[PATCH v2] fetch --prune: exit with error if pruning fails

[Thomas Gummerer <t.gummerer@gmail.com>]

When pruning refs fails, we currently print an error to stderr, but
still exit 0 from 'git fetch'.  Since this is a genuine error fetch
should be exiting with some non-zero exit code.  Make it so.

The --prune option was introduced in f360d844de ("builtin-fetch: add
--prune option", 2009-11-10).  Unfortunately it's unclear from that
commit whether ignoring the exit code was an oversight or
intentional, but it feels like an oversight.

Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
---

changes in v2:
- retcode will now always be 1 if we get an error from prune_refs,
  no matter what the original error code was.
- we will now continue the fetch, and only exit with a non-zero
  exit code after having finished the rest of the fetch operation
- added a comment in the test explaining why creating a packed-refs.new
  file will make the fetch --prune fail.

 builtin/fetch.c  | 10 ++++++----
 t/t5510-fetch.sh | 11 +++++++++++
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 5f06b21f8e..648f0694f2 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1609,12 +1609,14 @@ static int do_fetch(struct transport *transport,
 		 * don't care whether --tags was specified.
 		 */
 		if (rs->nr) {
-			prune_refs(rs, ref_map, transport->url);
+			retcode = prune_refs(rs, ref_map, transport->url);
 		} else {
-			prune_refs(&transport->remote->fetch,
-				   ref_map,
-				   transport->url);
+			retcode = prune_refs(&transport->remote->fetch,
+					     ref_map,
+					     transport->url);
 		}
+		if (retcode != 0)
+			retcode = 1;
 	}
 	if (fetch_and_consume_refs(transport, ref_map, worktrees)) {
 		free_refs(ref_map);
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index 20f7110ec1..ef0da0a63b 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -164,6 +164,17 @@ test_expect_success 'fetch --prune --tags with refspec prunes based on refspec'
 	git rev-parse sometag
 '
 
+test_expect_success REFFILES 'fetch --prune fails to delete branches' '
+	cd "$D" &&
+	git clone . prune-fail &&
+	cd prune-fail &&
+	git update-ref refs/remotes/origin/extrabranch main &&
+	: this will prevent --prune from locking packed-refs for deleting refs, but adding loose refs still succeeds  &&
+	>.git/packed-refs.new &&
+
+	test_must_fail git fetch --prune origin
+'
+
 test_expect_success 'fetch --atomic works with a single branch' '
 	test_when_finished "rm -rf \"$D\"/atomic" &&
 
-- 
2.31.1