1 files changed, 359 insertions, 0 deletions
diff --git a/merge-tree.c b/merge-tree.c
new file mode 100644
index 000000000..2d1413efb
--- /dev/null
+++ b/merge-tree.c
@@ -0,0 +1,359 @@
+#include "cache.h"
+#include "tree-walk.h"
+#include "xdiff-interface.h"
+#include "blob.h"
+
+static const char merge_tree_usage[] = "git-merge-tree <base-tree> <branch1> <branch2>";
+static int resolve_directories = 1;
+
+struct merge_list {
+	struct merge_list *next;
+	struct merge_list *link;	/* other stages for this object */
+
+	unsigned int stage : 2,
+		     flags : 30;
+	unsigned int mode;
+	const char *path;
+	struct blob *blob;
+};
+
+static struct merge_list *merge_result, **merge_result_end = &merge_result;
+
+static void add_merge_entry(struct merge_list *entry)
+{
+	*merge_result_end = entry;
+	merge_result_end = &entry->next;
+}
+
+static void merge_trees(struct tree_desc t[3], const char *base);
+
+static const char *explanation(struct merge_list *entry)
+{
+	switch (entry->stage) {
+	case 0:
+		return "merged";
+	case 3:
+		return "added in remote";
+	case 2:
+		if (entry->link)
+			return "added in both";
+		return "added in local";
+	}
+
+	/* Existed in base */
+	entry = entry->link;
+	if (!entry)
+		return "removed in both";
+
+	if (entry->link)
+		return "changed in both";
+
+	if (entry->stage == 3)
+		return "removed in local";
+	return "removed in remote";
+}
+
+extern void *merge_file(struct blob *, struct blob *, struct blob *, unsigned long *);
+
+static void *result(struct merge_list *entry, unsigned long *size)
+{
+	enum object_type type;
+	struct blob *base, *our, *their;
+
+	if (!entry->stage)
+		return read_sha1_file(entry->blob->object.sha1, &type, size);
+	base = NULL;
+	if (entry->stage == 1) {
+		base = entry->blob;
+		entry = entry->link;
+	}
+	our = NULL;
+	if (entry && entry->stage == 2) {
+		our = entry->blob;
+		entry = entry->link;
+	}
+	their = NULL;
+	if (entry)
+		their = entry->blob;
+	return merge_file(base, our, their, size);
+}
+
+static void *origin(struct merge_list *entry, unsigned long *size)
+{
+	enum object_type type;
+	while (entry) {
+		if (entry->stage == 2)
+			return read_sha1_file(entry->blob->object.sha1, &type, size);
+		entry = entry->link;
+	}
+	return NULL;
+}
+
+static int show_outf(void *priv_, mmbuffer_t *mb, int nbuf)
+{
+	int i;
+	for (i = 0; i < nbuf; i++)
+		printf("%.*s", (int) mb[i].size, mb[i].ptr);
+	return 0;
+}
+
+static void show_diff(struct merge_list *entry)
+{
+	unsigned long size;
+	mmfile_t src, dst;
+	xpparam_t xpp;
+	xdemitconf_t xecfg;
+	xdemitcb_t ecb;
+
+	xpp.flags = XDF_NEED_MINIMAL;
+	memset(&xecfg, 0, sizeof(xecfg));
+	xecfg.ctxlen = 3;
+	ecb.outf = show_outf;
+	ecb.priv = NULL;
+
+	src.ptr = origin(entry, &size);
+	if (!src.ptr)
+		size = 0;
+	src.size = size;
+	dst.ptr = result(entry, &size);
+	if (!dst.ptr)
+		size = 0;
+	dst.size = size;
+	xdi_diff(&src, &dst, &xpp, &xecfg, &ecb);
+	free(src.ptr);
+	free(dst.ptr);
+}
+
+static void show_result_list(struct merge_list *entry)
+{
+	printf("%s\n", explanation(entry));
+	do {
+		struct merge_list *link = entry->link;
+		static const char *desc[4] = { "result", "base", "our", "their" };
+		printf("  %-6s %o %s %s\n", desc[entry->stage], entry->mode, sha1_to_hex(entry->blob->object.sha1), entry->path);
+		entry = link;
+	} while (entry);
+}
+
+static void show_result(void)
+{
+	struct merge_list *walk;
+
+	walk = merge_result;
+	while (walk) {
+		show_result_list(walk);
+		show_diff(walk);
+		walk = walk->next;
+	}
+}
+
+/* An empty entry never compares same, not even to another empty entry */
+static int same_entry(struct name_entry *a, struct name_entry *b)
+{
+	return	a->sha1 &&
+		b->sha1 &&
+		!hashcmp(a->sha1, b->sha1) &&
+		a->mode == b->mode;
+}
+
+static struct merge_list *create_entry(unsigned stage, unsigned mode, const unsigned char *sha1, const char *path)
+{
+	struct merge_list *res = xcalloc(1, sizeof(*res));
+
+	res->stage = stage;
+	res->path = path;
+	res->mode = mode;
+	res->blob = lookup_blob(sha1);
+	return res;
+}
+
+static char *traverse_path(const struct traverse_info *info, const struct name_entry *n)
+{
+	char *path = xmalloc(traverse_path_len(info, n) + 1);
+	return make_traverse_path(path, info, n);
+}
+
+static void resolve(const struct traverse_info *info, struct name_entry *branch1, struct name_entry *result)
+{
+	struct merge_list *orig, *final;
+	const char *path;
+
+	/* If it's already branch1, don't bother showing it */
+	if (!branch1)
+		return;
+
+	path = traverse_path(info, result);
+	orig = create_entry(2, branch1->mode, branch1->sha1, path);
+	final = create_entry(0, result->mode, result->sha1, path);
+
+	final->link = orig;
+
+	add_merge_entry(final);
+}
+
+static int unresolved_directory(const struct traverse_info *info, struct name_entry n[3])
+{
+	char *newbase;
+	struct name_entry *p;
+	struct tree_desc t[3];
+	void *buf0, *buf1, *buf2;
+
+	if (!resolve_directories)
+		return 0;
+	p = n;
+	if (!p->mode) {
+		p++;
+		if (!p->mode)
+			p++;
+	}
+	if (!S_ISDIR(p->mode))
+		return 0;
+	newbase = traverse_path(info, p);
+	buf0 = fill_tree_descriptor(t+0, n[0].sha1);
+	buf1 = fill_tree_descriptor(t+1, n[1].sha1);
+	buf2 = fill_tree_descriptor(t+2, n[2].sha1);
+	merge_trees(t, newbase);
+
+	free(buf0);
+	free(buf1);
+	free(buf2);
+	free(newbase);
+	return 1;
+}
+
+
+static struct merge_list *link_entry(unsigned stage, const struct traverse_info *info, struct name_entry *n, struct merge_list *entry)
+{
+	const char *path;
+	struct merge_list *link;
+
+	if (!n->mode)
+		return entry;
+	if (entry)
+		path = entry->path;
+	else
+		path = traverse_path(info, n);
+	link = create_entry(stage, n->mode, n->sha1, path);
+	link->link = entry;
+	return link;
+}
+
+static void unresolved(const struct traverse_info *info, struct name_entry n[3])
+{
+	struct merge_list *entry = NULL;
+
+	if (unresolved_directory(info, n))
+		return;
+
+	/*
+	 * Do them in reverse order so that the resulting link
+	 * list has the stages in order - link_entry adds new
+	 * links at the front.
+	 */
+	entry = link_entry(3, info, n + 2, entry);
+	entry = link_entry(2, info, n + 1, entry);
+	entry = link_entry(1, info, n + 0, entry);
+
+	add_merge_entry(entry);
+}
+
+/*
+ * Merge two trees together (t[1] and t[2]), using a common base (t[0])
+ * as the origin.
+ *
+ * This walks the (sorted) trees in lock-step, checking every possible
+ * name. Note that directories automatically sort differently from other
+ * files (see "base_name_compare"), so you'll never see file/directory
+ * conflicts, because they won't ever compare the same.
+ *
+ * IOW, if a directory changes to a filename, it will automatically be
+ * seen as the directory going away, and the filename being created.
+ *
+ * Think of this as a three-way diff.
+ *
+ * The output will be either:
+ *  - successful merge
+ *	 "0 mode sha1 filename"
+ *    NOTE NOTE NOTE! FIXME! We really really need to walk the index
+ *    in parallel with this too!
+ *
+ *  - conflict:
+ *	"1 mode sha1 filename"
+ *	"2 mode sha1 filename"
+ *	"3 mode sha1 filename"
+ *    where not all of the 1/2/3 lines may exist, of course.
+ *
+ * The successful merge rules are the same as for the three-way merge
+ * in git-read-tree.
+ */
+static int threeway_callback(int n, unsigned long mask, unsigned long dirmask, struct name_entry *entry, struct traverse_info *info)
+{
+	/* Same in both? */
+	if (same_entry(entry+1, entry+2)) {
+		if (entry[0].sha1) {
+			resolve(info, NULL, entry+1);
+			return mask;
+		}
+	}
+
+	if (same_entry(entry+0, entry+1)) {
+		if (entry[2].sha1 && !S_ISDIR(entry[2].mode)) {
+			resolve(info, entry+1, entry+2);
+			return mask;
+		}
+	}
+
+	if (same_entry(entry+0, entry+2)) {
+		if (entry[1].sha1 && !S_ISDIR(entry[1].mode)) {
+			resolve(info, NULL, entry+1);
+			return mask;
+		}
+	}
+
+	unresolved(info, entry);
+	return mask;
+}
+
+static void merge_trees(struct tree_desc t[3], const char *base)
+{
+	struct traverse_info info;
+
+	setup_traverse_info(&info, base);
+	info.fn = threeway_callback;
+	traverse_trees(3, t, &info);
+}
+
+static void *get_tree_descriptor(struct tree_desc *desc, const char *rev)
+{
+	unsigned char sha1[20];
+	void *buf;
+
+	if (get_sha1(rev, sha1))
+		die("unknown rev %s", rev);
+	buf = fill_tree_descriptor(desc, sha1);
+	if (!buf)
+		die("%s is not a tree", rev);
+	return buf;
+}
+
+int main(int argc, char **argv)
+{
+	struct tree_desc t[3];
+	void *buf1, *buf2, *buf3;
+
+	if (argc != 4)
+		usage(merge_tree_usage);
+
+	setup_git_directory();
+
+	buf1 = get_tree_descriptor(t+0, argv[1]);
+	buf2 = get_tree_descriptor(t+1, argv[2]);
+	buf3 = get_tree_descriptor(t+2, argv[3]);
+	merge_trees(t, "");
+	free(buf1);
+	free(buf2);
+	free(buf3);
+
+	show_result();
+	return 0;
+}