sha1-name.c: for ":/", find detached HEAD commits

This patch broadens the set of commits matched by ":/<pattern>" to
include commits reachable from HEAD but not any named ref. This avoids
surprising behavior when working with a detached HEAD and trying to
refer to a commit that was recently created and only exists within the
detached state.

If multiple worktrees exist, only the current worktree's HEAD is
considered reachable. This is consistent with the existing behavior for
other per-worktree refs: e.g., bisect refs are considered reachable, but
only within the relevant worktree.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: William Chargin <wchargin@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/Documentation/revisions.txt b/Documentation/revisions.txt
index dfcc49c72c..0845c3f590 100644
--- a/Documentation/revisions.txt
+++ b/Documentation/revisions.txt
@@ -180,7 +180,8 @@ existing tag object.
   A colon, followed by a slash, followed by a text, names
   a commit whose commit message matches the specified regular expression.
   This name returns the youngest matching commit which is
-  reachable from any ref. The regular expression can match any part of the
+  reachable from any ref, including HEAD.
+  The regular expression can match any part of the
   commit message. To match messages starting with a string, one can use
   e.g. ':/^foo'. The special sequence ':/!' is reserved for modifiers to what
   is matched. ':/!-foo' performs a negative match, while ':/!!foo' matches a