[PATCH v2] fetch: limit shared symref check only for local branches

["Orgad Shaneh via GitGitGadget" <gitgitgadget@gmail.com>]

From: Orgad Shaneh <orgads@gmail.com>

This check was introduced in 8ee5d73137f (Fix fetch/pull when run without
--update-head-ok, 2008-10-13) in order to protect against replacing the ref
of the active branch by mistake, for example by running git fetch origin
master:master.

It was later extended in 8bc1f39f411 (fetch: protect branches checked out
in all worktrees, 2021-12-01) to scan all worktrees.

This operation is very expensive (takes about 30s in my repository) when
there are many tags or branches, and it is executed on every fetch, even if
no local heads are updated at all.

Limit it to protect only refs/heads/* to improve fetch performance.

Signed-off-by: Orgad Shaneh <orgads@gmail.com>
---
    fetch: limit shared symref check only for local branches

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1266%2Forgads%2Ffetch-perf-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1266/orgads/fetch-perf-v2
Pull-Request: https://github.com/git/git/pull/1266

Range-diff vs v1:

 1:  5e86dc86d3d ! 1:  72bea90b26f fetch: limit shared symref check only for local branches
     @@ builtin/fetch.c: static void check_not_current_branch(struct ref *ref_map,
       	const struct worktree *wt;
       	for (; ref_map; ref_map = ref_map->next)
       		if (ref_map->peer_ref &&
     -+			starts_with(ref_map->peer_ref->name, "refs/heads/") &&
     ++		    starts_with(ref_map->peer_ref->name, "refs/heads/") &&
       		    (wt = find_shared_symref(worktrees, "HEAD",
       					     ref_map->peer_ref->name)) &&
       		    !wt->is_bare)


 builtin/fetch.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index e3791f09ed5..eeee5ac8f15 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1440,6 +1440,7 @@ static void check_not_current_branch(struct ref *ref_map,
 	const struct worktree *wt;
 	for (; ref_map; ref_map = ref_map->next)
 		if (ref_map->peer_ref &&
+		    starts_with(ref_map->peer_ref->name, "refs/heads/") &&
 		    (wt = find_shared_symref(worktrees, "HEAD",
 					     ref_map->peer_ref->name)) &&
 		    !wt->is_bare)

base-commit: 277cf0bc36094f6dc4297d8c9cef79df045b735d
-- 
gitgitgadget