survey: stub in treewalk of reachable commits and objects

Add treewalk on the commits and objects reachable from the set
of refs.

This commit sets up the treewalk, but only stubs in the traverse
callbacks.  We'll actually look at the commit and object data
in the next commit.

Signed-off-by: Jeff Hostetler <jeffhostetler@github.com>

builtin/survey.c

@@ -1,15 +1,20 @@
 #include "builtin.h"
 #include "config.h"
+#include "environment.h"
 #include "json-writer.h"
+#include "list-objects.h"
+#include "object-name.h"
 #include "object-store.h"
 #include "parse-options.h"
 #include "progress.h"
 #include "ref-filter.h"
 #include "refs.h"
+#include "revision.h"
 #include "strbuf.h"
 #include "strmap.h"
 #include "strvec.h"
 #include "trace2.h"
+#include "tree-walk.h"
 
 static const char * const survey_usage[] = {
 	N_("(EXPERIMENTAL!) git survey <options>"),
@@ -244,6 +249,93 @@ static void do_load_refs(struct ref_array *ref_array)
 	ref_sorting_release(sorting);
 }
 
+/*
+ * Populate a "rev_info" with the OIDs of the REFS of interest.
+ * The treewalk will start from all of those starting points
+ * and walk backwards in the DAG to get the set of all reachable
+ * objects from those starting points.
+ */
+static void load_rev_info(struct rev_info *rev_info,
+			  struct ref_array *ref_array)
+{
+	unsigned int add_flags = 0;
+	int k;
+
+	for (k = 0; k < ref_array->nr; k++) {
+		struct ref_array_item *p = ref_array->items[k];
+		struct object_id peeled;
+
+		switch (p->kind) {
+		case FILTER_REFS_TAGS:
+			if (!peel_iterated_oid(rev_info->repo, &p->objectname, &peeled))
+				add_pending_oid(rev_info, NULL, &peeled, add_flags);
+			else
+				add_pending_oid(rev_info, NULL, &p->objectname, add_flags);
+			break;
+		case FILTER_REFS_BRANCHES:
+			add_pending_oid(rev_info, NULL, &p->objectname, add_flags);
+			break;
+		case FILTER_REFS_REMOTES:
+			add_pending_oid(rev_info, NULL, &p->objectname, add_flags);
+			break;
+		case FILTER_REFS_OTHERS:
+			/*
+			 * This may be a note, stash, or custom namespace branch.
+			 */
+			add_pending_oid(rev_info, NULL, &p->objectname, add_flags);
+			break;
+		case FILTER_REFS_DETACHED_HEAD:
+			add_pending_oid(rev_info, NULL, &p->objectname, add_flags);
+			break;
+		default:
+			break;
+		}
+	}
+}
+
+static void traverse_commit_cb(struct commit *commit, void *data)
+{
+	if ((++survey_progress_total % 1000) == 0)
+		display_progress(survey_progress, survey_progress_total);
+}
+
+static void traverse_object_cb(struct object *obj, const char *name, void *data)
+{
+	if ((++survey_progress_total % 1000) == 0)
+		display_progress(survey_progress, survey_progress_total);
+}
+
+/*
+ * Treewalk all of the commits and objects reachable from the
+ * set of refs.
+ */
+static void do_treewalk_reachable(struct ref_array *ref_array)
+{
+	struct rev_info rev_info = REV_INFO_INIT;
+
+	repo_init_revisions(the_repository, &rev_info, NULL);
+	rev_info.tree_objects = 1;
+	rev_info.blob_objects = 1;
+	load_rev_info(&rev_info, ref_array);
+	if (prepare_revision_walk(&rev_info))
+		die(_("revision walk setup failed"));
+
+	if (survey_opts.show_progress) {
+		survey_progress_total = 0;
+		survey_progress = start_progress(_("Walking reachable objects..."), 0);
+	}
+
+	traverse_commit_list(&rev_info,
+			     traverse_commit_cb,
+			     traverse_object_cb,
+			     NULL);
+
+	if (survey_opts.show_progress)
+		stop_progress(&survey_progress);
+
+	release_revisions(&rev_info);
+}
+
 /*
  * If we want this type of ref, increment counters and return 1.
  */
@@ -438,6 +530,10 @@ static void survey_phase_refs(struct repository *r)
 	do_load_refs(&ref_array);
 	trace2_region_leave("survey", "phase/refs", the_repository);
 
+	trace2_region_enter("survey", "phase/treewalk", the_repository);
+	do_treewalk_reachable(&ref_array);
+	trace2_region_leave("survey", "phase/treewalk", the_repository);
+
 	trace2_region_enter("survey", "phase/calcstats", the_repository);
 	do_calc_stats_refs(r, &ref_array);
 	trace2_region_leave("survey", "phase/calcstats", the_repository);