[PATCH v3 1/3] branch: avoid unnecessary worktrees traversals

["Rubén Justo" <rjusto@gmail.com>]

"reject_rebase_or_bisect_branch()" was introduced [1] to prevent a
branch under bisect or rebase from being renamed or copied.  It
traverses all worktrees in the repository and dies if the specified
branch is being rebased or bisected in any of them.

"replace_each_worktree_head_symref()" was introduced [2] to adjust the
HEAD in all worktrees after a branch rename succeeded.  It traverses all
worktrees in the repository and if any of them have their HEAD pointing
to the renamed ref, it adjusts it.

If we could know in advance if the renamed branch is not HEAD in any
worktree we could avoid calling "replace_each_worktree_head_symref()",
and so avoid that unnecessary second traversing.

Let's rename "reject_rebase_or_bisect_branch()" to a more meaningful
name "die_if_branch_is_being_rebased_or_bisected()" and make it return,
if it does not die(), if the specified branch is HEAD in any worktree.
Use this new information to avoid unnecessary calls to
"replace_each_worktree_head_symref()".

  1.- 14ace5b (branch: do not rename a branch under bisect or rebase,
      2016-04-22)

  2.- 70999e9 (branch -m: update all per-worktree HEADs, 2016-03-27)

Signed-off-by: Rubén Justo <rjusto@gmail.com>
---
 builtin/branch.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/builtin/branch.c b/builtin/branch.c
index f63fd45edb..89198fa5bf 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -486,14 +486,21 @@ static void print_current_branch_name(void)
 		die(_("HEAD (%s) points outside of refs/heads/"), refname);
 }
 
-static void reject_rebase_or_bisect_branch(const char *target)
+/*
+ * Dies if the specified branch is being rebased or bisected.  Otherwise returns
+ * 0 or, if the branch is HEAD in any worktree, returns 1.
+ */
+static int die_if_branch_is_being_rebased_or_bisected(const char *target)
 {
 	struct worktree **worktrees = get_worktrees();
-	int i;
+	int i, ret = 0;
 
 	for (i = 0; worktrees[i]; i++) {
 		struct worktree *wt = worktrees[i];
 
+		if (wt->head_ref && !strcmp(target, wt->head_ref))
+			ret = 1;
+
 		if (!wt->is_detached)
 			continue;
 
@@ -507,6 +514,7 @@ static void reject_rebase_or_bisect_branch(const char *target)
 	}
 
 	free_worktrees(worktrees);
+	return ret;
 }
 
 static void copy_or_rename_branch(const char *oldname, const char *newname, int copy, int force)
@@ -515,7 +523,7 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
 	struct strbuf oldsection = STRBUF_INIT, newsection = STRBUF_INIT;
 	const char *interpreted_oldname = NULL;
 	const char *interpreted_newname = NULL;
-	int recovery = 0;
+	int recovery = 0, oldref_is_head;
 
 	if (strbuf_check_branch_ref(&oldref, oldname)) {
 		/*
@@ -544,7 +552,7 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
 	else
 		validate_new_branchname(newname, &newref, force);
 
-	reject_rebase_or_bisect_branch(oldref.buf);
+	oldref_is_head = die_if_branch_is_being_rebased_or_bisected(oldref.buf);
 
 	if (!skip_prefix(oldref.buf, "refs/heads/", &interpreted_oldname) ||
 	    !skip_prefix(newref.buf, "refs/heads/", &interpreted_newname)) {
@@ -574,7 +582,7 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
 				interpreted_oldname);
 	}
 
-	if (!copy &&
+	if (!copy && oldref_is_head &&
 	    replace_each_worktree_head_symref(oldref.buf, newref.buf, logmsg.buf))
 		die(_("Branch renamed to %s, but HEAD is not updated!"), newname);
 
-- 
2.39.0