[PATCH v2 14/25] shallow.c: implement a generic shallow boundary finder based on rev-list

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Instead of a custom commit walker like get_shallow_commits(), this new
function uses rev-list to mark NOT_SHALLOW to all reachable commits,
except borders. The definition of reachable is to be defined by the
protocol later. This makes it more flexible to define shallow boundary.

Note: if a commit has one NOT_SHALLOW parent and one SHALLOW parent,
then it's considered the boundary. Which means in the client side, this
commit has _no_ parents. This could lead to surprising cuts if we're not
careful.

Another option is to include more commits and only mark commits whose
all parents are SHALLOW as boundary.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 commit.h  |  2 ++
 shallow.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+)

diff --git a/commit.h b/commit.h
index 5d58be0..b717be1 100644
--- a/commit.h
+++ b/commit.h
@@ -258,6 +258,8 @@ extern int for_each_commit_graft(each_commit_graft_fn, void *);
 extern int is_repository_shallow(void);
 extern struct commit_list *get_shallow_commits(struct object_array *heads,
 		int depth, int shallow_flag, int not_shallow_flag);
+extern struct commit_list *get_shallow_commits_by_rev_list(
+		int ac, const char **av, int shallow_flag, int not_shallow_flag);
 extern void set_alternate_shallow_file(const char *path, int override);
 extern int write_shallow_commits(struct strbuf *out, int use_pack_protocol,
 				 const struct sha1_array *extra);
diff --git a/shallow.c b/shallow.c
index 60f1505..f5d5c1d 100644
--- a/shallow.c
+++ b/shallow.c
@@ -10,6 +10,8 @@
 #include "diff.h"
 #include "revision.h"
 #include "commit-slab.h"
+#include "revision.h"
+#include "list-objects.h"
 
 static int is_shallow = -1;
 static struct stat_validity shallow_stat;
@@ -137,6 +139,89 @@ struct commit_list *get_shallow_commits(struct object_array *heads, int depth,
 	return result;
 }
 
+static void show_commit(struct commit *commit, void *data)
+{
+	commit->object.flags |= *(int *)data;
+}
+
+/*
+ * Given rev-list arguments, run rev-list. All reachable commits
+ * except border ones are marked with not_shallow_flag. Border commits
+ * are marked with shallow_flag. The list of border/shallow commits
+ * are also returned.
+ */
+struct commit_list *get_shallow_commits_by_rev_list(int ac, const char **av,
+						    int shallow_flag,
+						    int not_shallow_flag)
+{
+	struct commit_list *result = NULL, *p;
+	struct rev_info revs;
+	unsigned int i, nr;
+
+	/*
+	 * SHALLOW (excluded) and NOT_SHALLOW (included) should not be
+	 * set at this point. But better be safe than sorry.
+	 */
+	nr = get_max_object_index();
+	for (i = 0; i < nr; i++) {
+		struct object *o = get_indexed_object(i);
+		if (!o || o->type != OBJ_COMMIT)
+			continue;
+		o->flags &= ~(shallow_flag | not_shallow_flag);
+	}
+
+	is_repository_shallow(); /* make sure shallows are read */
+
+	init_revisions(&revs, NULL);
+	save_commit_buffer = 0;
+	setup_revisions(ac, av, &revs, NULL);
+
+	/* Mark all reachable commits as NOT_SHALLOW */
+	if (prepare_revision_walk(&revs))
+		die("revision walk setup failed");
+	traverse_commit_list(&revs, show_commit, NULL, &not_shallow_flag);
+
+	/*
+	 * mark border commits SHALLOW + NOT_SHALLOW.
+	 * We cannot clear NOT_SHALLOW right now. Imagine border
+	 * commit A is processed first, then commit B, whose parent is
+	 * A, later. If NOT_SHALLOW on A is cleared at step 1, B
+	 * itself is considered border at step 2, which is incorrect.
+	 */
+	nr = get_max_object_index();
+	for (i = 0; i < nr; i++) {
+		struct object *o = get_indexed_object(i);
+		struct commit *c = (struct commit *)o;
+
+		if (!o || o->type != OBJ_COMMIT ||
+		    !(o->flags & not_shallow_flag))
+			continue;
+
+		if (parse_commit(c))
+			die("unable to parse commit %s",
+			    oid_to_hex(&c->object.oid));
+
+		for (p = c->parents; p; p = p->next)
+			if (!(p->item->object.flags & not_shallow_flag)) {
+				o->flags |= shallow_flag;
+				commit_list_insert(c, &result);
+				break;
+			}
+	}
+
+	/*
+	 * Now we can clean up NOT_SHALLOW on border commits. Having
+	 * both flags set can confuse the caller.
+	 */
+	for (p = result; p; p = p->next) {
+		struct object *ro = &p->item->object;
+		if ((ro->flags & not_shallow_flag) &&
+		    (ro->flags & shallow_flag))
+			ro->flags &= ~not_shallow_flag;
+	}
+	return result;
+}
+
 static void check_shallow_file_for_update(void)
 {
 	if (is_shallow == -1)
-- 
2.7.0.377.g4cd97dd