setup: introduce the discover_git_directory() function

We modified the setup_git_directory_gently_1() function earlier to make
it possible to discover the GIT_DIR without changing global state.

However, it is still a bit cumbersome to use if you only need to figure
out the (possibly absolute) path of the .git/ directory. Let's just
provide a convenient wrapper function with an easier signature that
*just* discovers the .git/ directory.

We will use it in a subsequent patch to fix the early config.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/setup.c b/setup.c
index 27a31de33f..d08730d94d 100644
--- a/setup.c
+++ b/setup.c
@@ -924,6 +924,49 @@ static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir,
 	}
 }
 
+const char *discover_git_directory(struct strbuf *gitdir)
+{
+	struct strbuf dir = STRBUF_INIT, err = STRBUF_INIT;
+	size_t gitdir_offset = gitdir->len, cwd_len;
+	struct repository_format candidate;
+
+	if (strbuf_getcwd(&dir))
+		return NULL;
+
+	cwd_len = dir.len;
+	if (setup_git_directory_gently_1(&dir, gitdir) <= 0) {
+		strbuf_release(&dir);
+		return NULL;
+	}
+
+	/*
+	 * The returned gitdir is relative to dir, and if dir does not reflect
+	 * the current working directory, we simply make the gitdir absolute.
+	 */
+	if (dir.len < cwd_len && !is_absolute_path(gitdir->buf + gitdir_offset)) {
+		/* Avoid a trailing "/." */
+		if (!strcmp(".", gitdir->buf + gitdir_offset))
+			strbuf_setlen(gitdir, gitdir_offset);
+		else
+			strbuf_addch(&dir, '/');
+		strbuf_insert(gitdir, gitdir_offset, dir.buf, dir.len);
+	}
+
+	strbuf_reset(&dir);
+	strbuf_addf(&dir, "%s/config", gitdir->buf + gitdir_offset);
+	read_repository_format(&candidate, dir.buf);
+	strbuf_release(&dir);
+
+	if (verify_repository_format(&candidate, &err) < 0) {
+		warning("ignoring git dir '%s': %s",
+			gitdir->buf + gitdir_offset, err.buf);
+		strbuf_release(&err);
+		return NULL;
+	}
+
+	return gitdir->buf + gitdir_offset;
+}
+
 const char *setup_git_directory_gently(int *nongit_ok)
 {
 	static struct strbuf cwd = STRBUF_INIT;