Merge branch 'mv/merge-recursive'

* mv/merge-recursive:
  builtin-merge: release the lockfile in try_merge_strategy()
  merge-recursive: get rid of virtual_id
  merge-recursive: move current_{file,directory}_set to struct merge_options
  merge-recursive: move the global obuf to struct merge_options
  merge-recursive: get rid of the index_only global variable
  merge-recursive: move call_depth to struct merge_options
  cherry-pick/revert: make direct internal call to merge_tree()
  builtin-merge: avoid run_command_v_opt() for recursive and subtree
  merge-recursive: introduce merge_options
  merge-recursive.c: Add more generic merge_recursive_generic()
  Split out merge_recursive() to merge-recursive.c

8 files changed, 1580 insertions, 1454 deletions

diff --git a/Makefile b/Makefile
index 48547a2113..e0c03c3eec 100644
--- a/Makefile
+++ b/Makefile
@@ -443,6 +443,7 @@ LIB_OBJS += log-tree.o
 LIB_OBJS += mailmap.o
 LIB_OBJS += match-trees.o
 LIB_OBJS += merge-file.o
+LIB_OBJS += merge-recursive.o
 LIB_OBJS += name-hash.o
 LIB_OBJS += object.o
 LIB_OBJS += pack-check.o
diff --git a/builtin-checkout.c b/builtin-checkout.c
index 9a0c173c14..075667c9cc 100644
--- a/builtin-checkout.c
+++ b/builtin-checkout.c
@@ -293,6 +293,7 @@ static int merge_working_tree(struct checkout_opts *opts,
 			 */
 			struct tree *result;
 			struct tree *work;
+			struct merge_options o;
 			if (!opts->merge)
 				return 1;
 			parse_commit(old->commit);
@@ -311,13 +312,17 @@ static int merge_working_tree(struct checkout_opts *opts,
 			 */
 
 			add_files_to_cache(NULL, NULL, 0);
-			work = write_tree_from_memory();
+			init_merge_options(&o);
+			o.verbosity = 0;
+			work = write_tree_from_memory(&o);
 
 			ret = reset_tree(new->commit->tree, opts, 1);
 			if (ret)
 				return ret;
-			merge_trees(new->commit->tree, work, old->commit->tree,
-				    new->name, "local", &result);
+			o.branch1 = new->name;
+			o.branch2 = "local";
+			merge_trees(&o, new->commit->tree, work,
+				old->commit->tree, &result);
 			ret = reset_tree(new->commit->tree, opts, 0);
 			if (ret)
 				return ret;
diff --git a/builtin-merge-recursive.c b/builtin-merge-recursive.c
index dfb363ee2f..6b534c1a66 100644
--- a/builtin-merge-recursive.c
+++ b/builtin-merge-recursive.c
@@ -1,1307 +1,8 @@
-/*
- * Recursive Merge algorithm stolen from git-merge-recursive.py by
- * Fredrik Kuivinen.
- * The thieves were Alex Riesen and Johannes Schindelin, in June/July 2006
- */
 #include "cache.h"
-#include "cache-tree.h"
 #include "commit.h"
-#include "blob.h"
-#include "builtin.h"
-#include "tree-walk.h"
-#include "diff.h"
-#include "diffcore.h"
 #include "tag.h"
-#include "unpack-trees.h"
-#include "string-list.h"
-#include "xdiff-interface.h"
-#include "ll-merge.h"
-#include "interpolate.h"
-#include "attr.h"
 #include "merge-recursive.h"
 
-static int subtree_merge;
-
-static struct tree *shift_tree_object(struct tree *one, struct tree *two)
-{
-	unsigned char shifted[20];
-
-	/*
-	 * NEEDSWORK: this limits the recursion depth to hardcoded
-	 * value '2' to avoid excessive overhead.
-	 */
-	shift_tree(one->object.sha1, two->object.sha1, shifted, 2);
-	if (!hashcmp(two->object.sha1, shifted))
-		return two;
-	return lookup_tree(shifted);
-}
-
-/*
- * A virtual commit has
- * - (const char *)commit->util set to the name, and
- * - *(int *)commit->object.sha1 set to the virtual id.
- */
-
-static struct commit *make_virtual_commit(struct tree *tree, const char *comment)
-{
-	struct commit *commit = xcalloc(1, sizeof(struct commit));
-	static unsigned virtual_id = 1;
-	commit->tree = tree;
-	commit->util = (void*)comment;
-	*(int*)commit->object.sha1 = virtual_id++;
-	/* avoid warnings */
-	commit->object.parsed = 1;
-	return commit;
-}
-
-/*
- * Since we use get_tree_entry(), which does not put the read object into
- * the object pool, we cannot rely on a == b.
- */
-static int sha_eq(const unsigned char *a, const unsigned char *b)
-{
-	if (!a && !b)
-		return 2;
-	return a && b && hashcmp(a, b) == 0;
-}
-
-/*
- * Since we want to write the index eventually, we cannot reuse the index
- * for these (temporary) data.
- */
-struct stage_data
-{
-	struct
-	{
-		unsigned mode;
-		unsigned char sha[20];
-	} stages[4];
-	unsigned processed:1;
-};
-
-static struct string_list current_file_set = {NULL, 0, 0, 1};
-static struct string_list current_directory_set = {NULL, 0, 0, 1};
-
-static int call_depth = 0;
-static int verbosity = 2;
-static int diff_rename_limit = -1;
-static int merge_rename_limit = -1;
-static int buffer_output = 1;
-static struct strbuf obuf = STRBUF_INIT;
-
-static int show(int v)
-{
-	return (!call_depth && verbosity >= v) || verbosity >= 5;
-}
-
-static void flush_output(void)
-{
-	if (obuf.len) {
-		fputs(obuf.buf, stdout);
-		strbuf_reset(&obuf);
-	}
-}
-
-static void output(int v, const char *fmt, ...)
-{
-	int len;
-	va_list ap;
-
-	if (!show(v))
-		return;
-
-	strbuf_grow(&obuf, call_depth * 2 + 2);
-	memset(obuf.buf + obuf.len, ' ', call_depth * 2);
-	strbuf_setlen(&obuf, obuf.len + call_depth * 2);
-
-	va_start(ap, fmt);
-	len = vsnprintf(obuf.buf + obuf.len, strbuf_avail(&obuf), fmt, ap);
-	va_end(ap);
-
-	if (len < 0)
-		len = 0;
-	if (len >= strbuf_avail(&obuf)) {
-		strbuf_grow(&obuf, len + 2);
-		va_start(ap, fmt);
-		len = vsnprintf(obuf.buf + obuf.len, strbuf_avail(&obuf), fmt, ap);
-		va_end(ap);
-		if (len >= strbuf_avail(&obuf)) {
-			die("this should not happen, your snprintf is broken");
-		}
-	}
-	strbuf_setlen(&obuf, obuf.len + len);
-	strbuf_add(&obuf, "\n", 1);
-	if (!buffer_output)
-		flush_output();
-}
-
-static void output_commit_title(struct commit *commit)
-{
-	int i;
-	flush_output();
-	for (i = call_depth; i--;)
-		fputs("  ", stdout);
-	if (commit->util)
-		printf("virtual %s\n", (char *)commit->util);
-	else {
-		printf("%s ", find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV));
-		if (parse_commit(commit) != 0)
-			printf("(bad commit)\n");
-		else {
-			const char *s;
-			int len;
-			for (s = commit->buffer; *s; s++)
-				if (*s == '\n' && s[1] == '\n') {
-					s += 2;
-					break;
-				}
-			for (len = 0; s[len] && '\n' != s[len]; len++)
-				; /* do nothing */
-			printf("%.*s\n", len, s);
-		}
-	}
-}
-
-static int add_cacheinfo(unsigned int mode, const unsigned char *sha1,
-		const char *path, int stage, int refresh, int options)
-{
-	struct cache_entry *ce;
-	ce = make_cache_entry(mode, sha1 ? sha1 : null_sha1, path, stage, refresh);
-	if (!ce)
-		return error("addinfo_cache failed for path '%s'", path);
-	return add_cache_entry(ce, options);
-}
-
-/*
- * This is a global variable which is used in a number of places but
- * only written to in the 'merge' function.
- *
- * index_only == 1    => Don't leave any non-stage 0 entries in the cache and
- *                       don't update the working directory.
- *               0    => Leave unmerged entries in the cache and update
- *                       the working directory.
- */
-static int index_only = 0;
-
-static void init_tree_desc_from_tree(struct tree_desc *desc, struct tree *tree)
-{
-	parse_tree(tree);
-	init_tree_desc(desc, tree->buffer, tree->size);
-}
-
-static int git_merge_trees(int index_only,
-			   struct tree *common,
-			   struct tree *head,
-			   struct tree *merge)
-{
-	int rc;
-	struct tree_desc t[3];
-	struct unpack_trees_options opts;
-
-	memset(&opts, 0, sizeof(opts));
-	if (index_only)
-		opts.index_only = 1;
-	else
-		opts.update = 1;
-	opts.merge = 1;
-	opts.head_idx = 2;
-	opts.fn = threeway_merge;
-	opts.src_index = &the_index;
-	opts.dst_index = &the_index;
-
-	init_tree_desc_from_tree(t+0, common);
-	init_tree_desc_from_tree(t+1, head);
-	init_tree_desc_from_tree(t+2, merge);
-
-	rc = unpack_trees(3, t, &opts);
-	cache_tree_free(&active_cache_tree);
-	return rc;
-}
-
-struct tree *write_tree_from_memory(void)
-{
-	struct tree *result = NULL;
-
-	if (unmerged_cache()) {
-		int i;
-		output(0, "There are unmerged index entries:");
-		for (i = 0; i < active_nr; i++) {
-			struct cache_entry *ce = active_cache[i];
-			if (ce_stage(ce))
-				output(0, "%d %.*s", ce_stage(ce), ce_namelen(ce), ce->name);
-		}
-		return NULL;
-	}
-
-	if (!active_cache_tree)
-		active_cache_tree = cache_tree();
-
-	if (!cache_tree_fully_valid(active_cache_tree) &&
-	    cache_tree_update(active_cache_tree,
-			      active_cache, active_nr, 0, 0) < 0)
-		die("error building trees");
-
-	result = lookup_tree(active_cache_tree->sha1);
-
-	return result;
-}
-
-static int save_files_dirs(const unsigned char *sha1,
-		const char *base, int baselen, const char *path,
-		unsigned int mode, int stage, void *context)
-{
-	int len = strlen(path);
-	char *newpath = xmalloc(baselen + len + 1);
-	memcpy(newpath, base, baselen);
-	memcpy(newpath + baselen, path, len);
-	newpath[baselen + len] = '\0';
-
-	if (S_ISDIR(mode))
-		string_list_insert(newpath, &current_directory_set);
-	else
-		string_list_insert(newpath, &current_file_set);
-	free(newpath);
-
-	return READ_TREE_RECURSIVE;
-}
-
-static int get_files_dirs(struct tree *tree)
-{
-	int n;
-	if (read_tree_recursive(tree, "", 0, 0, NULL, save_files_dirs, NULL))
-		return 0;
-	n = current_file_set.nr + current_directory_set.nr;
-	return n;
-}
-
-/*
- * Returns an index_entry instance which doesn't have to correspond to
- * a real cache entry in Git's index.
- */
-static struct stage_data *insert_stage_data(const char *path,
-		struct tree *o, struct tree *a, struct tree *b,
-		struct string_list *entries)
-{
-	struct string_list_item *item;
-	struct stage_data *e = xcalloc(1, sizeof(struct stage_data));
-	get_tree_entry(o->object.sha1, path,
-			e->stages[1].sha, &e->stages[1].mode);
-	get_tree_entry(a->object.sha1, path,
-			e->stages[2].sha, &e->stages[2].mode);
-	get_tree_entry(b->object.sha1, path,
-			e->stages[3].sha, &e->stages[3].mode);
-	item = string_list_insert(path, entries);
-	item->util = e;
-	return e;
-}
-
-/*
- * Create a dictionary mapping file names to stage_data objects. The
- * dictionary contains one entry for every path with a non-zero stage entry.
- */
-static struct string_list *get_unmerged(void)
-{
-	struct string_list *unmerged = xcalloc(1, sizeof(struct string_list));
-	int i;
-
-	unmerged->strdup_strings = 1;
-
-	for (i = 0; i < active_nr; i++) {
-		struct string_list_item *item;
-		struct stage_data *e;
-		struct cache_entry *ce = active_cache[i];
-		if (!ce_stage(ce))
-			continue;
-
-		item = string_list_lookup(ce->name, unmerged);
-		if (!item) {
-			item = string_list_insert(ce->name, unmerged);
-			item->util = xcalloc(1, sizeof(struct stage_data));
-		}
-		e = item->util;
-		e->stages[ce_stage(ce)].mode = ce->ce_mode;
-		hashcpy(e->stages[ce_stage(ce)].sha, ce->sha1);
-	}
-
-	return unmerged;
-}
-
-struct rename
-{
-	struct diff_filepair *pair;
-	struct stage_data *src_entry;
-	struct stage_data *dst_entry;
-	unsigned processed:1;
-};
-
-/*
- * Get information of all renames which occurred between 'o_tree' and
- * 'tree'. We need the three trees in the merge ('o_tree', 'a_tree' and
- * 'b_tree') to be able to associate the correct cache entries with
- * the rename information. 'tree' is always equal to either a_tree or b_tree.
- */
-static struct string_list *get_renames(struct tree *tree,
-					struct tree *o_tree,
-					struct tree *a_tree,
-					struct tree *b_tree,
-					struct string_list *entries)
-{
-	int i;
-	struct string_list *renames;
-	struct diff_options opts;
-
-	renames = xcalloc(1, sizeof(struct string_list));
-	diff_setup(&opts);
-	DIFF_OPT_SET(&opts, RECURSIVE);
-	opts.detect_rename = DIFF_DETECT_RENAME;
-	opts.rename_limit = merge_rename_limit >= 0 ? merge_rename_limit :
-			    diff_rename_limit >= 0 ? diff_rename_limit :
-			    500;
-	opts.warn_on_too_large_rename = 1;
-	opts.output_format = DIFF_FORMAT_NO_OUTPUT;
-	if (diff_setup_done(&opts) < 0)
-		die("diff setup failed");
-	diff_tree_sha1(o_tree->object.sha1, tree->object.sha1, "", &opts);
-	diffcore_std(&opts);
-	for (i = 0; i < diff_queued_diff.nr; ++i) {
-		struct string_list_item *item;
-		struct rename *re;
-		struct diff_filepair *pair = diff_queued_diff.queue[i];
-		if (pair->status != 'R') {
-			diff_free_filepair(pair);
-			continue;
-		}
-		re = xmalloc(sizeof(*re));
-		re->processed = 0;
-		re->pair = pair;
-		item = string_list_lookup(re->pair->one->path, entries);
-		if (!item)
-			re->src_entry = insert_stage_data(re->pair->one->path,
-					o_tree, a_tree, b_tree, entries);
-		else
-			re->src_entry = item->util;
-
-		item = string_list_lookup(re->pair->two->path, entries);
-		if (!item)
-			re->dst_entry = insert_stage_data(re->pair->two->path,
-					o_tree, a_tree, b_tree, entries);
-		else
-			re->dst_entry = item->util;
-		item = string_list_insert(pair->one->path, renames);
-		item->util = re;
-	}
-	opts.output_format = DIFF_FORMAT_NO_OUTPUT;
-	diff_queued_diff.nr = 0;
-	diff_flush(&opts);
-	return renames;
-}
-
-static int update_stages(const char *path, struct diff_filespec *o,
-			 struct diff_filespec *a, struct diff_filespec *b,
-			 int clear)
-{
-	int options = ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE;
-	if (clear)
-		if (remove_file_from_cache(path))
-			return -1;
-	if (o)
-		if (add_cacheinfo(o->mode, o->sha1, path, 1, 0, options))
-			return -1;
-	if (a)
-		if (add_cacheinfo(a->mode, a->sha1, path, 2, 0, options))
-			return -1;
-	if (b)
-		if (add_cacheinfo(b->mode, b->sha1, path, 3, 0, options))
-			return -1;
-	return 0;
-}
-
-static int remove_path(const char *name)
-{
-	int ret;
-	char *slash, *dirs;
-
-	ret = unlink(name);
-	if (ret)
-		return ret;
-	dirs = xstrdup(name);
-	while ((slash = strrchr(name, '/'))) {
-		*slash = '\0';
-		if (rmdir(name) != 0)
-			break;
-	}
-	free(dirs);
-	return ret;
-}
-
-static int remove_file(int clean, const char *path, int no_wd)
-{
-	int update_cache = index_only || clean;
-	int update_working_directory = !index_only && !no_wd;
-
-	if (update_cache) {
-		if (remove_file_from_cache(path))
-			return -1;
-	}
-	if (update_working_directory) {
-		unlink(path);
-		if (errno != ENOENT || errno != EISDIR)
-			return -1;
-		remove_path(path);
-	}
-	return 0;
-}
-
-static char *unique_path(const char *path, const char *branch)
-{
-	char *newpath = xmalloc(strlen(path) + 1 + strlen(branch) + 8 + 1);
-	int suffix = 0;
-	struct stat st;
-	char *p = newpath + strlen(path);
-	strcpy(newpath, path);
-	*(p++) = '~';
-	strcpy(p, branch);
-	for (; *p; ++p)
-		if ('/' == *p)
-			*p = '_';
-	while (string_list_has_string(&current_file_set, newpath) ||
-	       string_list_has_string(&current_directory_set, newpath) ||
-	       lstat(newpath, &st) == 0)
-		sprintf(p, "_%d", suffix++);
-
-	string_list_insert(newpath, &current_file_set);
-	return newpath;
-}
-
-static void flush_buffer(int fd, const char *buf, unsigned long size)
-{
-	while (size > 0) {
-		long ret = write_in_full(fd, buf, size);
-		if (ret < 0) {
-			/* Ignore epipe */
-			if (errno == EPIPE)
-				break;
-			die("merge-recursive: %s", strerror(errno));
-		} else if (!ret) {
-			die("merge-recursive: disk full?");
-		}
-		size -= ret;
-		buf += ret;
-	}
-}
-
-static int make_room_for_path(const char *path)
-{
-	int status;
-	const char *msg = "failed to create path '%s'%s";
-
-	status = safe_create_leading_directories_const(path);
-	if (status) {
-		if (status == -3) {
-			/* something else exists */
-			error(msg, path, ": perhaps a D/F conflict?");
-			return -1;
-		}
-		die(msg, path, "");
-	}
-
-	/* Successful unlink is good.. */
-	if (!unlink(path))
-		return 0;
-	/* .. and so is no existing file */
-	if (errno == ENOENT)
-		return 0;
-	/* .. but not some other error (who really cares what?) */
-	return error(msg, path, ": perhaps a D/F conflict?");
-}
-
-static void update_file_flags(const unsigned char *sha,
-			      unsigned mode,
-			      const char *path,
-			      int update_cache,
-			      int update_wd)
-{
-	if (index_only)
-		update_wd = 0;
-
-	if (update_wd) {
-		enum object_type type;
-		void *buf;
-		unsigned long size;
-
-		if (S_ISGITLINK(mode))
-			die("cannot read object %s '%s': It is a submodule!",
-			    sha1_to_hex(sha), path);
-
-		buf = read_sha1_file(sha, &type, &size);
-		if (!buf)
-			die("cannot read object %s '%s'", sha1_to_hex(sha), path);
-		if (type != OBJ_BLOB)
-			die("blob expected for %s '%s'", sha1_to_hex(sha), path);
-		if (S_ISREG(mode)) {
-			struct strbuf strbuf;
-			strbuf_init(&strbuf, 0);
-			if (convert_to_working_tree(path, buf, size, &strbuf)) {
-				free(buf);
-				size = strbuf.len;
-				buf = strbuf_detach(&strbuf, NULL);
-			}
-		}
-
-		if (make_room_for_path(path) < 0) {
-			update_wd = 0;
-			free(buf);
-			goto update_index;
-		}
-		if (S_ISREG(mode) || (!has_symlinks && S_ISLNK(mode))) {
-			int fd;
-			if (mode & 0100)
-				mode = 0777;
-			else
-				mode = 0666;
-			fd = open(path, O_WRONLY | O_TRUNC | O_CREAT, mode);
-			if (fd < 0)
-				die("failed to open %s: %s", path, strerror(errno));
-			flush_buffer(fd, buf, size);
-			close(fd);
-		} else if (S_ISLNK(mode)) {
-			char *lnk = xmemdupz(buf, size);
-			safe_create_leading_directories_const(path);
-			unlink(path);
-			symlink(lnk, path);
-			free(lnk);
-		} else
-			die("do not know what to do with %06o %s '%s'",
-			    mode, sha1_to_hex(sha), path);
-		free(buf);
-	}
- update_index:
-	if (update_cache)
-		add_cacheinfo(mode, sha, path, 0, update_wd, ADD_CACHE_OK_TO_ADD);
-}
-
-static void update_file(int clean,
-			const unsigned char *sha,
-			unsigned mode,
-			const char *path)
-{
-	update_file_flags(sha, mode, path, index_only || clean, !index_only);
-}
-
-/* Low level file merging, update and removal */
-
-struct merge_file_info
-{
-	unsigned char sha[20];
-	unsigned mode;
-	unsigned clean:1,
-		 merge:1;
-};
-
-static void fill_mm(const unsigned char *sha1, mmfile_t *mm)
-{
-	unsigned long size;
-	enum object_type type;
-
-	if (!hashcmp(sha1, null_sha1)) {
-		mm->ptr = xstrdup("");
-		mm->size = 0;
-		return;
-	}
-
-	mm->ptr = read_sha1_file(sha1, &type, &size);
-	if (!mm->ptr || type != OBJ_BLOB)
-		die("unable to read blob object %s", sha1_to_hex(sha1));
-	mm->size = size;
-}
-
-static int merge_3way(mmbuffer_t *result_buf,
-		      struct diff_filespec *o,
-		      struct diff_filespec *a,
-		      struct diff_filespec *b,
-		      const char *branch1,
-		      const char *branch2)
-{
-	mmfile_t orig, src1, src2;
-	char *name1, *name2;
-	int merge_status;
-
-	name1 = xstrdup(mkpath("%s:%s", branch1, a->path));
-	name2 = xstrdup(mkpath("%s:%s", branch2, b->path));
-
-	fill_mm(o->sha1, &orig);
-	fill_mm(a->sha1, &src1);
-	fill_mm(b->sha1, &src2);
-
-	merge_status = ll_merge(result_buf, a->path, &orig,
-				&src1, name1, &src2, name2,
-				index_only);
-
-	free(name1);
-	free(name2);
-	free(orig.ptr);
-	free(src1.ptr);
-	free(src2.ptr);
-	return merge_status;
-}
-
-static struct merge_file_info merge_file(struct diff_filespec *o,
-		struct diff_filespec *a, struct diff_filespec *b,
-		const char *branch1, const char *branch2)
-{
-	struct merge_file_info result;
-	result.merge = 0;
-	result.clean = 1;
-
-	if ((S_IFMT & a->mode) != (S_IFMT & b->mode)) {
-		result.clean = 0;
-		if (S_ISREG(a->mode)) {
-			result.mode = a->mode;
-			hashcpy(result.sha, a->sha1);
-		} else {
-			result.mode = b->mode;
-			hashcpy(result.sha, b->sha1);
-		}
-	} else {
-		if (!sha_eq(a->sha1, o->sha1) && !sha_eq(b->sha1, o->sha1))
-			result.merge = 1;
-
-		/*
-		 * Merge modes
-		 */
-		if (a->mode == b->mode || a->mode == o->mode)
-			result.mode = b->mode;
-		else {
-			result.mode = a->mode;
-			if (b->mode != o->mode) {
-				result.clean = 0;
-				result.merge = 1;
-			}
-		}
-
-		if (sha_eq(a->sha1, b->sha1) || sha_eq(a->sha1, o->sha1))
-			hashcpy(result.sha, b->sha1);
-		else if (sha_eq(b->sha1, o->sha1))
-			hashcpy(result.sha, a->sha1);
-		else if (S_ISREG(a->mode)) {
-			mmbuffer_t result_buf;
-			int merge_status;
-
-			merge_status = merge_3way(&result_buf, o, a, b,
-						  branch1, branch2);
-
-			if ((merge_status < 0) || !result_buf.ptr)
-				die("Failed to execute internal merge");
-
-			if (write_sha1_file(result_buf.ptr, result_buf.size,
-					    blob_type, result.sha))
-				die("Unable to add %s to database",
-				    a->path);
-
-			free(result_buf.ptr);
-			result.clean = (merge_status == 0);
-		} else if (S_ISGITLINK(a->mode)) {
-			result.clean = 0;
-			hashcpy(result.sha, a->sha1);
-		} else if (S_ISLNK(a->mode)) {
-			hashcpy(result.sha, a->sha1);
-
-			if (!sha_eq(a->sha1, b->sha1))
-				result.clean = 0;
-		} else {
-			die("unsupported object type in the tree");
-		}
-	}
-
-	return result;
-}
-
-static void conflict_rename_rename(struct rename *ren1,
-				   const char *branch1,
-				   struct rename *ren2,
-				   const char *branch2)
-{
-	char *del[2];
-	int delp = 0;
-	const char *ren1_dst = ren1->pair->two->path;
-	const char *ren2_dst = ren2->pair->two->path;
-	const char *dst_name1 = ren1_dst;
-	const char *dst_name2 = ren2_dst;
-	if (string_list_has_string(&current_directory_set, ren1_dst)) {
-		dst_name1 = del[delp++] = unique_path(ren1_dst, branch1);
-		output(1, "%s is a directory in %s adding as %s instead",
-		       ren1_dst, branch2, dst_name1);
-		remove_file(0, ren1_dst, 0);
-	}
-	if (string_list_has_string(&current_directory_set, ren2_dst)) {
-		dst_name2 = del[delp++] = unique_path(ren2_dst, branch2);
-		output(1, "%s is a directory in %s adding as %s instead",
-		       ren2_dst, branch1, dst_name2);
-		remove_file(0, ren2_dst, 0);
-	}
-	if (index_only) {
-		remove_file_from_cache(dst_name1);
-		remove_file_from_cache(dst_name2);
-		/*
-		 * Uncomment to leave the conflicting names in the resulting tree
-		 *
-		 * update_file(0, ren1->pair->two->sha1, ren1->pair->two->mode, dst_name1);
-		 * update_file(0, ren2->pair->two->sha1, ren2->pair->two->mode, dst_name2);
-		 */
-	} else {
-		update_stages(dst_name1, NULL, ren1->pair->two, NULL, 1);
-		update_stages(dst_name2, NULL, NULL, ren2->pair->two, 1);
-	}
-	while (delp--)
-		free(del[delp]);
-}
-
-static void conflict_rename_dir(struct rename *ren1,
-				const char *branch1)
-{
-	char *new_path = unique_path(ren1->pair->two->path, branch1);
-	output(1, "Renaming %s to %s instead", ren1->pair->one->path, new_path);
-	remove_file(0, ren1->pair->two->path, 0);
-	update_file(0, ren1->pair->two->sha1, ren1->pair->two->mode, new_path);
-	free(new_path);
-}
-
-static void conflict_rename_rename_2(struct rename *ren1,
-				     const char *branch1,
-				     struct rename *ren2,
-				     const char *branch2)
-{
-	char *new_path1 = unique_path(ren1->pair->two->path, branch1);
-	char *new_path2 = unique_path(ren2->pair->two->path, branch2);
-	output(1, "Renaming %s to %s and %s to %s instead",
-	       ren1->pair->one->path, new_path1,
-	       ren2->pair->one->path, new_path2);
-	remove_file(0, ren1->pair->two->path, 0);
-	update_file(0, ren1->pair->two->sha1, ren1->pair->two->mode, new_path1);
-	update_file(0, ren2->pair->two->sha1, ren2->pair->two->mode, new_path2);
-	free(new_path2);
-	free(new_path1);
-}
-
-static int process_renames(struct string_list *a_renames,
-			   struct string_list *b_renames,
-			   const char *a_branch,
-			   const char *b_branch)
-{
-	int clean_merge = 1, i, j;
-	struct string_list a_by_dst = {NULL, 0, 0, 0}, b_by_dst = {NULL, 0, 0, 0};
-	const struct rename *sre;
-
-	for (i = 0; i < a_renames->nr; i++) {
-		sre = a_renames->items[i].util;
-		string_list_insert(sre->pair->two->path, &a_by_dst)->util
-			= sre->dst_entry;
-	}
-	for (i = 0; i < b_renames->nr; i++) {
-		sre = b_renames->items[i].util;
-		string_list_insert(sre->pair->two->path, &b_by_dst)->util
-			= sre->dst_entry;
-	}
-
-	for (i = 0, j = 0; i < a_renames->nr || j < b_renames->nr;) {
-		int compare;
-		char *src;
-		struct string_list *renames1, *renames2, *renames2Dst;
-		struct rename *ren1 = NULL, *ren2 = NULL;
-		const char *branch1, *branch2;
-		const char *ren1_src, *ren1_dst;
-
-		if (i >= a_renames->nr) {
-			compare = 1;
-			ren2 = b_renames->items[j++].util;
-		} else if (j >= b_renames->nr) {
-			compare = -1;
-			ren1 = a_renames->items[i++].util;
-		} else {
-			compare = strcmp(a_renames->items[i].string,
-					b_renames->items[j].string);
-			if (compare <= 0)
-				ren1 = a_renames->items[i++].util;
-			if (compare >= 0)
-				ren2 = b_renames->items[j++].util;
-		}
-
-		/* TODO: refactor, so that 1/2 are not needed */
-		if (ren1) {
-			renames1 = a_renames;
-			renames2 = b_renames;
-			renames2Dst = &b_by_dst;
-			branch1 = a_branch;
-			branch2 = b_branch;
-		} else {
-			struct rename *tmp;
-			renames1 = b_renames;
-			renames2 = a_renames;
-			renames2Dst = &a_by_dst;
-			branch1 = b_branch;
-			branch2 = a_branch;
-			tmp = ren2;
-			ren2 = ren1;
-			ren1 = tmp;
-		}
-		src = ren1->pair->one->path;
-
-		ren1->dst_entry->processed = 1;
-		ren1->src_entry->processed = 1;
-
-		if (ren1->processed)
-			continue;
-		ren1->processed = 1;
-
-		ren1_src = ren1->pair->one->path;
-		ren1_dst = ren1->pair->two->path;
-
-		if (ren2) {
-			const char *ren2_src = ren2->pair->one->path;
-			const char *ren2_dst = ren2->pair->two->path;
-			/* Renamed in 1 and renamed in 2 */
-			if (strcmp(ren1_src, ren2_src) != 0)
-				die("ren1.src != ren2.src");
-			ren2->dst_entry->processed = 1;
-			ren2->processed = 1;
-			if (strcmp(ren1_dst, ren2_dst) != 0) {
-				clean_merge = 0;
-				output(1, "CONFLICT (rename/rename): "
-				       "Rename \"%s\"->\"%s\" in branch \"%s\" "
-				       "rename \"%s\"->\"%s\" in \"%s\"%s",
-				       src, ren1_dst, branch1,
-				       src, ren2_dst, branch2,
-				       index_only ? " (left unresolved)": "");
-				if (index_only) {
-					remove_file_from_cache(src);
-					update_file(0, ren1->pair->one->sha1,
-						    ren1->pair->one->mode, src);
-				}
-				conflict_rename_rename(ren1, branch1, ren2, branch2);
-			} else {
-				struct merge_file_info mfi;
-				remove_file(1, ren1_src, 1);
-				mfi = merge_file(ren1->pair->one,
-						 ren1->pair->two,
-						 ren2->pair->two,
-						 branch1,
-						 branch2);
-				if (mfi.merge || !mfi.clean)
-					output(1, "Renaming %s->%s", src, ren1_dst);
-
-				if (mfi.merge)
-					output(2, "Auto-merging %s", ren1_dst);
-
-				if (!mfi.clean) {
-					output(1, "CONFLICT (content): merge conflict in %s",
-					       ren1_dst);
-					clean_merge = 0;
-
-					if (!index_only)
-						update_stages(ren1_dst,
-							      ren1->pair->one,
-							      ren1->pair->two,
-							      ren2->pair->two,
-							      1 /* clear */);
-				}
-				update_file(mfi.clean, mfi.sha, mfi.mode, ren1_dst);
-			}
-		} else {
-			/* Renamed in 1, maybe changed in 2 */
-			struct string_list_item *item;
-			/* we only use sha1 and mode of these */
-			struct diff_filespec src_other, dst_other;
-			int try_merge, stage = a_renames == renames1 ? 3: 2;
-
-			remove_file(1, ren1_src, index_only || stage == 3);
-
-			hashcpy(src_other.sha1, ren1->src_entry->stages[stage].sha);
-			src_other.mode = ren1->src_entry->stages[stage].mode;
-			hashcpy(dst_other.sha1, ren1->dst_entry->stages[stage].sha);
-			dst_other.mode = ren1->dst_entry->stages[stage].mode;
-
-			try_merge = 0;
-
-			if (string_list_has_string(&current_directory_set, ren1_dst)) {
-				clean_merge = 0;
-				output(1, "CONFLICT (rename/directory): Rename %s->%s in %s "
-				       " directory %s added in %s",
-				       ren1_src, ren1_dst, branch1,
-				       ren1_dst, branch2);
-				conflict_rename_dir(ren1, branch1);
-			} else if (sha_eq(src_other.sha1, null_sha1)) {
-				clean_merge = 0;
-				output(1, "CONFLICT (rename/delete): Rename %s->%s in %s "
-				       "and deleted in %s",
-				       ren1_src, ren1_dst, branch1,
-				       branch2);
-				update_file(0, ren1->pair->two->sha1, ren1->pair->two->mode, ren1_dst);
-			} else if (!sha_eq(dst_other.sha1, null_sha1)) {
-				const char *new_path;
-				clean_merge = 0;
-				try_merge = 1;
-				output(1, "CONFLICT (rename/add): Rename %s->%s in %s. "
-				       "%s added in %s",
-				       ren1_src, ren1_dst, branch1,
-				       ren1_dst, branch2);
-				new_path = unique_path(ren1_dst, branch2);
-				output(1, "Adding as %s instead", new_path);
-				update_file(0, dst_other.sha1, dst_other.mode, new_path);
-			} else if ((item = string_list_lookup(ren1_dst, renames2Dst))) {
-				ren2 = item->util;
-				clean_merge = 0;
-				ren2->processed = 1;
-				output(1, "CONFLICT (rename/rename): Rename %s->%s in %s. "
-				       "Rename %s->%s in %s",
-				       ren1_src, ren1_dst, branch1,
-				       ren2->pair->one->path, ren2->pair->two->path, branch2);
-				conflict_rename_rename_2(ren1, branch1, ren2, branch2);
-			} else
-				try_merge = 1;
-
-			if (try_merge) {
-				struct diff_filespec *o, *a, *b;
-				struct merge_file_info mfi;
-				src_other.path = (char *)ren1_src;
-
-				o = ren1->pair->one;
-				if (a_renames == renames1) {
-					a = ren1->pair->two;
-					b = &src_other;
-				} else {
-					b = ren1->pair->two;
-					a = &src_other;
-				}
-				mfi = merge_file(o, a, b,
-						a_branch, b_branch);
-
-				if (mfi.clean &&
-				    sha_eq(mfi.sha, ren1->pair->two->sha1) &&
-				    mfi.mode == ren1->pair->two->mode)
-					/*
-					 * This messaged is part of
-					 * t6022 test. If you change
-					 * it update the test too.
-					 */
-					output(3, "Skipped %s (merged same as existing)", ren1_dst);
-				else {
-					if (mfi.merge || !mfi.clean)
-						output(1, "Renaming %s => %s", ren1_src, ren1_dst);
-					if (mfi.merge)
-						output(2, "Auto-merging %s", ren1_dst);
-					if (!mfi.clean) {
-						output(1, "CONFLICT (rename/modify): Merge conflict in %s",
-						       ren1_dst);
-						clean_merge = 0;
-
-						if (!index_only)
-							update_stages(ren1_dst,
-								      o, a, b, 1);
-					}
-					update_file(mfi.clean, mfi.sha, mfi.mode, ren1_dst);
-				}
-			}
-		}
-	}
-	string_list_clear(&a_by_dst, 0);
-	string_list_clear(&b_by_dst, 0);
-
-	return clean_merge;
-}
-
-static unsigned char *stage_sha(const unsigned char *sha, unsigned mode)
-{
-	return (is_null_sha1(sha) || mode == 0) ? NULL: (unsigned char *)sha;
-}
-
-/* Per entry merge function */
-static int process_entry(const char *path, struct stage_data *entry,
-			 const char *branch1,
-			 const char *branch2)
-{
-	/*
-	printf("processing entry, clean cache: %s\n", index_only ? "yes": "no");
-	print_index_entry("\tpath: ", entry);
-	*/
-	int clean_merge = 1;
-	unsigned o_mode = entry->stages[1].mode;
-	unsigned a_mode = entry->stages[2].mode;
-	unsigned b_mode = entry->stages[3].mode;
-	unsigned char *o_sha = stage_sha(entry->stages[1].sha, o_mode);
-	unsigned char *a_sha = stage_sha(entry->stages[2].sha, a_mode);
-	unsigned char *b_sha = stage_sha(entry->stages[3].sha, b_mode);
-
-	if (o_sha && (!a_sha || !b_sha)) {
-		/* Case A: Deleted in one */
-		if ((!a_sha && !b_sha) ||
-		    (sha_eq(a_sha, o_sha) && !b_sha) ||
-		    (!a_sha && sha_eq(b_sha, o_sha))) {
-			/* Deleted in both or deleted in one and
-			 * unchanged in the other */
-			if (a_sha)
-				output(2, "Removing %s", path);
-			/* do not touch working file if it did not exist */
-			remove_file(1, path, !a_sha);
-		} else {
-			/* Deleted in one and changed in the other */
-			clean_merge = 0;
-			if (!a_sha) {
-				output(1, "CONFLICT (delete/modify): %s deleted in %s "
-				       "and modified in %s. Version %s of %s left in tree.",
-				       path, branch1,
-				       branch2, branch2, path);
-				update_file(0, b_sha, b_mode, path);
-			} else {
-				output(1, "CONFLICT (delete/modify): %s deleted in %s "
-				       "and modified in %s. Version %s of %s left in tree.",
-				       path, branch2,
-				       branch1, branch1, path);
-				update_file(0, a_sha, a_mode, path);
-			}
-		}
-
-	} else if ((!o_sha && a_sha && !b_sha) ||
-		   (!o_sha && !a_sha && b_sha)) {
-		/* Case B: Added in one. */
-		const char *add_branch;
-		const char *other_branch;
-		unsigned mode;
-		const unsigned char *sha;
-		const char *conf;
-
-		if (a_sha) {
-			add_branch = branch1;
-			other_branch = branch2;
-			mode = a_mode;
-			sha = a_sha;
-			conf = "file/directory";
-		} else {
-			add_branch = branch2;
-			other_branch = branch1;
-			mode = b_mode;
-			sha = b_sha;
-			conf = "directory/file";
-		}
-		if (string_list_has_string(&current_directory_set, path)) {
-			const char *new_path = unique_path(path, add_branch);
-			clean_merge = 0;
-			output(1, "CONFLICT (%s): There is a directory with name %s in %s. "
-			       "Adding %s as %s",
-			       conf, path, other_branch, path, new_path);
-			remove_file(0, path, 0);
-			update_file(0, sha, mode, new_path);
-		} else {
-			output(2, "Adding %s", path);
-			update_file(1, sha, mode, path);
-		}
-	} else if (a_sha && b_sha) {
-		/* Case C: Added in both (check for same permissions) and */
-		/* case D: Modified in both, but differently. */
-		const char *reason = "content";
-		struct merge_file_info mfi;
-		struct diff_filespec o, a, b;
-
-		if (!o_sha) {
-			reason = "add/add";
-			o_sha = (unsigned char *)null_sha1;
-		}
-		output(2, "Auto-merging %s", path);
-		o.path = a.path = b.path = (char *)path;
-		hashcpy(o.sha1, o_sha);
-		o.mode = o_mode;
-		hashcpy(a.sha1, a_sha);
-		a.mode = a_mode;
-		hashcpy(b.sha1, b_sha);
-		b.mode = b_mode;
-
-		mfi = merge_file(&o, &a, &b,
-				 branch1, branch2);
-
-		clean_merge = mfi.clean;
-		if (mfi.clean)
-			update_file(1, mfi.sha, mfi.mode, path);
-		else if (S_ISGITLINK(mfi.mode))
-			output(1, "CONFLICT (submodule): Merge conflict in %s "
-			       "- needs %s", path, sha1_to_hex(b.sha1));
-		else {
-			output(1, "CONFLICT (%s): Merge conflict in %s",
-					reason, path);
-
-			if (index_only)
-				update_file(0, mfi.sha, mfi.mode, path);
-			else
-				update_file_flags(mfi.sha, mfi.mode, path,
-					      0 /* update_cache */, 1 /* update_working_directory */);
-		}
-	} else if (!o_sha && !a_sha && !b_sha) {
-		/*
-		 * this entry was deleted altogether. a_mode == 0 means
-		 * we had that path and want to actively remove it.
-		 */
-		remove_file(1, path, !a_mode);
-	} else
-		die("Fatal merge failure, shouldn't happen.");
-
-	return clean_merge;
-}
-
-int merge_trees(struct tree *head,
-		struct tree *merge,
-		struct tree *common,
-		const char *branch1,
-		const char *branch2,
-		struct tree **result)
-{
-	int code, clean;
-
-	if (subtree_merge) {
-		merge = shift_tree_object(head, merge);
-		common = shift_tree_object(head, common);
-	}
-
-	if (sha_eq(common->object.sha1, merge->object.sha1)) {
-		output(0, "Already uptodate!");
-		*result = head;
-		return 1;
-	}
-
-	code = git_merge_trees(index_only, common, head, merge);
-
-	if (code != 0)
-		die("merging of trees %s and %s failed",
-		    sha1_to_hex(head->object.sha1),
-		    sha1_to_hex(merge->object.sha1));
-
-	if (unmerged_cache()) {
-		struct string_list *entries, *re_head, *re_merge;
-		int i;
-		string_list_clear(&current_file_set, 1);
-		string_list_clear(&current_directory_set, 1);
-		get_files_dirs(head);
-		get_files_dirs(merge);
-
-		entries = get_unmerged();
-		re_head  = get_renames(head, common, head, merge, entries);
-		re_merge = get_renames(merge, common, head, merge, entries);
-		clean = process_renames(re_head, re_merge,
-				branch1, branch2);
-		for (i = 0; i < entries->nr; i++) {
-			const char *path = entries->items[i].string;
-			struct stage_data *e = entries->items[i].util;
-			if (!e->processed
-				&& !process_entry(path, e, branch1, branch2))
-				clean = 0;
-		}
-
-		string_list_clear(re_merge, 0);
-		string_list_clear(re_head, 0);
-		string_list_clear(entries, 1);
-
-	}
-	else
-		clean = 1;
-
-	if (index_only)
-		*result = write_tree_from_memory();
-
-	return clean;
-}
-
-static struct commit_list *reverse_commit_list(struct commit_list *list)
-{
-	struct commit_list *next = NULL, *current, *backup;
-	for (current = list; current; current = backup) {
-		backup = current->next;
-		current->next = next;
-		next = current;
-	}
-	return next;
-}
-
-/*
- * Merge the commits h1 and h2, return the resulting virtual
- * commit object and a flag indicating the cleanness of the merge.
- */
-int merge_recursive(struct commit *h1,
-		    struct commit *h2,
-		    const char *branch1,
-		    const char *branch2,
-		    struct commit_list *ca,
-		    struct commit **result)
-{
-	struct commit_list *iter;
-	struct commit *merged_common_ancestors;
-	struct tree *mrtree = mrtree;
-	int clean;
-
-	if (show(4)) {
-		output(4, "Merging:");
-		output_commit_title(h1);
-		output_commit_title(h2);
-	}
-
-	if (!ca) {
-		ca = get_merge_bases(h1, h2, 1);
-		ca = reverse_commit_list(ca);
-	}
-
-	if (show(5)) {
-		output(5, "found %u common ancestor(s):", commit_list_count(ca));
-		for (iter = ca; iter; iter = iter->next)
-			output_commit_title(iter->item);
-	}
-
-	merged_common_ancestors = pop_commit(&ca);
-	if (merged_common_ancestors == NULL) {
-		/* if there is no common ancestor, make an empty tree */
-		struct tree *tree = xcalloc(1, sizeof(struct tree));
-
-		tree->object.parsed = 1;
-		tree->object.type = OBJ_TREE;
-		pretend_sha1_file(NULL, 0, OBJ_TREE, tree->object.sha1);
-		merged_common_ancestors = make_virtual_commit(tree, "ancestor");
-	}
-
-	for (iter = ca; iter; iter = iter->next) {
-		call_depth++;
-		/*
-		 * When the merge fails, the result contains files
-		 * with conflict markers. The cleanness flag is
-		 * ignored, it was never actually used, as result of
-		 * merge_trees has always overwritten it: the committed
-		 * "conflicts" were already resolved.
-		 */
-		discard_cache();
-		merge_recursive(merged_common_ancestors, iter->item,
-				"Temporary merge branch 1",
-				"Temporary merge branch 2",
-				NULL,
-				&merged_common_ancestors);
-		call_depth--;
-
-		if (!merged_common_ancestors)
-			die("merge returned no commit");
-	}
-
-	discard_cache();
-	if (!call_depth) {
-		read_cache();
-		index_only = 0;
-	} else
-		index_only = 1;
-
-	clean = merge_trees(h1->tree, h2->tree, merged_common_ancestors->tree,
-			    branch1, branch2, &mrtree);
-
-	if (index_only) {
-		*result = make_virtual_commit(mrtree, "merged tree");
-		commit_list_insert(h1, &(*result)->parents);
-		commit_list_insert(h2, &(*result)->parents->next);
-	}
-	flush_output();
-	return clean;
-}
-
 static const char *better_branch_name(const char *branch)
 {
 	static char githead_env[8 + 40 + 1];
@@ -1314,103 +15,58 @@ static const char *better_branch_name(const char *branch)
 	return name ? name : branch;
 }
 
-static struct commit *get_ref(const char *ref)
-{
-	unsigned char sha1[20];
-	struct object *object;
-
-	if (get_sha1(ref, sha1))
-		die("Could not resolve ref '%s'", ref);
-	object = deref_tag(parse_object(sha1), ref, strlen(ref));
-	if (!object)
-		return NULL;
-	if (object->type == OBJ_TREE)
-		return make_virtual_commit((struct tree*)object,
-			better_branch_name(ref));
-	if (object->type != OBJ_COMMIT)
-		return NULL;
-	if (parse_commit((struct commit *)object))
-		die("Could not parse commit '%s'", sha1_to_hex(object->sha1));
-	return (struct commit *)object;
-}
-
-static int merge_config(const char *var, const char *value, void *cb)
-{
-	if (!strcasecmp(var, "merge.verbosity")) {
-		verbosity = git_config_int(var, value);
-		return 0;
-	}
-	if (!strcasecmp(var, "diff.renamelimit")) {
-		diff_rename_limit = git_config_int(var, value);
-		return 0;
-	}
-	if (!strcasecmp(var, "merge.renamelimit")) {
-		merge_rename_limit = git_config_int(var, value);
-		return 0;
-	}
-	return git_default_config(var, value, cb);
-}
-
 int cmd_merge_recursive(int argc, const char **argv, const char *prefix)
 {
-	static const char *bases[20];
-	static unsigned bases_count = 0;
-	int i, clean;
-	const char *branch1, *branch2;
-	struct commit *result, *h1, *h2;
-	struct commit_list *ca = NULL;
-	struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
-	int index_fd;
+	const unsigned char *bases[21];
+	unsigned bases_count = 0;
+	int i, failed;
+	unsigned char h1[20], h2[20];
+	struct merge_options o;
+	struct commit *result;
 
+	init_merge_options(&o);
 	if (argv[0]) {
 		int namelen = strlen(argv[0]);
 		if (8 < namelen &&
 		    !strcmp(argv[0] + namelen - 8, "-subtree"))
-			subtree_merge = 1;
+			o.subtree_merge = 1;
 	}
 
-	git_config(merge_config, NULL);
-	if (getenv("GIT_MERGE_VERBOSITY"))
-		verbosity = strtol(getenv("GIT_MERGE_VERBOSITY"), NULL, 10);
-
 	if (argc < 4)
 		die("Usage: %s <base>... -- <head> <remote> ...\n", argv[0]);
 
 	for (i = 1; i < argc; ++i) {
 		if (!strcmp(argv[i], "--"))
 			break;
-		if (bases_count < sizeof(bases)/sizeof(*bases))
-			bases[bases_count++] = argv[i];
+		if (bases_count < ARRAY_SIZE(bases)-1) {
+			unsigned char *sha = xmalloc(20);
+			if (get_sha1(argv[i], sha))
+				die("Could not parse object '%s'", argv[i]);
+			bases[bases_count++] = sha;
+		}
+		else
+			warning("Cannot handle more than %zu bases. "
+				"Ignoring %s.", ARRAY_SIZE(bases)-1, argv[i]);
 	}
 	if (argc - i != 3) /* "--" "<head>" "<remote>" */
 		die("Not handling anything other than two heads merge.");
-	if (verbosity >= 5)
-		buffer_output = 0;
 
-	branch1 = argv[++i];
-	branch2 = argv[++i];
+	o.branch1 = argv[++i];
+	o.branch2 = argv[++i];
 
-	h1 = get_ref(branch1);
-	h2 = get_ref(branch2);
+	if (get_sha1(o.branch1, h1))
+		die("Could not resolve ref '%s'", o.branch1);
+	if (get_sha1(o.branch2, h2))
+		die("Could not resolve ref '%s'", o.branch2);
 
-	branch1 = better_branch_name(branch1);
-	branch2 = better_branch_name(branch2);
-
-	if (show(3))
-		printf("Merging %s with %s\n", branch1, branch2);
-
-	index_fd = hold_locked_index(lock, 1);
-
-	for (i = 0; i < bases_count; i++) {
-		struct commit *ancestor = get_ref(bases[i]);
-		ca = commit_list_insert(ancestor, &ca);
-	}
-	clean = merge_recursive(h1, h2, branch1, branch2, ca, &result);
+	o.branch1 = better_branch_name(o.branch1);
+	o.branch2 = better_branch_name(o.branch2);
 
-	if (active_cache_changed &&
-	    (write_cache(index_fd, active_cache, active_nr) ||
-	     commit_locked_index(lock)))
-			die ("unable to write %s", get_index_file());
+	if (o.verbosity >= 3)
+		printf("Merging %s with %s\n", o.branch1, o.branch2);
 
-	return clean ? 0: 1;
+	failed = merge_recursive_generic(&o, h1, h2, bases_count, bases, &result);
+	if (failed < 0)
+		return 128; /* die() error code */
+	return failed;
 }
diff --git a/builtin-merge.c b/builtin-merge.c
index 1942e72aaf..5c65a58699 100644
--- a/builtin-merge.c
+++ b/builtin-merge.c
@@ -23,6 +23,7 @@
 #include "color.h"
 #include "rerere.h"
 #include "help.h"
+#include "merge-recursive.h"
 
 #define DEFAULT_TWOHEAD (1<<0)
 #define DEFAULT_OCTOPUS (1<<1)
@@ -547,28 +548,65 @@ static int try_merge_strategy(const char *strategy, struct commit_list *common,
 	struct commit_list *j;
 	struct strbuf buf;
 
-	args = xmalloc((4 + commit_list_count(common) +
-			commit_list_count(remoteheads)) * sizeof(char *));
-	strbuf_init(&buf, 0);
-	strbuf_addf(&buf, "merge-%s", strategy);
-	args[i++] = buf.buf;
-	for (j = common; j; j = j->next)
-		args[i++] = xstrdup(sha1_to_hex(j->item->object.sha1));
-	args[i++] = "--";
-	args[i++] = head_arg;
-	for (j = remoteheads; j; j = j->next)
-		args[i++] = xstrdup(sha1_to_hex(j->item->object.sha1));
-	args[i] = NULL;
-	ret = run_command_v_opt(args, RUN_GIT_CMD);
-	strbuf_release(&buf);
-	i = 1;
-	for (j = common; j; j = j->next)
-		free((void *)args[i++]);
-	i += 2;
-	for (j = remoteheads; j; j = j->next)
-		free((void *)args[i++]);
-	free(args);
-	return -ret;
+	if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree")) {
+		int clean;
+		struct commit *result;
+		struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
+		int index_fd;
+		struct commit_list *reversed = NULL;
+		struct merge_options o;
+
+		if (remoteheads->next) {
+			error("Not handling anything other than two heads merge.");
+			return 2;
+		}
+
+		init_merge_options(&o);
+		if (!strcmp(strategy, "subtree"))
+			o.subtree_merge = 1;
+
+		o.branch1 = head_arg;
+		o.branch2 = remoteheads->item->util;
+
+		for (j = common; j; j = j->next)
+			commit_list_insert(j->item, &reversed);
+
+		index_fd = hold_locked_index(lock, 1);
+		clean = merge_recursive(&o, lookup_commit(head),
+				remoteheads->item, reversed, &result);
+		if (active_cache_changed &&
+				(write_cache(index_fd, active_cache, active_nr) ||
+				 commit_locked_index(lock)))
+			die ("unable to write %s", get_index_file());
+		rollback_lock_file(lock);
+		return clean ? 0 : 1;
+	} else {
+		args = xmalloc((4 + commit_list_count(common) +
+					commit_list_count(remoteheads)) * sizeof(char *));
+		strbuf_init(&buf, 0);
+		strbuf_addf(&buf, "merge-%s", strategy);
+		args[i++] = buf.buf;
+		for (j = common; j; j = j->next)
+			args[i++] = xstrdup(sha1_to_hex(j->item->object.sha1));
+		args[i++] = "--";
+		args[i++] = head_arg;
+		for (j = remoteheads; j; j = j->next)
+			args[i++] = xstrdup(sha1_to_hex(j->item->object.sha1));
+		args[i] = NULL;
+		ret = run_command_v_opt(args, RUN_GIT_CMD);
+		strbuf_release(&buf);
+		i = 1;
+		for (j = common; j; j = j->next)
+			free((void *)args[i++]);
+		i += 2;
+		for (j = remoteheads; j; j = j->next)
+			free((void *)args[i++]);
+		free(args);
+		discard_cache();
+		if (read_cache() < 0)
+			die("failed to read the cache");
+		return -ret;
+	}
 }
 
 static void count_diff_files(struct diff_queue_struct *q,
@@ -779,10 +817,6 @@ static int evaluate_result(void)
 	int cnt = 0;
 	struct rev_info rev;
 
-	discard_cache();
-	if (read_cache() < 0)
-		die("failed to read the cache");
-
 	/* Check how many files differ. */
 	init_revisions(&rev, "");
 	setup_revisions(0, NULL, &rev, NULL);
@@ -916,12 +950,14 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 
 	for (i = 0; i < argc; i++) {
 		struct object *o;
+		struct commit *commit;
 
 		o = peel_to_type(argv[i], 0, NULL, OBJ_COMMIT);
 		if (!o)
 			die("%s - not something we can merge", argv[i]);
-		remotes = &commit_list_insert(lookup_commit(o->sha1),
-			remotes)->next;
+		commit = lookup_commit(o->sha1);
+		commit->util = (void *)argv[i];
+		remotes = &commit_list_insert(commit, remotes)->next;
 
 		strbuf_addf(&buf, "GITHEAD_%s", sha1_to_hex(o->sha1));
 		setenv(buf.buf, argv[i], 1);
@@ -1115,7 +1151,6 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		}
 
 		/* Automerge succeeded. */
-		discard_cache();
 		write_tree_trivial(result_tree);
 		automerge_was_ok = 1;
 		break;
diff --git a/builtin-revert.c b/builtin-revert.c
index 36677053f8..8486539740 100644
--- a/builtin-revert.c
+++ b/builtin-revert.c
@@ -12,6 +12,7 @@
 #include "diff.h"
 #include "revision.h"
 #include "rerere.h"
+#include "merge-recursive.h"
 
 /*
  * This implements the builtins revert and cherry-pick.
@@ -201,36 +202,6 @@ static void set_author_ident_env(const char *message)
 			sha1_to_hex(commit->object.sha1));
 }
 
-static int merge_recursive(const char *base_sha1,
-		const char *head_sha1, const char *head_name,
-		const char *next_sha1, const char *next_name)
-{
-	char buffer[256];
-	const char *argv[6];
-	int i = 0;
-
-	sprintf(buffer, "GITHEAD_%s", head_sha1);
-	setenv(buffer, head_name, 1);
-	sprintf(buffer, "GITHEAD_%s", next_sha1);
-	setenv(buffer, next_name, 1);
-
-	/*
-	 * This three way merge is an interesting one.  We are at
-	 * $head, and would want to apply the change between $commit
-	 * and $prev on top of us (when reverting), or the change between
-	 * $prev and $commit on top of us (when cherry-picking or replaying).
-	 */
-	argv[i++] = "merge-recursive";
-	if (base_sha1)
-		argv[i++] = base_sha1;
-	argv[i++] = "--";
-	argv[i++] = head_sha1;
-	argv[i++] = next_sha1;
-	argv[i++] = NULL;
-
-	return run_command_v_opt(argv, RUN_COMMAND_NO_STDIN | RUN_GIT_CMD);
-}
-
 static char *help_msg(const unsigned char *sha1)
 {
 	static char helpbuf[1024];
@@ -263,14 +234,27 @@ static int index_is_dirty(void)
 	return !!DIFF_OPT_TST(&rev.diffopt, HAS_CHANGES);
 }
 
+static struct tree *empty_tree(void)
+{
+	struct tree *tree = xcalloc(1, sizeof(struct tree));
+
+	tree->object.parsed = 1;
+	tree->object.type = OBJ_TREE;
+	pretend_sha1_file(NULL, 0, OBJ_TREE, tree->object.sha1);
+	return tree;
+}
+
 static int revert_or_cherry_pick(int argc, const char **argv)
 {
 	unsigned char head[20];
 	struct commit *base, *next, *parent;
-	int i;
+	int i, index_fd, clean;
 	char *oneline, *reencoded_message = NULL;
 	const char *message, *encoding;
 	const char *defmsg = xstrdup(git_path("MERGE_MSG"));
+	struct merge_options o;
+	struct tree *result, *next_tree, *base_tree, *head_tree;
+	static struct lock_file index_lock;
 
 	git_config(git_default_config, NULL);
 	me = action == REVERT ? "revert" : "cherry-pick";
@@ -281,6 +265,8 @@ static int revert_or_cherry_pick(int argc, const char **argv)
 	if (action == REVERT && !no_replay)
 		die("revert is incompatible with replay");
 
+	if (read_cache() < 0)
+		die("git %s: failed to read the index", me);
 	if (no_commit) {
 		/*
 		 * We do not intend to commit immediately.  We just want to
@@ -293,12 +279,12 @@ static int revert_or_cherry_pick(int argc, const char **argv)
 	} else {
 		if (get_sha1("HEAD", head))
 			die ("You do not have a valid HEAD");
-		if (read_cache() < 0)
-			die("could not read the index");
 		if (index_is_dirty())
 			die ("Dirty index: cannot %s", me);
-		discard_cache();
 	}
+	discard_cache();
+
+	index_fd = hold_locked_index(&index_lock, 1);
 
 	if (!commit->parents) {
 		if (action == REVERT)
@@ -332,6 +318,10 @@ static int revert_or_cherry_pick(int argc, const char **argv)
 		die ("Cannot get commit message for %s",
 				sha1_to_hex(commit->object.sha1));
 
+	if (parent && parse_commit(parent) < 0)
+		die("%s: cannot parse parent commit %s",
+		    me, sha1_to_hex(parent->object.sha1));
+
 	/*
 	 * "commit" is an existing commit.  We would want to apply
 	 * the difference it introduces since its first parent "prev"
@@ -374,13 +364,26 @@ static int revert_or_cherry_pick(int argc, const char **argv)
 		}
 	}
 
-	if (merge_recursive(base == NULL ?
-				NULL : sha1_to_hex(base->object.sha1),
-				sha1_to_hex(head), "HEAD",
-				sha1_to_hex(next->object.sha1), oneline) ||
-			write_cache_as_tree(head, 0, NULL)) {
+	read_cache();
+	init_merge_options(&o);
+	o.branch1 = "HEAD";
+	o.branch2 = oneline;
+
+	head_tree = parse_tree_indirect(head);
+	next_tree = next ? next->tree : empty_tree();
+	base_tree = base ? base->tree : empty_tree();
+
+	clean = merge_trees(&o,
+			    head_tree,
+			    next_tree, base_tree, &result);
+
+	if (active_cache_changed &&
+	    (write_cache(index_fd, active_cache, active_nr) ||
+	     commit_locked_index(&index_lock)))
+		die("%s: Unable to write new index file", me);
+
+	if (!clean) {
 		add_to_msg("\nConflicts:\n\n");
-		read_cache();
 		for (i = 0; i < active_nr;) {
 			struct cache_entry *ce = active_cache[i++];
 			if (ce_stage(ce)) {
diff --git a/merge-recursive.c b/merge-recursive.c
new file mode 100644
index 0000000000..dbdb9ac2c4
--- /dev/null
+++ b/merge-recursive.c
@@ -0,0 +1,1376 @@
+/*
+ * Recursive Merge algorithm stolen from git-merge-recursive.py by
+ * Fredrik Kuivinen.
+ * The thieves were Alex Riesen and Johannes Schindelin, in June/July 2006
+ */
+#include "cache.h"
+#include "cache-tree.h"
+#include "commit.h"
+#include "blob.h"
+#include "builtin.h"
+#include "tree-walk.h"
+#include "diff.h"
+#include "diffcore.h"
+#include "tag.h"
+#include "unpack-trees.h"
+#include "string-list.h"
+#include "xdiff-interface.h"
+#include "ll-merge.h"
+#include "interpolate.h"
+#include "attr.h"
+#include "merge-recursive.h"
+
+static struct tree *shift_tree_object(struct tree *one, struct tree *two)
+{
+	unsigned char shifted[20];
+
+	/*
+	 * NEEDSWORK: this limits the recursion depth to hardcoded
+	 * value '2' to avoid excessive overhead.
+	 */
+	shift_tree(one->object.sha1, two->object.sha1, shifted, 2);
+	if (!hashcmp(two->object.sha1, shifted))
+		return two;
+	return lookup_tree(shifted);
+}
+
+/*
+ * A virtual commit has (const char *)commit->util set to the name.
+ */
+
+struct commit *make_virtual_commit(struct tree *tree, const char *comment)
+{
+	struct commit *commit = xcalloc(1, sizeof(struct commit));
+	commit->tree = tree;
+	commit->util = (void*)comment;
+	/* avoid warnings */
+	commit->object.parsed = 1;
+	return commit;
+}
+
+/*
+ * Since we use get_tree_entry(), which does not put the read object into
+ * the object pool, we cannot rely on a == b.
+ */
+static int sha_eq(const unsigned char *a, const unsigned char *b)
+{
+	if (!a && !b)
+		return 2;
+	return a && b && hashcmp(a, b) == 0;
+}
+
+/*
+ * Since we want to write the index eventually, we cannot reuse the index
+ * for these (temporary) data.
+ */
+struct stage_data
+{
+	struct
+	{
+		unsigned mode;
+		unsigned char sha[20];
+	} stages[4];
+	unsigned processed:1;
+};
+
+static int show(struct merge_options *o, int v)
+{
+	return (!o->call_depth && o->verbosity >= v) || o->verbosity >= 5;
+}
+
+static void flush_output(struct merge_options *o)
+{
+	if (o->obuf.len) {
+		fputs(o->obuf.buf, stdout);
+		strbuf_reset(&o->obuf);
+	}
+}
+
+static void output(struct merge_options *o, int v, const char *fmt, ...)
+{
+	int len;
+	va_list ap;
+
+	if (!show(o, v))
+		return;
+
+	strbuf_grow(&o->obuf, o->call_depth * 2 + 2);
+	memset(o->obuf.buf + o->obuf.len, ' ', o->call_depth * 2);
+	strbuf_setlen(&o->obuf, o->obuf.len + o->call_depth * 2);
+
+	va_start(ap, fmt);
+	len = vsnprintf(o->obuf.buf + o->obuf.len, strbuf_avail(&o->obuf), fmt, ap);
+	va_end(ap);
+
+	if (len < 0)
+		len = 0;
+	if (len >= strbuf_avail(&o->obuf)) {
+		strbuf_grow(&o->obuf, len + 2);
+		va_start(ap, fmt);
+		len = vsnprintf(o->obuf.buf + o->obuf.len, strbuf_avail(&o->obuf), fmt, ap);
+		va_end(ap);
+		if (len >= strbuf_avail(&o->obuf)) {
+			die("this should not happen, your snprintf is broken");
+		}
+	}
+	strbuf_setlen(&o->obuf, o->obuf.len + len);
+	strbuf_add(&o->obuf, "\n", 1);
+	if (!o->buffer_output)
+		flush_output(o);
+}
+
+static void output_commit_title(struct merge_options *o, struct commit *commit)
+{
+	int i;
+	flush_output(o);
+	for (i = o->call_depth; i--;)
+		fputs("  ", stdout);
+	if (commit->util)
+		printf("virtual %s\n", (char *)commit->util);
+	else {
+		printf("%s ", find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV));
+		if (parse_commit(commit) != 0)
+			printf("(bad commit)\n");
+		else {
+			const char *s;
+			int len;
+			for (s = commit->buffer; *s; s++)
+				if (*s == '\n' && s[1] == '\n') {
+					s += 2;
+					break;
+				}
+			for (len = 0; s[len] && '\n' != s[len]; len++)
+				; /* do nothing */
+			printf("%.*s\n", len, s);
+		}
+	}
+}
+
+static int add_cacheinfo(unsigned int mode, const unsigned char *sha1,
+		const char *path, int stage, int refresh, int options)
+{
+	struct cache_entry *ce;
+	ce = make_cache_entry(mode, sha1 ? sha1 : null_sha1, path, stage, refresh);
+	if (!ce)
+		return error("addinfo_cache failed for path '%s'", path);
+	return add_cache_entry(ce, options);
+}
+
+static void init_tree_desc_from_tree(struct tree_desc *desc, struct tree *tree)
+{
+	parse_tree(tree);
+	init_tree_desc(desc, tree->buffer, tree->size);
+}
+
+static int git_merge_trees(int index_only,
+			   struct tree *common,
+			   struct tree *head,
+			   struct tree *merge)
+{
+	int rc;
+	struct tree_desc t[3];
+	struct unpack_trees_options opts;
+
+	memset(&opts, 0, sizeof(opts));
+	if (index_only)
+		opts.index_only = 1;
+	else
+		opts.update = 1;
+	opts.merge = 1;
+	opts.head_idx = 2;
+	opts.fn = threeway_merge;
+	opts.src_index = &the_index;
+	opts.dst_index = &the_index;
+
+	init_tree_desc_from_tree(t+0, common);
+	init_tree_desc_from_tree(t+1, head);
+	init_tree_desc_from_tree(t+2, merge);
+
+	rc = unpack_trees(3, t, &opts);
+	cache_tree_free(&active_cache_tree);
+	return rc;
+}
+
+struct tree *write_tree_from_memory(struct merge_options *o)
+{
+	struct tree *result = NULL;
+
+	if (unmerged_cache()) {
+		int i;
+		output(o, 0, "There are unmerged index entries:");
+		for (i = 0; i < active_nr; i++) {
+			struct cache_entry *ce = active_cache[i];
+			if (ce_stage(ce))
+				output(o, 0, "%d %.*s", ce_stage(ce), ce_namelen(ce), ce->name);
+		}
+		return NULL;
+	}
+
+	if (!active_cache_tree)
+		active_cache_tree = cache_tree();
+
+	if (!cache_tree_fully_valid(active_cache_tree) &&
+	    cache_tree_update(active_cache_tree,
+			      active_cache, active_nr, 0, 0) < 0)
+		die("error building trees");
+
+	result = lookup_tree(active_cache_tree->sha1);
+
+	return result;
+}
+
+static int save_files_dirs(const unsigned char *sha1,
+		const char *base, int baselen, const char *path,
+		unsigned int mode, int stage, void *context)
+{
+	int len = strlen(path);
+	char *newpath = xmalloc(baselen + len + 1);
+	struct merge_options *o = context;
+
+	memcpy(newpath, base, baselen);
+	memcpy(newpath + baselen, path, len);
+	newpath[baselen + len] = '\0';
+
+	if (S_ISDIR(mode))
+		string_list_insert(newpath, &o->current_directory_set);
+	else
+		string_list_insert(newpath, &o->current_file_set);
+	free(newpath);
+
+	return READ_TREE_RECURSIVE;
+}
+
+static int get_files_dirs(struct merge_options *o, struct tree *tree)
+{
+	int n;
+	if (read_tree_recursive(tree, "", 0, 0, NULL, save_files_dirs, o))
+		return 0;
+	n = o->current_file_set.nr + o->current_directory_set.nr;
+	return n;
+}
+
+/*
+ * Returns an index_entry instance which doesn't have to correspond to
+ * a real cache entry in Git's index.
+ */
+static struct stage_data *insert_stage_data(const char *path,
+		struct tree *o, struct tree *a, struct tree *b,
+		struct string_list *entries)
+{
+	struct string_list_item *item;
+	struct stage_data *e = xcalloc(1, sizeof(struct stage_data));
+	get_tree_entry(o->object.sha1, path,
+			e->stages[1].sha, &e->stages[1].mode);
+	get_tree_entry(a->object.sha1, path,
+			e->stages[2].sha, &e->stages[2].mode);
+	get_tree_entry(b->object.sha1, path,
+			e->stages[3].sha, &e->stages[3].mode);
+	item = string_list_insert(path, entries);
+	item->util = e;
+	return e;
+}
+
+/*
+ * Create a dictionary mapping file names to stage_data objects. The
+ * dictionary contains one entry for every path with a non-zero stage entry.
+ */
+static struct string_list *get_unmerged(void)
+{
+	struct string_list *unmerged = xcalloc(1, sizeof(struct string_list));
+	int i;
+
+	unmerged->strdup_strings = 1;
+
+	for (i = 0; i < active_nr; i++) {
+		struct string_list_item *item;
+		struct stage_data *e;
+		struct cache_entry *ce = active_cache[i];
+		if (!ce_stage(ce))
+			continue;
+
+		item = string_list_lookup(ce->name, unmerged);
+		if (!item) {
+			item = string_list_insert(ce->name, unmerged);
+			item->util = xcalloc(1, sizeof(struct stage_data));
+		}
+		e = item->util;
+		e->stages[ce_stage(ce)].mode = ce->ce_mode;
+		hashcpy(e->stages[ce_stage(ce)].sha, ce->sha1);
+	}
+
+	return unmerged;
+}
+
+struct rename
+{
+	struct diff_filepair *pair;
+	struct stage_data *src_entry;
+	struct stage_data *dst_entry;
+	unsigned processed:1;
+};
+
+/*
+ * Get information of all renames which occurred between 'o_tree' and
+ * 'tree'. We need the three trees in the merge ('o_tree', 'a_tree' and
+ * 'b_tree') to be able to associate the correct cache entries with
+ * the rename information. 'tree' is always equal to either a_tree or b_tree.
+ */
+static struct string_list *get_renames(struct merge_options *o,
+				       struct tree *tree,
+				       struct tree *o_tree,
+				       struct tree *a_tree,
+				       struct tree *b_tree,
+				       struct string_list *entries)
+{
+	int i;
+	struct string_list *renames;
+	struct diff_options opts;
+
+	renames = xcalloc(1, sizeof(struct string_list));
+	diff_setup(&opts);
+	DIFF_OPT_SET(&opts, RECURSIVE);
+	opts.detect_rename = DIFF_DETECT_RENAME;
+	opts.rename_limit = o->merge_rename_limit >= 0 ? o->merge_rename_limit :
+			    o->diff_rename_limit >= 0 ? o->diff_rename_limit :
+			    500;
+	opts.warn_on_too_large_rename = 1;
+	opts.output_format = DIFF_FORMAT_NO_OUTPUT;
+	if (diff_setup_done(&opts) < 0)
+		die("diff setup failed");
+	diff_tree_sha1(o_tree->object.sha1, tree->object.sha1, "", &opts);
+	diffcore_std(&opts);
+	for (i = 0; i < diff_queued_diff.nr; ++i) {
+		struct string_list_item *item;
+		struct rename *re;
+		struct diff_filepair *pair = diff_queued_diff.queue[i];
+		if (pair->status != 'R') {
+			diff_free_filepair(pair);
+			continue;
+		}
+		re = xmalloc(sizeof(*re));
+		re->processed = 0;
+		re->pair = pair;
+		item = string_list_lookup(re->pair->one->path, entries);
+		if (!item)
+			re->src_entry = insert_stage_data(re->pair->one->path,
+					o_tree, a_tree, b_tree, entries);
+		else
+			re->src_entry = item->util;
+
+		item = string_list_lookup(re->pair->two->path, entries);
+		if (!item)
+			re->dst_entry = insert_stage_data(re->pair->two->path,
+					o_tree, a_tree, b_tree, entries);
+		else
+			re->dst_entry = item->util;
+		item = string_list_insert(pair->one->path, renames);
+		item->util = re;
+	}
+	opts.output_format = DIFF_FORMAT_NO_OUTPUT;
+	diff_queued_diff.nr = 0;
+	diff_flush(&opts);
+	return renames;
+}
+
+static int update_stages(const char *path, struct diff_filespec *o,
+			 struct diff_filespec *a, struct diff_filespec *b,
+			 int clear)
+{
+	int options = ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE;
+	if (clear)
+		if (remove_file_from_cache(path))
+			return -1;
+	if (o)
+		if (add_cacheinfo(o->mode, o->sha1, path, 1, 0, options))
+			return -1;
+	if (a)
+		if (add_cacheinfo(a->mode, a->sha1, path, 2, 0, options))
+			return -1;
+	if (b)
+		if (add_cacheinfo(b->mode, b->sha1, path, 3, 0, options))
+			return -1;
+	return 0;
+}
+
+static int remove_path(const char *name)
+{
+	int ret;
+	char *slash, *dirs;
+
+	ret = unlink(name);
+	if (ret)
+		return ret;
+	dirs = xstrdup(name);
+	while ((slash = strrchr(name, '/'))) {
+		*slash = '\0';
+		if (rmdir(name) != 0)
+			break;
+	}
+	free(dirs);
+	return ret;
+}
+
+static int remove_file(struct merge_options *o, int clean,
+		       const char *path, int no_wd)
+{
+	int update_cache = o->call_depth || clean;
+	int update_working_directory = !o->call_depth && !no_wd;
+
+	if (update_cache) {
+		if (remove_file_from_cache(path))
+			return -1;
+	}
+	if (update_working_directory) {
+		unlink(path);
+		if (errno != ENOENT || errno != EISDIR)
+			return -1;
+		remove_path(path);
+	}
+	return 0;
+}
+
+static char *unique_path(struct merge_options *o, const char *path, const char *branch)
+{
+	char *newpath = xmalloc(strlen(path) + 1 + strlen(branch) + 8 + 1);
+	int suffix = 0;
+	struct stat st;
+	char *p = newpath + strlen(path);
+	strcpy(newpath, path);
+	*(p++) = '~';
+	strcpy(p, branch);
+	for (; *p; ++p)
+		if ('/' == *p)
+			*p = '_';
+	while (string_list_has_string(&o->current_file_set, newpath) ||
+	       string_list_has_string(&o->current_directory_set, newpath) ||
+	       lstat(newpath, &st) == 0)
+		sprintf(p, "_%d", suffix++);
+
+	string_list_insert(newpath, &o->current_file_set);
+	return newpath;
+}
+
+static void flush_buffer(int fd, const char *buf, unsigned long size)
+{
+	while (size > 0) {
+		long ret = write_in_full(fd, buf, size);
+		if (ret < 0) {
+			/* Ignore epipe */
+			if (errno == EPIPE)
+				break;
+			die("merge-recursive: %s", strerror(errno));
+		} else if (!ret) {
+			die("merge-recursive: disk full?");
+		}
+		size -= ret;
+		buf += ret;
+	}
+}
+
+static int make_room_for_path(const char *path)
+{
+	int status;
+	const char *msg = "failed to create path '%s'%s";
+
+	status = safe_create_leading_directories_const(path);
+	if (status) {
+		if (status == -3) {
+			/* something else exists */
+			error(msg, path, ": perhaps a D/F conflict?");
+			return -1;
+		}
+		die(msg, path, "");
+	}
+
+	/* Successful unlink is good.. */
+	if (!unlink(path))
+		return 0;
+	/* .. and so is no existing file */
+	if (errno == ENOENT)
+		return 0;
+	/* .. but not some other error (who really cares what?) */
+	return error(msg, path, ": perhaps a D/F conflict?");
+}
+
+static void update_file_flags(struct merge_options *o,
+			      const unsigned char *sha,
+			      unsigned mode,
+			      const char *path,
+			      int update_cache,
+			      int update_wd)
+{
+	if (o->call_depth)
+		update_wd = 0;
+
+	if (update_wd) {
+		enum object_type type;
+		void *buf;
+		unsigned long size;
+
+		if (S_ISGITLINK(mode))
+			die("cannot read object %s '%s': It is a submodule!",
+			    sha1_to_hex(sha), path);
+
+		buf = read_sha1_file(sha, &type, &size);
+		if (!buf)
+			die("cannot read object %s '%s'", sha1_to_hex(sha), path);
+		if (type != OBJ_BLOB)
+			die("blob expected for %s '%s'", sha1_to_hex(sha), path);
+		if (S_ISREG(mode)) {
+			struct strbuf strbuf;
+			strbuf_init(&strbuf, 0);
+			if (convert_to_working_tree(path, buf, size, &strbuf)) {
+				free(buf);
+				size = strbuf.len;
+				buf = strbuf_detach(&strbuf, NULL);
+			}
+		}
+
+		if (make_room_for_path(path) < 0) {
+			update_wd = 0;
+			free(buf);
+			goto update_index;
+		}
+		if (S_ISREG(mode) || (!has_symlinks && S_ISLNK(mode))) {
+			int fd;
+			if (mode & 0100)
+				mode = 0777;
+			else
+				mode = 0666;
+			fd = open(path, O_WRONLY | O_TRUNC | O_CREAT, mode);
+			if (fd < 0)
+				die("failed to open %s: %s", path, strerror(errno));
+			flush_buffer(fd, buf, size);
+			close(fd);
+		} else if (S_ISLNK(mode)) {
+			char *lnk = xmemdupz(buf, size);
+			safe_create_leading_directories_const(path);
+			unlink(path);
+			symlink(lnk, path);
+			free(lnk);
+		} else
+			die("do not know what to do with %06o %s '%s'",
+			    mode, sha1_to_hex(sha), path);
+		free(buf);
+	}
+ update_index:
+	if (update_cache)
+		add_cacheinfo(mode, sha, path, 0, update_wd, ADD_CACHE_OK_TO_ADD);
+}
+
+static void update_file(struct merge_options *o,
+			int clean,
+			const unsigned char *sha,
+			unsigned mode,
+			const char *path)
+{
+	update_file_flags(o, sha, mode, path, o->call_depth || clean, !o->call_depth);
+}
+
+/* Low level file merging, update and removal */
+
+struct merge_file_info
+{
+	unsigned char sha[20];
+	unsigned mode;
+	unsigned clean:1,
+		 merge:1;
+};
+
+static void fill_mm(const unsigned char *sha1, mmfile_t *mm)
+{
+	unsigned long size;
+	enum object_type type;
+
+	if (!hashcmp(sha1, null_sha1)) {
+		mm->ptr = xstrdup("");
+		mm->size = 0;
+		return;
+	}
+
+	mm->ptr = read_sha1_file(sha1, &type, &size);
+	if (!mm->ptr || type != OBJ_BLOB)
+		die("unable to read blob object %s", sha1_to_hex(sha1));
+	mm->size = size;
+}
+
+static int merge_3way(struct merge_options *o,
+		      mmbuffer_t *result_buf,
+		      struct diff_filespec *one,
+		      struct diff_filespec *a,
+		      struct diff_filespec *b,
+		      const char *branch1,
+		      const char *branch2)
+{
+	mmfile_t orig, src1, src2;
+	char *name1, *name2;
+	int merge_status;
+
+	name1 = xstrdup(mkpath("%s:%s", branch1, a->path));
+	name2 = xstrdup(mkpath("%s:%s", branch2, b->path));
+
+	fill_mm(one->sha1, &orig);
+	fill_mm(a->sha1, &src1);
+	fill_mm(b->sha1, &src2);
+
+	merge_status = ll_merge(result_buf, a->path, &orig,
+				&src1, name1, &src2, name2,
+				o->call_depth);
+
+	free(name1);
+	free(name2);
+	free(orig.ptr);
+	free(src1.ptr);
+	free(src2.ptr);
+	return merge_status;
+}
+
+static struct merge_file_info merge_file(struct merge_options *o,
+				         struct diff_filespec *one,
+					 struct diff_filespec *a,
+					 struct diff_filespec *b,
+					 const char *branch1,
+					 const char *branch2)
+{
+	struct merge_file_info result;
+	result.merge = 0;
+	result.clean = 1;
+
+	if ((S_IFMT & a->mode) != (S_IFMT & b->mode)) {
+		result.clean = 0;
+		if (S_ISREG(a->mode)) {
+			result.mode = a->mode;
+			hashcpy(result.sha, a->sha1);
+		} else {
+			result.mode = b->mode;
+			hashcpy(result.sha, b->sha1);
+		}
+	} else {
+		if (!sha_eq(a->sha1, one->sha1) && !sha_eq(b->sha1, one->sha1))
+			result.merge = 1;
+
+		/*
+		 * Merge modes
+		 */
+		if (a->mode == b->mode || a->mode == one->mode)
+			result.mode = b->mode;
+		else {
+			result.mode = a->mode;
+			if (b->mode != one->mode) {
+				result.clean = 0;
+				result.merge = 1;
+			}
+		}
+
+		if (sha_eq(a->sha1, b->sha1) || sha_eq(a->sha1, one->sha1))
+			hashcpy(result.sha, b->sha1);
+		else if (sha_eq(b->sha1, one->sha1))
+			hashcpy(result.sha, a->sha1);
+		else if (S_ISREG(a->mode)) {
+			mmbuffer_t result_buf;
+			int merge_status;
+
+			merge_status = merge_3way(o, &result_buf, one, a, b,
+						  branch1, branch2);
+
+			if ((merge_status < 0) || !result_buf.ptr)
+				die("Failed to execute internal merge");
+
+			if (write_sha1_file(result_buf.ptr, result_buf.size,
+					    blob_type, result.sha))
+				die("Unable to add %s to database",
+				    a->path);
+
+			free(result_buf.ptr);
+			result.clean = (merge_status == 0);
+		} else if (S_ISGITLINK(a->mode)) {
+			result.clean = 0;
+			hashcpy(result.sha, a->sha1);
+		} else if (S_ISLNK(a->mode)) {
+			hashcpy(result.sha, a->sha1);
+
+			if (!sha_eq(a->sha1, b->sha1))
+				result.clean = 0;
+		} else {
+			die("unsupported object type in the tree");
+		}
+	}
+
+	return result;
+}
+
+static void conflict_rename_rename(struct merge_options *o,
+				   struct rename *ren1,
+				   const char *branch1,
+				   struct rename *ren2,
+				   const char *branch2)
+{
+	char *del[2];
+	int delp = 0;
+	const char *ren1_dst = ren1->pair->two->path;
+	const char *ren2_dst = ren2->pair->two->path;
+	const char *dst_name1 = ren1_dst;
+	const char *dst_name2 = ren2_dst;
+	if (string_list_has_string(&o->current_directory_set, ren1_dst)) {
+		dst_name1 = del[delp++] = unique_path(o, ren1_dst, branch1);
+		output(o, 1, "%s is a directory in %s adding as %s instead",
+		       ren1_dst, branch2, dst_name1);
+		remove_file(o, 0, ren1_dst, 0);
+	}
+	if (string_list_has_string(&o->current_directory_set, ren2_dst)) {
+		dst_name2 = del[delp++] = unique_path(o, ren2_dst, branch2);
+		output(o, 1, "%s is a directory in %s adding as %s instead",
+		       ren2_dst, branch1, dst_name2);
+		remove_file(o, 0, ren2_dst, 0);
+	}
+	if (o->call_depth) {
+		remove_file_from_cache(dst_name1);
+		remove_file_from_cache(dst_name2);
+		/*
+		 * Uncomment to leave the conflicting names in the resulting tree
+		 *
+		 * update_file(o, 0, ren1->pair->two->sha1, ren1->pair->two->mode, dst_name1);
+		 * update_file(o, 0, ren2->pair->two->sha1, ren2->pair->two->mode, dst_name2);
+		 */
+	} else {
+		update_stages(dst_name1, NULL, ren1->pair->two, NULL, 1);
+		update_stages(dst_name2, NULL, NULL, ren2->pair->two, 1);
+	}
+	while (delp--)
+		free(del[delp]);
+}
+
+static void conflict_rename_dir(struct merge_options *o,
+				struct rename *ren1,
+				const char *branch1)
+{
+	char *new_path = unique_path(o, ren1->pair->two->path, branch1);
+	output(o, 1, "Renaming %s to %s instead", ren1->pair->one->path, new_path);
+	remove_file(o, 0, ren1->pair->two->path, 0);
+	update_file(o, 0, ren1->pair->two->sha1, ren1->pair->two->mode, new_path);
+	free(new_path);
+}
+
+static void conflict_rename_rename_2(struct merge_options *o,
+				     struct rename *ren1,
+				     const char *branch1,
+				     struct rename *ren2,
+				     const char *branch2)
+{
+	char *new_path1 = unique_path(o, ren1->pair->two->path, branch1);
+	char *new_path2 = unique_path(o, ren2->pair->two->path, branch2);
+	output(o, 1, "Renaming %s to %s and %s to %s instead",
+	       ren1->pair->one->path, new_path1,
+	       ren2->pair->one->path, new_path2);
+	remove_file(o, 0, ren1->pair->two->path, 0);
+	update_file(o, 0, ren1->pair->two->sha1, ren1->pair->two->mode, new_path1);
+	update_file(o, 0, ren2->pair->two->sha1, ren2->pair->two->mode, new_path2);
+	free(new_path2);
+	free(new_path1);
+}
+
+static int process_renames(struct merge_options *o,
+			   struct string_list *a_renames,
+			   struct string_list *b_renames)
+{
+	int clean_merge = 1, i, j;
+	struct string_list a_by_dst = {NULL, 0, 0, 0}, b_by_dst = {NULL, 0, 0, 0};
+	const struct rename *sre;
+
+	for (i = 0; i < a_renames->nr; i++) {
+		sre = a_renames->items[i].util;
+		string_list_insert(sre->pair->two->path, &a_by_dst)->util
+			= sre->dst_entry;
+	}
+	for (i = 0; i < b_renames->nr; i++) {
+		sre = b_renames->items[i].util;
+		string_list_insert(sre->pair->two->path, &b_by_dst)->util
+			= sre->dst_entry;
+	}
+
+	for (i = 0, j = 0; i < a_renames->nr || j < b_renames->nr;) {
+		int compare;
+		char *src;
+		struct string_list *renames1, *renames2, *renames2Dst;
+		struct rename *ren1 = NULL, *ren2 = NULL;
+		const char *branch1, *branch2;
+		const char *ren1_src, *ren1_dst;
+
+		if (i >= a_renames->nr) {
+			compare = 1;
+			ren2 = b_renames->items[j++].util;
+		} else if (j >= b_renames->nr) {
+			compare = -1;
+			ren1 = a_renames->items[i++].util;
+		} else {
+			compare = strcmp(a_renames->items[i].string,
+					b_renames->items[j].string);
+			if (compare <= 0)
+				ren1 = a_renames->items[i++].util;
+			if (compare >= 0)
+				ren2 = b_renames->items[j++].util;
+		}
+
+		/* TODO: refactor, so that 1/2 are not needed */
+		if (ren1) {
+			renames1 = a_renames;
+			renames2 = b_renames;
+			renames2Dst = &b_by_dst;
+			branch1 = o->branch1;
+			branch2 = o->branch2;
+		} else {
+			struct rename *tmp;
+			renames1 = b_renames;
+			renames2 = a_renames;
+			renames2Dst = &a_by_dst;
+			branch1 = o->branch2;
+			branch2 = o->branch1;
+			tmp = ren2;
+			ren2 = ren1;
+			ren1 = tmp;
+		}
+		src = ren1->pair->one->path;
+
+		ren1->dst_entry->processed = 1;
+		ren1->src_entry->processed = 1;
+
+		if (ren1->processed)
+			continue;
+		ren1->processed = 1;
+
+		ren1_src = ren1->pair->one->path;
+		ren1_dst = ren1->pair->two->path;
+
+		if (ren2) {
+			const char *ren2_src = ren2->pair->one->path;
+			const char *ren2_dst = ren2->pair->two->path;
+			/* Renamed in 1 and renamed in 2 */
+			if (strcmp(ren1_src, ren2_src) != 0)
+				die("ren1.src != ren2.src");
+			ren2->dst_entry->processed = 1;
+			ren2->processed = 1;
+			if (strcmp(ren1_dst, ren2_dst) != 0) {
+				clean_merge = 0;
+				output(o, 1, "CONFLICT (rename/rename): "
+				       "Rename \"%s\"->\"%s\" in branch \"%s\" "
+				       "rename \"%s\"->\"%s\" in \"%s\"%s",
+				       src, ren1_dst, branch1,
+				       src, ren2_dst, branch2,
+				       o->call_depth ? " (left unresolved)": "");
+				if (o->call_depth) {
+					remove_file_from_cache(src);
+					update_file(o, 0, ren1->pair->one->sha1,
+						    ren1->pair->one->mode, src);
+				}
+				conflict_rename_rename(o, ren1, branch1, ren2, branch2);
+			} else {
+				struct merge_file_info mfi;
+				remove_file(o, 1, ren1_src, 1);
+				mfi = merge_file(o,
+						 ren1->pair->one,
+						 ren1->pair->two,
+						 ren2->pair->two,
+						 branch1,
+						 branch2);
+				if (mfi.merge || !mfi.clean)
+					output(o, 1, "Renaming %s->%s", src, ren1_dst);
+
+				if (mfi.merge)
+					output(o, 2, "Auto-merging %s", ren1_dst);
+
+				if (!mfi.clean) {
+					output(o, 1, "CONFLICT (content): merge conflict in %s",
+					       ren1_dst);
+					clean_merge = 0;
+
+					if (!o->call_depth)
+						update_stages(ren1_dst,
+							      ren1->pair->one,
+							      ren1->pair->two,
+							      ren2->pair->two,
+							      1 /* clear */);
+				}
+				update_file(o, mfi.clean, mfi.sha, mfi.mode, ren1_dst);
+			}
+		} else {
+			/* Renamed in 1, maybe changed in 2 */
+			struct string_list_item *item;
+			/* we only use sha1 and mode of these */
+			struct diff_filespec src_other, dst_other;
+			int try_merge, stage = a_renames == renames1 ? 3: 2;
+
+			remove_file(o, 1, ren1_src, o->call_depth || stage == 3);
+
+			hashcpy(src_other.sha1, ren1->src_entry->stages[stage].sha);
+			src_other.mode = ren1->src_entry->stages[stage].mode;
+			hashcpy(dst_other.sha1, ren1->dst_entry->stages[stage].sha);
+			dst_other.mode = ren1->dst_entry->stages[stage].mode;
+
+			try_merge = 0;
+
+			if (string_list_has_string(&o->current_directory_set, ren1_dst)) {
+				clean_merge = 0;
+				output(o, 1, "CONFLICT (rename/directory): Rename %s->%s in %s "
+				       " directory %s added in %s",
+				       ren1_src, ren1_dst, branch1,
+				       ren1_dst, branch2);
+				conflict_rename_dir(o, ren1, branch1);
+			} else if (sha_eq(src_other.sha1, null_sha1)) {
+				clean_merge = 0;
+				output(o, 1, "CONFLICT (rename/delete): Rename %s->%s in %s "
+				       "and deleted in %s",
+				       ren1_src, ren1_dst, branch1,
+				       branch2);
+				update_file(o, 0, ren1->pair->two->sha1, ren1->pair->two->mode, ren1_dst);
+			} else if (!sha_eq(dst_other.sha1, null_sha1)) {
+				const char *new_path;
+				clean_merge = 0;
+				try_merge = 1;
+				output(o, 1, "CONFLICT (rename/add): Rename %s->%s in %s. "
+				       "%s added in %s",
+				       ren1_src, ren1_dst, branch1,
+				       ren1_dst, branch2);
+				new_path = unique_path(o, ren1_dst, branch2);
+				output(o, 1, "Adding as %s instead", new_path);
+				update_file(o, 0, dst_other.sha1, dst_other.mode, new_path);
+			} else if ((item = string_list_lookup(ren1_dst, renames2Dst))) {
+				ren2 = item->util;
+				clean_merge = 0;
+				ren2->processed = 1;
+				output(o, 1, "CONFLICT (rename/rename): "
+				       "Rename %s->%s in %s. "
+				       "Rename %s->%s in %s",
+				       ren1_src, ren1_dst, branch1,
+				       ren2->pair->one->path, ren2->pair->two->path, branch2);
+				conflict_rename_rename_2(o, ren1, branch1, ren2, branch2);
+			} else
+				try_merge = 1;
+
+			if (try_merge) {
+				struct diff_filespec *one, *a, *b;
+				struct merge_file_info mfi;
+				src_other.path = (char *)ren1_src;
+
+				one = ren1->pair->one;
+				if (a_renames == renames1) {
+					a = ren1->pair->two;
+					b = &src_other;
+				} else {
+					b = ren1->pair->two;
+					a = &src_other;
+				}
+				mfi = merge_file(o, one, a, b,
+						o->branch1, o->branch2);
+
+				if (mfi.clean &&
+				    sha_eq(mfi.sha, ren1->pair->two->sha1) &&
+				    mfi.mode == ren1->pair->two->mode)
+					/*
+					 * This messaged is part of
+					 * t6022 test. If you change
+					 * it update the test too.
+					 */
+					output(o, 3, "Skipped %s (merged same as existing)", ren1_dst);
+				else {
+					if (mfi.merge || !mfi.clean)
+						output(o, 1, "Renaming %s => %s", ren1_src, ren1_dst);
+					if (mfi.merge)
+						output(o, 2, "Auto-merging %s", ren1_dst);
+					if (!mfi.clean) {
+						output(o, 1, "CONFLICT (rename/modify): Merge conflict in %s",
+						       ren1_dst);
+						clean_merge = 0;
+
+						if (!o->call_depth)
+							update_stages(ren1_dst,
+								      one, a, b, 1);
+					}
+					update_file(o, mfi.clean, mfi.sha, mfi.mode, ren1_dst);
+				}
+			}
+		}
+	}
+	string_list_clear(&a_by_dst, 0);
+	string_list_clear(&b_by_dst, 0);
+
+	return clean_merge;
+}
+
+static unsigned char *stage_sha(const unsigned char *sha, unsigned mode)
+{
+	return (is_null_sha1(sha) || mode == 0) ? NULL: (unsigned char *)sha;
+}
+
+/* Per entry merge function */
+static int process_entry(struct merge_options *o,
+			 const char *path, struct stage_data *entry)
+{
+	/*
+	printf("processing entry, clean cache: %s\n", index_only ? "yes": "no");
+	print_index_entry("\tpath: ", entry);
+	*/
+	int clean_merge = 1;
+	unsigned o_mode = entry->stages[1].mode;
+	unsigned a_mode = entry->stages[2].mode;
+	unsigned b_mode = entry->stages[3].mode;
+	unsigned char *o_sha = stage_sha(entry->stages[1].sha, o_mode);
+	unsigned char *a_sha = stage_sha(entry->stages[2].sha, a_mode);
+	unsigned char *b_sha = stage_sha(entry->stages[3].sha, b_mode);
+
+	if (o_sha && (!a_sha || !b_sha)) {
+		/* Case A: Deleted in one */
+		if ((!a_sha && !b_sha) ||
+		    (sha_eq(a_sha, o_sha) && !b_sha) ||
+		    (!a_sha && sha_eq(b_sha, o_sha))) {
+			/* Deleted in both or deleted in one and
+			 * unchanged in the other */
+			if (a_sha)
+				output(o, 2, "Removing %s", path);
+			/* do not touch working file if it did not exist */
+			remove_file(o, 1, path, !a_sha);
+		} else {
+			/* Deleted in one and changed in the other */
+			clean_merge = 0;
+			if (!a_sha) {
+				output(o, 1, "CONFLICT (delete/modify): %s deleted in %s "
+				       "and modified in %s. Version %s of %s left in tree.",
+				       path, o->branch1,
+				       o->branch2, o->branch2, path);
+				update_file(o, 0, b_sha, b_mode, path);
+			} else {
+				output(o, 1, "CONFLICT (delete/modify): %s deleted in %s "
+				       "and modified in %s. Version %s of %s left in tree.",
+				       path, o->branch2,
+				       o->branch1, o->branch1, path);
+				update_file(o, 0, a_sha, a_mode, path);
+			}
+		}
+
+	} else if ((!o_sha && a_sha && !b_sha) ||
+		   (!o_sha && !a_sha && b_sha)) {
+		/* Case B: Added in one. */
+		const char *add_branch;
+		const char *other_branch;
+		unsigned mode;
+		const unsigned char *sha;
+		const char *conf;
+
+		if (a_sha) {
+			add_branch = o->branch1;
+			other_branch = o->branch2;
+			mode = a_mode;
+			sha = a_sha;
+			conf = "file/directory";
+		} else {
+			add_branch = o->branch2;
+			other_branch = o->branch1;
+			mode = b_mode;
+			sha = b_sha;
+			conf = "directory/file";
+		}
+		if (string_list_has_string(&o->current_directory_set, path)) {
+			const char *new_path = unique_path(o, path, add_branch);
+			clean_merge = 0;
+			output(o, 1, "CONFLICT (%s): There is a directory with name %s in %s. "
+			       "Adding %s as %s",
+			       conf, path, other_branch, path, new_path);
+			remove_file(o, 0, path, 0);
+			update_file(o, 0, sha, mode, new_path);
+		} else {
+			output(o, 2, "Adding %s", path);
+			update_file(o, 1, sha, mode, path);
+		}
+	} else if (a_sha && b_sha) {
+		/* Case C: Added in both (check for same permissions) and */
+		/* case D: Modified in both, but differently. */
+		const char *reason = "content";
+		struct merge_file_info mfi;
+		struct diff_filespec one, a, b;
+
+		if (!o_sha) {
+			reason = "add/add";
+			o_sha = (unsigned char *)null_sha1;
+		}
+		output(o, 2, "Auto-merging %s", path);
+		one.path = a.path = b.path = (char *)path;
+		hashcpy(one.sha1, o_sha);
+		one.mode = o_mode;
+		hashcpy(a.sha1, a_sha);
+		a.mode = a_mode;
+		hashcpy(b.sha1, b_sha);
+		b.mode = b_mode;
+
+		mfi = merge_file(o, &one, &a, &b,
+				 o->branch1, o->branch2);
+
+		clean_merge = mfi.clean;
+		if (mfi.clean)
+			update_file(o, 1, mfi.sha, mfi.mode, path);
+		else if (S_ISGITLINK(mfi.mode))
+			output(o, 1, "CONFLICT (submodule): Merge conflict in %s "
+			       "- needs %s", path, sha1_to_hex(b.sha1));
+		else {
+			output(o, 1, "CONFLICT (%s): Merge conflict in %s",
+					reason, path);
+
+			if (o->call_depth)
+				update_file(o, 0, mfi.sha, mfi.mode, path);
+			else
+				update_file_flags(o, mfi.sha, mfi.mode, path,
+					      0 /* update_cache */, 1 /* update_working_directory */);
+		}
+	} else if (!o_sha && !a_sha && !b_sha) {
+		/*
+		 * this entry was deleted altogether. a_mode == 0 means
+		 * we had that path and want to actively remove it.
+		 */
+		remove_file(o, 1, path, !a_mode);
+	} else
+		die("Fatal merge failure, shouldn't happen.");
+
+	return clean_merge;
+}
+
+int merge_trees(struct merge_options *o,
+		struct tree *head,
+		struct tree *merge,
+		struct tree *common,
+		struct tree **result)
+{
+	int code, clean;
+
+	if (o->subtree_merge) {
+		merge = shift_tree_object(head, merge);
+		common = shift_tree_object(head, common);
+	}
+
+	if (sha_eq(common->object.sha1, merge->object.sha1)) {
+		output(o, 0, "Already uptodate!");
+		*result = head;
+		return 1;
+	}
+
+	code = git_merge_trees(o->call_depth, common, head, merge);
+
+	if (code != 0)
+		die("merging of trees %s and %s failed",
+		    sha1_to_hex(head->object.sha1),
+		    sha1_to_hex(merge->object.sha1));
+
+	if (unmerged_cache()) {
+		struct string_list *entries, *re_head, *re_merge;
+		int i;
+		string_list_clear(&o->current_file_set, 1);
+		string_list_clear(&o->current_directory_set, 1);
+		get_files_dirs(o, head);
+		get_files_dirs(o, merge);
+
+		entries = get_unmerged();
+		re_head  = get_renames(o, head, common, head, merge, entries);
+		re_merge = get_renames(o, merge, common, head, merge, entries);
+		clean = process_renames(o, re_head, re_merge);
+		for (i = 0; i < entries->nr; i++) {
+			const char *path = entries->items[i].string;
+			struct stage_data *e = entries->items[i].util;
+			if (!e->processed
+				&& !process_entry(o, path, e))
+				clean = 0;
+		}
+
+		string_list_clear(re_merge, 0);
+		string_list_clear(re_head, 0);
+		string_list_clear(entries, 1);
+
+	}
+	else
+		clean = 1;
+
+	if (o->call_depth)
+		*result = write_tree_from_memory(o);
+
+	return clean;
+}
+
+static struct commit_list *reverse_commit_list(struct commit_list *list)
+{
+	struct commit_list *next = NULL, *current, *backup;
+	for (current = list; current; current = backup) {
+		backup = current->next;
+		current->next = next;
+		next = current;
+	}
+	return next;
+}
+
+/*
+ * Merge the commits h1 and h2, return the resulting virtual
+ * commit object and a flag indicating the cleanness of the merge.
+ */
+int merge_recursive(struct merge_options *o,
+		    struct commit *h1,
+		    struct commit *h2,
+		    struct commit_list *ca,
+		    struct commit **result)
+{
+	struct commit_list *iter;
+	struct commit *merged_common_ancestors;
+	struct tree *mrtree = mrtree;
+	int clean;
+
+	if (show(o, 4)) {
+		output(o, 4, "Merging:");
+		output_commit_title(o, h1);
+		output_commit_title(o, h2);
+	}
+
+	if (!ca) {
+		ca = get_merge_bases(h1, h2, 1);
+		ca = reverse_commit_list(ca);
+	}
+
+	if (show(o, 5)) {
+		output(o, 5, "found %u common ancestor(s):", commit_list_count(ca));
+		for (iter = ca; iter; iter = iter->next)
+			output_commit_title(o, iter->item);
+	}
+
+	merged_common_ancestors = pop_commit(&ca);
+	if (merged_common_ancestors == NULL) {
+		/* if there is no common ancestor, make an empty tree */
+		struct tree *tree = xcalloc(1, sizeof(struct tree));
+
+		tree->object.parsed = 1;
+		tree->object.type = OBJ_TREE;
+		pretend_sha1_file(NULL, 0, OBJ_TREE, tree->object.sha1);
+		merged_common_ancestors = make_virtual_commit(tree, "ancestor");
+	}
+
+	for (iter = ca; iter; iter = iter->next) {
+		const char *saved_b1, *saved_b2;
+		o->call_depth++;
+		/*
+		 * When the merge fails, the result contains files
+		 * with conflict markers. The cleanness flag is
+		 * ignored, it was never actually used, as result of
+		 * merge_trees has always overwritten it: the committed
+		 * "conflicts" were already resolved.
+		 */
+		discard_cache();
+		saved_b1 = o->branch1;
+		saved_b2 = o->branch2;
+		o->branch1 = "Temporary merge branch 1";
+		o->branch2 = "Temporary merge branch 2";
+		merge_recursive(o, merged_common_ancestors, iter->item,
+				NULL, &merged_common_ancestors);
+		o->branch1 = saved_b1;
+		o->branch2 = saved_b2;
+		o->call_depth--;
+
+		if (!merged_common_ancestors)
+			die("merge returned no commit");
+	}
+
+	discard_cache();
+	if (!o->call_depth)
+		read_cache();
+
+	clean = merge_trees(o, h1->tree, h2->tree, merged_common_ancestors->tree,
+			    &mrtree);
+
+	if (o->call_depth) {
+		*result = make_virtual_commit(mrtree, "merged tree");
+		commit_list_insert(h1, &(*result)->parents);
+		commit_list_insert(h2, &(*result)->parents->next);
+	}
+	flush_output(o);
+	return clean;
+}
+
+static struct commit *get_ref(const unsigned char *sha1, const char *name)
+{
+	struct object *object;
+
+	object = deref_tag(parse_object(sha1), name, strlen(name));
+	if (!object)
+		return NULL;
+	if (object->type == OBJ_TREE)
+		return make_virtual_commit((struct tree*)object, name);
+	if (object->type != OBJ_COMMIT)
+		return NULL;
+	if (parse_commit((struct commit *)object))
+		return NULL;
+	return (struct commit *)object;
+}
+
+int merge_recursive_generic(struct merge_options *o,
+			    const unsigned char *head,
+			    const unsigned char *merge,
+			    int num_base_list,
+			    const unsigned char **base_list,
+			    struct commit **result)
+{
+	int clean, index_fd;
+	struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
+	struct commit *head_commit = get_ref(head, o->branch1);
+	struct commit *next_commit = get_ref(merge, o->branch2);
+	struct commit_list *ca = NULL;
+
+	if (base_list) {
+		int i;
+		for (i = 0; i < num_base_list; ++i) {
+			struct commit *base;
+			if (!(base = get_ref(base_list[i], sha1_to_hex(base_list[i]))))
+				return error("Could not parse object '%s'",
+					sha1_to_hex(base_list[i]));
+			commit_list_insert(base, &ca);
+		}
+	}
+
+	index_fd = hold_locked_index(lock, 1);
+	clean = merge_recursive(o, head_commit, next_commit, ca,
+			result);
+	if (active_cache_changed &&
+			(write_cache(index_fd, active_cache, active_nr) ||
+			 commit_locked_index(lock)))
+		return error("Unable to write index.");
+
+	return clean ? 0 : 1;
+}
+
+static int merge_recursive_config(const char *var, const char *value, void *cb)
+{
+	struct merge_options *o = cb;
+	if (!strcasecmp(var, "merge.verbosity")) {
+		o->verbosity = git_config_int(var, value);
+		return 0;
+	}
+	if (!strcasecmp(var, "diff.renamelimit")) {
+		o->diff_rename_limit = git_config_int(var, value);
+		return 0;
+	}
+	if (!strcasecmp(var, "merge.renamelimit")) {
+		o->merge_rename_limit = git_config_int(var, value);
+		return 0;
+	}
+	return git_default_config(var, value, cb);
+}
+
+void init_merge_options(struct merge_options *o)
+{
+	memset(o, 0, sizeof(struct merge_options));
+	o->verbosity = 2;
+	o->buffer_output = 1;
+	o->diff_rename_limit = -1;
+	o->merge_rename_limit = -1;
+	git_config(merge_recursive_config, o);
+	if (getenv("GIT_MERGE_VERBOSITY"))
+		o->verbosity =
+			strtol(getenv("GIT_MERGE_VERBOSITY"), NULL, 10);
+	if (o->verbosity >= 5)
+		o->buffer_output = 0;
+	strbuf_init(&o->obuf, 0);
+	memset(&o->current_file_set, 0, sizeof(struct string_list));
+	o->current_file_set.strdup_strings = 1;
+	memset(&o->current_directory_set, 0, sizeof(struct string_list));
+	o->current_directory_set.strdup_strings = 1;
+}
diff --git a/merge-recursive.h b/merge-recursive.h
index f37630a8ad..fd138ca140 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -1,20 +1,48 @@
 #ifndef MERGE_RECURSIVE_H
 #define MERGE_RECURSIVE_H
 
-int merge_recursive(struct commit *h1,
+#include "string-list.h"
+
+struct merge_options {
+	const char *branch1;
+	const char *branch2;
+	unsigned subtree_merge : 1;
+	unsigned buffer_output : 1;
+	int verbosity;
+	int diff_rename_limit;
+	int merge_rename_limit;
+	int call_depth;
+	struct strbuf obuf;
+	struct string_list current_file_set;
+	struct string_list current_directory_set;
+};
+
+/* merge_trees() but with recursive ancestor consolidation */
+int merge_recursive(struct merge_options *o,
+		    struct commit *h1,
 		    struct commit *h2,
-		    const char *branch1,
-		    const char *branch2,
 		    struct commit_list *ancestors,
 		    struct commit **result);
 
-int merge_trees(struct tree *head,
+/* rename-detecting three-way merge, no recursion */
+int merge_trees(struct merge_options *o,
+		struct tree *head,
 		struct tree *merge,
 		struct tree *common,
-		const char *branch1,
-		const char *branch2,
 		struct tree **result);
 
-struct tree *write_tree_from_memory(void);
+/*
+ * "git-merge-recursive" can be fed trees; wrap them into
+ * virtual commits and call merge_recursive() proper.
+ */
+int merge_recursive_generic(struct merge_options *o,
+			    const unsigned char *head,
+			    const unsigned char *merge,
+			    int num_ca,
+			    const unsigned char **ca,
+			    struct commit **result);
+
+void init_merge_options(struct merge_options *o);
+struct tree *write_tree_from_memory(struct merge_options *o);
 
 #endif
diff --git a/t/t6026-merge-attr.sh b/t/t6026-merge-attr.sh
index 4b423e937d..1ba0a25223 100755
--- a/t/t6026-merge-attr.sh
+++ b/t/t6026-merge-attr.sh
@@ -142,4 +142,26 @@ test_expect_success 'custom merge backend' '
 	rm -f $o $a $b
 '
 
+test_expect_success 'up-to-date merge without common ancestor' '
+	test_create_repo repo1 &&
+	test_create_repo repo2 &&
+	test_tick &&
+	(
+		cd repo1 &&
+		>a &&
+		git add a &&
+		git commit -m initial
+	) &&
+	test_tick &&
+	(
+		cd repo2 &&
+		git commit --allow-empty -m initial
+	) &&
+	test_tick &&
+	(
+		cd repo1 &&
+		git pull ../repo2 master
+	)
+'
+
 test_done