setup_git_directory_gently_1(): avoid die()ing

This function now has a new caller in addition to setup_git_directory():
the newly introduced discover_git_directory(). That function wants to
discover the current .git/ directory, and in case of a corrupted one
simply pretend that there is none to be found.

Example: if a stale .git file exists in the parent directory, and the
user calls `git -p init`, we want Git to simply *not* read any
repository config for the pager (instead of aborting with a message that
the .git file is corrupt).

Let's actually pretend that there was no GIT_DIR to be found in that case
when being called from discover_git_directory(), but keep the previous
behavior (i.e. to die()) for the setup_git_directory() case.

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

Author: dscho

setup.c

@@ -825,7 +825,8 @@ enum discovery_result {
 	GIT_DIR_BARE,
 	/* these are errors */
 	GIT_DIR_HIT_CEILING = -1,
-	GIT_DIR_HIT_MOUNT_POINT = -2
+	GIT_DIR_HIT_MOUNT_POINT = -2,
+	GIT_DIR_INVALID_GITFILE = -3
 };
 
 /*
@@ -842,7 +843,8 @@ enum discovery_result {
  * is relative to `dir` (i.e. *not* necessarily the cwd).
  */
 static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir,
-							  struct strbuf *gitdir)
+							  struct strbuf *gitdir,
+							  int die_on_error)
 {
 	const char *env_ceiling_dirs = getenv(CEILING_DIRECTORIES_ENVIRONMENT);
 	struct string_list ceiling_dirs = STRING_LIST_INIT_DUP;
@@ -890,14 +892,21 @@ static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir,
 	if (one_filesystem)
 		current_device = get_device_or_die(dir->buf, NULL, 0);
 	for (;;) {
-		int offset = dir->len;
+		int offset = dir->len, error_code = 0;
 
 		if (offset > min_offset)
 			strbuf_addch(dir, '/');
 		strbuf_addstr(dir, DEFAULT_GIT_DIR_ENVIRONMENT);
-		gitdirenv = read_gitfile(dir->buf);
-		if (!gitdirenv && is_git_directory(dir->buf))
-			gitdirenv = DEFAULT_GIT_DIR_ENVIRONMENT;
+		gitdirenv = read_gitfile_gently(dir->buf, die_on_error ?
+						NULL : &error_code);
+		if (!gitdirenv) {
+			if (die_on_error ||
+			    error_code == READ_GITFILE_ERR_NOT_A_FILE) {
+				if (is_git_directory(dir->buf))
+					gitdirenv = DEFAULT_GIT_DIR_ENVIRONMENT;
+			} else if (error_code != READ_GITFILE_ERR_STAT_FAILED)
+				return GIT_DIR_INVALID_GITFILE;
+		}
 		strbuf_setlen(dir, offset);
 		if (gitdirenv) {
 			strbuf_addstr(gitdir, gitdirenv);
@@ -934,7 +943,7 @@ const char *discover_git_directory(struct strbuf *gitdir)
 		return NULL;
 
 	cwd_len = dir.len;
-	if (setup_git_directory_gently_1(&dir, gitdir) <= 0) {
+	if (setup_git_directory_gently_1(&dir, gitdir, 0) <= 0) {
 		strbuf_release(&dir);
 		return NULL;
 	}
@@ -994,7 +1003,7 @@ const char *setup_git_directory_gently(int *nongit_ok)
 		die_errno(_("Unable to read current working directory"));
 	strbuf_addbuf(&dir, &cwd);
 
-	switch (setup_git_directory_gently_1(&dir, &gitdir)) {
+	switch (setup_git_directory_gently_1(&dir, &gitdir, 1)) {
 	case GIT_DIR_NONE:
 		prefix = NULL;
 		break;