Adding upstream version 1:2.39.2.upstream/1%2.39.2upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3963 insertions, 0 deletions

diff --git a/merge-recursive.c b/merge-recursive.c
new file mode 100644
index 0000000..2fd0aa9
--- /dev/null
+++ b/merge-recursive.c
@@ -0,0 +1,3963 @@
+/*
+ * 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 "merge-recursive.h"
+
+#include "advice.h"
+#include "alloc.h"
+#include "attr.h"
+#include "blob.h"
+#include "builtin.h"
+#include "cache-tree.h"
+#include "commit.h"
+#include "commit-reach.h"
+#include "config.h"
+#include "diff.h"
+#include "diffcore.h"
+#include "dir.h"
+#include "ll-merge.h"
+#include "lockfile.h"
+#include "object-store.h"
+#include "repository.h"
+#include "revision.h"
+#include "string-list.h"
+#include "submodule-config.h"
+#include "submodule.h"
+#include "tag.h"
+#include "tree-walk.h"
+#include "unpack-trees.h"
+#include "xdiff-interface.h"
+
+struct merge_options_internal {
+	int call_depth;
+	int needed_rename_limit;
+	struct hashmap current_file_dir_set;
+	struct string_list df_conflict_file_set;
+	struct unpack_trees_options unpack_opts;
+	struct index_state orig_index;
+};
+
+struct path_hashmap_entry {
+	struct hashmap_entry e;
+	char path[FLEX_ARRAY];
+};
+
+static int path_hashmap_cmp(const void *cmp_data UNUSED,
+			    const struct hashmap_entry *eptr,
+			    const struct hashmap_entry *entry_or_key,
+			    const void *keydata)
+{
+	const struct path_hashmap_entry *a, *b;
+	const char *key = keydata;
+
+	a = container_of(eptr, const struct path_hashmap_entry, e);
+	b = container_of(entry_or_key, const struct path_hashmap_entry, e);
+
+	return fspathcmp(a->path, key ? key : b->path);
+}
+
+/*
+ * For dir_rename_entry, directory names are stored as a full path from the
+ * toplevel of the repository and do not include a trailing '/'.  Also:
+ *
+ *   dir:                original name of directory being renamed
+ *   non_unique_new_dir: if true, could not determine new_dir
+ *   new_dir:            final name of directory being renamed
+ *   possible_new_dirs:  temporary used to help determine new_dir; see comments
+ *                       in get_directory_renames() for details
+ */
+struct dir_rename_entry {
+	struct hashmap_entry ent;
+	char *dir;
+	unsigned non_unique_new_dir:1;
+	struct strbuf new_dir;
+	struct string_list possible_new_dirs;
+};
+
+static struct dir_rename_entry *dir_rename_find_entry(struct hashmap *hashmap,
+						      char *dir)
+{
+	struct dir_rename_entry key;
+
+	if (!dir)
+		return NULL;
+	hashmap_entry_init(&key.ent, strhash(dir));
+	key.dir = dir;
+	return hashmap_get_entry(hashmap, &key, ent, NULL);
+}
+
+static int dir_rename_cmp(const void *cmp_data UNUSED,
+			  const struct hashmap_entry *eptr,
+			  const struct hashmap_entry *entry_or_key,
+			  const void *keydata UNUSED)
+{
+	const struct dir_rename_entry *e1, *e2;
+
+	e1 = container_of(eptr, const struct dir_rename_entry, ent);
+	e2 = container_of(entry_or_key, const struct dir_rename_entry, ent);
+
+	return strcmp(e1->dir, e2->dir);
+}
+
+static void dir_rename_init(struct hashmap *map)
+{
+	hashmap_init(map, dir_rename_cmp, NULL, 0);
+}
+
+static void dir_rename_entry_init(struct dir_rename_entry *entry,
+				  char *directory)
+{
+	hashmap_entry_init(&entry->ent, strhash(directory));
+	entry->dir = directory;
+	entry->non_unique_new_dir = 0;
+	strbuf_init(&entry->new_dir, 0);
+	string_list_init_nodup(&entry->possible_new_dirs);
+}
+
+struct collision_entry {
+	struct hashmap_entry ent;
+	char *target_file;
+	struct string_list source_files;
+	unsigned reported_already:1;
+};
+
+static struct collision_entry *collision_find_entry(struct hashmap *hashmap,
+						    char *target_file)
+{
+	struct collision_entry key;
+
+	hashmap_entry_init(&key.ent, strhash(target_file));
+	key.target_file = target_file;
+	return hashmap_get_entry(hashmap, &key, ent, NULL);
+}
+
+static int collision_cmp(const void *cmp_data UNUSED,
+			 const struct hashmap_entry *eptr,
+			 const struct hashmap_entry *entry_or_key,
+			 const void *keydata UNUSED)
+{
+	const struct collision_entry *e1, *e2;
+
+	e1 = container_of(eptr, const struct collision_entry, ent);
+	e2 = container_of(entry_or_key, const struct collision_entry, ent);
+
+	return strcmp(e1->target_file, e2->target_file);
+}
+
+static void collision_init(struct hashmap *map)
+{
+	hashmap_init(map, collision_cmp, NULL, 0);
+}
+
+static void flush_output(struct merge_options *opt)
+{
+	if (opt->buffer_output < 2 && opt->obuf.len) {
+		fputs(opt->obuf.buf, stdout);
+		strbuf_reset(&opt->obuf);
+	}
+}
+
+__attribute__((format (printf, 2, 3)))
+static int err(struct merge_options *opt, const char *err, ...)
+{
+	va_list params;
+
+	if (opt->buffer_output < 2)
+		flush_output(opt);
+	else {
+		strbuf_complete(&opt->obuf, '\n');
+		strbuf_addstr(&opt->obuf, "error: ");
+	}
+	va_start(params, err);
+	strbuf_vaddf(&opt->obuf, err, params);
+	va_end(params);
+	if (opt->buffer_output > 1)
+		strbuf_addch(&opt->obuf, '\n');
+	else {
+		error("%s", opt->obuf.buf);
+		strbuf_reset(&opt->obuf);
+	}
+
+	return -1;
+}
+
+static struct tree *shift_tree_object(struct repository *repo,
+				      struct tree *one, struct tree *two,
+				      const char *subtree_shift)
+{
+	struct object_id shifted;
+
+	if (!*subtree_shift) {
+		shift_tree(repo, &one->object.oid, &two->object.oid, &shifted, 0);
+	} else {
+		shift_tree_by(repo, &one->object.oid, &two->object.oid, &shifted,
+			      subtree_shift);
+	}
+	if (oideq(&two->object.oid, &shifted))
+		return two;
+	return lookup_tree(repo, &shifted);
+}
+
+static inline void set_commit_tree(struct commit *c, struct tree *t)
+{
+	c->maybe_tree = t;
+}
+
+static struct commit *make_virtual_commit(struct repository *repo,
+					  struct tree *tree,
+					  const char *comment)
+{
+	struct commit *commit = alloc_commit_node(repo);
+
+	set_merge_remote_desc(commit, comment, (struct object *)commit);
+	set_commit_tree(commit, tree);
+	commit->object.parsed = 1;
+	return commit;
+}
+
+enum rename_type {
+	RENAME_NORMAL = 0,
+	RENAME_VIA_DIR,
+	RENAME_ADD,
+	RENAME_DELETE,
+	RENAME_ONE_FILE_TO_ONE,
+	RENAME_ONE_FILE_TO_TWO,
+	RENAME_TWO_FILES_TO_ONE
+};
+
+/*
+ * Since we want to write the index eventually, we cannot reuse the index
+ * for these (temporary) data.
+ */
+struct stage_data {
+	struct diff_filespec stages[4]; /* mostly for oid & mode; maybe path */
+	struct rename_conflict_info *rename_conflict_info;
+	unsigned processed:1;
+};
+
+struct rename {
+	unsigned processed:1;
+	struct diff_filepair *pair;
+	const char *branch; /* branch that the rename occurred on */
+	/*
+	 * If directory rename detection affected this rename, what was its
+	 * original type ('A' or 'R') and it's original destination before
+	 * the directory rename (otherwise, '\0' and NULL for these two vars).
+	 */
+	char dir_rename_original_type;
+	char *dir_rename_original_dest;
+	/*
+	 * Purpose of src_entry and dst_entry:
+	 *
+	 * If 'before' is renamed to 'after' then src_entry will contain
+	 * the versions of 'before' from the merge_base, HEAD, and MERGE in
+	 * stages 1, 2, and 3; dst_entry will contain the respective
+	 * versions of 'after' in corresponding locations.  Thus, we have a
+	 * total of six modes and oids, though some will be null.  (Stage 0
+	 * is ignored; we're interested in handling conflicts.)
+	 *
+	 * Since we don't turn on break-rewrites by default, neither
+	 * src_entry nor dst_entry can have all three of their stages have
+	 * non-null oids, meaning at most four of the six will be non-null.
+	 * Also, since this is a rename, both src_entry and dst_entry will
+	 * have at least one non-null oid, meaning at least two will be
+	 * non-null.  Of the six oids, a typical rename will have three be
+	 * non-null.  Only two implies a rename/delete, and four implies a
+	 * rename/add.
+	 */
+	struct stage_data *src_entry;
+	struct stage_data *dst_entry;
+};
+
+struct rename_conflict_info {
+	enum rename_type rename_type;
+	struct rename *ren1;
+	struct rename *ren2;
+};
+
+static inline void setup_rename_conflict_info(enum rename_type rename_type,
+					      struct merge_options *opt,
+					      struct rename *ren1,
+					      struct rename *ren2)
+{
+	struct rename_conflict_info *ci;
+
+	/*
+	 * When we have two renames involved, it's easiest to get the
+	 * correct things into stage 2 and 3, and to make sure that the
+	 * content merge puts HEAD before the other branch if we just
+	 * ensure that branch1 == opt->branch1.  So, simply flip arguments
+	 * around if we don't have that.
+	 */
+	if (ren2 && ren1->branch != opt->branch1) {
+		setup_rename_conflict_info(rename_type, opt, ren2, ren1);
+		return;
+	}
+
+	CALLOC_ARRAY(ci, 1);
+	ci->rename_type = rename_type;
+	ci->ren1 = ren1;
+	ci->ren2 = ren2;
+
+	ci->ren1->dst_entry->processed = 0;
+	ci->ren1->dst_entry->rename_conflict_info = ci;
+	if (ren2) {
+		ci->ren2->dst_entry->rename_conflict_info = ci;
+	}
+}
+
+static int show(struct merge_options *opt, int v)
+{
+	return (!opt->priv->call_depth && opt->verbosity >= v) ||
+		opt->verbosity >= 5;
+}
+
+__attribute__((format (printf, 3, 4)))
+static void output(struct merge_options *opt, int v, const char *fmt, ...)
+{
+	va_list ap;
+
+	if (!show(opt, v))
+		return;
+
+	strbuf_addchars(&opt->obuf, ' ', opt->priv->call_depth * 2);
+
+	va_start(ap, fmt);
+	strbuf_vaddf(&opt->obuf, fmt, ap);
+	va_end(ap);
+
+	strbuf_addch(&opt->obuf, '\n');
+	if (!opt->buffer_output)
+		flush_output(opt);
+}
+
+static void repo_output_commit_title(struct merge_options *opt,
+				     struct repository *repo,
+				     struct commit *commit)
+{
+	struct merge_remote_desc *desc;
+
+	strbuf_addchars(&opt->obuf, ' ', opt->priv->call_depth * 2);
+	desc = merge_remote_util(commit);
+	if (desc)
+		strbuf_addf(&opt->obuf, "virtual %s\n", desc->name);
+	else {
+		strbuf_repo_add_unique_abbrev(&opt->obuf, repo,
+					      &commit->object.oid,
+					      DEFAULT_ABBREV);
+		strbuf_addch(&opt->obuf, ' ');
+		if (repo_parse_commit(repo, commit) != 0)
+			strbuf_addstr(&opt->obuf, _("(bad commit)\n"));
+		else {
+			const char *title;
+			const char *msg = repo_get_commit_buffer(repo, commit, NULL);
+			int len = find_commit_subject(msg, &title);
+			if (len)
+				strbuf_addf(&opt->obuf, "%.*s\n", len, title);
+			repo_unuse_commit_buffer(repo, commit, msg);
+		}
+	}
+	flush_output(opt);
+}
+
+static void output_commit_title(struct merge_options *opt, struct commit *commit)
+{
+	repo_output_commit_title(opt, the_repository, commit);
+}
+
+static int add_cacheinfo(struct merge_options *opt,
+			 const struct diff_filespec *blob,
+			 const char *path, int stage, int refresh, int options)
+{
+	struct index_state *istate = opt->repo->index;
+	struct cache_entry *ce;
+	int ret;
+
+	ce = make_cache_entry(istate, blob->mode, &blob->oid, path, stage, 0);
+	if (!ce)
+		return err(opt, _("add_cacheinfo failed for path '%s'; merge aborting."), path);
+
+	ret = add_index_entry(istate, ce, options);
+	if (refresh) {
+		struct cache_entry *nce;
+
+		nce = refresh_cache_entry(istate, ce,
+					  CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
+		if (!nce)
+			return err(opt, _("add_cacheinfo failed to refresh for path '%s'; merge aborting."), path);
+		if (nce != ce)
+			ret = add_index_entry(istate, nce, options);
+	}
+	return ret;
+}
+
+static inline int merge_detect_rename(struct merge_options *opt)
+{
+	return (opt->detect_renames >= 0) ? opt->detect_renames : 1;
+}
+
+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 unpack_trees_start(struct merge_options *opt,
+			      struct tree *common,
+			      struct tree *head,
+			      struct tree *merge)
+{
+	int rc;
+	struct tree_desc t[3];
+	struct index_state tmp_index = { NULL };
+
+	memset(&opt->priv->unpack_opts, 0, sizeof(opt->priv->unpack_opts));
+	if (opt->priv->call_depth)
+		opt->priv->unpack_opts.index_only = 1;
+	else {
+		opt->priv->unpack_opts.update = 1;
+		/* FIXME: should only do this if !overwrite_ignore */
+		opt->priv->unpack_opts.preserve_ignored = 0;
+	}
+	opt->priv->unpack_opts.merge = 1;
+	opt->priv->unpack_opts.head_idx = 2;
+	opt->priv->unpack_opts.fn = threeway_merge;
+	opt->priv->unpack_opts.src_index = opt->repo->index;
+	opt->priv->unpack_opts.dst_index = &tmp_index;
+	opt->priv->unpack_opts.aggressive = !merge_detect_rename(opt);
+	setup_unpack_trees_porcelain(&opt->priv->unpack_opts, "merge");
+
+	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, &opt->priv->unpack_opts);
+	cache_tree_free(&opt->repo->index->cache_tree);
+
+	/*
+	 * Update opt->repo->index to match the new results, AFTER saving a
+	 * copy in opt->priv->orig_index.  Update src_index to point to the
+	 * saved copy.  (verify_uptodate() checks src_index, and the original
+	 * index is the one that had the necessary modification timestamps.)
+	 */
+	opt->priv->orig_index = *opt->repo->index;
+	*opt->repo->index = tmp_index;
+	opt->priv->unpack_opts.src_index = &opt->priv->orig_index;
+
+	return rc;
+}
+
+static void unpack_trees_finish(struct merge_options *opt)
+{
+	discard_index(&opt->priv->orig_index);
+	clear_unpack_trees_porcelain(&opt->priv->unpack_opts);
+}
+
+static int save_files_dirs(const struct object_id *oid UNUSED,
+			   struct strbuf *base, const char *path,
+			   unsigned int mode, void *context)
+{
+	struct path_hashmap_entry *entry;
+	int baselen = base->len;
+	struct merge_options *opt = context;
+
+	strbuf_addstr(base, path);
+
+	FLEX_ALLOC_MEM(entry, path, base->buf, base->len);
+	hashmap_entry_init(&entry->e, fspathhash(entry->path));
+	hashmap_add(&opt->priv->current_file_dir_set, &entry->e);
+
+	strbuf_setlen(base, baselen);
+	return (S_ISDIR(mode) ? READ_TREE_RECURSIVE : 0);
+}
+
+static void get_files_dirs(struct merge_options *opt, struct tree *tree)
+{
+	struct pathspec match_all;
+	memset(&match_all, 0, sizeof(match_all));
+	read_tree(opt->repo, tree,
+		  &match_all, save_files_dirs, opt);
+}
+
+static int get_tree_entry_if_blob(struct repository *r,
+				  const struct object_id *tree,
+				  const char *path,
+				  struct diff_filespec *dfs)
+{
+	int ret;
+
+	ret = get_tree_entry(r, tree, path, &dfs->oid, &dfs->mode);
+	if (S_ISDIR(dfs->mode)) {
+		oidcpy(&dfs->oid, null_oid());
+		dfs->mode = 0;
+	}
+	return ret;
+}
+
+/*
+ * 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(struct repository *r,
+		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_if_blob(r, &o->object.oid, path, &e->stages[1]);
+	get_tree_entry_if_blob(r, &a->object.oid, path, &e->stages[2]);
+	get_tree_entry_if_blob(r, &b->object.oid, path, &e->stages[3]);
+	item = string_list_insert(entries, path);
+	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(struct index_state *istate)
+{
+	struct string_list *unmerged = xmalloc(sizeof(struct string_list));
+	int i;
+
+	string_list_init_dup(unmerged);
+
+	/* TODO: audit for interaction with sparse-index. */
+	ensure_full_index(istate);
+	for (i = 0; i < istate->cache_nr; i++) {
+		struct string_list_item *item;
+		struct stage_data *e;
+		const struct cache_entry *ce = istate->cache[i];
+		if (!ce_stage(ce))
+			continue;
+
+		item = string_list_lookup(unmerged, ce->name);
+		if (!item) {
+			item = string_list_insert(unmerged, ce->name);
+			item->util = xcalloc(1, sizeof(struct stage_data));
+		}
+		e = item->util;
+		e->stages[ce_stage(ce)].mode = ce->ce_mode;
+		oidcpy(&e->stages[ce_stage(ce)].oid, &ce->oid);
+	}
+
+	return unmerged;
+}
+
+static int string_list_df_name_compare(const char *one, const char *two)
+{
+	int onelen = strlen(one);
+	int twolen = strlen(two);
+	/*
+	 * Here we only care that entries for D/F conflicts are
+	 * adjacent, in particular with the file of the D/F conflict
+	 * appearing before files below the corresponding directory.
+	 * The order of the rest of the list is irrelevant for us.
+	 *
+	 * To achieve this, we sort with df_name_compare and provide
+	 * the mode S_IFDIR so that D/F conflicts will sort correctly.
+	 * We use the mode S_IFDIR for everything else for simplicity,
+	 * since in other cases any changes in their order due to
+	 * sorting cause no problems for us.
+	 */
+	int cmp = df_name_compare(one, onelen, S_IFDIR,
+				  two, twolen, S_IFDIR);
+	/*
+	 * Now that 'foo' and 'foo/bar' compare equal, we have to make sure
+	 * that 'foo' comes before 'foo/bar'.
+	 */
+	if (cmp)
+		return cmp;
+	return onelen - twolen;
+}
+
+static void record_df_conflict_files(struct merge_options *opt,
+				     struct string_list *entries)
+{
+	/* If there is a D/F conflict and the file for such a conflict
+	 * currently exists in the working tree, we want to allow it to be
+	 * removed to make room for the corresponding directory if needed.
+	 * The files underneath the directories of such D/F conflicts will
+	 * be processed before the corresponding file involved in the D/F
+	 * conflict.  If the D/F directory ends up being removed by the
+	 * merge, then we won't have to touch the D/F file.  If the D/F
+	 * directory needs to be written to the working copy, then the D/F
+	 * file will simply be removed (in make_room_for_path()) to make
+	 * room for the necessary paths.  Note that if both the directory
+	 * and the file need to be present, then the D/F file will be
+	 * reinstated with a new unique name at the time it is processed.
+	 */
+	struct string_list df_sorted_entries = STRING_LIST_INIT_NODUP;
+	const char *last_file = NULL;
+	int last_len = 0;
+	int i;
+
+	/*
+	 * If we're merging merge-bases, we don't want to bother with
+	 * any working directory changes.
+	 */
+	if (opt->priv->call_depth)
+		return;
+
+	/* Ensure D/F conflicts are adjacent in the entries list. */
+	for (i = 0; i < entries->nr; i++) {
+		struct string_list_item *next = &entries->items[i];
+		string_list_append(&df_sorted_entries, next->string)->util =
+				   next->util;
+	}
+	df_sorted_entries.cmp = string_list_df_name_compare;
+	string_list_sort(&df_sorted_entries);
+
+	string_list_clear(&opt->priv->df_conflict_file_set, 1);
+	for (i = 0; i < df_sorted_entries.nr; i++) {
+		const char *path = df_sorted_entries.items[i].string;
+		int len = strlen(path);
+		struct stage_data *e = df_sorted_entries.items[i].util;
+
+		/*
+		 * Check if last_file & path correspond to a D/F conflict;
+		 * i.e. whether path is last_file+'/'+<something>.
+		 * If so, record that it's okay to remove last_file to make
+		 * room for path and friends if needed.
+		 */
+		if (last_file &&
+		    len > last_len &&
+		    memcmp(path, last_file, last_len) == 0 &&
+		    path[last_len] == '/') {
+			string_list_insert(&opt->priv->df_conflict_file_set, last_file);
+		}
+
+		/*
+		 * Determine whether path could exist as a file in the
+		 * working directory as a possible D/F conflict.  This
+		 * will only occur when it exists in stage 2 as a
+		 * file.
+		 */
+		if (S_ISREG(e->stages[2].mode) || S_ISLNK(e->stages[2].mode)) {
+			last_file = path;
+			last_len = len;
+		} else {
+			last_file = NULL;
+		}
+	}
+	string_list_clear(&df_sorted_entries, 0);
+}
+
+static int update_stages(struct merge_options *opt, const char *path,
+			 const struct diff_filespec *o,
+			 const struct diff_filespec *a,
+			 const struct diff_filespec *b)
+{
+
+	/*
+	 * NOTE: It is usually a bad idea to call update_stages on a path
+	 * before calling update_file on that same path, since it can
+	 * sometimes lead to spurious "refusing to lose untracked file..."
+	 * messages from update_file (via make_room_for path via
+	 * would_lose_untracked).  Instead, reverse the order of the calls
+	 * (executing update_file first and then update_stages).
+	 */
+	int clear = 1;
+	int options = ADD_CACHE_OK_TO_ADD | ADD_CACHE_SKIP_DFCHECK;
+	if (clear)
+		if (remove_file_from_index(opt->repo->index, path))
+			return -1;
+	if (o)
+		if (add_cacheinfo(opt, o, path, 1, 0, options))
+			return -1;
+	if (a)
+		if (add_cacheinfo(opt, a, path, 2, 0, options))
+			return -1;
+	if (b)
+		if (add_cacheinfo(opt, b, path, 3, 0, options))
+			return -1;
+	return 0;
+}
+
+static void update_entry(struct stage_data *entry,
+			 struct diff_filespec *o,
+			 struct diff_filespec *a,
+			 struct diff_filespec *b)
+{
+	entry->processed = 0;
+	entry->stages[1].mode = o->mode;
+	entry->stages[2].mode = a->mode;
+	entry->stages[3].mode = b->mode;
+	oidcpy(&entry->stages[1].oid, &o->oid);
+	oidcpy(&entry->stages[2].oid, &a->oid);
+	oidcpy(&entry->stages[3].oid, &b->oid);
+}
+
+static int remove_file(struct merge_options *opt, int clean,
+		       const char *path, int no_wd)
+{
+	int update_cache = opt->priv->call_depth || clean;
+	int update_working_directory = !opt->priv->call_depth && !no_wd;
+
+	if (update_cache) {
+		if (remove_file_from_index(opt->repo->index, path))
+			return -1;
+	}
+	if (update_working_directory) {
+		if (ignore_case) {
+			struct cache_entry *ce;
+			ce = index_file_exists(opt->repo->index, path, strlen(path),
+					       ignore_case);
+			if (ce && ce_stage(ce) == 0 && strcmp(path, ce->name))
+				return 0;
+		}
+		if (remove_path(path))
+			return -1;
+	}
+	return 0;
+}
+
+/* add a string to a strbuf, but converting "/" to "_" */
+static void add_flattened_path(struct strbuf *out, const char *s)
+{
+	size_t i = out->len;
+	strbuf_addstr(out, s);
+	for (; i < out->len; i++)
+		if (out->buf[i] == '/')
+			out->buf[i] = '_';
+}
+
+static char *unique_path(struct merge_options *opt,
+			 const char *path,
+			 const char *branch)
+{
+	struct path_hashmap_entry *entry;
+	struct strbuf newpath = STRBUF_INIT;
+	int suffix = 0;
+	size_t base_len;
+
+	strbuf_addf(&newpath, "%s~", path);
+	add_flattened_path(&newpath, branch);
+
+	base_len = newpath.len;
+	while (hashmap_get_from_hash(&opt->priv->current_file_dir_set,
+				     fspathhash(newpath.buf), newpath.buf) ||
+	       (!opt->priv->call_depth && file_exists(newpath.buf))) {
+		strbuf_setlen(&newpath, base_len);
+		strbuf_addf(&newpath, "_%d", suffix++);
+	}
+
+	FLEX_ALLOC_MEM(entry, path, newpath.buf, newpath.len);
+	hashmap_entry_init(&entry->e, fspathhash(entry->path));
+	hashmap_add(&opt->priv->current_file_dir_set, &entry->e);
+	return strbuf_detach(&newpath, NULL);
+}
+
+/**
+ * Check whether a directory in the index is in the way of an incoming
+ * file.  Return 1 if so.  If check_working_copy is non-zero, also
+ * check the working directory.  If empty_ok is non-zero, also return
+ * 0 in the case where the working-tree dir exists but is empty.
+ */
+static int dir_in_way(struct index_state *istate, const char *path,
+		      int check_working_copy, int empty_ok)
+{
+	int pos;
+	struct strbuf dirpath = STRBUF_INIT;
+	struct stat st;
+
+	strbuf_addstr(&dirpath, path);
+	strbuf_addch(&dirpath, '/');
+
+	pos = index_name_pos(istate, dirpath.buf, dirpath.len);
+
+	if (pos < 0)
+		pos = -1 - pos;
+	if (pos < istate->cache_nr &&
+	    !strncmp(dirpath.buf, istate->cache[pos]->name, dirpath.len)) {
+		strbuf_release(&dirpath);
+		return 1;
+	}
+
+	strbuf_release(&dirpath);
+	return check_working_copy && !lstat(path, &st) && S_ISDIR(st.st_mode) &&
+		!(empty_ok && is_empty_dir(path)) &&
+		!has_symlink_leading_path(path, strlen(path));
+}
+
+/*
+ * Returns whether path was tracked in the index before the merge started,
+ * and its oid and mode match the specified values
+ */
+static int was_tracked_and_matches(struct merge_options *opt, const char *path,
+				   const struct diff_filespec *blob)
+{
+	int pos = index_name_pos(&opt->priv->orig_index, path, strlen(path));
+	struct cache_entry *ce;
+
+	if (0 > pos)
+		/* we were not tracking this path before the merge */
+		return 0;
+
+	/* See if the file we were tracking before matches */
+	ce = opt->priv->orig_index.cache[pos];
+	return (oideq(&ce->oid, &blob->oid) && ce->ce_mode == blob->mode);
+}
+
+/*
+ * Returns whether path was tracked in the index before the merge started
+ */
+static int was_tracked(struct merge_options *opt, const char *path)
+{
+	int pos = index_name_pos(&opt->priv->orig_index, path, strlen(path));
+
+	if (0 <= pos)
+		/* we were tracking this path before the merge */
+		return 1;
+
+	return 0;
+}
+
+static int would_lose_untracked(struct merge_options *opt, const char *path)
+{
+	struct index_state *istate = opt->repo->index;
+
+	/*
+	 * This may look like it can be simplified to:
+	 *   return !was_tracked(opt, path) && file_exists(path)
+	 * but it can't.  This function needs to know whether path was in
+	 * the working tree due to EITHER having been tracked in the index
+	 * before the merge OR having been put into the working copy and
+	 * index by unpack_trees().  Due to that either-or requirement, we
+	 * check the current index instead of the original one.
+	 *
+	 * Note that we do not need to worry about merge-recursive itself
+	 * updating the index after unpack_trees() and before calling this
+	 * function, because we strictly require all code paths in
+	 * merge-recursive to update the working tree first and the index
+	 * second.  Doing otherwise would break
+	 * update_file()/would_lose_untracked(); see every comment in this
+	 * file which mentions "update_stages".
+	 */
+	int pos = index_name_pos(istate, path, strlen(path));
+
+	if (pos < 0)
+		pos = -1 - pos;
+	while (pos < istate->cache_nr &&
+	       !strcmp(path, istate->cache[pos]->name)) {
+		/*
+		 * If stage #0, it is definitely tracked.
+		 * If it has stage #2 then it was tracked
+		 * before this merge started.  All other
+		 * cases the path was not tracked.
+		 */
+		switch (ce_stage(istate->cache[pos])) {
+		case 0:
+		case 2:
+			return 0;
+		}
+		pos++;
+	}
+	return file_exists(path);
+}
+
+static int was_dirty(struct merge_options *opt, const char *path)
+{
+	struct cache_entry *ce;
+	int dirty = 1;
+
+	if (opt->priv->call_depth || !was_tracked(opt, path))
+		return !dirty;
+
+	ce = index_file_exists(opt->priv->unpack_opts.src_index,
+			       path, strlen(path), ignore_case);
+	dirty = verify_uptodate(ce, &opt->priv->unpack_opts) != 0;
+	return dirty;
+}
+
+static int make_room_for_path(struct merge_options *opt, const char *path)
+{
+	int status, i;
+	const char *msg = _("failed to create path '%s'%s");
+
+	/* Unlink any D/F conflict files that are in the way */
+	for (i = 0; i < opt->priv->df_conflict_file_set.nr; i++) {
+		const char *df_path = opt->priv->df_conflict_file_set.items[i].string;
+		size_t pathlen = strlen(path);
+		size_t df_pathlen = strlen(df_path);
+		if (df_pathlen < pathlen &&
+		    path[df_pathlen] == '/' &&
+		    strncmp(path, df_path, df_pathlen) == 0) {
+			output(opt, 3,
+			       _("Removing %s to make room for subdirectory\n"),
+			       df_path);
+			unlink(df_path);
+			unsorted_string_list_delete_item(&opt->priv->df_conflict_file_set,
+							 i, 0);
+			break;
+		}
+	}
+
+	/* Make sure leading directories are created */
+	status = safe_create_leading_directories_const(path);
+	if (status) {
+		if (status == SCLD_EXISTS)
+			/* something else exists */
+			return err(opt, msg, path, _(": perhaps a D/F conflict?"));
+		return err(opt, msg, path, "");
+	}
+
+	/*
+	 * Do not unlink a file in the work tree if we are not
+	 * tracking it.
+	 */
+	if (would_lose_untracked(opt, path))
+		return err(opt, _("refusing to lose untracked file at '%s'"),
+			   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 err(opt, msg, path, _(": perhaps a D/F conflict?"));
+}
+
+static int update_file_flags(struct merge_options *opt,
+			     const struct diff_filespec *contents,
+			     const char *path,
+			     int update_cache,
+			     int update_wd)
+{
+	int ret = 0;
+
+	if (opt->priv->call_depth)
+		update_wd = 0;
+
+	if (update_wd) {
+		enum object_type type;
+		void *buf;
+		unsigned long size;
+
+		if (S_ISGITLINK(contents->mode)) {
+			/*
+			 * We may later decide to recursively descend into
+			 * the submodule directory and update its index
+			 * and/or work tree, but we do not do that now.
+			 */
+			update_wd = 0;
+			goto update_index;
+		}
+
+		buf = read_object_file(&contents->oid, &type, &size);
+		if (!buf) {
+			ret = err(opt, _("cannot read object %s '%s'"),
+				  oid_to_hex(&contents->oid), path);
+			goto free_buf;
+		}
+		if (type != OBJ_BLOB) {
+			ret = err(opt, _("blob expected for %s '%s'"),
+				  oid_to_hex(&contents->oid), path);
+			goto free_buf;
+		}
+		if (S_ISREG(contents->mode)) {
+			struct strbuf strbuf = STRBUF_INIT;
+			if (convert_to_working_tree(opt->repo->index,
+						    path, buf, size, &strbuf, NULL)) {
+				free(buf);
+				size = strbuf.len;
+				buf = strbuf_detach(&strbuf, NULL);
+			}
+		}
+
+		if (make_room_for_path(opt, path) < 0) {
+			update_wd = 0;
+			goto free_buf;
+		}
+		if (S_ISREG(contents->mode) ||
+		    (!has_symlinks && S_ISLNK(contents->mode))) {
+			int fd;
+			int mode = (contents->mode & 0100 ? 0777 : 0666);
+
+			fd = open(path, O_WRONLY | O_TRUNC | O_CREAT, mode);
+			if (fd < 0) {
+				ret = err(opt, _("failed to open '%s': %s"),
+					  path, strerror(errno));
+				goto free_buf;
+			}
+			write_in_full(fd, buf, size);
+			close(fd);
+		} else if (S_ISLNK(contents->mode)) {
+			char *lnk = xmemdupz(buf, size);
+			safe_create_leading_directories_const(path);
+			unlink(path);
+			if (symlink(lnk, path))
+				ret = err(opt, _("failed to symlink '%s': %s"),
+					  path, strerror(errno));
+			free(lnk);
+		} else
+			ret = err(opt,
+				  _("do not know what to do with %06o %s '%s'"),
+				  contents->mode, oid_to_hex(&contents->oid), path);
+	free_buf:
+		free(buf);
+	}
+update_index:
+	if (!ret && update_cache) {
+		int refresh = (!opt->priv->call_depth &&
+			       contents->mode != S_IFGITLINK);
+		if (add_cacheinfo(opt, contents, path, 0, refresh,
+				  ADD_CACHE_OK_TO_ADD))
+			return -1;
+	}
+	return ret;
+}
+
+static int update_file(struct merge_options *opt,
+		       int clean,
+		       const struct diff_filespec *contents,
+		       const char *path)
+{
+	return update_file_flags(opt, contents, path,
+				 opt->priv->call_depth || clean, !opt->priv->call_depth);
+}
+
+/* Low level file merging, update and removal */
+
+struct merge_file_info {
+	struct diff_filespec blob; /* mostly use oid & mode; sometimes path */
+	unsigned clean:1,
+		 merge:1;
+};
+
+static int merge_3way(struct merge_options *opt,
+		      mmbuffer_t *result_buf,
+		      const struct diff_filespec *o,
+		      const struct diff_filespec *a,
+		      const struct diff_filespec *b,
+		      const char *branch1,
+		      const char *branch2,
+		      const int extra_marker_size)
+{
+	mmfile_t orig, src1, src2;
+	struct ll_merge_options ll_opts = {0};
+	char *base, *name1, *name2;
+	enum ll_merge_result merge_status;
+
+	ll_opts.renormalize = opt->renormalize;
+	ll_opts.extra_marker_size = extra_marker_size;
+	ll_opts.xdl_opts = opt->xdl_opts;
+
+	if (opt->priv->call_depth) {
+		ll_opts.virtual_ancestor = 1;
+		ll_opts.variant = 0;
+	} else {
+		switch (opt->recursive_variant) {
+		case MERGE_VARIANT_OURS:
+			ll_opts.variant = XDL_MERGE_FAVOR_OURS;
+			break;
+		case MERGE_VARIANT_THEIRS:
+			ll_opts.variant = XDL_MERGE_FAVOR_THEIRS;
+			break;
+		default:
+			ll_opts.variant = 0;
+			break;
+		}
+	}
+
+	assert(a->path && b->path && o->path && opt->ancestor);
+	if (strcmp(a->path, b->path) || strcmp(a->path, o->path) != 0) {
+		base  = mkpathdup("%s:%s", opt->ancestor, o->path);
+		name1 = mkpathdup("%s:%s", branch1, a->path);
+		name2 = mkpathdup("%s:%s", branch2, b->path);
+	} else {
+		base  = mkpathdup("%s", opt->ancestor);
+		name1 = mkpathdup("%s", branch1);
+		name2 = mkpathdup("%s", branch2);
+	}
+
+	read_mmblob(&orig, &o->oid);
+	read_mmblob(&src1, &a->oid);
+	read_mmblob(&src2, &b->oid);
+
+	/*
+	 * FIXME: Using a->path for normalization rules in ll_merge could be
+	 * wrong if we renamed from a->path to b->path.  We should use the
+	 * target path for where the file will be written.
+	 */
+	merge_status = ll_merge(result_buf, a->path, &orig, base,
+				&src1, name1, &src2, name2,
+				opt->repo->index, &ll_opts);
+	if (merge_status == LL_MERGE_BINARY_CONFLICT)
+		warning("Cannot merge binary files: %s (%s vs. %s)",
+			a->path, name1, name2);
+
+	free(base);
+	free(name1);
+	free(name2);
+	free(orig.ptr);
+	free(src1.ptr);
+	free(src2.ptr);
+	return merge_status;
+}
+
+static int find_first_merges(struct repository *repo,
+			     struct object_array *result, const char *path,
+			     struct commit *a, struct commit *b)
+{
+	int i, j;
+	struct object_array merges = OBJECT_ARRAY_INIT;
+	struct commit *commit;
+	int contains_another;
+
+	char merged_revision[GIT_MAX_HEXSZ + 2];
+	const char *rev_args[] = { "rev-list", "--merges", "--ancestry-path",
+				   "--all", merged_revision, NULL };
+	struct rev_info revs;
+	struct setup_revision_opt rev_opts;
+
+	memset(result, 0, sizeof(struct object_array));
+	memset(&rev_opts, 0, sizeof(rev_opts));
+
+	/* get all revisions that merge commit a */
+	xsnprintf(merged_revision, sizeof(merged_revision), "^%s",
+		  oid_to_hex(&a->object.oid));
+	repo_init_revisions(repo, &revs, NULL);
+	/* FIXME: can't handle linked worktrees in submodules yet */
+	revs.single_worktree = path != NULL;
+	setup_revisions(ARRAY_SIZE(rev_args)-1, rev_args, &revs, &rev_opts);
+
+	/* save all revisions from the above list that contain b */
+	if (prepare_revision_walk(&revs))
+		die("revision walk setup failed");
+	while ((commit = get_revision(&revs)) != NULL) {
+		struct object *o = &(commit->object);
+		if (repo_in_merge_bases(repo, b, commit))
+			add_object_array(o, NULL, &merges);
+	}
+	reset_revision_walk();
+
+	/* Now we've got all merges that contain a and b. Prune all
+	 * merges that contain another found merge and save them in
+	 * result.
+	 */
+	for (i = 0; i < merges.nr; i++) {
+		struct commit *m1 = (struct commit *) merges.objects[i].item;
+
+		contains_another = 0;
+		for (j = 0; j < merges.nr; j++) {
+			struct commit *m2 = (struct commit *) merges.objects[j].item;
+			if (i != j && repo_in_merge_bases(repo, m2, m1)) {
+				contains_another = 1;
+				break;
+			}
+		}
+
+		if (!contains_another)
+			add_object_array(merges.objects[i].item, NULL, result);
+	}
+
+	object_array_clear(&merges);
+	release_revisions(&revs);
+	return result->nr;
+}
+
+static void print_commit(struct repository *repo, struct commit *commit)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct pretty_print_context ctx = {0};
+	ctx.date_mode.type = DATE_NORMAL;
+	/* FIXME: Merge this with output_commit_title() */
+	assert(!merge_remote_util(commit));
+	repo_format_commit_message(repo, commit, " %h: %m %s", &sb, &ctx);
+	fprintf(stderr, "%s\n", sb.buf);
+	strbuf_release(&sb);
+}
+
+static int is_valid(const struct diff_filespec *dfs)
+{
+	return dfs->mode != 0 && !is_null_oid(&dfs->oid);
+}
+
+static int merge_submodule(struct merge_options *opt,
+			   struct object_id *result, const char *path,
+			   const struct object_id *base, const struct object_id *a,
+			   const struct object_id *b)
+{
+	struct repository subrepo;
+	int ret = 0;
+	struct commit *commit_base, *commit_a, *commit_b;
+	int parent_count;
+	struct object_array merges;
+
+	int i;
+	int search = !opt->priv->call_depth;
+
+	/* store a in result in case we fail */
+	/* FIXME: This is the WRONG resolution for the recursive case when
+	 * we need to be careful to avoid accidentally matching either side.
+	 * Should probably use o instead there, much like we do for merging
+	 * binaries.
+	 */
+	oidcpy(result, a);
+
+	/* we can not handle deletion conflicts */
+	if (is_null_oid(base))
+		return 0;
+	if (is_null_oid(a))
+		return 0;
+	if (is_null_oid(b))
+		return 0;
+
+	if (repo_submodule_init(&subrepo, opt->repo, path, null_oid())) {
+		output(opt, 1, _("Failed to merge submodule %s (not checked out)"), path);
+		return 0;
+	}
+
+	if (!(commit_base = lookup_commit_reference(&subrepo, base)) ||
+	    !(commit_a = lookup_commit_reference(&subrepo, a)) ||
+	    !(commit_b = lookup_commit_reference(&subrepo, b))) {
+		output(opt, 1, _("Failed to merge submodule %s (commits not present)"), path);
+		goto cleanup;
+	}
+
+	/* check whether both changes are forward */
+	if (!repo_in_merge_bases(&subrepo, commit_base, commit_a) ||
+	    !repo_in_merge_bases(&subrepo, commit_base, commit_b)) {
+		output(opt, 1, _("Failed to merge submodule %s (commits don't follow merge-base)"), path);
+		goto cleanup;
+	}
+
+	/* Case #1: a is contained in b or vice versa */
+	if (repo_in_merge_bases(&subrepo, commit_a, commit_b)) {
+		oidcpy(result, b);
+		if (show(opt, 3)) {
+			output(opt, 3, _("Fast-forwarding submodule %s to the following commit:"), path);
+			repo_output_commit_title(opt, &subrepo, commit_b);
+		} else if (show(opt, 2))
+			output(opt, 2, _("Fast-forwarding submodule %s"), path);
+		else
+			; /* no output */
+
+		ret = 1;
+		goto cleanup;
+	}
+	if (repo_in_merge_bases(&subrepo, commit_b, commit_a)) {
+		oidcpy(result, a);
+		if (show(opt, 3)) {
+			output(opt, 3, _("Fast-forwarding submodule %s to the following commit:"), path);
+			repo_output_commit_title(opt, &subrepo, commit_a);
+		} else if (show(opt, 2))
+			output(opt, 2, _("Fast-forwarding submodule %s"), path);
+		else
+			; /* no output */
+
+		ret = 1;
+		goto cleanup;
+	}
+
+	/*
+	 * Case #2: There are one or more merges that contain a and b in
+	 * the submodule. If there is only one, then present it as a
+	 * suggestion to the user, but leave it marked unmerged so the
+	 * user needs to confirm the resolution.
+	 */
+
+	/* Skip the search if makes no sense to the calling context.  */
+	if (!search)
+		goto cleanup;
+
+	/* find commit which merges them */
+	parent_count = find_first_merges(&subrepo, &merges, path,
+					 commit_a, commit_b);
+	switch (parent_count) {
+	case 0:
+		output(opt, 1, _("Failed to merge submodule %s (merge following commits not found)"), path);
+		break;
+
+	case 1:
+		output(opt, 1, _("Failed to merge submodule %s (not fast-forward)"), path);
+		output(opt, 2, _("Found a possible merge resolution for the submodule:\n"));
+		print_commit(&subrepo, (struct commit *) merges.objects[0].item);
+		output(opt, 2, _(
+		       "If this is correct simply add it to the index "
+		       "for example\n"
+		       "by using:\n\n"
+		       "  git update-index --cacheinfo 160000 %s \"%s\"\n\n"
+		       "which will accept this suggestion.\n"),
+		       oid_to_hex(&merges.objects[0].item->oid), path);
+		break;
+
+	default:
+		output(opt, 1, _("Failed to merge submodule %s (multiple merges found)"), path);
+		for (i = 0; i < merges.nr; i++)
+			print_commit(&subrepo, (struct commit *) merges.objects[i].item);
+	}
+
+	object_array_clear(&merges);
+cleanup:
+	repo_clear(&subrepo);
+	return ret;
+}
+
+static int merge_mode_and_contents(struct merge_options *opt,
+				   const struct diff_filespec *o,
+				   const struct diff_filespec *a,
+				   const struct diff_filespec *b,
+				   const char *filename,
+				   const char *branch1,
+				   const char *branch2,
+				   const int extra_marker_size,
+				   struct merge_file_info *result)
+{
+	if (opt->branch1 != branch1) {
+		/*
+		 * It's weird getting a reverse merge with HEAD on the bottom
+		 * side of the conflict markers and the other branch on the
+		 * top.  Fix that.
+		 */
+		return merge_mode_and_contents(opt, o, b, a,
+					       filename,
+					       branch2, branch1,
+					       extra_marker_size, result);
+	}
+
+	result->merge = 0;
+	result->clean = 1;
+
+	if ((S_IFMT & a->mode) != (S_IFMT & b->mode)) {
+		result->clean = 0;
+		/*
+		 * FIXME: This is a bad resolution for recursive case; for
+		 * the recursive case we want something that is unlikely to
+		 * accidentally match either side.  Also, while it makes
+		 * sense to prefer regular files over symlinks, it doesn't
+		 * make sense to prefer regular files over submodules.
+		 */
+		if (S_ISREG(a->mode)) {
+			result->blob.mode = a->mode;
+			oidcpy(&result->blob.oid, &a->oid);
+		} else {
+			result->blob.mode = b->mode;
+			oidcpy(&result->blob.oid, &b->oid);
+		}
+	} else {
+		if (!oideq(&a->oid, &o->oid) && !oideq(&b->oid, &o->oid))
+			result->merge = 1;
+
+		/*
+		 * Merge modes
+		 */
+		if (a->mode == b->mode || a->mode == o->mode)
+			result->blob.mode = b->mode;
+		else {
+			result->blob.mode = a->mode;
+			if (b->mode != o->mode) {
+				result->clean = 0;
+				result->merge = 1;
+			}
+		}
+
+		if (oideq(&a->oid, &b->oid) || oideq(&a->oid, &o->oid))
+			oidcpy(&result->blob.oid, &b->oid);
+		else if (oideq(&b->oid, &o->oid))
+			oidcpy(&result->blob.oid, &a->oid);
+		else if (S_ISREG(a->mode)) {
+			mmbuffer_t result_buf;
+			int ret = 0, merge_status;
+
+			merge_status = merge_3way(opt, &result_buf, o, a, b,
+						  branch1, branch2,
+						  extra_marker_size);
+
+			if ((merge_status < 0) || !result_buf.ptr)
+				ret = err(opt, _("Failed to execute internal merge"));
+
+			if (!ret &&
+			    write_object_file(result_buf.ptr, result_buf.size,
+					      OBJ_BLOB, &result->blob.oid))
+				ret = err(opt, _("Unable to add %s to database"),
+					  a->path);
+
+			free(result_buf.ptr);
+			if (ret)
+				return ret;
+			/* FIXME: bug, what if modes didn't match? */
+			result->clean = (merge_status == 0);
+		} else if (S_ISGITLINK(a->mode)) {
+			result->clean = merge_submodule(opt, &result->blob.oid,
+							o->path,
+							&o->oid,
+							&a->oid,
+							&b->oid);
+		} else if (S_ISLNK(a->mode)) {
+			switch (opt->recursive_variant) {
+			case MERGE_VARIANT_NORMAL:
+				oidcpy(&result->blob.oid, &a->oid);
+				if (!oideq(&a->oid, &b->oid))
+					result->clean = 0;
+				break;
+			case MERGE_VARIANT_OURS:
+				oidcpy(&result->blob.oid, &a->oid);
+				break;
+			case MERGE_VARIANT_THEIRS:
+				oidcpy(&result->blob.oid, &b->oid);
+				break;
+			}
+		} else
+			BUG("unsupported object type in the tree");
+	}
+
+	if (result->merge)
+		output(opt, 2, _("Auto-merging %s"), filename);
+
+	return 0;
+}
+
+static int handle_rename_via_dir(struct merge_options *opt,
+				 struct rename_conflict_info *ci)
+{
+	/*
+	 * Handle file adds that need to be renamed due to directory rename
+	 * detection.  This differs from handle_rename_normal, because
+	 * there is no content merge to do; just move the file into the
+	 * desired final location.
+	 */
+	const struct rename *ren = ci->ren1;
+	const struct diff_filespec *dest = ren->pair->two;
+	char *file_path = dest->path;
+	int mark_conflicted = (opt->detect_directory_renames ==
+			       MERGE_DIRECTORY_RENAMES_CONFLICT);
+	assert(ren->dir_rename_original_dest);
+
+	if (!opt->priv->call_depth && would_lose_untracked(opt, dest->path)) {
+		mark_conflicted = 1;
+		file_path = unique_path(opt, dest->path, ren->branch);
+		output(opt, 1, _("Error: Refusing to lose untracked file at %s; "
+				 "writing to %s instead."),
+		       dest->path, file_path);
+	}
+
+	if (mark_conflicted) {
+		/*
+		 * Write the file in worktree at file_path.  In the index,
+		 * only record the file at dest->path in the appropriate
+		 * higher stage.
+		 */
+		if (update_file(opt, 0, dest, file_path))
+			return -1;
+		if (file_path != dest->path)
+			free(file_path);
+		if (update_stages(opt, dest->path, NULL,
+				  ren->branch == opt->branch1 ? dest : NULL,
+				  ren->branch == opt->branch1 ? NULL : dest))
+			return -1;
+		return 0; /* not clean, but conflicted */
+	} else {
+		/* Update dest->path both in index and in worktree */
+		if (update_file(opt, 1, dest, dest->path))
+			return -1;
+		return 1; /* clean */
+	}
+}
+
+static int handle_change_delete(struct merge_options *opt,
+				const char *path, const char *old_path,
+				const struct diff_filespec *o,
+				const struct diff_filespec *changed,
+				const char *change_branch,
+				const char *delete_branch,
+				const char *change, const char *change_past)
+{
+	char *alt_path = NULL;
+	const char *update_path = path;
+	int ret = 0;
+
+	if (dir_in_way(opt->repo->index, path, !opt->priv->call_depth, 0) ||
+	    (!opt->priv->call_depth && would_lose_untracked(opt, path))) {
+		update_path = alt_path = unique_path(opt, path, change_branch);
+	}
+
+	if (opt->priv->call_depth) {
+		/*
+		 * We cannot arbitrarily accept either a_sha or b_sha as
+		 * correct; since there is no true "middle point" between
+		 * them, simply reuse the base version for virtual merge base.
+		 */
+		ret = remove_file_from_index(opt->repo->index, path);
+		if (!ret)
+			ret = update_file(opt, 0, o, update_path);
+	} else {
+		/*
+		 * Despite the four nearly duplicate messages and argument
+		 * lists below and the ugliness of the nested if-statements,
+		 * having complete messages makes the job easier for
+		 * translators.
+		 *
+		 * The slight variance among the cases is due to the fact
+		 * that:
+		 *   1) directory/file conflicts (in effect if
+		 *      !alt_path) could cause us to need to write the
+		 *      file to a different path.
+		 *   2) renames (in effect if !old_path) could mean that
+		 *      there are two names for the path that the user
+		 *      may know the file by.
+		 */
+		if (!alt_path) {
+			if (!old_path) {
+				output(opt, 1, _("CONFLICT (%s/delete): %s deleted in %s "
+				       "and %s in %s. Version %s of %s left in tree."),
+				       change, path, delete_branch, change_past,
+				       change_branch, change_branch, path);
+			} else {
+				output(opt, 1, _("CONFLICT (%s/delete): %s deleted in %s "
+				       "and %s to %s in %s. Version %s of %s left in tree."),
+				       change, old_path, delete_branch, change_past, path,
+				       change_branch, change_branch, path);
+			}
+		} else {
+			if (!old_path) {
+				output(opt, 1, _("CONFLICT (%s/delete): %s deleted in %s "
+				       "and %s in %s. Version %s of %s left in tree at %s."),
+				       change, path, delete_branch, change_past,
+				       change_branch, change_branch, path, alt_path);
+			} else {
+				output(opt, 1, _("CONFLICT (%s/delete): %s deleted in %s "
+				       "and %s to %s in %s. Version %s of %s left in tree at %s."),
+				       change, old_path, delete_branch, change_past, path,
+				       change_branch, change_branch, path, alt_path);
+			}
+		}
+		/*
+		 * No need to call update_file() on path when change_branch ==
+		 * opt->branch1 && !alt_path, since that would needlessly touch
+		 * path.  We could call update_file_flags() with update_cache=0
+		 * and update_wd=0, but that's a no-op.
+		 */
+		if (change_branch != opt->branch1 || alt_path)
+			ret = update_file(opt, 0, changed, update_path);
+	}
+	free(alt_path);
+
+	return ret;
+}
+
+static int handle_rename_delete(struct merge_options *opt,
+				struct rename_conflict_info *ci)
+{
+	const struct rename *ren = ci->ren1;
+	const struct diff_filespec *orig = ren->pair->one;
+	const struct diff_filespec *dest = ren->pair->two;
+	const char *rename_branch = ren->branch;
+	const char *delete_branch = (opt->branch1 == ren->branch ?
+				     opt->branch2 : opt->branch1);
+
+	if (handle_change_delete(opt,
+				 opt->priv->call_depth ? orig->path : dest->path,
+				 opt->priv->call_depth ? NULL : orig->path,
+				 orig, dest,
+				 rename_branch, delete_branch,
+				 _("rename"), _("renamed")))
+		return -1;
+
+	if (opt->priv->call_depth)
+		return remove_file_from_index(opt->repo->index, dest->path);
+	else
+		return update_stages(opt, dest->path, NULL,
+				     rename_branch == opt->branch1 ? dest : NULL,
+				     rename_branch == opt->branch1 ? NULL : dest);
+}
+
+static int handle_file_collision(struct merge_options *opt,
+				 const char *collide_path,
+				 const char *prev_path1,
+				 const char *prev_path2,
+				 const char *branch1, const char *branch2,
+				 struct diff_filespec *a,
+				 struct diff_filespec *b)
+{
+	struct merge_file_info mfi;
+	struct diff_filespec null;
+	char *alt_path = NULL;
+	const char *update_path = collide_path;
+
+	/*
+	 * It's easiest to get the correct things into stage 2 and 3, and
+	 * to make sure that the content merge puts HEAD before the other
+	 * branch if we just ensure that branch1 == opt->branch1.  So, simply
+	 * flip arguments around if we don't have that.
+	 */
+	if (branch1 != opt->branch1) {
+		return handle_file_collision(opt, collide_path,
+					     prev_path2, prev_path1,
+					     branch2, branch1,
+					     b, a);
+	}
+
+	/* Remove rename sources if rename/add or rename/rename(2to1) */
+	if (prev_path1)
+		remove_file(opt, 1, prev_path1,
+			    opt->priv->call_depth || would_lose_untracked(opt, prev_path1));
+	if (prev_path2)
+		remove_file(opt, 1, prev_path2,
+			    opt->priv->call_depth || would_lose_untracked(opt, prev_path2));
+
+	/*
+	 * Remove the collision path, if it wouldn't cause dirty contents
+	 * or an untracked file to get lost.  We'll either overwrite with
+	 * merged contents, or just write out to differently named files.
+	 */
+	if (was_dirty(opt, collide_path)) {
+		output(opt, 1, _("Refusing to lose dirty file at %s"),
+		       collide_path);
+		update_path = alt_path = unique_path(opt, collide_path, "merged");
+	} else if (would_lose_untracked(opt, collide_path)) {
+		/*
+		 * Only way we get here is if both renames were from
+		 * a directory rename AND user had an untracked file
+		 * at the location where both files end up after the
+		 * two directory renames.  See testcase 10d of t6043.
+		 */
+		output(opt, 1, _("Refusing to lose untracked file at "
+			       "%s, even though it's in the way."),
+		       collide_path);
+		update_path = alt_path = unique_path(opt, collide_path, "merged");
+	} else {
+		/*
+		 * FIXME: It's possible that the two files are identical
+		 * and that the current working copy happens to match, in
+		 * which case we are unnecessarily touching the working
+		 * tree file.  It's not a likely enough scenario that I
+		 * want to code up the checks for it and a better fix is
+		 * available if we restructure how unpack_trees() and
+		 * merge-recursive interoperate anyway, so punting for
+		 * now...
+		 */
+		remove_file(opt, 0, collide_path, 0);
+	}
+
+	/* Store things in diff_filespecs for functions that need it */
+	null.path = (char *)collide_path;
+	oidcpy(&null.oid, null_oid());
+	null.mode = 0;
+
+	if (merge_mode_and_contents(opt, &null, a, b, collide_path,
+				    branch1, branch2, opt->priv->call_depth * 2, &mfi))
+		return -1;
+	mfi.clean &= !alt_path;
+	if (update_file(opt, mfi.clean, &mfi.blob, update_path))
+		return -1;
+	if (!mfi.clean && !opt->priv->call_depth &&
+	    update_stages(opt, collide_path, NULL, a, b))
+		return -1;
+	free(alt_path);
+	/*
+	 * FIXME: If both a & b both started with conflicts (only possible
+	 * if they came from a rename/rename(2to1)), but had IDENTICAL
+	 * contents including those conflicts, then in the next line we claim
+	 * it was clean.  If someone cares about this case, we should have the
+	 * caller notify us if we started with conflicts.
+	 */
+	return mfi.clean;
+}
+
+static int handle_rename_add(struct merge_options *opt,
+			     struct rename_conflict_info *ci)
+{
+	/* a was renamed to c, and a separate c was added. */
+	struct diff_filespec *a = ci->ren1->pair->one;
+	struct diff_filespec *c = ci->ren1->pair->two;
+	char *path = c->path;
+	char *prev_path_desc;
+	struct merge_file_info mfi;
+
+	const char *rename_branch = ci->ren1->branch;
+	const char *add_branch = (opt->branch1 == rename_branch ?
+				  opt->branch2 : opt->branch1);
+	int other_stage = (ci->ren1->branch == opt->branch1 ? 3 : 2);
+
+	output(opt, 1, _("CONFLICT (rename/add): "
+	       "Rename %s->%s in %s.  Added %s in %s"),
+	       a->path, c->path, rename_branch,
+	       c->path, add_branch);
+
+	prev_path_desc = xstrfmt("version of %s from %s", path, a->path);
+	ci->ren1->src_entry->stages[other_stage].path = a->path;
+	if (merge_mode_and_contents(opt, a, c,
+				    &ci->ren1->src_entry->stages[other_stage],
+				    prev_path_desc,
+				    opt->branch1, opt->branch2,
+				    1 + opt->priv->call_depth * 2, &mfi))
+		return -1;
+	free(prev_path_desc);
+
+	ci->ren1->dst_entry->stages[other_stage].path = mfi.blob.path = c->path;
+	return handle_file_collision(opt,
+				     c->path, a->path, NULL,
+				     rename_branch, add_branch,
+				     &mfi.blob,
+				     &ci->ren1->dst_entry->stages[other_stage]);
+}
+
+static char *find_path_for_conflict(struct merge_options *opt,
+				    const char *path,
+				    const char *branch1,
+				    const char *branch2)
+{
+	char *new_path = NULL;
+	if (dir_in_way(opt->repo->index, path, !opt->priv->call_depth, 0)) {
+		new_path = unique_path(opt, path, branch1);
+		output(opt, 1, _("%s is a directory in %s adding "
+			       "as %s instead"),
+		       path, branch2, new_path);
+	} else if (would_lose_untracked(opt, path)) {
+		new_path = unique_path(opt, path, branch1);
+		output(opt, 1, _("Refusing to lose untracked file"
+			       " at %s; adding as %s instead"),
+		       path, new_path);
+	}
+
+	return new_path;
+}
+
+/*
+ * Toggle the stage number between "ours" and "theirs" (2 and 3).
+ */
+static inline int flip_stage(int stage)
+{
+	return (2 + 3) - stage;
+}
+
+static int handle_rename_rename_1to2(struct merge_options *opt,
+				     struct rename_conflict_info *ci)
+{
+	/* One file was renamed in both branches, but to different names. */
+	struct merge_file_info mfi;
+	struct diff_filespec *add;
+	struct diff_filespec *o = ci->ren1->pair->one;
+	struct diff_filespec *a = ci->ren1->pair->two;
+	struct diff_filespec *b = ci->ren2->pair->two;
+	char *path_desc;
+
+	output(opt, 1, _("CONFLICT (rename/rename): "
+	       "Rename \"%s\"->\"%s\" in branch \"%s\" "
+	       "rename \"%s\"->\"%s\" in \"%s\"%s"),
+	       o->path, a->path, ci->ren1->branch,
+	       o->path, b->path, ci->ren2->branch,
+	       opt->priv->call_depth ? _(" (left unresolved)") : "");
+
+	path_desc = xstrfmt("%s and %s, both renamed from %s",
+			    a->path, b->path, o->path);
+	if (merge_mode_and_contents(opt, o, a, b, path_desc,
+				    ci->ren1->branch, ci->ren2->branch,
+				    opt->priv->call_depth * 2, &mfi))
+		return -1;
+	free(path_desc);
+
+	if (opt->priv->call_depth)
+		remove_file_from_index(opt->repo->index, o->path);
+
+	/*
+	 * For each destination path, we need to see if there is a
+	 * rename/add collision.  If not, we can write the file out
+	 * to the specified location.
+	 */
+	add = &ci->ren1->dst_entry->stages[flip_stage(2)];
+	if (is_valid(add)) {
+		add->path = mfi.blob.path = a->path;
+		if (handle_file_collision(opt, a->path,
+					  NULL, NULL,
+					  ci->ren1->branch,
+					  ci->ren2->branch,
+					  &mfi.blob, add) < 0)
+			return -1;
+	} else {
+		char *new_path = find_path_for_conflict(opt, a->path,
+							ci->ren1->branch,
+							ci->ren2->branch);
+		if (update_file(opt, 0, &mfi.blob,
+				new_path ? new_path : a->path))
+			return -1;
+		free(new_path);
+		if (!opt->priv->call_depth &&
+		    update_stages(opt, a->path, NULL, a, NULL))
+			return -1;
+	}
+
+	if (!mfi.clean && mfi.blob.mode == a->mode &&
+	    oideq(&mfi.blob.oid, &a->oid)) {
+		/*
+		 * Getting here means we were attempting to merge a binary
+		 * blob.  Since we can't merge binaries, the merge algorithm
+		 * just takes one side.  But we don't want to copy the
+		 * contents of one side to both paths; we'd rather use the
+		 * original content at the given path for each path.
+		 */
+		oidcpy(&mfi.blob.oid, &b->oid);
+		mfi.blob.mode = b->mode;
+	}
+	add = &ci->ren2->dst_entry->stages[flip_stage(3)];
+	if (is_valid(add)) {
+		add->path = mfi.blob.path = b->path;
+		if (handle_file_collision(opt, b->path,
+					  NULL, NULL,
+					  ci->ren1->branch,
+					  ci->ren2->branch,
+					  add, &mfi.blob) < 0)
+			return -1;
+	} else {
+		char *new_path = find_path_for_conflict(opt, b->path,
+							ci->ren2->branch,
+							ci->ren1->branch);
+		if (update_file(opt, 0, &mfi.blob,
+				new_path ? new_path : b->path))
+			return -1;
+		free(new_path);
+		if (!opt->priv->call_depth &&
+		    update_stages(opt, b->path, NULL, NULL, b))
+			return -1;
+	}
+
+	return 0;
+}
+
+static int handle_rename_rename_2to1(struct merge_options *opt,
+				     struct rename_conflict_info *ci)
+{
+	/* Two files, a & b, were renamed to the same thing, c. */
+	struct diff_filespec *a = ci->ren1->pair->one;
+	struct diff_filespec *b = ci->ren2->pair->one;
+	struct diff_filespec *c1 = ci->ren1->pair->two;
+	struct diff_filespec *c2 = ci->ren2->pair->two;
+	char *path = c1->path; /* == c2->path */
+	char *path_side_1_desc;
+	char *path_side_2_desc;
+	struct merge_file_info mfi_c1;
+	struct merge_file_info mfi_c2;
+	int ostage1, ostage2;
+
+	output(opt, 1, _("CONFLICT (rename/rename): "
+	       "Rename %s->%s in %s. "
+	       "Rename %s->%s in %s"),
+	       a->path, c1->path, ci->ren1->branch,
+	       b->path, c2->path, ci->ren2->branch);
+
+	path_side_1_desc = xstrfmt("version of %s from %s", path, a->path);
+	path_side_2_desc = xstrfmt("version of %s from %s", path, b->path);
+	ostage1 = ci->ren1->branch == opt->branch1 ? 3 : 2;
+	ostage2 = flip_stage(ostage1);
+	ci->ren1->src_entry->stages[ostage1].path = a->path;
+	ci->ren2->src_entry->stages[ostage2].path = b->path;
+	if (merge_mode_and_contents(opt, a, c1,
+				    &ci->ren1->src_entry->stages[ostage1],
+				    path_side_1_desc,
+				    opt->branch1, opt->branch2,
+				    1 + opt->priv->call_depth * 2, &mfi_c1) ||
+	    merge_mode_and_contents(opt, b,
+				    &ci->ren2->src_entry->stages[ostage2],
+				    c2, path_side_2_desc,
+				    opt->branch1, opt->branch2,
+				    1 + opt->priv->call_depth * 2, &mfi_c2))
+		return -1;
+	free(path_side_1_desc);
+	free(path_side_2_desc);
+	mfi_c1.blob.path = path;
+	mfi_c2.blob.path = path;
+
+	return handle_file_collision(opt, path, a->path, b->path,
+				     ci->ren1->branch, ci->ren2->branch,
+				     &mfi_c1.blob, &mfi_c2.blob);
+}
+
+/*
+ * Get the diff_filepairs changed between o_tree and tree.
+ */
+static struct diff_queue_struct *get_diffpairs(struct merge_options *opt,
+					       struct tree *o_tree,
+					       struct tree *tree)
+{
+	struct diff_queue_struct *ret;
+	struct diff_options opts;
+
+	repo_diff_setup(opt->repo, &opts);
+	opts.flags.recursive = 1;
+	opts.flags.rename_empty = 0;
+	opts.detect_rename = merge_detect_rename(opt);
+	/*
+	 * We do not have logic to handle the detection of copies.  In
+	 * fact, it may not even make sense to add such logic: would we
+	 * really want a change to a base file to be propagated through
+	 * multiple other files by a merge?
+	 */
+	if (opts.detect_rename > DIFF_DETECT_RENAME)
+		opts.detect_rename = DIFF_DETECT_RENAME;
+	opts.rename_limit = (opt->rename_limit >= 0) ? opt->rename_limit : 7000;
+	opts.rename_score = opt->rename_score;
+	opts.show_rename_progress = opt->show_rename_progress;
+	opts.output_format = DIFF_FORMAT_NO_OUTPUT;
+	diff_setup_done(&opts);
+	diff_tree_oid(&o_tree->object.oid, &tree->object.oid, "", &opts);
+	diffcore_std(&opts);
+	if (opts.needed_rename_limit > opt->priv->needed_rename_limit)
+		opt->priv->needed_rename_limit = opts.needed_rename_limit;
+
+	ret = xmalloc(sizeof(*ret));
+	*ret = diff_queued_diff;
+
+	opts.output_format = DIFF_FORMAT_NO_OUTPUT;
+	diff_queued_diff.nr = 0;
+	diff_queued_diff.queue = NULL;
+	diff_flush(&opts);
+	return ret;
+}
+
+static int tree_has_path(struct repository *r, struct tree *tree,
+			 const char *path)
+{
+	struct object_id hashy;
+	unsigned short mode_o;
+
+	return !get_tree_entry(r,
+			       &tree->object.oid, path,
+			       &hashy, &mode_o);
+}
+
+/*
+ * Return a new string that replaces the beginning portion (which matches
+ * entry->dir), with entry->new_dir.  In perl-speak:
+ *   new_path_name = (old_path =~ s/entry->dir/entry->new_dir/);
+ * NOTE:
+ *   Caller must ensure that old_path starts with entry->dir + '/'.
+ */
+static char *apply_dir_rename(struct dir_rename_entry *entry,
+			      const char *old_path)
+{
+	struct strbuf new_path = STRBUF_INIT;
+	int oldlen, newlen;
+
+	if (entry->non_unique_new_dir)
+		return NULL;
+
+	oldlen = strlen(entry->dir);
+	if (entry->new_dir.len == 0)
+		/*
+		 * If someone renamed/merged a subdirectory into the root
+		 * directory (e.g. 'some/subdir' -> ''), then we want to
+		 * avoid returning
+		 *     '' + '/filename'
+		 * as the rename; we need to make old_path + oldlen advance
+		 * past the '/' character.
+		 */
+		oldlen++;
+	newlen = entry->new_dir.len + (strlen(old_path) - oldlen) + 1;
+	strbuf_grow(&new_path, newlen);
+	strbuf_addbuf(&new_path, &entry->new_dir);
+	strbuf_addstr(&new_path, &old_path[oldlen]);
+
+	return strbuf_detach(&new_path, NULL);
+}
+
+static void get_renamed_dir_portion(const char *old_path, const char *new_path,
+				    char **old_dir, char **new_dir)
+{
+	char *end_of_old, *end_of_new;
+
+	/* Default return values: NULL, meaning no rename */
+	*old_dir = NULL;
+	*new_dir = NULL;
+
+	/*
+	 * For
+	 *    "a/b/c/d/e/foo.c" -> "a/b/some/thing/else/e/foo.c"
+	 * the "e/foo.c" part is the same, we just want to know that
+	 *    "a/b/c/d" was renamed to "a/b/some/thing/else"
+	 * so, for this example, this function returns "a/b/c/d" in
+	 * *old_dir and "a/b/some/thing/else" in *new_dir.
+	 */
+
+	/*
+	 * If the basename of the file changed, we don't care.  We want
+	 * to know which portion of the directory, if any, changed.
+	 */
+	end_of_old = strrchr(old_path, '/');
+	end_of_new = strrchr(new_path, '/');
+
+	/*
+	 * If end_of_old is NULL, old_path wasn't in a directory, so there
+	 * could not be a directory rename (our rule elsewhere that a
+	 * directory which still exists is not considered to have been
+	 * renamed means the root directory can never be renamed -- because
+	 * the root directory always exists).
+	 */
+	if (!end_of_old)
+		return; /* Note: *old_dir and *new_dir are still NULL */
+
+	/*
+	 * If new_path contains no directory (end_of_new is NULL), then we
+	 * have a rename of old_path's directory to the root directory.
+	 */
+	if (!end_of_new) {
+		*old_dir = xstrndup(old_path, end_of_old - old_path);
+		*new_dir = xstrdup("");
+		return;
+	}
+
+	/* Find the first non-matching character traversing backwards */
+	while (*--end_of_new == *--end_of_old &&
+	       end_of_old != old_path &&
+	       end_of_new != new_path)
+		; /* Do nothing; all in the while loop */
+
+	/*
+	 * If both got back to the beginning of their strings, then the
+	 * directory didn't change at all, only the basename did.
+	 */
+	if (end_of_old == old_path && end_of_new == new_path &&
+	    *end_of_old == *end_of_new)
+		return; /* Note: *old_dir and *new_dir are still NULL */
+
+	/*
+	 * If end_of_new got back to the beginning of its string, and
+	 * end_of_old got back to the beginning of some subdirectory, then
+	 * we have a rename/merge of a subdirectory into the root, which
+	 * needs slightly special handling.
+	 *
+	 * Note: There is no need to consider the opposite case, with a
+	 * rename/merge of the root directory into some subdirectory
+	 * because as noted above the root directory always exists so it
+	 * cannot be considered to be renamed.
+	 */
+	if (end_of_new == new_path &&
+	    end_of_old != old_path && end_of_old[-1] == '/') {
+		*old_dir = xstrndup(old_path, --end_of_old - old_path);
+		*new_dir = xstrdup("");
+		return;
+	}
+
+	/*
+	 * We've found the first non-matching character in the directory
+	 * paths.  That means the current characters we were looking at
+	 * were part of the first non-matching subdir name going back from
+	 * the end of the strings.  Get the whole name by advancing both
+	 * end_of_old and end_of_new to the NEXT '/' character.  That will
+	 * represent the entire directory rename.
+	 *
+	 * The reason for the increment is cases like
+	 *    a/b/star/foo/whatever.c -> a/b/tar/foo/random.c
+	 * After dropping the basename and going back to the first
+	 * non-matching character, we're now comparing:
+	 *    a/b/s          and         a/b/
+	 * and we want to be comparing:
+	 *    a/b/star/      and         a/b/tar/
+	 * but without the pre-increment, the one on the right would stay
+	 * a/b/.
+	 */
+	end_of_old = strchr(++end_of_old, '/');
+	end_of_new = strchr(++end_of_new, '/');
+
+	/* Copy the old and new directories into *old_dir and *new_dir. */
+	*old_dir = xstrndup(old_path, end_of_old - old_path);
+	*new_dir = xstrndup(new_path, end_of_new - new_path);
+}
+
+static void remove_hashmap_entries(struct hashmap *dir_renames,
+				   struct string_list *items_to_remove)
+{
+	int i;
+	struct dir_rename_entry *entry;
+
+	for (i = 0; i < items_to_remove->nr; i++) {
+		entry = items_to_remove->items[i].util;
+		hashmap_remove(dir_renames, &entry->ent, NULL);
+	}
+	string_list_clear(items_to_remove, 0);
+}
+
+/*
+ * See if there is a directory rename for path, and if there are any file
+ * level conflicts for the renamed location.  If there is a rename and
+ * there are no conflicts, return the new name.  Otherwise, return NULL.
+ */
+static char *handle_path_level_conflicts(struct merge_options *opt,
+					 const char *path,
+					 struct dir_rename_entry *entry,
+					 struct hashmap *collisions,
+					 struct tree *tree)
+{
+	char *new_path = NULL;
+	struct collision_entry *collision_ent;
+	int clean = 1;
+	struct strbuf collision_paths = STRBUF_INIT;
+
+	/*
+	 * entry has the mapping of old directory name to new directory name
+	 * that we want to apply to path.
+	 */
+	new_path = apply_dir_rename(entry, path);
+
+	if (!new_path) {
+		/* This should only happen when entry->non_unique_new_dir set */
+		if (!entry->non_unique_new_dir)
+			BUG("entry->non_unique_new_dir not set and !new_path");
+		output(opt, 1, _("CONFLICT (directory rename split): "
+			       "Unclear where to place %s because directory "
+			       "%s was renamed to multiple other directories, "
+			       "with no destination getting a majority of the "
+			       "files."),
+		       path, entry->dir);
+		clean = 0;
+		return NULL;
+	}
+
+	/*
+	 * The caller needs to have ensured that it has pre-populated
+	 * collisions with all paths that map to new_path.  Do a quick check
+	 * to ensure that's the case.
+	 */
+	collision_ent = collision_find_entry(collisions, new_path);
+	if (!collision_ent)
+		BUG("collision_ent is NULL");
+
+	/*
+	 * Check for one-sided add/add/.../add conflicts, i.e.
+	 * where implicit renames from the other side doing
+	 * directory rename(s) can affect this side of history
+	 * to put multiple paths into the same location.  Warn
+	 * and bail on directory renames for such paths.
+	 */
+	if (collision_ent->reported_already) {
+		clean = 0;
+	} else if (tree_has_path(opt->repo, tree, new_path)) {
+		collision_ent->reported_already = 1;
+		strbuf_add_separated_string_list(&collision_paths, ", ",
+						 &collision_ent->source_files);
+		output(opt, 1, _("CONFLICT (implicit dir rename): Existing "
+			       "file/dir at %s in the way of implicit "
+			       "directory rename(s) putting the following "
+			       "path(s) there: %s."),
+		       new_path, collision_paths.buf);
+		clean = 0;
+	} else if (collision_ent->source_files.nr > 1) {
+		collision_ent->reported_already = 1;
+		strbuf_add_separated_string_list(&collision_paths, ", ",
+						 &collision_ent->source_files);
+		output(opt, 1, _("CONFLICT (implicit dir rename): Cannot map "
+			       "more than one path to %s; implicit directory "
+			       "renames tried to put these paths there: %s"),
+		       new_path, collision_paths.buf);
+		clean = 0;
+	}
+
+	/* Free memory we no longer need */
+	strbuf_release(&collision_paths);
+	if (!clean && new_path) {
+		free(new_path);
+		return NULL;
+	}
+
+	return new_path;
+}
+
+/*
+ * There are a couple things we want to do at the directory level:
+ *   1. Check for both sides renaming to the same thing, in order to avoid
+ *      implicit renaming of files that should be left in place.  (See
+ *      testcase 6b in t6043 for details.)
+ *   2. Prune directory renames if there are still files left in the
+ *      original directory.  These represent a partial directory rename,
+ *      i.e. a rename where only some of the files within the directory
+ *      were renamed elsewhere.  (Technically, this could be done earlier
+ *      in get_directory_renames(), except that would prevent us from
+ *      doing the previous check and thus failing testcase 6b.)
+ *   3. Check for rename/rename(1to2) conflicts (at the directory level).
+ *      In the future, we could potentially record this info as well and
+ *      omit reporting rename/rename(1to2) conflicts for each path within
+ *      the affected directories, thus cleaning up the merge output.
+ *   NOTE: We do NOT check for rename/rename(2to1) conflicts at the
+ *         directory level, because merging directories is fine.  If it
+ *         causes conflicts for files within those merged directories, then
+ *         that should be detected at the individual path level.
+ */
+static void handle_directory_level_conflicts(struct merge_options *opt,
+					     struct hashmap *dir_re_head,
+					     struct tree *head,
+					     struct hashmap *dir_re_merge,
+					     struct tree *merge)
+{
+	struct hashmap_iter iter;
+	struct dir_rename_entry *head_ent;
+	struct dir_rename_entry *merge_ent;
+
+	struct string_list remove_from_head = STRING_LIST_INIT_NODUP;
+	struct string_list remove_from_merge = STRING_LIST_INIT_NODUP;
+
+	hashmap_for_each_entry(dir_re_head, &iter, head_ent,
+				ent /* member name */) {
+		merge_ent = dir_rename_find_entry(dir_re_merge, head_ent->dir);
+		if (merge_ent &&
+		    !head_ent->non_unique_new_dir &&
+		    !merge_ent->non_unique_new_dir &&
+		    !strbuf_cmp(&head_ent->new_dir, &merge_ent->new_dir)) {
+			/* 1. Renamed identically; remove it from both sides */
+			string_list_append(&remove_from_head,
+					   head_ent->dir)->util = head_ent;
+			strbuf_release(&head_ent->new_dir);
+			string_list_append(&remove_from_merge,
+					   merge_ent->dir)->util = merge_ent;
+			strbuf_release(&merge_ent->new_dir);
+		} else if (tree_has_path(opt->repo, head, head_ent->dir)) {
+			/* 2. This wasn't a directory rename after all */
+			string_list_append(&remove_from_head,
+					   head_ent->dir)->util = head_ent;
+			strbuf_release(&head_ent->new_dir);
+		}
+	}
+
+	remove_hashmap_entries(dir_re_head, &remove_from_head);
+	remove_hashmap_entries(dir_re_merge, &remove_from_merge);
+
+	hashmap_for_each_entry(dir_re_merge, &iter, merge_ent,
+				ent /* member name */) {
+		head_ent = dir_rename_find_entry(dir_re_head, merge_ent->dir);
+		if (tree_has_path(opt->repo, merge, merge_ent->dir)) {
+			/* 2. This wasn't a directory rename after all */
+			string_list_append(&remove_from_merge,
+					   merge_ent->dir)->util = merge_ent;
+		} else if (head_ent &&
+			   !head_ent->non_unique_new_dir &&
+			   !merge_ent->non_unique_new_dir) {
+			/* 3. rename/rename(1to2) */
+			/*
+			 * We can assume it's not rename/rename(1to1) because
+			 * that was case (1), already checked above.  So we
+			 * know that head_ent->new_dir and merge_ent->new_dir
+			 * are different strings.
+			 */
+			output(opt, 1, _("CONFLICT (rename/rename): "
+				       "Rename directory %s->%s in %s. "
+				       "Rename directory %s->%s in %s"),
+			       head_ent->dir, head_ent->new_dir.buf, opt->branch1,
+			       head_ent->dir, merge_ent->new_dir.buf, opt->branch2);
+			string_list_append(&remove_from_head,
+					   head_ent->dir)->util = head_ent;
+			strbuf_release(&head_ent->new_dir);
+			string_list_append(&remove_from_merge,
+					   merge_ent->dir)->util = merge_ent;
+			strbuf_release(&merge_ent->new_dir);
+		}
+	}
+
+	remove_hashmap_entries(dir_re_head, &remove_from_head);
+	remove_hashmap_entries(dir_re_merge, &remove_from_merge);
+}
+
+static struct hashmap *get_directory_renames(struct diff_queue_struct *pairs)
+{
+	struct hashmap *dir_renames;
+	struct hashmap_iter iter;
+	struct dir_rename_entry *entry;
+	int i;
+
+	/*
+	 * Typically, we think of a directory rename as all files from a
+	 * certain directory being moved to a target directory.  However,
+	 * what if someone first moved two files from the original
+	 * directory in one commit, and then renamed the directory
+	 * somewhere else in a later commit?  At merge time, we just know
+	 * that files from the original directory went to two different
+	 * places, and that the bulk of them ended up in the same place.
+	 * We want each directory rename to represent where the bulk of the
+	 * files from that directory end up; this function exists to find
+	 * where the bulk of the files went.
+	 *
+	 * The first loop below simply iterates through the list of file
+	 * renames, finding out how often each directory rename pair
+	 * possibility occurs.
+	 */
+	dir_renames = xmalloc(sizeof(*dir_renames));
+	dir_rename_init(dir_renames);
+	for (i = 0; i < pairs->nr; ++i) {
+		struct string_list_item *item;
+		int *count;
+		struct diff_filepair *pair = pairs->queue[i];
+		char *old_dir, *new_dir;
+
+		/* File not part of directory rename if it wasn't renamed */
+		if (pair->status != 'R')
+			continue;
+
+		get_renamed_dir_portion(pair->one->path, pair->two->path,
+					&old_dir,        &new_dir);
+		if (!old_dir)
+			/* Directory didn't change at all; ignore this one. */
+			continue;
+
+		entry = dir_rename_find_entry(dir_renames, old_dir);
+		if (!entry) {
+			entry = xmalloc(sizeof(*entry));
+			dir_rename_entry_init(entry, old_dir);
+			hashmap_put(dir_renames, &entry->ent);
+		} else {
+			free(old_dir);
+		}
+		item = string_list_lookup(&entry->possible_new_dirs, new_dir);
+		if (!item) {
+			item = string_list_insert(&entry->possible_new_dirs,
+						  new_dir);
+			item->util = xcalloc(1, sizeof(int));
+		} else {
+			free(new_dir);
+		}
+		count = item->util;
+		*count += 1;
+	}
+
+	/*
+	 * For each directory with files moved out of it, we find out which
+	 * target directory received the most files so we can declare it to
+	 * be the "winning" target location for the directory rename.  This
+	 * winner gets recorded in new_dir.  If there is no winner
+	 * (multiple target directories received the same number of files),
+	 * we set non_unique_new_dir.  Once we've determined the winner (or
+	 * that there is no winner), we no longer need possible_new_dirs.
+	 */
+	hashmap_for_each_entry(dir_renames, &iter, entry,
+				ent /* member name */) {
+		int max = 0;
+		int bad_max = 0;
+		char *best = NULL;
+
+		for (i = 0; i < entry->possible_new_dirs.nr; i++) {
+			int *count = entry->possible_new_dirs.items[i].util;
+
+			if (*count == max)
+				bad_max = max;
+			else if (*count > max) {
+				max = *count;
+				best = entry->possible_new_dirs.items[i].string;
+			}
+		}
+		if (bad_max == max)
+			entry->non_unique_new_dir = 1;
+		else {
+			assert(entry->new_dir.len == 0);
+			strbuf_addstr(&entry->new_dir, best);
+		}
+		/*
+		 * The relevant directory sub-portion of the original full
+		 * filepaths were xstrndup'ed before inserting into
+		 * possible_new_dirs, and instead of manually iterating the
+		 * list and free'ing each, just lie and tell
+		 * possible_new_dirs that it did the strdup'ing so that it
+		 * will free them for us.
+		 */
+		entry->possible_new_dirs.strdup_strings = 1;
+		string_list_clear(&entry->possible_new_dirs, 1);
+	}
+
+	return dir_renames;
+}
+
+static struct dir_rename_entry *check_dir_renamed(const char *path,
+						  struct hashmap *dir_renames)
+{
+	char *temp = xstrdup(path);
+	char *end;
+	struct dir_rename_entry *entry = NULL;
+
+	while ((end = strrchr(temp, '/'))) {
+		*end = '\0';
+		entry = dir_rename_find_entry(dir_renames, temp);
+		if (entry)
+			break;
+	}
+	free(temp);
+	return entry;
+}
+
+static void compute_collisions(struct hashmap *collisions,
+			       struct hashmap *dir_renames,
+			       struct diff_queue_struct *pairs)
+{
+	int i;
+
+	/*
+	 * Multiple files can be mapped to the same path due to directory
+	 * renames done by the other side of history.  Since that other
+	 * side of history could have merged multiple directories into one,
+	 * if our side of history added the same file basename to each of
+	 * those directories, then all N of them would get implicitly
+	 * renamed by the directory rename detection into the same path,
+	 * and we'd get an add/add/.../add conflict, and all those adds
+	 * from *this* side of history.  This is not representable in the
+	 * index, and users aren't going to easily be able to make sense of
+	 * it.  So we need to provide a good warning about what's
+	 * happening, and fall back to no-directory-rename detection
+	 * behavior for those paths.
+	 *
+	 * See testcases 9e and all of section 5 from t6043 for examples.
+	 */
+	collision_init(collisions);
+
+	for (i = 0; i < pairs->nr; ++i) {
+		struct dir_rename_entry *dir_rename_ent;
+		struct collision_entry *collision_ent;
+		char *new_path;
+		struct diff_filepair *pair = pairs->queue[i];
+
+		if (pair->status != 'A' && pair->status != 'R')
+			continue;
+		dir_rename_ent = check_dir_renamed(pair->two->path,
+						   dir_renames);
+		if (!dir_rename_ent)
+			continue;
+
+		new_path = apply_dir_rename(dir_rename_ent, pair->two->path);
+		if (!new_path)
+			/*
+			 * dir_rename_ent->non_unique_new_path is true, which
+			 * means there is no directory rename for us to use,
+			 * which means it won't cause us any additional
+			 * collisions.
+			 */
+			continue;
+		collision_ent = collision_find_entry(collisions, new_path);
+		if (!collision_ent) {
+			CALLOC_ARRAY(collision_ent, 1);
+			hashmap_entry_init(&collision_ent->ent,
+						strhash(new_path));
+			hashmap_put(collisions, &collision_ent->ent);
+			collision_ent->target_file = new_path;
+		} else {
+			free(new_path);
+		}
+		string_list_insert(&collision_ent->source_files,
+				   pair->two->path);
+	}
+}
+
+static char *check_for_directory_rename(struct merge_options *opt,
+					const char *path,
+					struct tree *tree,
+					struct hashmap *dir_renames,
+					struct hashmap *dir_rename_exclusions,
+					struct hashmap *collisions,
+					int *clean_merge)
+{
+	char *new_path = NULL;
+	struct dir_rename_entry *entry = check_dir_renamed(path, dir_renames);
+	struct dir_rename_entry *oentry = NULL;
+
+	if (!entry)
+		return new_path;
+
+	/*
+	 * This next part is a little weird.  We do not want to do an
+	 * implicit rename into a directory we renamed on our side, because
+	 * that will result in a spurious rename/rename(1to2) conflict.  An
+	 * example:
+	 *   Base commit: dumbdir/afile, otherdir/bfile
+	 *   Side 1:      smrtdir/afile, otherdir/bfile
+	 *   Side 2:      dumbdir/afile, dumbdir/bfile
+	 * Here, while working on Side 1, we could notice that otherdir was
+	 * renamed/merged to dumbdir, and change the diff_filepair for
+	 * otherdir/bfile into a rename into dumbdir/bfile.  However, Side
+	 * 2 will notice the rename from dumbdir to smrtdir, and do the
+	 * transitive rename to move it from dumbdir/bfile to
+	 * smrtdir/bfile.  That gives us bfile in dumbdir vs being in
+	 * smrtdir, a rename/rename(1to2) conflict.  We really just want
+	 * the file to end up in smrtdir.  And the way to achieve that is
+	 * to not let Side1 do the rename to dumbdir, since we know that is
+	 * the source of one of our directory renames.
+	 *
+	 * That's why oentry and dir_rename_exclusions is here.
+	 *
+	 * As it turns out, this also prevents N-way transient rename
+	 * confusion; See testcases 9c and 9d of t6043.
+	 */
+	oentry = dir_rename_find_entry(dir_rename_exclusions, entry->new_dir.buf);
+	if (oentry) {
+		output(opt, 1, _("WARNING: Avoiding applying %s -> %s rename "
+			       "to %s, because %s itself was renamed."),
+		       entry->dir, entry->new_dir.buf, path, entry->new_dir.buf);
+	} else {
+		new_path = handle_path_level_conflicts(opt, path, entry,
+						       collisions, tree);
+		*clean_merge &= (new_path != NULL);
+	}
+
+	return new_path;
+}
+
+static void apply_directory_rename_modifications(struct merge_options *opt,
+						 struct diff_filepair *pair,
+						 char *new_path,
+						 struct rename *re,
+						 struct tree *tree,
+						 struct tree *o_tree,
+						 struct tree *a_tree,
+						 struct tree *b_tree,
+						 struct string_list *entries)
+{
+	struct string_list_item *item;
+	int stage = (tree == a_tree ? 2 : 3);
+	int update_wd;
+
+	/*
+	 * In all cases where we can do directory rename detection,
+	 * unpack_trees() will have read pair->two->path into the
+	 * index and the working copy.  We need to remove it so that
+	 * we can instead place it at new_path.  It is guaranteed to
+	 * not be untracked (unpack_trees() would have errored out
+	 * saying the file would have been overwritten), but it might
+	 * be dirty, though.
+	 */
+	update_wd = !was_dirty(opt, pair->two->path);
+	if (!update_wd)
+		output(opt, 1, _("Refusing to lose dirty file at %s"),
+		       pair->two->path);
+	remove_file(opt, 1, pair->two->path, !update_wd);
+
+	/* Find or create a new re->dst_entry */
+	item = string_list_lookup(entries, new_path);
+	if (item) {
+		/*
+		 * Since we're renaming on this side of history, and it's
+		 * due to a directory rename on the other side of history
+		 * (which we only allow when the directory in question no
+		 * longer exists on the other side of history), the
+		 * original entry for re->dst_entry is no longer
+		 * necessary...
+		 */
+		re->dst_entry->processed = 1;
+
+		/*
+		 * ...because we'll be using this new one.
+		 */
+		re->dst_entry = item->util;
+	} else {
+		/*
+		 * re->dst_entry is for the before-dir-rename path, and we
+		 * need it to hold information for the after-dir-rename
+		 * path.  Before creating a new entry, we need to mark the
+		 * old one as unnecessary (...unless it is shared by
+		 * src_entry, i.e. this didn't use to be a rename, in which
+		 * case we can just allow the normal processing to happen
+		 * for it).
+		 */
+		if (pair->status == 'R')
+			re->dst_entry->processed = 1;
+
+		re->dst_entry = insert_stage_data(opt->repo, new_path,
+						  o_tree, a_tree, b_tree,
+						  entries);
+		item = string_list_insert(entries, new_path);
+		item->util = re->dst_entry;
+	}
+
+	/*
+	 * Update the stage_data with the information about the path we are
+	 * moving into place.  That slot will be empty and available for us
+	 * to write to because of the collision checks in
+	 * handle_path_level_conflicts().  In other words,
+	 * re->dst_entry->stages[stage].oid will be the null_oid, so it's
+	 * open for us to write to.
+	 *
+	 * It may be tempting to actually update the index at this point as
+	 * well, using update_stages_for_stage_data(), but as per the big
+	 * "NOTE" in update_stages(), doing so will modify the current
+	 * in-memory index which will break calls to would_lose_untracked()
+	 * that we need to make.  Instead, we need to just make sure that
+	 * the various handle_rename_*() functions update the index
+	 * explicitly rather than relying on unpack_trees() to have done it.
+	 */
+	get_tree_entry(opt->repo,
+		       &tree->object.oid,
+		       pair->two->path,
+		       &re->dst_entry->stages[stage].oid,
+		       &re->dst_entry->stages[stage].mode);
+
+	/*
+	 * Record the original change status (or 'type' of change).  If it
+	 * was originally an add ('A'), this lets us differentiate later
+	 * between a RENAME_DELETE conflict and RENAME_VIA_DIR (they
+	 * otherwise look the same).  If it was originally a rename ('R'),
+	 * this lets us remember and report accurately about the transitive
+	 * renaming that occurred via the directory rename detection.  Also,
+	 * record the original destination name.
+	 */
+	re->dir_rename_original_type = pair->status;
+	re->dir_rename_original_dest = pair->two->path;
+
+	/*
+	 * We don't actually look at pair->status again, but it seems
+	 * pedagogically correct to adjust it.
+	 */
+	pair->status = 'R';
+
+	/*
+	 * Finally, record the new location.
+	 */
+	pair->two->path = new_path;
+}
+
+/*
+ * Get information of all renames which occurred in 'pairs', making use of
+ * any implicit directory renames inferred from the other side of history.
+ * 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 *opt,
+				       const char *branch,
+				       struct diff_queue_struct *pairs,
+				       struct hashmap *dir_renames,
+				       struct hashmap *dir_rename_exclusions,
+				       struct tree *tree,
+				       struct tree *o_tree,
+				       struct tree *a_tree,
+				       struct tree *b_tree,
+				       struct string_list *entries,
+				       int *clean_merge)
+{
+	int i;
+	struct hashmap collisions;
+	struct hashmap_iter iter;
+	struct collision_entry *e;
+	struct string_list *renames;
+
+	compute_collisions(&collisions, dir_renames, pairs);
+	CALLOC_ARRAY(renames, 1);
+
+	for (i = 0; i < pairs->nr; ++i) {
+		struct string_list_item *item;
+		struct rename *re;
+		struct diff_filepair *pair = pairs->queue[i];
+		char *new_path; /* non-NULL only with directory renames */
+
+		if (pair->status != 'A' && pair->status != 'R') {
+			diff_free_filepair(pair);
+			continue;
+		}
+		new_path = check_for_directory_rename(opt, pair->two->path, tree,
+						      dir_renames,
+						      dir_rename_exclusions,
+						      &collisions,
+						      clean_merge);
+		if (pair->status != 'R' && !new_path) {
+			diff_free_filepair(pair);
+			continue;
+		}
+
+		re = xmalloc(sizeof(*re));
+		re->processed = 0;
+		re->pair = pair;
+		re->branch = branch;
+		re->dir_rename_original_type = '\0';
+		re->dir_rename_original_dest = NULL;
+		item = string_list_lookup(entries, re->pair->one->path);
+		if (!item)
+			re->src_entry = insert_stage_data(opt->repo,
+					re->pair->one->path,
+					o_tree, a_tree, b_tree, entries);
+		else
+			re->src_entry = item->util;
+
+		item = string_list_lookup(entries, re->pair->two->path);
+		if (!item)
+			re->dst_entry = insert_stage_data(opt->repo,
+					re->pair->two->path,
+					o_tree, a_tree, b_tree, entries);
+		else
+			re->dst_entry = item->util;
+		item = string_list_insert(renames, pair->one->path);
+		item->util = re;
+		if (new_path)
+			apply_directory_rename_modifications(opt, pair, new_path,
+							     re, tree, o_tree,
+							     a_tree, b_tree,
+							     entries);
+	}
+
+	hashmap_for_each_entry(&collisions, &iter, e,
+				ent /* member name */) {
+		free(e->target_file);
+		string_list_clear(&e->source_files, 0);
+	}
+	hashmap_clear_and_free(&collisions, struct collision_entry, ent);
+	return renames;
+}
+
+static int process_renames(struct merge_options *opt,
+			   struct string_list *a_renames,
+			   struct string_list *b_renames)
+{
+	int clean_merge = 1, i, j;
+	struct string_list a_by_dst = STRING_LIST_INIT_NODUP;
+	struct string_list b_by_dst = STRING_LIST_INIT_NODUP;
+	const struct rename *sre;
+
+	/*
+	 * FIXME: As string-list.h notes, it's O(n^2) to build a sorted
+	 * string_list one-by-one, but O(n log n) to build it unsorted and
+	 * then sort it.  Note that as we build the list, we do not need to
+	 * check if the existing destination path is already in the list,
+	 * because the structure of diffcore_rename guarantees we won't
+	 * have duplicates.
+	 */
+	for (i = 0; i < a_renames->nr; i++) {
+		sre = a_renames->items[i].util;
+		string_list_insert(&a_by_dst, sre->pair->two->path)->util
+			= (void *)sre;
+	}
+	for (i = 0; i < b_renames->nr; i++) {
+		sre = b_renames->items[i].util;
+		string_list_insert(&b_by_dst, sre->pair->two->path)->util
+			= (void *)sre;
+	}
+
+	for (i = 0, j = 0; i < a_renames->nr || j < b_renames->nr;) {
+		struct string_list *renames1, *renames2Dst;
+		struct rename *ren1 = NULL, *ren2 = NULL;
+		const char *ren1_src, *ren1_dst;
+		struct string_list_item *lookup;
+
+		if (i >= a_renames->nr) {
+			ren2 = b_renames->items[j++].util;
+		} else if (j >= b_renames->nr) {
+			ren1 = a_renames->items[i++].util;
+		} else {
+			int 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;
+			renames2Dst = &b_by_dst;
+		} else {
+			renames1 = b_renames;
+			renames2Dst = &a_by_dst;
+			SWAP(ren2, ren1);
+		}
+
+		if (ren1->processed)
+			continue;
+		ren1->processed = 1;
+		ren1->dst_entry->processed = 1;
+		/* BUG: We should only mark src_entry as processed if we
+		 * are not dealing with a rename + add-source case.
+		 */
+		ren1->src_entry->processed = 1;
+
+		ren1_src = ren1->pair->one->path;
+		ren1_dst = ren1->pair->two->path;
+
+		if (ren2) {
+			/* One file renamed on both sides */
+			const char *ren2_src = ren2->pair->one->path;
+			const char *ren2_dst = ren2->pair->two->path;
+			enum rename_type rename_type;
+			if (strcmp(ren1_src, ren2_src) != 0)
+				BUG("ren1_src != ren2_src");
+			ren2->dst_entry->processed = 1;
+			ren2->processed = 1;
+			if (strcmp(ren1_dst, ren2_dst) != 0) {
+				rename_type = RENAME_ONE_FILE_TO_TWO;
+				clean_merge = 0;
+			} else {
+				rename_type = RENAME_ONE_FILE_TO_ONE;
+				/* BUG: We should only remove ren1_src in
+				 * the base stage (think of rename +
+				 * add-source cases).
+				 */
+				remove_file(opt, 1, ren1_src, 1);
+				update_entry(ren1->dst_entry,
+					     ren1->pair->one,
+					     ren1->pair->two,
+					     ren2->pair->two);
+			}
+			setup_rename_conflict_info(rename_type, opt, ren1, ren2);
+		} else if ((lookup = string_list_lookup(renames2Dst, ren1_dst))) {
+			/* Two different files renamed to the same thing */
+			char *ren2_dst;
+			ren2 = lookup->util;
+			ren2_dst = ren2->pair->two->path;
+			if (strcmp(ren1_dst, ren2_dst) != 0)
+				BUG("ren1_dst != ren2_dst");
+
+			clean_merge = 0;
+			ren2->processed = 1;
+			/*
+			 * BUG: We should only mark src_entry as processed
+			 * if we are not dealing with a rename + add-source
+			 * case.
+			 */
+			ren2->src_entry->processed = 1;
+
+			setup_rename_conflict_info(RENAME_TWO_FILES_TO_ONE,
+						   opt, ren1, ren2);
+		} else {
+			/* Renamed in 1, maybe changed in 2 */
+			/* we only use sha1 and mode of these */
+			struct diff_filespec src_other, dst_other;
+			int try_merge;
+
+			/*
+			 * unpack_trees loads entries from common-commit
+			 * into stage 1, from head-commit into stage 2, and
+			 * from merge-commit into stage 3.  We keep track
+			 * of which side corresponds to the rename.
+			 */
+			int renamed_stage = a_renames == renames1 ? 2 : 3;
+			int other_stage =   a_renames == renames1 ? 3 : 2;
+
+			/*
+			 * Directory renames have a funny corner case...
+			 */
+			int renamed_to_self = !strcmp(ren1_src, ren1_dst);
+
+			/* BUG: We should only remove ren1_src in the base
+			 * stage and in other_stage (think of rename +
+			 * add-source case).
+			 */
+			if (!renamed_to_self)
+				remove_file(opt, 1, ren1_src,
+					    renamed_stage == 2 ||
+					    !was_tracked(opt, ren1_src));
+
+			oidcpy(&src_other.oid,
+			       &ren1->src_entry->stages[other_stage].oid);
+			src_other.mode = ren1->src_entry->stages[other_stage].mode;
+			oidcpy(&dst_other.oid,
+			       &ren1->dst_entry->stages[other_stage].oid);
+			dst_other.mode = ren1->dst_entry->stages[other_stage].mode;
+			try_merge = 0;
+
+			if (oideq(&src_other.oid, null_oid()) &&
+			    ren1->dir_rename_original_type == 'A') {
+				setup_rename_conflict_info(RENAME_VIA_DIR,
+							   opt, ren1, NULL);
+			} else if (renamed_to_self) {
+				setup_rename_conflict_info(RENAME_NORMAL,
+							   opt, ren1, NULL);
+			} else if (oideq(&src_other.oid, null_oid())) {
+				setup_rename_conflict_info(RENAME_DELETE,
+							   opt, ren1, NULL);
+			} else if ((dst_other.mode == ren1->pair->two->mode) &&
+				   oideq(&dst_other.oid, &ren1->pair->two->oid)) {
+				/*
+				 * Added file on the other side identical to
+				 * the file being renamed: clean merge.
+				 * Also, there is no need to overwrite the
+				 * file already in the working copy, so call
+				 * update_file_flags() instead of
+				 * update_file().
+				 */
+				if (update_file_flags(opt,
+						      ren1->pair->two,
+						      ren1_dst,
+						      1, /* update_cache */
+						      0  /* update_wd    */))
+					clean_merge = -1;
+			} else if (!oideq(&dst_other.oid, null_oid())) {
+				/*
+				 * Probably not a clean merge, but it's
+				 * premature to set clean_merge to 0 here,
+				 * because if the rename merges cleanly and
+				 * the merge exactly matches the newly added
+				 * file, then the merge will be clean.
+				 */
+				setup_rename_conflict_info(RENAME_ADD,
+							   opt, ren1, NULL);
+			} else
+				try_merge = 1;
+
+			if (clean_merge < 0)
+				goto cleanup_and_return;
+			if (try_merge) {
+				struct diff_filespec *o, *a, *b;
+				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;
+				}
+				update_entry(ren1->dst_entry, o, a, b);
+				setup_rename_conflict_info(RENAME_NORMAL,
+							   opt, ren1, NULL);
+			}
+		}
+	}
+cleanup_and_return:
+	string_list_clear(&a_by_dst, 0);
+	string_list_clear(&b_by_dst, 0);
+
+	return clean_merge;
+}
+
+struct rename_info {
+	struct string_list *head_renames;
+	struct string_list *merge_renames;
+};
+
+static void initial_cleanup_rename(struct diff_queue_struct *pairs,
+				   struct hashmap *dir_renames)
+{
+	struct hashmap_iter iter;
+	struct dir_rename_entry *e;
+
+	hashmap_for_each_entry(dir_renames, &iter, e,
+				ent /* member name */) {
+		free(e->dir);
+		strbuf_release(&e->new_dir);
+		/* possible_new_dirs already cleared in get_directory_renames */
+	}
+	hashmap_clear_and_free(dir_renames, struct dir_rename_entry, ent);
+	free(dir_renames);
+
+	free(pairs->queue);
+	free(pairs);
+}
+
+static int detect_and_process_renames(struct merge_options *opt,
+				      struct tree *common,
+				      struct tree *head,
+				      struct tree *merge,
+				      struct string_list *entries,
+				      struct rename_info *ri)
+{
+	struct diff_queue_struct *head_pairs, *merge_pairs;
+	struct hashmap *dir_re_head, *dir_re_merge;
+	int clean = 1;
+
+	ri->head_renames = NULL;
+	ri->merge_renames = NULL;
+
+	if (!merge_detect_rename(opt))
+		return 1;
+
+	head_pairs = get_diffpairs(opt, common, head);
+	merge_pairs = get_diffpairs(opt, common, merge);
+
+	if ((opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_TRUE) ||
+	    (opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_CONFLICT &&
+	     !opt->priv->call_depth)) {
+		dir_re_head = get_directory_renames(head_pairs);
+		dir_re_merge = get_directory_renames(merge_pairs);
+
+		handle_directory_level_conflicts(opt,
+						 dir_re_head, head,
+						 dir_re_merge, merge);
+	} else {
+		dir_re_head  = xmalloc(sizeof(*dir_re_head));
+		dir_re_merge = xmalloc(sizeof(*dir_re_merge));
+		dir_rename_init(dir_re_head);
+		dir_rename_init(dir_re_merge);
+	}
+
+	ri->head_renames  = get_renames(opt, opt->branch1, head_pairs,
+					dir_re_merge, dir_re_head, head,
+					common, head, merge, entries,
+					&clean);
+	if (clean < 0)
+		goto cleanup;
+	ri->merge_renames = get_renames(opt, opt->branch2, merge_pairs,
+					dir_re_head, dir_re_merge, merge,
+					common, head, merge, entries,
+					&clean);
+	if (clean < 0)
+		goto cleanup;
+	clean &= process_renames(opt, ri->head_renames, ri->merge_renames);
+
+cleanup:
+	/*
+	 * Some cleanup is deferred until cleanup_renames() because the
+	 * data structures are still needed and referenced in
+	 * process_entry().  But there are a few things we can free now.
+	 */
+	initial_cleanup_rename(head_pairs, dir_re_head);
+	initial_cleanup_rename(merge_pairs, dir_re_merge);
+
+	return clean;
+}
+
+static void final_cleanup_rename(struct string_list *rename)
+{
+	const struct rename *re;
+	int i;
+
+	if (!rename)
+		return;
+
+	for (i = 0; i < rename->nr; i++) {
+		re = rename->items[i].util;
+		diff_free_filepair(re->pair);
+	}
+	string_list_clear(rename, 1);
+	free(rename);
+}
+
+static void final_cleanup_renames(struct rename_info *re_info)
+{
+	final_cleanup_rename(re_info->head_renames);
+	final_cleanup_rename(re_info->merge_renames);
+}
+
+static int read_oid_strbuf(struct merge_options *opt,
+			   const struct object_id *oid,
+			   struct strbuf *dst)
+{
+	void *buf;
+	enum object_type type;
+	unsigned long size;
+	buf = read_object_file(oid, &type, &size);
+	if (!buf)
+		return err(opt, _("cannot read object %s"), oid_to_hex(oid));
+	if (type != OBJ_BLOB) {
+		free(buf);
+		return err(opt, _("object %s is not a blob"), oid_to_hex(oid));
+	}
+	strbuf_attach(dst, buf, size, size + 1);
+	return 0;
+}
+
+static int blob_unchanged(struct merge_options *opt,
+			  const struct diff_filespec *o,
+			  const struct diff_filespec *a,
+			  int renormalize, const char *path)
+{
+	struct strbuf obuf = STRBUF_INIT;
+	struct strbuf abuf = STRBUF_INIT;
+	int ret = 0; /* assume changed for safety */
+	struct index_state *idx = opt->repo->index;
+
+	if (a->mode != o->mode)
+		return 0;
+	if (oideq(&o->oid, &a->oid))
+		return 1;
+	if (!renormalize)
+		return 0;
+
+	if (read_oid_strbuf(opt, &o->oid, &obuf) ||
+	    read_oid_strbuf(opt, &a->oid, &abuf))
+		goto error_return;
+	/*
+	 * Note: binary | is used so that both renormalizations are
+	 * performed.  Comparison can be skipped if both files are
+	 * unchanged since their sha1s have already been compared.
+	 */
+	if (renormalize_buffer(idx, path, obuf.buf, obuf.len, &obuf) |
+	    renormalize_buffer(idx, path, abuf.buf, abuf.len, &abuf))
+		ret = (obuf.len == abuf.len && !memcmp(obuf.buf, abuf.buf, obuf.len));
+
+error_return:
+	strbuf_release(&obuf);
+	strbuf_release(&abuf);
+	return ret;
+}
+
+static int handle_modify_delete(struct merge_options *opt,
+				const char *path,
+				const struct diff_filespec *o,
+				const struct diff_filespec *a,
+				const struct diff_filespec *b)
+{
+	const char *modify_branch, *delete_branch;
+	const struct diff_filespec *changed;
+
+	if (is_valid(a)) {
+		modify_branch = opt->branch1;
+		delete_branch = opt->branch2;
+		changed = a;
+	} else {
+		modify_branch = opt->branch2;
+		delete_branch = opt->branch1;
+		changed = b;
+	}
+
+	return handle_change_delete(opt,
+				    path, NULL,
+				    o, changed,
+				    modify_branch, delete_branch,
+				    _("modify"), _("modified"));
+}
+
+static int handle_content_merge(struct merge_file_info *mfi,
+				struct merge_options *opt,
+				const char *path,
+				int is_dirty,
+				const struct diff_filespec *o,
+				const struct diff_filespec *a,
+				const struct diff_filespec *b,
+				struct rename_conflict_info *ci)
+{
+	const char *reason = _("content");
+	unsigned df_conflict_remains = 0;
+
+	if (!is_valid(o))
+		reason = _("add/add");
+
+	assert(o->path && a->path && b->path);
+	if (ci && dir_in_way(opt->repo->index, path, !opt->priv->call_depth,
+			     S_ISGITLINK(ci->ren1->pair->two->mode)))
+		df_conflict_remains = 1;
+
+	if (merge_mode_and_contents(opt, o, a, b, path,
+				    opt->branch1, opt->branch2,
+				    opt->priv->call_depth * 2, mfi))
+		return -1;
+
+	/*
+	 * We can skip updating the working tree file iff:
+	 *   a) The merge is clean
+	 *   b) The merge matches what was in HEAD (content, mode, pathname)
+	 *   c) The target path is usable (i.e. not involved in D/F conflict)
+	 */
+	if (mfi->clean && was_tracked_and_matches(opt, path, &mfi->blob) &&
+	    !df_conflict_remains) {
+		int pos;
+		struct cache_entry *ce;
+
+		output(opt, 3, _("Skipped %s (merged same as existing)"), path);
+		if (add_cacheinfo(opt, &mfi->blob, path,
+				  0, (!opt->priv->call_depth && !is_dirty), 0))
+			return -1;
+		/*
+		 * However, add_cacheinfo() will delete the old cache entry
+		 * and add a new one.  We need to copy over any skip_worktree
+		 * flag to avoid making the file appear as if it were
+		 * deleted by the user.
+		 */
+		pos = index_name_pos(&opt->priv->orig_index, path, strlen(path));
+		ce = opt->priv->orig_index.cache[pos];
+		if (ce_skip_worktree(ce)) {
+			pos = index_name_pos(opt->repo->index, path, strlen(path));
+			ce = opt->repo->index->cache[pos];
+			ce->ce_flags |= CE_SKIP_WORKTREE;
+		}
+		return mfi->clean;
+	}
+
+	if (!mfi->clean) {
+		if (S_ISGITLINK(mfi->blob.mode))
+			reason = _("submodule");
+		output(opt, 1, _("CONFLICT (%s): Merge conflict in %s"),
+				reason, path);
+		if (ci && !df_conflict_remains)
+			if (update_stages(opt, path, o, a, b))
+				return -1;
+	}
+
+	if (df_conflict_remains || is_dirty) {
+		char *new_path;
+		if (opt->priv->call_depth) {
+			remove_file_from_index(opt->repo->index, path);
+		} else {
+			if (!mfi->clean) {
+				if (update_stages(opt, path, o, a, b))
+					return -1;
+			} else {
+				int file_from_stage2 = was_tracked(opt, path);
+
+				if (update_stages(opt, path, NULL,
+						  file_from_stage2 ? &mfi->blob : NULL,
+						  file_from_stage2 ? NULL : &mfi->blob))
+					return -1;
+			}
+
+		}
+		new_path = unique_path(opt, path, ci->ren1->branch);
+		if (is_dirty) {
+			output(opt, 1, _("Refusing to lose dirty file at %s"),
+			       path);
+		}
+		output(opt, 1, _("Adding as %s instead"), new_path);
+		if (update_file(opt, 0, &mfi->blob, new_path)) {
+			free(new_path);
+			return -1;
+		}
+		free(new_path);
+		mfi->clean = 0;
+	} else if (update_file(opt, mfi->clean, &mfi->blob, path))
+		return -1;
+	return !is_dirty && mfi->clean;
+}
+
+static int handle_rename_normal(struct merge_options *opt,
+				const char *path,
+				const struct diff_filespec *o,
+				const struct diff_filespec *a,
+				const struct diff_filespec *b,
+				struct rename_conflict_info *ci)
+{
+	struct rename *ren = ci->ren1;
+	struct merge_file_info mfi;
+	int clean;
+
+	/* Merge the content and write it out */
+	clean = handle_content_merge(&mfi, opt, path, was_dirty(opt, path),
+				     o, a, b, ci);
+
+	if (clean &&
+	    opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_CONFLICT &&
+	    ren->dir_rename_original_dest) {
+		if (update_stages(opt, path,
+				  &mfi.blob, &mfi.blob, &mfi.blob))
+			return -1;
+		clean = 0; /* not clean, but conflicted */
+	}
+	return clean;
+}
+
+static void dir_rename_warning(const char *msg,
+			       int is_add,
+			       int clean,
+			       struct merge_options *opt,
+			       struct rename *ren)
+{
+	const char *other_branch;
+	other_branch = (ren->branch == opt->branch1 ?
+			opt->branch2 : opt->branch1);
+	if (is_add) {
+		output(opt, clean ? 2 : 1, msg,
+		       ren->pair->one->path, ren->branch,
+		       other_branch, ren->pair->two->path);
+		return;
+	}
+	output(opt, clean ? 2 : 1, msg,
+	       ren->pair->one->path, ren->dir_rename_original_dest, ren->branch,
+	       other_branch, ren->pair->two->path);
+}
+static int warn_about_dir_renamed_entries(struct merge_options *opt,
+					  struct rename *ren)
+{
+	const char *msg;
+	int clean = 1, is_add;
+
+	if (!ren)
+		return clean;
+
+	/* Return early if ren was not affected/created by a directory rename */
+	if (!ren->dir_rename_original_dest)
+		return clean;
+
+	/* Sanity checks */
+	assert(opt->detect_directory_renames > MERGE_DIRECTORY_RENAMES_NONE);
+	assert(ren->dir_rename_original_type == 'A' ||
+	       ren->dir_rename_original_type == 'R');
+
+	/* Check whether to treat directory renames as a conflict */
+	clean = (opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_TRUE);
+
+	is_add = (ren->dir_rename_original_type == 'A');
+	if (ren->dir_rename_original_type == 'A' && clean) {
+		msg = _("Path updated: %s added in %s inside a "
+			"directory that was renamed in %s; moving it to %s.");
+	} else if (ren->dir_rename_original_type == 'A' && !clean) {
+		msg = _("CONFLICT (file location): %s added in %s "
+			"inside a directory that was renamed in %s, "
+			"suggesting it should perhaps be moved to %s.");
+	} else if (ren->dir_rename_original_type == 'R' && clean) {
+		msg = _("Path updated: %s renamed to %s in %s, inside a "
+			"directory that was renamed in %s; moving it to %s.");
+	} else if (ren->dir_rename_original_type == 'R' && !clean) {
+		msg = _("CONFLICT (file location): %s renamed to %s in %s, "
+			"inside a directory that was renamed in %s, "
+			"suggesting it should perhaps be moved to %s.");
+	} else {
+		BUG("Impossible dir_rename_original_type/clean combination");
+	}
+	dir_rename_warning(msg, is_add, clean, opt, ren);
+
+	return clean;
+}
+
+/* Per entry merge function */
+static int process_entry(struct merge_options *opt,
+			 const char *path, struct stage_data *entry)
+{
+	int clean_merge = 1;
+	int normalize = opt->renormalize;
+
+	struct diff_filespec *o = &entry->stages[1];
+	struct diff_filespec *a = &entry->stages[2];
+	struct diff_filespec *b = &entry->stages[3];
+	int o_valid = is_valid(o);
+	int a_valid = is_valid(a);
+	int b_valid = is_valid(b);
+	o->path = a->path = b->path = (char*)path;
+
+	entry->processed = 1;
+	if (entry->rename_conflict_info) {
+		struct rename_conflict_info *ci = entry->rename_conflict_info;
+		struct diff_filespec *temp;
+		int path_clean;
+
+		path_clean = warn_about_dir_renamed_entries(opt, ci->ren1);
+		path_clean &= warn_about_dir_renamed_entries(opt, ci->ren2);
+
+		/*
+		 * For cases with a single rename, {o,a,b}->path have all been
+		 * set to the rename target path; we need to set two of these
+		 * back to the rename source.
+		 * For rename/rename conflicts, we'll manually fix paths below.
+		 */
+		temp = (opt->branch1 == ci->ren1->branch) ? b : a;
+		o->path = temp->path = ci->ren1->pair->one->path;
+		if (ci->ren2) {
+			assert(opt->branch1 == ci->ren1->branch);
+		}
+
+		switch (ci->rename_type) {
+		case RENAME_NORMAL:
+		case RENAME_ONE_FILE_TO_ONE:
+			clean_merge = handle_rename_normal(opt, path, o, a, b,
+							   ci);
+			break;
+		case RENAME_VIA_DIR:
+			clean_merge = handle_rename_via_dir(opt, ci);
+			break;
+		case RENAME_ADD:
+			/*
+			 * Probably unclean merge, but if the renamed file
+			 * merges cleanly and the result can then be
+			 * two-way merged cleanly with the added file, I
+			 * guess it's a clean merge?
+			 */
+			clean_merge = handle_rename_add(opt, ci);
+			break;
+		case RENAME_DELETE:
+			clean_merge = 0;
+			if (handle_rename_delete(opt, ci))
+				clean_merge = -1;
+			break;
+		case RENAME_ONE_FILE_TO_TWO:
+			/*
+			 * Manually fix up paths; note:
+			 * ren[12]->pair->one->path are equal.
+			 */
+			o->path = ci->ren1->pair->one->path;
+			a->path = ci->ren1->pair->two->path;
+			b->path = ci->ren2->pair->two->path;
+
+			clean_merge = 0;
+			if (handle_rename_rename_1to2(opt, ci))
+				clean_merge = -1;
+			break;
+		case RENAME_TWO_FILES_TO_ONE:
+			/*
+			 * Manually fix up paths; note,
+			 * ren[12]->pair->two->path are actually equal.
+			 */
+			o->path = NULL;
+			a->path = ci->ren1->pair->two->path;
+			b->path = ci->ren2->pair->two->path;
+
+			/*
+			 * Probably unclean merge, but if the two renamed
+			 * files merge cleanly and the two resulting files
+			 * can then be two-way merged cleanly, I guess it's
+			 * a clean merge?
+			 */
+			clean_merge = handle_rename_rename_2to1(opt, ci);
+			break;
+		default:
+			entry->processed = 0;
+			break;
+		}
+		if (path_clean < clean_merge)
+			clean_merge = path_clean;
+	} else if (o_valid && (!a_valid || !b_valid)) {
+		/* Case A: Deleted in one */
+		if ((!a_valid && !b_valid) ||
+		    (!b_valid && blob_unchanged(opt, o, a, normalize, path)) ||
+		    (!a_valid && blob_unchanged(opt, o, b, normalize, path))) {
+			/* Deleted in both or deleted in one and
+			 * unchanged in the other */
+			if (a_valid)
+				output(opt, 2, _("Removing %s"), path);
+			/* do not touch working file if it did not exist */
+			remove_file(opt, 1, path, !a_valid);
+		} else {
+			/* Modify/delete; deleted side may have put a directory in the way */
+			clean_merge = 0;
+			if (handle_modify_delete(opt, path, o, a, b))
+				clean_merge = -1;
+		}
+	} else if ((!o_valid && a_valid && !b_valid) ||
+		   (!o_valid && !a_valid && b_valid)) {
+		/* Case B: Added in one. */
+		/* [nothing|directory] -> ([nothing|directory], file) */
+
+		const char *add_branch;
+		const char *other_branch;
+		const char *conf;
+		const struct diff_filespec *contents;
+
+		if (a_valid) {
+			add_branch = opt->branch1;
+			other_branch = opt->branch2;
+			contents = a;
+			conf = _("file/directory");
+		} else {
+			add_branch = opt->branch2;
+			other_branch = opt->branch1;
+			contents = b;
+			conf = _("directory/file");
+		}
+		if (dir_in_way(opt->repo->index, path,
+			       !opt->priv->call_depth && !S_ISGITLINK(a->mode),
+			       0)) {
+			char *new_path = unique_path(opt, path, add_branch);
+			clean_merge = 0;
+			output(opt, 1, _("CONFLICT (%s): There is a directory with name %s in %s. "
+			       "Adding %s as %s"),
+			       conf, path, other_branch, path, new_path);
+			if (update_file(opt, 0, contents, new_path))
+				clean_merge = -1;
+			else if (opt->priv->call_depth)
+				remove_file_from_index(opt->repo->index, path);
+			free(new_path);
+		} else {
+			output(opt, 2, _("Adding %s"), path);
+			/* do not overwrite file if already present */
+			if (update_file_flags(opt, contents, path, 1, !a_valid))
+				clean_merge = -1;
+		}
+	} else if (a_valid && b_valid) {
+		if (!o_valid) {
+			/* Case C: Added in both (check for same permissions) */
+			output(opt, 1,
+			       _("CONFLICT (add/add): Merge conflict in %s"),
+			       path);
+			clean_merge = handle_file_collision(opt,
+							    path, NULL, NULL,
+							    opt->branch1,
+							    opt->branch2,
+							    a, b);
+		} else {
+			/* case D: Modified in both, but differently. */
+			struct merge_file_info mfi;
+			int is_dirty = 0; /* unpack_trees would have bailed if dirty */
+			clean_merge = handle_content_merge(&mfi, opt, path,
+							   is_dirty,
+							   o, a, b, NULL);
+		}
+	} else if (!o_valid && !a_valid && !b_valid) {
+		/*
+		 * this entry was deleted altogether. a_mode == 0 means
+		 * we had that path and want to actively remove it.
+		 */
+		remove_file(opt, 1, path, !a->mode);
+	} else
+		BUG("fatal merge failure, shouldn't happen.");
+
+	return clean_merge;
+}
+
+static int merge_trees_internal(struct merge_options *opt,
+				struct tree *head,
+				struct tree *merge,
+				struct tree *merge_base,
+				struct tree **result)
+{
+	struct index_state *istate = opt->repo->index;
+	int code, clean;
+
+	if (opt->subtree_shift) {
+		merge = shift_tree_object(opt->repo, head, merge,
+					  opt->subtree_shift);
+		merge_base = shift_tree_object(opt->repo, head, merge_base,
+					       opt->subtree_shift);
+	}
+
+	if (oideq(&merge_base->object.oid, &merge->object.oid)) {
+		output(opt, 0, _("Already up to date."));
+		*result = head;
+		return 1;
+	}
+
+	code = unpack_trees_start(opt, merge_base, head, merge);
+
+	if (code != 0) {
+		if (show(opt, 4) || opt->priv->call_depth)
+			err(opt, _("merging of trees %s and %s failed"),
+			    oid_to_hex(&head->object.oid),
+			    oid_to_hex(&merge->object.oid));
+		unpack_trees_finish(opt);
+		return -1;
+	}
+
+	if (unmerged_index(istate)) {
+		struct string_list *entries;
+		struct rename_info re_info;
+		int i;
+		/*
+		 * Only need the hashmap while processing entries, so
+		 * initialize it here and free it when we are done running
+		 * through the entries. Keeping it in the merge_options as
+		 * opposed to decaring a local hashmap is for convenience
+		 * so that we don't have to pass it to around.
+		 */
+		hashmap_init(&opt->priv->current_file_dir_set, path_hashmap_cmp,
+			     NULL, 512);
+		get_files_dirs(opt, head);
+		get_files_dirs(opt, merge);
+
+		entries = get_unmerged(opt->repo->index);
+		clean = detect_and_process_renames(opt, merge_base, head, merge,
+						   entries, &re_info);
+		record_df_conflict_files(opt, entries);
+		if (clean < 0)
+			goto cleanup;
+		for (i = entries->nr-1; 0 <= i; i--) {
+			const char *path = entries->items[i].string;
+			struct stage_data *e = entries->items[i].util;
+			if (!e->processed) {
+				int ret = process_entry(opt, path, e);
+				if (!ret)
+					clean = 0;
+				else if (ret < 0) {
+					clean = ret;
+					goto cleanup;
+				}
+			}
+		}
+		for (i = 0; i < entries->nr; i++) {
+			struct stage_data *e = entries->items[i].util;
+			if (!e->processed)
+				BUG("unprocessed path??? %s",
+				    entries->items[i].string);
+		}
+
+	cleanup:
+		final_cleanup_renames(&re_info);
+
+		string_list_clear(entries, 1);
+		free(entries);
+
+		hashmap_clear_and_free(&opt->priv->current_file_dir_set,
+					struct path_hashmap_entry, e);
+
+		if (clean < 0) {
+			unpack_trees_finish(opt);
+			return clean;
+		}
+	}
+	else
+		clean = 1;
+
+	unpack_trees_finish(opt);
+
+	if (opt->priv->call_depth &&
+	    !(*result = write_in_core_index_as_tree(opt->repo)))
+		return -1;
+
+	return clean;
+}
+
+/*
+ * Merge the commits h1 and h2, returning a flag (int) indicating the
+ * cleanness of the merge.  Also, if opt->priv->call_depth, create a
+ * virtual commit and write its location to *result.
+ */
+static int merge_recursive_internal(struct merge_options *opt,
+				    struct commit *h1,
+				    struct commit *h2,
+				    struct commit_list *merge_bases,
+				    struct commit **result)
+{
+	struct commit_list *iter;
+	struct commit *merged_merge_bases;
+	struct tree *result_tree;
+	int clean;
+	const char *ancestor_name;
+	struct strbuf merge_base_abbrev = STRBUF_INIT;
+
+	if (show(opt, 4)) {
+		output(opt, 4, _("Merging:"));
+		output_commit_title(opt, h1);
+		output_commit_title(opt, h2);
+	}
+
+	if (!merge_bases) {
+		merge_bases = get_merge_bases(h1, h2);
+		merge_bases = reverse_commit_list(merge_bases);
+	}
+
+	if (show(opt, 5)) {
+		unsigned cnt = commit_list_count(merge_bases);
+
+		output(opt, 5, Q_("found %u common ancestor:",
+				"found %u common ancestors:", cnt), cnt);
+		for (iter = merge_bases; iter; iter = iter->next)
+			output_commit_title(opt, iter->item);
+	}
+
+	merged_merge_bases = pop_commit(&merge_bases);
+	if (!merged_merge_bases) {
+		/* if there is no common ancestor, use an empty tree */
+		struct tree *tree;
+
+		tree = lookup_tree(opt->repo, opt->repo->hash_algo->empty_tree);
+		merged_merge_bases = make_virtual_commit(opt->repo, tree,
+							 "ancestor");
+		ancestor_name = "empty tree";
+	} else if (opt->ancestor && !opt->priv->call_depth) {
+		ancestor_name = opt->ancestor;
+	} else if (merge_bases) {
+		ancestor_name = "merged common ancestors";
+	} else {
+		strbuf_add_unique_abbrev(&merge_base_abbrev,
+					 &merged_merge_bases->object.oid,
+					 DEFAULT_ABBREV);
+		ancestor_name = merge_base_abbrev.buf;
+	}
+
+	for (iter = merge_bases; iter; iter = iter->next) {
+		const char *saved_b1, *saved_b2;
+		opt->priv->call_depth++;
+		/*
+		 * When the merge fails, the result contains files
+		 * with conflict markers. The cleanness flag is
+		 * ignored (unless indicating an error), it was never
+		 * actually used, as result of merge_trees has always
+		 * overwritten it: the committed "conflicts" were
+		 * already resolved.
+		 */
+		discard_index(opt->repo->index);
+		saved_b1 = opt->branch1;
+		saved_b2 = opt->branch2;
+		opt->branch1 = "Temporary merge branch 1";
+		opt->branch2 = "Temporary merge branch 2";
+		if (merge_recursive_internal(opt, merged_merge_bases, iter->item,
+					     NULL, &merged_merge_bases) < 0)
+			return -1;
+		opt->branch1 = saved_b1;
+		opt->branch2 = saved_b2;
+		opt->priv->call_depth--;
+
+		if (!merged_merge_bases)
+			return err(opt, _("merge returned no commit"));
+	}
+
+	/*
+	 * FIXME: Since merge_recursive_internal() is only ever called by
+	 * places that ensure the index is loaded first
+	 * (e.g. builtin/merge.c, rebase/sequencer, etc.), in the common
+	 * case where the merge base was unique that means when we get here
+	 * we immediately discard the index and re-read it, which is a
+	 * complete waste of time.  We should only be discarding and
+	 * re-reading if we were forced to recurse.
+	 */
+	discard_index(opt->repo->index);
+	if (!opt->priv->call_depth)
+		repo_read_index(opt->repo);
+
+	opt->ancestor = ancestor_name;
+	clean = merge_trees_internal(opt,
+				     repo_get_commit_tree(opt->repo, h1),
+				     repo_get_commit_tree(opt->repo, h2),
+				     repo_get_commit_tree(opt->repo,
+							  merged_merge_bases),
+				     &result_tree);
+	strbuf_release(&merge_base_abbrev);
+	opt->ancestor = NULL;  /* avoid accidental re-use of opt->ancestor */
+	if (clean < 0) {
+		flush_output(opt);
+		return clean;
+	}
+
+	if (opt->priv->call_depth) {
+		*result = make_virtual_commit(opt->repo, result_tree,
+					      "merged tree");
+		commit_list_insert(h1, &(*result)->parents);
+		commit_list_insert(h2, &(*result)->parents->next);
+	}
+	return clean;
+}
+
+static int merge_start(struct merge_options *opt, struct tree *head)
+{
+	struct strbuf sb = STRBUF_INIT;
+
+	/* Sanity checks on opt */
+	assert(opt->repo);
+
+	assert(opt->branch1 && opt->branch2);
+
+	assert(opt->detect_renames >= -1 &&
+	       opt->detect_renames <= DIFF_DETECT_COPY);
+	assert(opt->detect_directory_renames >= MERGE_DIRECTORY_RENAMES_NONE &&
+	       opt->detect_directory_renames <= MERGE_DIRECTORY_RENAMES_TRUE);
+	assert(opt->rename_limit >= -1);
+	assert(opt->rename_score >= 0 && opt->rename_score <= MAX_SCORE);
+	assert(opt->show_rename_progress >= 0 && opt->show_rename_progress <= 1);
+
+	assert(opt->xdl_opts >= 0);
+	assert(opt->recursive_variant >= MERGE_VARIANT_NORMAL &&
+	       opt->recursive_variant <= MERGE_VARIANT_THEIRS);
+
+	assert(opt->verbosity >= 0 && opt->verbosity <= 5);
+	assert(opt->buffer_output <= 2);
+	assert(opt->obuf.len == 0);
+
+	assert(opt->priv == NULL);
+
+	/* Not supported; option specific to merge-ort */
+	assert(!opt->record_conflict_msgs_as_headers);
+	assert(!opt->msg_header_prefix);
+
+	/* Sanity check on repo state; index must match head */
+	if (repo_index_has_changes(opt->repo, head, &sb)) {
+		err(opt, _("Your local changes to the following files would be overwritten by merge:\n  %s"),
+		    sb.buf);
+		strbuf_release(&sb);
+		return -1;
+	}
+
+	CALLOC_ARRAY(opt->priv, 1);
+	string_list_init_dup(&opt->priv->df_conflict_file_set);
+	return 0;
+}
+
+static void merge_finalize(struct merge_options *opt)
+{
+	flush_output(opt);
+	if (!opt->priv->call_depth && opt->buffer_output < 2)
+		strbuf_release(&opt->obuf);
+	if (show(opt, 2))
+		diff_warn_rename_limit("merge.renamelimit",
+				       opt->priv->needed_rename_limit, 0);
+	FREE_AND_NULL(opt->priv);
+}
+
+int merge_trees(struct merge_options *opt,
+		struct tree *head,
+		struct tree *merge,
+		struct tree *merge_base)
+{
+	int clean;
+	struct tree *ignored;
+
+	assert(opt->ancestor != NULL);
+
+	if (merge_start(opt, head))
+		return -1;
+	clean = merge_trees_internal(opt, head, merge, merge_base, &ignored);
+	merge_finalize(opt);
+
+	return clean;
+}
+
+int merge_recursive(struct merge_options *opt,
+		    struct commit *h1,
+		    struct commit *h2,
+		    struct commit_list *merge_bases,
+		    struct commit **result)
+{
+	int clean;
+
+	assert(opt->ancestor == NULL ||
+	       !strcmp(opt->ancestor, "constructed merge base"));
+
+	prepare_repo_settings(opt->repo);
+	opt->repo->settings.command_requires_full_index = 1;
+
+	if (merge_start(opt, repo_get_commit_tree(opt->repo, h1)))
+		return -1;
+	clean = merge_recursive_internal(opt, h1, h2, merge_bases, result);
+	merge_finalize(opt);
+
+	return clean;
+}
+
+static struct commit *get_ref(struct repository *repo,
+			      const struct object_id *oid,
+			      const char *name)
+{
+	struct object *object;
+
+	object = deref_tag(repo, parse_object(repo, oid),
+			   name, strlen(name));
+	if (!object)
+		return NULL;
+	if (object->type == OBJ_TREE)
+		return make_virtual_commit(repo, (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 *opt,
+			    const struct object_id *head,
+			    const struct object_id *merge,
+			    int num_merge_bases,
+			    const struct object_id **merge_bases,
+			    struct commit **result)
+{
+	int clean;
+	struct lock_file lock = LOCK_INIT;
+	struct commit *head_commit = get_ref(opt->repo, head, opt->branch1);
+	struct commit *next_commit = get_ref(opt->repo, merge, opt->branch2);
+	struct commit_list *ca = NULL;
+
+	if (merge_bases) {
+		int i;
+		for (i = 0; i < num_merge_bases; ++i) {
+			struct commit *base;
+			if (!(base = get_ref(opt->repo, merge_bases[i],
+					     oid_to_hex(merge_bases[i]))))
+				return err(opt, _("Could not parse object '%s'"),
+					   oid_to_hex(merge_bases[i]));
+			commit_list_insert(base, &ca);
+		}
+		if (num_merge_bases == 1)
+			opt->ancestor = "constructed merge base";
+	}
+
+	repo_hold_locked_index(opt->repo, &lock, LOCK_DIE_ON_ERROR);
+	clean = merge_recursive(opt, head_commit, next_commit, ca,
+				result);
+	if (clean < 0) {
+		rollback_lock_file(&lock);
+		return clean;
+	}
+
+	if (write_locked_index(opt->repo->index, &lock,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
+		return err(opt, _("Unable to write index."));
+
+	return clean ? 0 : 1;
+}
+
+static void merge_recursive_config(struct merge_options *opt)
+{
+	char *value = NULL;
+	int renormalize = 0;
+	git_config_get_int("merge.verbosity", &opt->verbosity);
+	git_config_get_int("diff.renamelimit", &opt->rename_limit);
+	git_config_get_int("merge.renamelimit", &opt->rename_limit);
+	git_config_get_bool("merge.renormalize", &renormalize);
+	opt->renormalize = renormalize;
+	if (!git_config_get_string("diff.renames", &value)) {
+		opt->detect_renames = git_config_rename("diff.renames", value);
+		free(value);
+	}
+	if (!git_config_get_string("merge.renames", &value)) {
+		opt->detect_renames = git_config_rename("merge.renames", value);
+		free(value);
+	}
+	if (!git_config_get_string("merge.directoryrenames", &value)) {
+		int boolval = git_parse_maybe_bool(value);
+		if (0 <= boolval) {
+			opt->detect_directory_renames = boolval ?
+				MERGE_DIRECTORY_RENAMES_TRUE :
+				MERGE_DIRECTORY_RENAMES_NONE;
+		} else if (!strcasecmp(value, "conflict")) {
+			opt->detect_directory_renames =
+				MERGE_DIRECTORY_RENAMES_CONFLICT;
+		} /* avoid erroring on values from future versions of git */
+		free(value);
+	}
+	git_config(git_xmerge_config, NULL);
+}
+
+void init_merge_options(struct merge_options *opt,
+			struct repository *repo)
+{
+	const char *merge_verbosity;
+	memset(opt, 0, sizeof(struct merge_options));
+
+	opt->repo = repo;
+
+	opt->detect_renames = -1;
+	opt->detect_directory_renames = MERGE_DIRECTORY_RENAMES_CONFLICT;
+	opt->rename_limit = -1;
+
+	opt->verbosity = 2;
+	opt->buffer_output = 1;
+	strbuf_init(&opt->obuf, 0);
+
+	opt->renormalize = 0;
+
+	merge_recursive_config(opt);
+	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
+	if (merge_verbosity)
+		opt->verbosity = strtol(merge_verbosity, NULL, 10);
+	if (opt->verbosity >= 5)
+		opt->buffer_output = 0;
+}
+
+int parse_merge_opt(struct merge_options *opt, const char *s)
+{
+	const char *arg;
+
+	if (!s || !*s)
+		return -1;
+	if (!strcmp(s, "ours"))
+		opt->recursive_variant = MERGE_VARIANT_OURS;
+	else if (!strcmp(s, "theirs"))
+		opt->recursive_variant = MERGE_VARIANT_THEIRS;
+	else if (!strcmp(s, "subtree"))
+		opt->subtree_shift = "";
+	else if (skip_prefix(s, "subtree=", &arg))
+		opt->subtree_shift = arg;
+	else if (!strcmp(s, "patience"))
+		opt->xdl_opts = DIFF_WITH_ALG(opt, PATIENCE_DIFF);
+	else if (!strcmp(s, "histogram"))
+		opt->xdl_opts = DIFF_WITH_ALG(opt, HISTOGRAM_DIFF);
+	else if (skip_prefix(s, "diff-algorithm=", &arg)) {
+		long value = parse_algorithm_value(arg);
+		if (value < 0)
+			return -1;
+		/* clear out previous settings */
+		DIFF_XDL_CLR(opt, NEED_MINIMAL);
+		opt->xdl_opts &= ~XDF_DIFF_ALGORITHM_MASK;
+		opt->xdl_opts |= value;
+	}
+	else if (!strcmp(s, "ignore-space-change"))
+		DIFF_XDL_SET(opt, IGNORE_WHITESPACE_CHANGE);
+	else if (!strcmp(s, "ignore-all-space"))
+		DIFF_XDL_SET(opt, IGNORE_WHITESPACE);
+	else if (!strcmp(s, "ignore-space-at-eol"))
+		DIFF_XDL_SET(opt, IGNORE_WHITESPACE_AT_EOL);
+	else if (!strcmp(s, "ignore-cr-at-eol"))
+		DIFF_XDL_SET(opt, IGNORE_CR_AT_EOL);
+	else if (!strcmp(s, "renormalize"))
+		opt->renormalize = 1;
+	else if (!strcmp(s, "no-renormalize"))
+		opt->renormalize = 0;
+	else if (!strcmp(s, "no-renames"))
+		opt->detect_renames = 0;
+	else if (!strcmp(s, "find-renames")) {
+		opt->detect_renames = 1;
+		opt->rename_score = 0;
+	}
+	else if (skip_prefix(s, "find-renames=", &arg) ||
+		 skip_prefix(s, "rename-threshold=", &arg)) {
+		if ((opt->rename_score = parse_rename_score(&arg)) == -1 || *arg != 0)
+			return -1;
+		opt->detect_renames = 1;
+	}
+	/*
+	 * Please update $__git_merge_strategy_options in
+	 * git-completion.bash when you add new options
+	 */
+	else
+		return -1;
+	return 0;
+}