support fetching into a shallow repository

A shallow commit is a commit which has parents, which in turn are
"grafted away", i.e. the commit appears as if it were a root.

Since these shallow commits should not be edited by the user, but
only by core git, they are recorded in the file $GIT_DIR/shallow.

A repository containing shallow commits is called shallow.

The advantage of a shallow repository is that even if the upstream
contains lots of history, your local (shallow) repository needs not
occupy much disk space.

The disadvantage is that you might miss a merge base when pulling
some remote branch.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 97 insertions, 0 deletions

diff --git a/shallow.c b/shallow.c
new file mode 100644
index 0000000..3cf2127
--- /dev/null
+++ b/shallow.c
@@ -0,0 +1,97 @@
+#include "cache.h"
+#include "commit.h"
+
+static int is_shallow = -1;
+
+int register_shallow(const unsigned char *sha1)
+{
+	struct commit_graft *graft =
+		xmalloc(sizeof(struct commit_graft));
+	struct commit *commit = lookup_commit(sha1);
+
+	hashcpy(graft->sha1, sha1);
+	graft->nr_parent = -1;
+	if (commit && commit->object.parsed)
+		commit->parents = NULL;
+	return register_commit_graft(graft, 0);
+}
+
+int is_repository_shallow()
+{
+	FILE *fp;
+	char buf[1024];
+
+	if (is_shallow >= 0)
+		return is_shallow;
+
+	fp = fopen(git_path("shallow"), "r");
+	if (!fp) {
+		is_shallow = 0;
+		return is_shallow;
+	}
+	is_shallow = 1;
+
+	while (fgets(buf, sizeof(buf), fp)) {
+		unsigned char sha1[20];
+		if (get_sha1_hex(buf, sha1))
+			die("bad shallow line: %s", buf);
+		register_shallow(sha1);
+	}
+	fclose(fp);
+	return is_shallow;
+}
+
+struct commit_list *get_shallow_commits(struct object_array *heads, int depth)
+{
+	int i = 0, cur_depth = 0;
+	struct commit_list *result = NULL;
+	struct object_array stack = {0, 0, NULL};
+	struct commit *commit = NULL;
+
+	while (commit || i < heads->nr || stack.nr) {
+		struct commit_list *p;
+		if (!commit) {
+			if (i < heads->nr) {
+				commit = (struct commit *)
+					heads->objects[i++].item;
+				if (commit->object.type != OBJ_COMMIT) {
+					commit = NULL;
+					continue;
+				}
+				commit->util = xcalloc(1, sizeof(int));
+				cur_depth = 0;
+			} else {
+				commit = (struct commit *)
+					stack.objects[--stack.nr].item;
+				cur_depth = *(int *)commit->util;
+			}
+		}
+		parse_commit(commit);
+		cur_depth++;
+		for (p = commit->parents, commit = NULL; p; p = p->next) {
+			if (!p->item->util) {
+				int *pointer = xmalloc(sizeof(int));
+				p->item->util = pointer;
+				*pointer =  cur_depth;
+			} else {
+				int *pointer = p->item->util;
+				if (cur_depth >= *pointer)
+					continue;
+				*pointer = cur_depth;
+			}
+			if (cur_depth < depth) {
+				if (p->next)
+					add_object_array(&p->item->object,
+							NULL, &stack);
+				else {
+					commit = p->item;
+					cur_depth = *(int *)commit->util;
+				}
+			} else
+				commit_list_insert(p->item, &result);
+		}
+	}
+
+	return result;
+}
+