From 20010b8c2030867c0e8d55caad7cda2042ac950f Mon Sep 17 00:00:00 2001 From: Jeff King Date: Sat, 8 Mar 2025 22:20:16 -0500 Subject: [PATCH] fetch: avoid ls-refs only to ask for HEAD symref update When we fetch from a configured remote, we may try to update the local refs/remotes//HEAD, and so we ask the server to advertise its HEAD to us. But if we aren't otherwise asking about any refs at all, then we know this HEAD update can never happen! To consider a new value for HEAD, the set_head() function uses guess_remote_head(). And even if it sees an explicit symref value for HEAD, it will only report that as a match if we also saw that remote ref advertised, and it mapped to a local tracking ref via get_fetch_map(). In other words, a fetch like this: git fetch origin $exact_oid:refs/heads/foo can never update HEAD, because we will never have fetched (nor even see the advertisement for) the ref that HEAD points to. Currently the command above will still call ls-refs to ask about the HEAD, even though it is pointless. This patch teaches it to skip the ls-refs call entirely in this case, which avoids a round-trip to the server. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- builtin/fetch.c | 5 ++--- t/t5702-protocol-v2.sh | 13 +++++++++++++ 2 files changed, 15 insertions(+), 3 deletions(-) diff --git a/builtin/fetch.c b/builtin/fetch.c index 6ab101fa6d..c26866e674 100644 --- a/builtin/fetch.c +++ b/builtin/fetch.c @@ -1782,11 +1782,10 @@ static int do_fetch(struct transport *transport, "refs/tags/"); } - if (uses_remote_tracking(transport, rs)) { - must_list_refs = 1; + if (must_list_refs && + uses_remote_tracking(transport, rs)) strvec_push(&transport_ls_refs_options.ref_prefixes, "HEAD"); - } if (must_list_refs) { trace2_region_enter("fetch", "remote_refs", the_repository); diff --git a/t/t5702-protocol-v2.sh b/t/t5702-protocol-v2.sh index 626deb05f0..4d0cbe9872 100755 --- a/t/t5702-protocol-v2.sh +++ b/t/t5702-protocol-v2.sh @@ -708,6 +708,19 @@ test_expect_success 'exact oid fetch with tag following' ' git -C exact-oid-tags rev-parse --verify my-tag ' +test_expect_success 'exact oid fetch avoids pointless HEAD request' ' + git init exact-oid-head && + git -C exact-oid-head remote add origin ../prefix-parent && + + commit=$(git -C prefix-parent rev-parse --verify HEAD) && + + test_when_finished "rm -f log" && + GIT_TRACE_PACKET="$(pwd)/log" \ + git -C exact-oid-head fetch --no-tags origin \ + $commit:refs/heads/exact && + test_grep ! command=ls-refs log +' + test_expect_success 'fetch supports various ways of have lines' ' rm -rf server client trace && git init server &&