Subject: Re: [PATCH v3 3/5] setup.c: create `discovery.bare`

From: Derrick Stolee <[email-masked]>
Date: Thu, 2 Jun 2022 09:11:30 -0400

On 5/27/2022 5:09 PM, Glen Choo via GitGitGadget wrote:
> +enum discovery_bare_config {
> +	DISCOVERY_BARE_UNKNOWN = -1,
> +	DISCOVERY_BARE_NEVER = 0,
> +	DISCOVERY_BARE_ALWAYS,
> +};
> +static enum discovery_bare_config discovery_bare_config =
> +	DISCOVERY_BARE_UNKNOWN;

Using this static global is fine, I think.

> +static int discovery_bare_cb(const char *key, const char *value, void *d)
> +{
> +	if (strcmp(key, "discovery.bare"))
> +		return 0;
> +
> +	if (!strcmp(value, "never")) {
> +		discovery_bare_config = DISCOVERY_BARE_NEVER;
> +		return 0;
> +	}
> +	if (!strcmp(value, "always")) {
> +		discovery_bare_config = DISCOVERY_BARE_ALWAYS;
> +		return 0;
> +	}
> +	return -1;
> +}

However, I do think that this _cb method could benefit from interpreting
the 'd' pointer as a 'enum discovery_bare_config *' and assigning the
value at the pointer. We can then pass the global to the
git_protected_config() call below.

This is probably over-defensive future-proofing, but this kind of change
would be necessary if we ever wanted to return the enum instead of
simply an integer, as below:

> +
> +static int check_bare_repo_allowed(void)
> +{
> +	if (discovery_bare_config == DISCOVERY_BARE_UNKNOWN) {
> +		discovery_bare_config = DISCOVERY_BARE_ALWAYS;
> +		git_protected_config(discovery_bare_cb, NULL);
> +	}
> +	switch (discovery_bare_config) {
> +	case DISCOVERY_BARE_NEVER:
> +		return 0;
> +	case DISCOVERY_BARE_ALWAYS:
> +		return 1;
> +	case DISCOVERY_BARE_UNKNOWN:
> +		BUG("invalid discovery_bare_config %d", discovery_bare_config);
> +	}
> +	return 0;
> +}

With the recommended change to the _cb method, we could rewrite this as

static enum discovery_bare_config get_discovery_bare(void)
{
	enum discovery_bare_config result = DISCOVERY_BARE_ALWAYS;
	git_protected_config(discovery_bare_cb, &result);
	return result;
}

With this, we can drop the UNKNOWN and let the caller treat the response
as a simple boolean.

I think this is simpler overall, but also makes it easier to extend in the
future to have "discovery.bare=non-embedded" by adding a new mode and
adjusting the consumer in setup_git_directory_gently_1() to use a switch()
on the resurned enum.

> +
> +static const char *discovery_bare_config_to_string(void)
> +{
> +	switch (discovery_bare_config) {
> +	case DISCOVERY_BARE_NEVER:
> +		return "never";
> +	case DISCOVERY_BARE_ALWAYS:
> +		return "always";
> +	case DISCOVERY_BARE_UNKNOWN:
> +		BUG("invalid discovery_bare_config %d", discovery_bare_config);

This case should be a "default:" in case somehow an arbitrary integer
value was placed in the variable. This could also take an enum as a
parameter, to avoid being coupled to the global.

> +++ b/t/t0035-discovery-bare.sh
> @@ -0,0 +1,64 @@
> +#!/bin/sh
> +
> +test_description='verify discovery.bare checks'
> +
> +. ./test-lib.sh
> +
> +pwd="$(pwd)"
> +
> +expect_rejected () {
> +	test_must_fail git rev-parse --git-dir 2>err &&
> +	grep "discovery.bare" err
> +}

Should we make a simple "expect_accepted" helper in case we ever
want to replace the "git rev-parse --git-dir" with anything else?

> +
> +test_expect_success 'setup bare repo in worktree' '
> +	git init outer-repo &&
> +	git init --bare outer-repo/bare-repo
> +'
> +
> +test_expect_success 'discovery.bare unset' '
> +	(
> +		cd outer-repo/bare-repo &&
> +		git rev-parse --git-dir
> +	)
> +'
> +
> +test_expect_success 'discovery.bare=always' '
> +	git config --global discovery.bare always &&
> +	(
> +		cd outer-repo/bare-repo &&
> +		git rev-parse --git-dir
> +	)
> +'
> +
> +test_expect_success 'discovery.bare=never' '
> +	git config --global discovery.bare never &&
> +	(
> +		cd outer-repo/bare-repo &&
> +		expect_rejected
> +	)
> +'
> +
> +test_expect_success 'discovery.bare in the repository' '
> +	(
> +		cd outer-repo/bare-repo &&
> +		# Temporarily set discovery.bare=always, otherwise git
> +		# config fails with "fatal: not in a git directory"
> +		# (like safe.directory)
> +		git config --global discovery.bare always &&
> +		git config discovery.bare always &&
> +		git config --global discovery.bare never &&
> +		expect_rejected
> +	)
> +'
> +
> +test_expect_success 'discovery.bare on the command line' '
> +	git config --global discovery.bare never &&> +	(
> +		cd outer-repo/bare-repo &&
> +		test_must_fail git -c discovery.bare=always rev-parse --git-dir 2>err &&
> +		grep "discovery.bare" err
> +	)

Ok, at the current place in the series, this test_must_fail matches
expectation. If you reorder to have this patch after your current patch 4,
then we can write this test immediately as a successful case.

We could also reuse some information from the expect_rejected helper by
adding this:

expect_rejected () {
	test_must_fail git $* rev-parse --git-dir 2>err &&
	grep "discovery.bare" err
}

Then you can test the -c options in the tests as

	expect_rejected -c discovery.bare=always

Thanks,
-Stolee