ref-filter: implement '--merged' and '--no-merged' options

In 'branch -l' we have '--merged' option which only lists refs (branches)
merged into the named commit and '--no-merged' option which only lists
refs (branches) not merged into the named commit. Implement these two
options in ref-filter.{c,h} so that other commands can benefit from this.

Based-on-patch-by: Jeff King <peff@peff.net>
Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/branch.c

@@ -635,6 +635,10 @@ static int print_ref_list(int kinds, int detached, int verbose, int abbrev, stru
 	cb.pattern = pattern;
 	cb.ret = 0;
 	for_each_rawref(append_ref, &cb);
+	/*
+	 * The following implementation is currently duplicated in ref-filter. It
+	 * will eventually be removed when we port branch.c to use ref-filter APIs.
+	 */
 	if (merge_filter != NO_FILTER) {
 		struct commit *filter;
 		filter = lookup_commit_reference_gently(merge_filter_ref, 0);

ref-filter.c

@@ -9,6 +9,7 @@
 #include "tag.h"
 #include "quote.h"
 #include "ref-filter.h"
+#include "revision.h"
 
 typedef enum { FIELD_STR, FIELD_ULONG, FIELD_TIME } cmp_type;
 
@@ -898,6 +899,7 @@ static int ref_filter_handler(const char *refname, const struct object_id *oid,
 	struct ref_filter_cbdata *ref_cbdata = cb_data;
 	struct ref_filter *filter = ref_cbdata->filter;
 	struct ref_array_item *ref;
+	struct commit *commit = NULL;
 
 	if (flag & REF_BAD_NAME) {
 		warning("ignoring ref with broken name %s", refname);
@@ -910,12 +912,24 @@ static int ref_filter_handler(const char *refname, const struct object_id *oid,
 	if (filter->points_at.nr && !match_points_at(&filter->points_at, oid->hash, refname))
 		return 0;
 
+	/*
+	 * A merge filter is applied on refs pointing to commits. Hence
+	 * obtain the commit using the 'oid' available and discard all
+	 * non-commits early. The actual filtering is done later.
+	 */
+	if (filter->merge_commit) {
+		commit = lookup_commit_reference_gently(oid->hash, 1);
+		if (!commit)
+			return 0;
+	}
+
 	/*
 	 * We do not open the object yet; sort may only need refname
 	 * to do its job and the resulting list may yet to be pruned
 	 * by maxcount logic.
 	 */
 	ref = new_ref_array_item(refname, oid->hash, flag);
+	ref->commit = commit;
 
 	REALLOC_ARRAY(ref_cbdata->array->items, ref_cbdata->array->nr + 1);
 	ref_cbdata->array->items[ref_cbdata->array->nr++] = ref;
@@ -941,6 +955,50 @@ void ref_array_clear(struct ref_array *array)
 	array->nr = array->alloc = 0;
 }
 
+static void do_merge_filter(struct ref_filter_cbdata *ref_cbdata)
+{
+	struct rev_info revs;
+	int i, old_nr;
+	struct ref_filter *filter = ref_cbdata->filter;
+	struct ref_array *array = ref_cbdata->array;
+	struct commit **to_clear = xcalloc(sizeof(struct commit *), array->nr);
+
+	init_revisions(&revs, NULL);
+
+	for (i = 0; i < array->nr; i++) {
+		struct ref_array_item *item = array->items[i];
+		add_pending_object(&revs, &item->commit->object, item->refname);
+		to_clear[i] = item->commit;
+	}
+
+	filter->merge_commit->object.flags |= UNINTERESTING;
+	add_pending_object(&revs, &filter->merge_commit->object, "");
+
+	revs.limited = 1;
+	if (prepare_revision_walk(&revs))
+		die(_("revision walk setup failed"));
+
+	old_nr = array->nr;
+	array->nr = 0;
+
+	for (i = 0; i < old_nr; i++) {
+		struct ref_array_item *item = array->items[i];
+		struct commit *commit = item->commit;
+
+		int is_merged = !!(commit->object.flags & UNINTERESTING);
+
+		if (is_merged == (filter->merge == REF_FILTER_MERGED_INCLUDE))
+			array->items[array->nr++] = array->items[i];
+		else
+			free_array_item(item);
+	}
+
+	for (i = 0; i < old_nr; i++)
+		clear_commit_marks(to_clear[i], ALL_REV_FLAGS);
+	clear_commit_marks(filter->merge_commit, ALL_REV_FLAGS);
+	free(to_clear);
+}
+
 /*
  * API for filtering a set of refs. Based on the type of refs the user
  * has requested, we iterate through those refs and apply filters
@@ -950,17 +1008,24 @@ void ref_array_clear(struct ref_array *array)
 int filter_refs(struct ref_array *array, struct ref_filter *filter, unsigned int type)
 {
 	struct ref_filter_cbdata ref_cbdata;
+	int ret = 0;
 
 	ref_cbdata.array = array;
 	ref_cbdata.filter = filter;
 
+	/*  Simple per-ref filtering */
 	if (type & (FILTER_REFS_ALL | FILTER_REFS_INCLUDE_BROKEN))
-		return for_each_rawref(ref_filter_handler, &ref_cbdata);
+		ret = for_each_rawref(ref_filter_handler, &ref_cbdata);
 	else if (type & FILTER_REFS_ALL)
-		return for_each_ref(ref_filter_handler, &ref_cbdata);
+		ret = for_each_ref(ref_filter_handler, &ref_cbdata);
-	else
+	else if (type)
 		die("filter_refs: invalid type");
-	return 0;
+
+	/*  Filters that need revision walking */
+	if (filter->merge_commit)
+		do_merge_filter(&ref_cbdata);
+
+	return ret;
 }
 
 static int cmp_ref_sorting(struct ref_sorting *s, struct ref_array_item *a, struct ref_array_item *b)

ref-filter.h

@@ -31,6 +31,7 @@ struct ref_array_item {
 	unsigned char objectname[20];
 	int flag;
 	const char *symref;
+	struct commit *commit;
 	struct atom_value *value;
 	char refname[FLEX_ARRAY];
 };
@@ -43,6 +44,13 @@ struct ref_array {
 struct ref_filter {
 	const char **name_patterns;
 	struct sha1_array points_at;
+
+	enum {
+		REF_FILTER_MERGED_NONE = 0,
+		REF_FILTER_MERGED_INCLUDE,
+		REF_FILTER_MERGED_OMIT
+	} merge;
+	struct commit *merge_commit;
 };
 
 struct ref_filter_cbdata {