remote: add meaningful exit code on missing/existing

Change the exit code for the likes of "git remote add/rename" to exit
with 2 if the remote in question doesn't exist, and 3 if it
does. Before we'd just die() and exit with the general 128 exit code.

This changes the output message from e.g.:

    fatal: remote origin already exists.

To:

    error: remote origin already exists.

Which I believe is a feature, since we generally use "fatal" for the
generic errors, and "error" for the more specific ones with a custom
exit code, but this part of the change may break code that already
relies on stderr parsing (not that we ever supported that...).

The motivation for this is a discussion around some code in GitLab's
gitaly which wanted to check this, and had to parse stderr to do so:
https://gitlab.com/gitlab-org/gitaly/-/merge_requests/2695

It's worth noting as an aside that a method of checking this that
doesn't rely on that is to check with "git config" whether the value
in question does or doesn't exist. That introduces a TOCTOU race
condition, but on the other hand this code (e.g. "git remote add")
already has a TOCTOU race.

We go through the config.lock for the actual setting of the config,
but the pseudocode logic is:

    read_config();
    check_config_and_arg_sanity();
    save_config();

So e.g. if a sleep() is added right after the remote_is_configured()
check in add() we'll clobber remote.NAME.url, and add another (usually
duplicate) remote.NAME.fetch entry (and other values, depending on
invocation).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 28 insertions, 14 deletions

diff --git a/builtin/remote.c b/builtin/remote.c
index 64b4b551eb..c1828ca7d2 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -191,8 +191,10 @@ static int add(int argc, const char **argv)
 	url = argv[1];
 
 	remote = remote_get(name);
-	if (remote_is_configured(remote, 1))
-		die(_("remote %s already exists."), name);
+	if (remote_is_configured(remote, 1)) {
+		error(_("remote %s already exists."), name);
+		exit(3);
+	}
 
 	strbuf_addf(&buf2, "refs/heads/test:refs/remotes/%s/test", name);
 	if (!valid_fetch_refspec(buf2.buf))
@@ -686,15 +688,19 @@ static int mv(int argc, const char **argv)
 	rename.remote_branches = &remote_branches;
 
 	oldremote = remote_get(rename.old_name);
-	if (!remote_is_configured(oldremote, 1))
-		die(_("No such remote: '%s'"), rename.old_name);
+	if (!remote_is_configured(oldremote, 1)) {
+		error(_("No such remote: '%s'"), rename.old_name);
+		exit(2);
+	}
 
 	if (!strcmp(rename.old_name, rename.new_name) && oldremote->origin != REMOTE_CONFIG)
 		return migrate_file(oldremote);
 
 	newremote = remote_get(rename.new_name);
-	if (remote_is_configured(newremote, 1))
-		die(_("remote %s already exists."), rename.new_name);
+	if (remote_is_configured(newremote, 1)) {
+		error(_("remote %s already exists."), rename.new_name);
+		exit(3);
+	}
 
 	strbuf_addf(&buf, "refs/heads/test:refs/remotes/%s/test", rename.new_name);
 	if (!valid_fetch_refspec(buf.buf))
@@ -829,8 +835,10 @@ static int rm(int argc, const char **argv)
 		usage_with_options(builtin_remote_rm_usage, options);
 
 	remote = remote_get(argv[1]);
-	if (!remote_is_configured(remote, 1))
-		die(_("No such remote: '%s'"), argv[1]);
+	if (!remote_is_configured(remote, 1)) {
+		error(_("No such remote: '%s'"), argv[1]);
+		exit(2);
+	}
 
 	known_remotes.to_delete = remote;
 	for_each_remote(add_known_remote, &known_remotes);
@@ -1511,8 +1519,10 @@ static int set_remote_branches(const char *remotename, const char **branches,
 	strbuf_addf(&key, "remote.%s.fetch", remotename);
 
 	remote = remote_get(remotename);
-	if (!remote_is_configured(remote, 1))
-		die(_("No such remote '%s'"), remotename);
+	if (!remote_is_configured(remote, 1)) {
+		error(_("No such remote '%s'"), remotename);
+		exit(2);
+	}
 
 	if (!add_mode && remove_all_fetch_refspecs(key.buf)) {
 		strbuf_release(&key);
@@ -1565,8 +1575,10 @@ static int get_url(int argc, const char **argv)
 	remotename = argv[0];
 
 	remote = remote_get(remotename);
-	if (!remote_is_configured(remote, 1))
-		die(_("No such remote '%s'"), remotename);
+	if (!remote_is_configured(remote, 1)) {
+		error(_("No such remote '%s'"), remotename);
+		exit(2);
+	}
 
 	url_nr = 0;
 	if (push_mode) {
@@ -1633,8 +1645,10 @@ static int set_url(int argc, const char **argv)
 		oldurl = newurl;
 
 	remote = remote_get(remotename);
-	if (!remote_is_configured(remote, 1))
-		die(_("No such remote '%s'"), remotename);
+	if (!remote_is_configured(remote, 1)) {
+		error(_("No such remote '%s'"), remotename);
+		exit(2);
+	}
 
 	if (push_mode) {
 		strbuf_addf(&name_buf, "remote.%s.pushurl", remotename);