refs: selectively set prefix in the seek functions

The ref iterator exposes a `ref_iterator_seek()` function. The name
suggests that this would seek the iterator to a specific reference in
some ways similar to how `fseek()` works for the filesystem.

However, the function actually sets the prefix for refs iteration. So
further iteration would only yield references which match the particular
prefix. This is a bit confusing.

Let's add a 'flags' field to the function, which when set with the
'REF_ITERATOR_SEEK_SET_PREFIX' flag, will set the prefix for the
iteration in-line with the existing behavior. Otherwise, the reference
backends will simply seek to the specified reference and clears any
previously set prefix. This allows users to start iteration from a
specific reference.

In the packed and reftable backend, since references are available in a
sorted list, the changes are simply setting the prefix if needed. The
changes on the files-backend are a little more involved, since the files
backend uses the 'ref-cache' mechanism. We move out the existing logic
within `cache_ref_iterator_seek()` to `cache_ref_iterator_set_prefix()`
which is called when the 'REF_ITERATOR_SEEK_SET_PREFIX' flag is set. We
then parse the provided seek string and set the required levels and
their indexes to ensure that seeking is possible.

Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/refs.c b/refs.c
index dce5c49ca2..243e6898b8 100644
--- a/refs.c
+++ b/refs.c
@@ -2666,12 +2666,12 @@ enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
 		if (!initial_transaction) {
 			int ok;
 
-			if (!iter) {
+			if (!iter)
 				iter = refs_ref_iterator_begin(refs, dirname.buf, NULL, 0,
 							       DO_FOR_EACH_INCLUDE_BROKEN);
-			} else if (ref_iterator_seek(iter, dirname.buf) < 0) {
+			else if (ref_iterator_seek(iter, dirname.buf,
+						   REF_ITERATOR_SEEK_SET_PREFIX) < 0)
 				goto cleanup;
-			}
 
 			while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
 				if (skip &&