revision: add mark_tree_uninteresting_sparse

In preparation for a new algorithm that walks fewer trees when
creating a pack from a set of revisions, create a method that
takes an oidset of tree oids and marks reachable objects as
UNINTERESTING.

The current implementation uses the existing
mark_tree_uninteresting to recursively walk the trees and blobs.
This will walk the same number of trees as the old mechanism. To
ensure that mark_tree_uninteresting walks the tree, we need to
remove the UNINTERESTING flag before calling the method. This
implementation will be replaced entirely in a later commit.

There is one new assumption in this approach: we are also given
the oids of the interesting trees. This implementation does not
use those trees at the moment, but we will use them in a later
rewrite of this method.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

revision.c

@@ -99,6 +99,31 @@ void mark_tree_uninteresting(struct repository *r, struct tree *tree)
 	mark_tree_contents_uninteresting(r, tree);
 }
 
+void mark_trees_uninteresting_sparse(struct repository *r,
+				     struct oidset *trees)
+{
+	struct object_id *oid;
+	struct oidset_iter iter;
+
+	oidset_iter_init(trees, &iter);
+	while ((oid = oidset_iter_next(&iter))) {
+		struct tree *tree = lookup_tree(r, oid);
+
+		if (!tree)
+			continue;
+
+		if (tree->object.flags & UNINTERESTING) {
+			/*
+			 * Remove the flag so the next call
+			 * is not a no-op. The flag is added
+			 * in mark_tree_unintersting().
+			 */
+			tree->object.flags ^= UNINTERESTING;
+			mark_tree_uninteresting(r, tree);
+		}
+	}
+}
+
 struct commit_stack {
 	struct commit **items;
 	size_t nr, alloc;

revision.h

@@ -67,6 +67,7 @@ struct rev_cmdline_info {
 #define REVISION_WALK_NO_WALK_SORTED 1
 #define REVISION_WALK_NO_WALK_UNSORTED 2
 
+struct oidset;
 struct topo_walk_info;
 
 struct rev_info {
@@ -327,6 +328,7 @@ void put_revision_mark(const struct rev_info *revs,
 
 void mark_parents_uninteresting(struct commit *commit);
 void mark_tree_uninteresting(struct repository *r, struct tree *tree);
+void mark_trees_uninteresting_sparse(struct repository *r, struct oidset *trees);
 
 void show_object_with_name(FILE *, struct object *, const char *);