Re: [PATCH v7 2/3] repository: keep a symlink-preserving copy of the worktree path

> diff --git a/repository.c b/repository.c
> index 73d80bcffdf5..a29d55a6fcd3 100644
> --- a/repository.c
> +++ b/repository.c
> @@ -149,6 +149,11 @@ const char *repo_get_work_tree(struct repository *repo)
>  	return repo->worktree;
>  }
>  
> +const char *repo_get_work_tree_original(struct repository *repo)
> +{
> +	return repo->worktree_original;
> +}

> diff --git a/setup.c b/setup.c
> index 0de56a074f7c..fbbeb95f99db 100644
> --- a/setup.c
> +++ b/setup.c
> @@ -1213,12 +1213,94 @@ static const char *setup_explicit_git_dir(struct repository *repo,
>  	return NULL;
>  }
>  
> +/*
> + * Do "a" and "b" refer to the same filesystem entry? Both must report a
> + * nonzero (dev,ino): some filesystems return (0,0) for unrelated paths,
> + * which would otherwise look identical.
> + */
> +static int same_entry(const char *a, const char *b)
> +{
> +	struct stat sa, sb;
> +
> +	if (stat(a, &sa) || stat(b, &sb))
> +		return 0;
> +	return (sa.st_dev || sa.st_ino) &&
> +	       sa.st_dev == sb.st_dev && sa.st_ino == sb.st_ino;
> +}
> +
> +/*
> + * Recover the symlink-preserving spelling of the worktree root.
> + *
> + * strbuf_add_absolute_path() already consults $PWD to keep symlinks when
> + * resolving a relative path, so set_git_work_tree()'s other callers get a
> + * symlink-preserving worktree path for free.  This function exists for the
> + * discovered-repository case: setup_git_directory_gently() chdir()s to the
> + * worktree root *before* set_git_work_tree(repo, ".") runs, so by the time
> + * "." is resolved $PWD still names the caller's original directory and no
> + * longer agrees with the physical cwd, and strbuf_add_absolute_path()
> + * falls back to the realpath.  We close that gap by deriving the logical
> + * root here, from $PWD, while we still have the original physical cwd and
> + * the root offset in hand.
> + *
> + * "cwd" is the physical current directory (getcwd), and "root_len" is the
> + * length of the worktree root within it; cwd->buf[root_len..] is therefore
> + * the part of the path below the root (empty when git ran at the root).
> + *
> + * $PWD, maintained by the shell, may spell that same directory through
> + * symlinks.  If we can confirm $PWD really names cwd's directory (same
> + * device/inode) and that the below-root suffix matches, we swap the
> + * physical root prefix for $PWD's prefix and keep the user's symlinks.
> + * Only symlinks in the root prefix itself are preserved: the below-root
> + * suffix is matched byte-for-byte, so a symlink below the root is not.
> + *
> + * Returns the allocated logical path, or NULL when $PWD is missing, already
> + * physical, or untrustworthy.
> + */

> +static char *logical_path_from_cwd(struct strbuf *cwd, int root_len)
> +{
> +	const char *pwd = getenv("PWD");
> +	size_t suffix_len, pwd_len;
> +	struct strbuf path = STRBUF_INIT;
> +
> +	if (!pwd || !is_absolute_path(pwd) || !strcmp(pwd, cwd->buf))
> +		return NULL;
> +	/*
> +	 * $PWD is a plain environment variable: it can be set to anything,
> +	 * or left stale after a chdir.  Only borrow its symlink-preserving
> +	 * spelling once we prove it still points at the same directory as
> +	 * the physical cwd; otherwise give up and return NULL.
> +	 */
> +	if (!same_entry(cwd->buf, pwd))
> +		return NULL;
> +
> +	/*
> +	 * Drop the below-root suffix from $PWD.  It must match the physical
> +	 * suffix exactly; the only spelling difference we accept is in the
> +	 * root prefix -- i.e. the symlinks we want to preserve.
> +	 */
> +	suffix_len = cwd->len - root_len;
> +	pwd_len = strlen(pwd);
> +	if (suffix_len) {
> +		const char *suffix = cwd->buf + root_len;
> +
> +		if (suffix_len > pwd_len ||
> +		    fspathcmp(pwd + pwd_len - suffix_len, suffix))
> +			return NULL;
> +		pwd_len -= suffix_len;
> +	}
> +
> +	strbuf_add(&path, pwd, pwd_len);
> +	return strbuf_detach(&path, NULL);
> +}