[PATCH] fetch: fix duplicate remote parallel fetch bug

[Calvin Wan <calvinwan@google.com>]

Fetching in parallel from a remote group with a duplicated remote results
in the following:

error: cannot lock ref '<ref>': is at <oid> but expected <oid>

This doesn't happen in serial since fetching from the same remote that
has already been fetched from is a noop. Therefore, remove any duplicated
remotes after remote groups are parsed.

Signed-off-by: Calvin Wan <calvinwan@google.com>
---
 builtin/fetch.c          | 1 +
 t/t5506-remote-groups.sh | 9 +++++++++
 2 files changed, 10 insertions(+)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index b06e454cbd..508ab2670c 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -2225,6 +2225,7 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 			argv++;
 		}
 	}
+	string_list_remove_duplicates(&list, 0);
 
 	if (negotiate_only) {
 		struct oidset acked_commits = OIDSET_INIT;
diff --git a/t/t5506-remote-groups.sh b/t/t5506-remote-groups.sh
index 5bac03ede8..0e176175a3 100755
--- a/t/t5506-remote-groups.sh
+++ b/t/t5506-remote-groups.sh
@@ -99,4 +99,13 @@ test_expect_success 'updating remote name updates that remote' '
 	! repo_fetched two
 '
 
+test_expect_success 'updating group in parallel with a duplicate remote does not fail (fetch)' '
+	mark fetch-group-duplicate &&
+	update_repo one &&
+	git config --add remotes.duplicate one &&
+	git config --add remotes.duplicate one &&
+	git -c fetch.parallel=2 remote update duplicate &&
+	repo_fetched one
+'
+
 test_done
-- 
2.39.0.246.g2a6d74b583-goog