implement GPG signing behavior

[chebbyChefNEQ]

This PR implements GPG signing behavior in ghstack.

This implementation mimics the behavior of git.

This PR resolves #77

[chebbyChefNEQ]

Haven't had the time to set up a test yet. I need to set up git config file generation and use the GIT_CONFIG=<path> envvar to control it. Directly invoking git config just has too much potential for polluting the host env.

[ezyang]

Probably should cache this so we don't keep whacking git config

[ezyang]

This looks pretty good! A test would be great.

[chebbyChefNEQ]

@ezyang Added a test to make sure are are adding -S when commit.gpgsign=true.

[ezyang]

leftover debug printf

[ezyang]

Modifying os.environ is generally frowned upon because it is global state that affects the rest of the process. So it would be better if os.environ was as an explicit argument to main(), so that we can more easily replace its contents when testing (as is the case here). Unfortunately, this is not the case, and I shouldn't really be asking you to do the free work of refactoring all of those sites haha. So I'll probably just take this as is.

[ezyang]

old test for future reference

ghstack/test_ghstack.py

Lines 2086 to 2125 in bb84c55

	def test_gpgsign_should_fail_if_no_default_key(self) -> None:
	print("####################")
	print("### test_gpgsign_should_fail_if_no_default_key")
	print("###")
	@contextlib.contextmanager
	def signing_enabled() -> Iterator[None]:
	# Create a config file that enables signing
	with tempfile.NamedTemporaryFile(delete=False) as f:
	f.writelines(f"{x}\n".encode() for x in [
	"[commit]",
	"\tgpgsign=true",
	])
	# Set the env var
	config = os.environ.get("GIT_CONFIG", None)
	os.environ["GIT_CONFIG"] = f.name
	# HACK: Since we cache the sign config, we need to manaully clear the cache
	import ghstack.gpg_sign
	ghstack.gpg_sign._should_sign = None
	try:
	yield
	finally:
	# Clean up
	if config is None:
	del os.environ["GIT_CONFIG"]
	else:
	os.environ["GIT_CONFIG"] = config
	# HACK: Reset the config again, because we changed the config
	ghstack.gpg_sign._should_sign = None
	# Make a commit WITHOUT signing, we are testing if we are correctly injecting '-S' during submit
	print("### Try to commit")
	self.writeFileAndAdd("a", "asdf")
	self.sh.git("commit", "-m", "Commit 1\n\nThis is my first commit")
	with signing_enabled():
	self.assertRaisesRegex(RuntimeError,
	r"^(git commit-tree -S -p)( )[0-9a-f]{40}( )[0-9a-f]{40} (failed with exit code )[0-9]{1,3}$",
	lambda: self.gh())

[ezyang]

once we have some sort of env plumbing, would feed env into this function and that would make it possible to override this setting in testing

[ezyang]

follow up issue at #80