refs: introduce wrapper struct for `each_ref_fn`

The `each_ref_fn` callback function type is used across our code base
for several different functions that iterate through reference. There's
a bunch of callbacks implementing this type, which makes any changes to
the callback signature extremely noisy. An example of the required churn
is e8207717f1 (refs: add referent to each_ref_fn, 2024-08-09): adding a
single argument required us to change 48 files.

It was already proposed back then [1] that we might want to introduce a
wrapper structure to alleviate the pain going forward. While this of
course requires the same kind of global refactoring as just introducing
a new parameter, it at least allows us to more change the callback type
afterwards by just extending the wrapper structure.

One counterargument to this refactoring is that it makes the structure
more opaque. While it is obvious which callsites need to be fixed up
when we change the function type, it's not obvious anymore once we use
a structure. That being said, we only have a handful of sites that
actually need to populate this wrapper structure: our ref backends,
"refs/iterator.c" as well as very few sites that invoke the iterator
callback functions directly.

Introduce this wrapper structure so that we can adapt the iterator
interfaces more readily.

[1]: <ZmarVcF5JjsZx0dl@tanuki>

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 13 insertions, 11 deletions

diff --git a/ref-filter.c b/ref-filter.c
index 30cc488d8a..6837fa60a9 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -2954,14 +2954,15 @@ struct ref_filter_cbdata {
  * A call-back given to for_each_ref().  Filter refs and keep them for
  * later object processing.
  */
-static int filter_one(const char *refname, const char *referent, const struct object_id *oid, int flag, void *cb_data)
+static int filter_one(const struct reference *ref, void *cb_data)
 {
 	struct ref_filter_cbdata *ref_cbdata = cb_data;
-	struct ref_array_item *ref;
+	struct ref_array_item *item;
 
-	ref = apply_ref_filter(refname, referent, oid, flag, ref_cbdata->filter);
-	if (ref)
-		ref_array_append(ref_cbdata->array, ref);
+	item = apply_ref_filter(ref->name, ref->target, ref->oid,
+				ref->flags, ref_cbdata->filter);
+	if (item)
+		ref_array_append(ref_cbdata->array, item);
 
 	return 0;
 }
@@ -2990,17 +2991,18 @@ struct ref_filter_and_format_cbdata {
 	} internal;
 };
 
-static int filter_and_format_one(const char *refname, const char *referent, const struct object_id *oid, int flag, void *cb_data)
+static int filter_and_format_one(const struct reference *ref, void *cb_data)
 {
 	struct ref_filter_and_format_cbdata *ref_cbdata = cb_data;
-	struct ref_array_item *ref;
+	struct ref_array_item *item;
 	struct strbuf output = STRBUF_INIT, err = STRBUF_INIT;
 
-	ref = apply_ref_filter(refname, referent, oid, flag, ref_cbdata->filter);
-	if (!ref)
+	item = apply_ref_filter(ref->name, ref->target, ref->oid,
+				ref->flags, ref_cbdata->filter);
+	if (!item)
 		return 0;
 
-	if (format_ref_array_item(ref, ref_cbdata->format, &output, &err))
+	if (format_ref_array_item(item, ref_cbdata->format, &output, &err))
 		die("%s", err.buf);
 
 	if (output.len || !ref_cbdata->format->array_opts.omit_empty) {
@@ -3010,7 +3012,7 @@ static int filter_and_format_one(const char *refname, const char *referent, cons
 
 	strbuf_release(&output);
 	strbuf_release(&err);
-	free_array_item(ref);
+	free_array_item(item);
 
 	/*
 	 * Increment the running count of refs that match the filter. If