Go bazelisk causes double-SIGINT in "bazel run"

[philsc]

With this py_binary():

import time
import signal

running = True

def _sigint_handler_debounced(signal_number, frame):
    global running
    if not running:
        print("Ignoring superfluous SIGINT")
        return

    print("Stopping the program")
    running = False


signal.signal(signal.SIGINT, _sigint_handler_debounced)

while running:
    time.sleep(1)

print("Almost there. Waiting for potential superfluous SIGINTs")
time.sleep(1)

And then when I run it and hit CTRL-C once:

$ bazel run //common/python/double_sigint:foo
^CStopping the program
Ignoring superfluous SIGINT
Almost there. Waiting for potential superfluous SIGINTs

This appears to be caused by the signal forwarding in the Go version:

bazelisk/core/core.go

Lines 438 to 442 in 15abf0e

	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
	go func() {
	s := <-c
	if runtime.GOOS != "windows" {
	cmd.Process.Signal(s)

The Python version notably does not have this behaviour:

bazelisk/bazelisk.py

Lines 445 to 452 in 81f38ed

	p = subprocess.Popen([cmd["exec"]] + cmd["args"], close_fds=os.name != "nt", env=cmd["env"])
	while True:
	try:
	return p.wait()
	except KeyboardInterrupt:
	# Bazel will also get the signal and terminate.
	# We should continue waiting until it does so.
	pass

I'd be tempted to say that bazelisk should only forward SIGTERM and not forward SIGINT.
I.e. hitting CTRL-C on an interactive program should only generate a single SIGINT in the running program. But sending a SIGTERM to bazelisk (via child PID after fork/exec) should also trigger a SIGTERM in the running process.

What do the maintainers here think?