patchSupport working directory located at root

> Git should work regardless where the working directory is located,
> even at root. This patch fixes two places where it assumes working
> directory always have parent directory.
>
> In setup_git_directory_gently(), when Git goes up to root and finds
> .git there, it happily sets worktree to "".

> Nguyễn Thái Ngọc Duy <pclouds@gmail.com> writes:
>
>> Git should work regardless where the working directory is located,
>> even at root. This patch fixes two places where it assumes working
>> directory always have parent directory.
>>
>> In setup_git_directory_gently(), when Git goes up to root and finds
>> .git there, it happily sets worktree to "".
>
> If you mean "instead set it to "/" and things will work much better."
> I agree with the reasoning (not suggesting to reword---just trying to
> make sure I understood what you meant).

>
>> In prefix_path(), loosen the outside repo check a little bit. Usually
>> when a path XXX is inside worktree /foo, it must be either "/foo", or
>> "/foo/...". When worktree is simply "/", we can safely ignore the
>> check: we have a slash at the beginning already.
>
> The logic for the "are we inside?" check above sounds correct.  When
> work_tree is at root, have "/" in it, and len inside the "if orig is
> absolute" block is 1, so memmove() strips out the leading '/' and makes
> the result relative to the root level.  Am I reading the code right?

> But I suspect my change in this code is not enough and caused
> the problem (on msys?) for Hannes. If the worktree somehow is '//' and
> sanitized is '/etc/resolv.conf', then we could end up eating two
> chars, leading to "'tc/resolv.conf' not match" error.
>
> Hannes, can you put a "printf("%s\n", work_tree);" in prefix_path() to
> see if it's the case?

> @@ -25,7 +25,7 @@ const char *prefix_path(const char *prefix, int len,
> const char *path) len = strlen(work_tree);
>  		total = strlen(sanitized) + 1;
>  		if (strncmp(sanitized, work_tree, len) ||
> -		    (sanitized[len] != '\0' && sanitized[len] != '/')) {
> +		    (len > 1 && sanitized[len] != '\0' && sanitized[len] != '/')) {
>  		error_out:
>  			die("'%s' is outside repository", orig);
>  		}
> @@ -403,7 +403,7 @@ const char *setup_git_directory_gently(int *nongit_ok)
>  			if (!work_tree_env)
>  				inside_work_tree = 0;
>  			if (offset != len) {
> -				cwd[offset] = '\0';
> +				cwd[offset ? offset : 1] = '\0';
>  				set_git_dir(cwd);
>  			} else
>  				set_git_dir(".");
> @@ -427,6 +427,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
>  	inside_git_dir = 0;
>  	if (!work_tree_env)
>  		inside_work_tree = 1;
> +	if (offset == 0) /* reached root, set worktree to '/' */
> +		offset = 1;
>  	git_work_tree_cfg = xstrndup(cwd, offset);
>  	if (check_repository_format_gently(nongit_ok))
>  		return NULL;