Re: [PATCH v2] Simplify handling of setup_git_directory_gently() failure cases.

[Jeff King <peff@peff.net>]

On Sat, Dec 15, 2018 at 05:05:08PM -0800, Erin Dahlgren wrote:

> setup_git_directory_gently() expects two types of failures to
> discover a git directory (e.g. .git/):
> [...]

When I read your subject line, I'll admit to having a funny feeling in
the pit of my stomach. This setup code has historically been full of
subtle corner cases, and I expected a very tricky review.

However, your explanation was so well-written that it was a pleasure to
read. :)

> Before this change are two misleading additional behaviors:
> 
>   - GIT_DIR_HIT_CEILING: setup_nongit() changes to the cwd for no
> 	apparent reason. We never had the chance to change directories
> 	up to this point so chdir(current cwd) is pointless.

That makes sense. I think this is a holdover from when we used to walk
backwards via chdir(), prior to ce9b8aab5d (setup_git_directory_1():
avoid changing global state, 2017-03-13). Back then, we needed to
restore the state at this point, but now we don't.

>   - GIT_DIR_HIT_MOUNT_POINT: strbuf_release() frees the buffer
> 	of a static struct strbuf (cwd). This is unnecessary because the
> 	struct is static so its buffer is always reachable. This is also
> 	misleading because nowhere else in the function is this buffer
> 	released.

Makes sense.

I do have one question, though:

>  	case GIT_DIR_HIT_CEILING:
> -		prefix = setup_nongit(cwd.buf, nongit_ok);
> -		break;
> +		if (!nongit_ok)
> +			die(_("not a git repository (or any of the parent directories): %s"),
>a +					DEFAULT_GIT_DIR_ENVIRONMENT);
> +		*nongit_ok = 1;
> +		strbuf_release(&dir);
> +		return NULL;

This case used to break out of the switch, and now returns early.

So we do not execute the later code which clears GIT_PREFIX_ENVIRONMENT,
and zeroes the fields in startup_info. Those probably don't matter in
most cases, but I wonder if there are some obscure ones where it might.

Might it make sense to make GIT_DIR_HIT_MOUNT_POINT more like
GIT_DIR_HIT_CEILING currently is, rather than the other way around?
I.e., something like:

  case GIT_DIR_HIT_CEILING:
	if (!nongit_ok)
		die(...);
	*nongit_ok = 1;
	prefix = NULL;
	break;
  case GIT_DIR_HIT_MOUNT_POINT:
	if (!nongit_ok)
		die(...);
	*nongit_ok = 1;
	prefix = NULL;
	break;

?

-Peff