelisk project
[...]
Frontend running on http://localhost:8000/

Then pkill -SIGHUP ob and verify that ghcid is still running, e.g. with pgrep or simply by causing a reload and verifying that the frontend is still running/updating:

$ pgrep ghcid
257475
$ pkill -SIGHUP ob
$ pgrep ghcid
257475

I think it'd be more natural for the ghcid process to be terminated when ob run is killed with SIGHUP, just like it's terminated when ob run is killed with SIGTERM.

[mankyKitty]

Similar issue: #633

[parenthetical]

Looking into this some more. (Caveat: I don't know much about process handling.)

Something interesting I noticed in that SIGHUP'ing the ghcid process rather than the Obelisk process leads to the same behavior, leaving behind a ghc process like above. Does that mean could be a ghcid problem?

The runGhcid' function uses Obelisk.Command.Project.nixShellWithoutPkgs. Inlining runProcess_` there looks like this:

nixShellWithoutPkgs
  :: MonadObelisk m
  => FilePath -- ^ Path to project root
  -> Bool -- ^ Should this be a pure shell?
  -> Bool -- ^ Should we chdir to the package root in the shell?
  -> Map Text FilePath -- ^ Package names mapped to their paths
  -> String -- ^ Shell attribute to use (e.g. @"ghc"@, @"ghcjs"@, etc.)
  -> Maybe String -- ^ If 'Just' run the given command; otherwise just open the interactive shell
  -> m ()
nixShellWithoutPkgs root isPure chdirToRoot packageNamesAndPaths shellAttr command = do
  pc <- mkObNixShellProc root isPure chdirToRoot packageNamesAndPaths shellAttr command
  bracketOnError
    (createProcess pc)
    (liftIO . Proc.cleanupProcess)
    (\((_, _, _, ph)) -> throwExitCode pc =<< waitForProcess ph)

Changing cleanupProcess to terminateProcess or terminating the process in a SIGHUP handler doesn't change the fact that the ghc process is left:

This is as far as I got before running out of ideas. 
     (\((_, _, _, ph)) -> do
        liftIO $ installHandler 1 (CatchInfo (\_ -> Proc.terminateProcess ph)) Nothing
        throwExitCode pc =<< waitForProcess ph)