X-Git-Url: http://git.ipfire.org/?a=blobdiff_plain;f=merge-ort.c;h=931b91438cf1bb5abaeb98fdd0b3292af66e5bd7;hb=608cc4f2738d5e2055e238b2a9e482180d948a05;hp=d36a92b59b76fe49424ae97e4cd2777badb7e318;hpb=27d7c8599b159862762e2bd121c22d516fb04e90;p=thirdparty%2Fgit.git

diff --git a/merge-ort.c b/merge-ort.c
index d36a92b59b..931b91438c 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -25,8 +25,11 @@
 #include "diff.h"
 #include "diffcore.h"
 #include "dir.h"
+#include "ll-merge.h"
 #include "object-store.h"
+#include "revision.h"
 #include "strmap.h"
+#include "submodule.h"
 #include "tree.h"
 #include "unpack-trees.h"
 #include "xdiff-interface.h"
@@ -49,14 +52,42 @@ enum merge_side {
 };
 
 struct rename_info {
+	/*
+	 * All variables that are arrays of size 3 correspond to data tracked
+	 * for the sides in enum merge_side.  Index 0 is almost always unused
+	 * because we often only need to track information for MERGE_SIDE1 and
+	 * MERGE_SIDE2 (MERGE_BASE can't have rename information since renames
+	 * are determined relative to what changed since the MERGE_BASE).
+	 */
+
 	/*
 	 * pairs: pairing of filenames from diffcore_rename()
-	 *
-	 * Index 1 and 2 correspond to sides 1 & 2 as used in
-	 * conflict_info.stages.  Index 0 unused.
 	 */
 	struct diff_queue_struct pairs[3];
 
+	/*
+	 * dirs_removed: directories removed on a given side of history.
+	 */
+	struct strset dirs_removed[3];
+
+	/*
+	 * dir_rename_count: tracking where parts of a directory were renamed to
+	 *
+	 * When files in a directory are renamed, they may not all go to the
+	 * same location.  Each strmap here tracks:
+	 *      old_dir => {new_dir => int}
+	 * That is, dir_rename_count[side] is a strmap to a strintmap.
+	 */
+	struct strmap dir_rename_count[3];
+
+	/*
+	 * dir_renames: computed directory renames
+	 *
+	 * This is a map of old_dir => new_dir and is derived in part from
+	 * dir_rename_count.
+	 */
+	struct strmap dir_renames[3];
+
 	/*
 	 * needed_limit: value needed for inexact rename detection to run
 	 *
@@ -140,12 +171,15 @@ struct merge_options_internal {
 	struct rename_info renames;
 
 	/*
-	 * current_dir_name: temporary var used in collect_merge_info_callback()
+	 * current_dir_name, toplevel_dir: temporary vars
 	 *
-	 * Used to set merged_info.directory_name; see documentation for that
-	 * variable and the requirements placed on that field.
+	 * These are used in collect_merge_info_callback(), and will set the
+	 * various merged_info.directory_name for the various paths we get;
+	 * see documentation for that variable and the requirements placed on
+	 * that field.
 	 */
 	const char *current_dir_name;
+	const char *toplevel_dir;
 
 	/* call_depth: recursion level counter for merging merge bases */
 	int call_depth;
@@ -280,8 +314,12 @@ static void free_strmap_strings(struct strmap *map)
 static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
 					  int reinitialize)
 {
+	struct rename_info *renames = &opti->renames;
+	int i;
 	void (*strmap_func)(struct strmap *, int) =
 		reinitialize ? strmap_partial_clear : strmap_clear;
+	void (*strset_func)(struct strset *) =
+		reinitialize ? strset_partial_clear : strset_clear;
 
 	/*
 	 * We marked opti->paths with strdup_strings = 0, so that we
@@ -311,6 +349,23 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
 	string_list_clear(&opti->paths_to_free, 0);
 	opti->paths_to_free.strdup_strings = 0;
 
+	/* Free memory used by various renames maps */
+	for (i = MERGE_SIDE1; i <= MERGE_SIDE2; ++i) {
+		struct hashmap_iter iter;
+		struct strmap_entry *entry;
+
+		strset_func(&renames->dirs_removed[i]);
+
+		strmap_for_each_entry(&renames->dir_rename_count[i],
+				      &iter, entry) {
+			struct strintmap *counts = entry->value;
+			strintmap_clear(counts);
+		}
+		strmap_func(&renames->dir_rename_count[i], 1);
+
+		strmap_func(&renames->dir_renames[i], 0);
+	}
+
 	if (!reinitialize) {
 		struct hashmap_iter iter;
 		struct strmap_entry *e;
@@ -349,6 +404,25 @@ static int err(struct merge_options *opt, const char *err, ...)
 	return -1;
 }
 
+static void format_commit(struct strbuf *sb,
+			  int indent,
+			  struct commit *commit)
+{
+	struct merge_remote_desc *desc;
+	struct pretty_print_context ctx = {0};
+	ctx.abbrev = DEFAULT_ABBREV;
+
+	strbuf_addchars(sb, ' ', indent);
+	desc = merge_remote_util(commit);
+	if (desc) {
+		strbuf_addf(sb, "virtual %s\n", desc->name);
+		return;
+	}
+
+	format_commit_message(commit, "%h %s", sb, &ctx);
+	strbuf_addch(sb, '\n');
+}
+
 __attribute__((format (printf, 4, 5)))
 static void path_msg(struct merge_options *opt,
 		     const char *path,
@@ -370,6 +444,36 @@ static void path_msg(struct merge_options *opt,
 	strbuf_addch(sb, '\n');
 }
 
+/* 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 strmap *existing_paths,
+			 const char *path,
+			 const char *branch)
+{
+	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 (strmap_contains(existing_paths, newpath.buf)) {
+		strbuf_setlen(&newpath, base_len);
+		strbuf_addf(&newpath, "_%d", suffix++);
+	}
+
+	return strbuf_detach(&newpath, NULL);
+}
+
 /*** Function Grouping: functions related to collect_merge_info() ***/
 
 static void setup_path_info(struct merge_options *opt,
@@ -431,6 +535,27 @@ static void setup_path_info(struct merge_options *opt,
 	result->util = mi;
 }
 
+static void collect_rename_info(struct merge_options *opt,
+				struct name_entry *names,
+				const char *dirname,
+				const char *fullname,
+				unsigned filemask,
+				unsigned dirmask,
+				unsigned match_mask)
+{
+	struct rename_info *renames = &opt->priv->renames;
+
+	/* Update dirs_removed, as needed */
+	if (dirmask == 1 || dirmask == 3 || dirmask == 5) {
+		/* absent_mask = 0x07 - dirmask; sides = absent_mask/2 */
+		unsigned sides = (0x07 - dirmask)/2;
+		if (sides & 1)
+			strset_add(&renames->dirs_removed[1], fullname);
+		if (sides & 2)
+			strset_add(&renames->dirs_removed[2], fullname);
+	}
+}
+
 static int collect_merge_info_callback(int n,
 				       unsigned long mask,
 				       unsigned long dirmask,
@@ -531,6 +656,12 @@ static int collect_merge_info_callback(int n,
 		return mask;
 	}
 
+	/*
+	 * Gather additional information used in rename detection.
+	 */
+	collect_rename_info(opt, names, dirname, fullpath,
+			    filemask, dirmask, match_mask);
+
 	/*
 	 * Record information about the path so we can resolve later in
 	 * process_entries.
@@ -606,10 +737,10 @@ static int collect_merge_info(struct merge_options *opt,
 	int ret;
 	struct tree_desc t[3];
 	struct traverse_info info;
-	const char *toplevel_dir_placeholder = "";
 
-	opt->priv->current_dir_name = toplevel_dir_placeholder;
-	setup_traverse_info(&info, toplevel_dir_placeholder);
+	opt->priv->toplevel_dir = "";
+	opt->priv->current_dir_name = opt->priv->toplevel_dir;
+	setup_traverse_info(&info, opt->priv->toplevel_dir);
 	info.fn = collect_merge_info_callback;
 	info.data = opt;
 	info.show_all_errors = 1;
@@ -621,13 +752,258 @@ static int collect_merge_info(struct merge_options *opt,
 	init_tree_desc(t + 1, side1->buffer, side1->size);
 	init_tree_desc(t + 2, side2->buffer, side2->size);
 
+	trace2_region_enter("merge", "traverse_trees", opt->repo);
 	ret = traverse_trees(NULL, 3, t, &info);
+	trace2_region_leave("merge", "traverse_trees", opt->repo);
 
 	return ret;
 }
 
 /*** Function Grouping: functions related to threeway content merges ***/
 
+static int find_first_merges(struct repository *repo,
+			     const char *path,
+			     struct commit *a,
+			     struct commit *b,
+			     struct object_array *result)
+{
+	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);
+	rev_opts.submodule = path;
+	/* 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 (in_merge_bases(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 && in_merge_bases(m2, m1)) {
+				contains_another = 1;
+				break;
+			}
+		}
+
+		if (!contains_another)
+			add_object_array(merges.objects[i].item, NULL, result);
+	}
+
+	object_array_clear(&merges);
+	return result->nr;
+}
+
+static int merge_submodule(struct merge_options *opt,
+			   const char *path,
+			   const struct object_id *o,
+			   const struct object_id *a,
+			   const struct object_id *b,
+			   struct object_id *result)
+{
+	struct commit *commit_o, *commit_a, *commit_b;
+	int parent_count;
+	struct object_array merges;
+	struct strbuf sb = STRBUF_INIT;
+
+	int i;
+	int search = !opt->priv->call_depth;
+
+	/* store fallback answer in result in case we fail */
+	oidcpy(result, opt->priv->call_depth ? o : a);
+
+	/* we can not handle deletion conflicts */
+	if (is_null_oid(o))
+		return 0;
+	if (is_null_oid(a))
+		return 0;
+	if (is_null_oid(b))
+		return 0;
+
+	if (add_submodule_odb(path)) {
+		path_msg(opt, path, 0,
+			 _("Failed to merge submodule %s (not checked out)"),
+			 path);
+		return 0;
+	}
+
+	if (!(commit_o = lookup_commit_reference(opt->repo, o)) ||
+	    !(commit_a = lookup_commit_reference(opt->repo, a)) ||
+	    !(commit_b = lookup_commit_reference(opt->repo, b))) {
+		path_msg(opt, path, 0,
+			 _("Failed to merge submodule %s (commits not present)"),
+			 path);
+		return 0;
+	}
+
+	/* check whether both changes are forward */
+	if (!in_merge_bases(commit_o, commit_a) ||
+	    !in_merge_bases(commit_o, commit_b)) {
+		path_msg(opt, path, 0,
+			 _("Failed to merge submodule %s "
+			   "(commits don't follow merge-base)"),
+			 path);
+		return 0;
+	}
+
+	/* Case #1: a is contained in b or vice versa */
+	if (in_merge_bases(commit_a, commit_b)) {
+		oidcpy(result, b);
+		path_msg(opt, path, 1,
+			 _("Note: Fast-forwarding submodule %s to %s"),
+			 path, oid_to_hex(b));
+		return 1;
+	}
+	if (in_merge_bases(commit_b, commit_a)) {
+		oidcpy(result, a);
+		path_msg(opt, path, 1,
+			 _("Note: Fast-forwarding submodule %s to %s"),
+			 path, oid_to_hex(a));
+		return 1;
+	}
+
+	/*
+	 * 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)
+		return 0;
+
+	/* find commit which merges them */
+	parent_count = find_first_merges(opt->repo, path, commit_a, commit_b,
+					 &merges);
+	switch (parent_count) {
+	case 0:
+		path_msg(opt, path, 0, _("Failed to merge submodule %s"), path);
+		break;
+
+	case 1:
+		format_commit(&sb, 4,
+			      (struct commit *)merges.objects[0].item);
+		path_msg(opt, path, 0,
+			 _("Failed to merge submodule %s, but a possible merge "
+			   "resolution exists:\n%s\n"),
+			 path, sb.buf);
+		path_msg(opt, path, 1,
+			 _("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);
+		strbuf_release(&sb);
+		break;
+	default:
+		for (i = 0; i < merges.nr; i++)
+			format_commit(&sb, 4,
+				      (struct commit *)merges.objects[i].item);
+		path_msg(opt, path, 0,
+			 _("Failed to merge submodule %s, but multiple "
+			   "possible merges exist:\n%s"), path, sb.buf);
+		strbuf_release(&sb);
+	}
+
+	object_array_clear(&merges);
+	return 0;
+}
+
+static int merge_3way(struct merge_options *opt,
+		      const char *path,
+		      const struct object_id *o,
+		      const struct object_id *a,
+		      const struct object_id *b,
+		      const char *pathnames[3],
+		      const int extra_marker_size,
+		      mmbuffer_t *result_buf)
+{
+	mmfile_t orig, src1, src2;
+	struct ll_merge_options ll_opts = {0};
+	char *base, *name1, *name2;
+	int 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(pathnames[0] && pathnames[1] && pathnames[2] && opt->ancestor);
+	if (pathnames[0] == pathnames[1] && pathnames[1] == pathnames[2]) {
+		base  = mkpathdup("%s", opt->ancestor);
+		name1 = mkpathdup("%s", opt->branch1);
+		name2 = mkpathdup("%s", opt->branch2);
+	} else {
+		base  = mkpathdup("%s:%s", opt->ancestor, pathnames[0]);
+		name1 = mkpathdup("%s:%s", opt->branch1,  pathnames[1]);
+		name2 = mkpathdup("%s:%s", opt->branch2,  pathnames[2]);
+	}
+
+	read_mmblob(&orig, o);
+	read_mmblob(&src1, a);
+	read_mmblob(&src2, b);
+
+	merge_status = ll_merge(result_buf, path, &orig, base,
+				&src1, name1, &src2, name2,
+				opt->repo->index, &ll_opts);
+
+	free(base);
+	free(name1);
+	free(name2);
+	free(orig.ptr);
+	free(src1.ptr);
+	free(src2.ptr);
+	return merge_status;
+}
+
 static int handle_content_merge(struct merge_options *opt,
 				const char *path,
 				const struct version_info *o,
@@ -637,7 +1013,130 @@ static int handle_content_merge(struct merge_options *opt,
 				const int extra_marker_size,
 				struct version_info *result)
 {
-	die("Not yet implemented");
+	/*
+	 * path is the target location where we want to put the file, and
+	 * is used to determine any normalization rules in ll_merge.
+	 *
+	 * The normal case is that path and all entries in pathnames are
+	 * identical, though renames can affect which path we got one of
+	 * the three blobs to merge on various sides of history.
+	 *
+	 * extra_marker_size is the amount to extend conflict markers in
+	 * ll_merge; this is neeed if we have content merges of content
+	 * merges, which happens for example with rename/rename(2to1) and
+	 * rename/add conflicts.
+	 */
+	unsigned clean = 1;
+
+	/*
+	 * handle_content_merge() needs both files to be of the same type, i.e.
+	 * both files OR both submodules OR both symlinks.  Conflicting types
+	 * needs to be handled elsewhere.
+	 */
+	assert((S_IFMT & a->mode) == (S_IFMT & b->mode));
+
+	/* Merge modes */
+	if (a->mode == b->mode || a->mode == o->mode)
+		result->mode = b->mode;
+	else {
+		/* must be the 100644/100755 case */
+		assert(S_ISREG(a->mode));
+		result->mode = a->mode;
+		clean = (b->mode == o->mode);
+		/*
+		 * FIXME: If opt->priv->call_depth && !clean, then we really
+		 * should not make result->mode match either a->mode or
+		 * b->mode; that causes t6036 "check conflicting mode for
+		 * regular file" to fail.  It would be best to use some other
+		 * mode, but we'll confuse all kinds of stuff if we use one
+		 * where S_ISREG(result->mode) isn't true, and if we use
+		 * something like 0100666, then tree-walk.c's calls to
+		 * canon_mode() will just normalize that to 100644 for us and
+		 * thus not solve anything.
+		 *
+		 * Figure out if there's some kind of way we can work around
+		 * this...
+		 */
+	}
+
+	/*
+	 * Trivial oid merge.
+	 *
+	 * Note: While one might assume that the next four lines would
+	 * be unnecessary due to the fact that match_mask is often
+	 * setup and already handled, renames don't always take care
+	 * of that.
+	 */
+	if (oideq(&a->oid, &b->oid) || oideq(&a->oid, &o->oid))
+		oidcpy(&result->oid, &b->oid);
+	else if (oideq(&b->oid, &o->oid))
+		oidcpy(&result->oid, &a->oid);
+
+	/* Remaining rules depend on file vs. submodule vs. symlink. */
+	else if (S_ISREG(a->mode)) {
+		mmbuffer_t result_buf;
+		int ret = 0, merge_status;
+		int two_way;
+
+		/*
+		 * If 'o' is different type, treat it as null so we do a
+		 * two-way merge.
+		 */
+		two_way = ((S_IFMT & o->mode) != (S_IFMT & a->mode));
+
+		merge_status = merge_3way(opt, path,
+					  two_way ? &null_oid : &o->oid,
+					  &a->oid, &b->oid,
+					  pathnames, extra_marker_size,
+					  &result_buf);
+
+		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,
+				      blob_type, &result->oid))
+			ret = err(opt, _("Unable to add %s to database"),
+				  path);
+
+		free(result_buf.ptr);
+		if (ret)
+			return -1;
+		clean &= (merge_status == 0);
+		path_msg(opt, path, 1, _("Auto-merging %s"), path);
+	} else if (S_ISGITLINK(a->mode)) {
+		int two_way = ((S_IFMT & o->mode) != (S_IFMT & a->mode));
+		clean = merge_submodule(opt, pathnames[0],
+					two_way ? &null_oid : &o->oid,
+					&a->oid, &b->oid, &result->oid);
+		if (opt->priv->call_depth && two_way && !clean) {
+			result->mode = o->mode;
+			oidcpy(&result->oid, &o->oid);
+		}
+	} else if (S_ISLNK(a->mode)) {
+		if (opt->priv->call_depth) {
+			clean = 0;
+			result->mode = o->mode;
+			oidcpy(&result->oid, &o->oid);
+		} else {
+			switch (opt->recursive_variant) {
+			case MERGE_VARIANT_NORMAL:
+				clean = 0;
+				oidcpy(&result->oid, &a->oid);
+				break;
+			case MERGE_VARIANT_OURS:
+				oidcpy(&result->oid, &a->oid);
+				break;
+			case MERGE_VARIANT_THEIRS:
+				oidcpy(&result->oid, &b->oid);
+				break;
+			}
+		}
+	} else
+		BUG("unsupported object type in the tree: %06o for %s",
+		    a->mode, path);
+
+	return clean;
 }
 
 /*** Function Grouping: functions related to detect_and_process_renames(), ***
@@ -645,6 +1144,649 @@ static int handle_content_merge(struct merge_options *opt,
 
 /*** Function Grouping: functions related to directory rename detection ***/
 
+struct collision_info {
+	struct string_list source_files;
+	unsigned reported_already:1;
+};
+
+/*
+ * Return a new string that replaces the beginning portion (which matches
+ * rename_info->key), with rename_info->util.new_dir.  In perl-speak:
+ *   new_path_name = (old_path =~ s/rename_info->key/rename_info->value/);
+ * NOTE:
+ *   Caller must ensure that old_path starts with rename_info->key + '/'.
+ */
+static char *apply_dir_rename(struct strmap_entry *rename_info,
+			      const char *old_path)
+{
+	struct strbuf new_path = STRBUF_INIT;
+	const char *old_dir = rename_info->key;
+	const char *new_dir = rename_info->value;
+	int oldlen, newlen, new_dir_len;
+
+	oldlen = strlen(old_dir);
+	if (*new_dir == '\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++;
+	new_dir_len = strlen(new_dir);
+	newlen = new_dir_len + (strlen(old_path) - oldlen) + 1;
+	strbuf_grow(&new_path, newlen);
+	strbuf_add(&new_path, new_dir, new_dir_len);
+	strbuf_addstr(&new_path, &old_path[oldlen]);
+
+	return strbuf_detach(&new_path, NULL);
+}
+
+static int path_in_way(struct strmap *paths, const char *path, unsigned side_mask)
+{
+	struct merged_info *mi = strmap_get(paths, path);
+	struct conflict_info *ci;
+	if (!mi)
+		return 0;
+	INITIALIZE_CI(ci, mi);
+	return mi->clean || (side_mask & (ci->filemask | ci->dirmask));
+}
+
+/*
+ * See if there is a directory rename for path, and if there are any file
+ * level conflicts on the given side 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,
+					 unsigned side_index,
+					 struct strmap_entry *rename_info,
+					 struct strmap *collisions)
+{
+	char *new_path = NULL;
+	struct collision_info *c_info;
+	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(rename_info, path);
+	if (!new_path)
+		BUG("Failed to apply directory rename!");
+
+	/*
+	 * 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.
+	 */
+	c_info = strmap_get(collisions, new_path);
+	if (c_info == NULL)
+		BUG("c_info 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 (c_info->reported_already) {
+		clean = 0;
+	} else if (path_in_way(&opt->priv->paths, new_path, 1 << side_index)) {
+		c_info->reported_already = 1;
+		strbuf_add_separated_string_list(&collision_paths, ", ",
+						 &c_info->source_files);
+		path_msg(opt, new_path, 0,
+			 _("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 (c_info->source_files.nr > 1) {
+		c_info->reported_already = 1;
+		strbuf_add_separated_string_list(&collision_paths, ", ",
+						 &c_info->source_files);
+		path_msg(opt, new_path, 0,
+			 _("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;
+}
+
+static void dirname_munge(char *filename)
+{
+	char *slash = strrchr(filename, '/');
+	if (!slash)
+		slash = filename;
+	*slash = '\0';
+}
+
+static void increment_count(struct strmap *dir_rename_count,
+			    char *old_dir,
+			    char *new_dir)
+{
+	struct strintmap *counts;
+	struct strmap_entry *e;
+
+	/* Get the {new_dirs -> counts} mapping using old_dir */
+	e = strmap_get_entry(dir_rename_count, old_dir);
+	if (e) {
+		counts = e->value;
+	} else {
+		counts = xmalloc(sizeof(*counts));
+		strintmap_init_with_options(counts, 0, NULL, 1);
+		strmap_put(dir_rename_count, old_dir, counts);
+	}
+
+	/* Increment the count for new_dir */
+	strintmap_incr(counts, new_dir, 1);
+}
+
+static void update_dir_rename_counts(struct strmap *dir_rename_count,
+				     struct strset *dirs_removed,
+				     const char *oldname,
+				     const char *newname)
+{
+	char *old_dir = xstrdup(oldname);
+	char *new_dir = xstrdup(newname);
+	char new_dir_first_char = new_dir[0];
+	int first_time_in_loop = 1;
+
+	while (1) {
+		dirname_munge(old_dir);
+		dirname_munge(new_dir);
+
+		/*
+		 * When renaming
+		 *   "a/b/c/d/e/foo.c" -> "a/b/some/thing/else/e/foo.c"
+		 * then this suggests that both
+		 *   a/b/c/d/e/ => a/b/some/thing/else/e/
+		 *   a/b/c/d/   => a/b/some/thing/else/
+		 * so we want to increment counters for both.  We do NOT,
+		 * however, also want to suggest that there was the following
+		 * rename:
+		 *   a/b/c/ => a/b/some/thing/
+		 * so we need to quit at that point.
+		 *
+		 * Note the when first_time_in_loop, we only strip off the
+		 * basename, and we don't care if that's different.
+		 */
+		if (!first_time_in_loop) {
+			char *old_sub_dir = strchr(old_dir, '\0')+1;
+			char *new_sub_dir = strchr(new_dir, '\0')+1;
+			if (!*new_dir) {
+				/*
+				 * Special case when renaming to root directory,
+				 * i.e. when new_dir == "".  In this case, we had
+				 * something like
+				 *    a/b/subdir => subdir
+				 * and so dirname_munge() sets things up so that
+				 *    old_dir = "a/b\0subdir\0"
+				 *    new_dir = "\0ubdir\0"
+				 * We didn't have a '/' to overwrite a '\0' onto
+				 * in new_dir, so we have to compare differently.
+				 */
+				if (new_dir_first_char != old_sub_dir[0] ||
+				    strcmp(old_sub_dir+1, new_sub_dir))
+					break;
+			} else {
+				if (strcmp(old_sub_dir, new_sub_dir))
+					break;
+			}
+		}
+
+		if (strset_contains(dirs_removed, old_dir))
+			increment_count(dir_rename_count, old_dir, new_dir);
+		else
+			break;
+
+		/* If we hit toplevel directory ("") for old or new dir, quit */
+		if (!*old_dir || !*new_dir)
+			break;
+
+		first_time_in_loop = 0;
+	}
+
+	/* Free resources we don't need anymore */
+	free(old_dir);
+	free(new_dir);
+}
+
+static void compute_rename_counts(struct diff_queue_struct *pairs,
+				  struct strmap *dir_rename_count,
+				  struct strset *dirs_removed)
+{
+	int i;
+
+	for (i = 0; i < pairs->nr; ++i) {
+		struct diff_filepair *pair = pairs->queue[i];
+
+		/* File not part of directory rename if it wasn't renamed */
+		if (pair->status != 'R')
+			continue;
+
+		/*
+		 * Make dir_rename_count contain a map of a map:
+		 *   old_directory -> {new_directory -> count}
+		 * In other words, for every pair look at the directories for
+		 * the old filename and the new filename and count how many
+		 * times that pairing occurs.
+		 */
+		update_dir_rename_counts(dir_rename_count, dirs_removed,
+					 pair->one->path,
+					 pair->two->path);
+	}
+}
+
+static void get_provisional_directory_renames(struct merge_options *opt,
+					      unsigned side,
+					      int *clean)
+{
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+	struct rename_info *renames = &opt->priv->renames;
+
+	compute_rename_counts(&renames->pairs[side],
+			      &renames->dir_rename_count[side],
+			      &renames->dirs_removed[side]);
+	/*
+	 * Collapse
+	 *    dir_rename_count: old_directory -> {new_directory -> count}
+	 * down to
+	 *    dir_renames: old_directory -> best_new_directory
+	 * where best_new_directory is the one with the unique highest count.
+	 */
+	strmap_for_each_entry(&renames->dir_rename_count[side], &iter, entry) {
+		const char *source_dir = entry->key;
+		struct strintmap *counts = entry->value;
+		struct hashmap_iter count_iter;
+		struct strmap_entry *count_entry;
+		int max = 0;
+		int bad_max = 0;
+		const char *best = NULL;
+
+		strintmap_for_each_entry(counts, &count_iter, count_entry) {
+			const char *target_dir = count_entry->key;
+			intptr_t count = (intptr_t)count_entry->value;
+
+			if (count == max)
+				bad_max = max;
+			else if (count > max) {
+				max = count;
+				best = target_dir;
+			}
+		}
+
+		if (bad_max == max) {
+			path_msg(opt, source_dir, 0,
+			       _("CONFLICT (directory rename split): "
+				 "Unclear where to rename %s to; it was "
+				 "renamed to multiple other directories, with "
+				 "no destination getting a majority of the "
+				 "files."),
+			       source_dir);
+			/*
+			 * We should mark this as unclean IF something attempts
+			 * to use this rename.  We do not yet have the logic
+			 * in place to detect if this directory rename is being
+			 * used, and optimizations that reduce the number of
+			 * renames cause this to falsely trigger.  For now,
+			 * just disable it, causing t6423 testcase 2a to break.
+			 * We'll later fix the detection, and when we do we
+			 * will re-enable setting *clean to 0 (and thereby fix
+			 * t6423 testcase 2a).
+			 */
+			/*   *clean = 0;   */
+		} else {
+			strmap_put(&renames->dir_renames[side],
+				   source_dir, (void*)best);
+		}
+	}
+}
+
+static void handle_directory_level_conflicts(struct merge_options *opt)
+{
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+	struct string_list duplicated = STRING_LIST_INIT_NODUP;
+	struct rename_info *renames = &opt->priv->renames;
+	struct strmap *side1_dir_renames = &renames->dir_renames[MERGE_SIDE1];
+	struct strmap *side2_dir_renames = &renames->dir_renames[MERGE_SIDE2];
+	int i;
+
+	strmap_for_each_entry(side1_dir_renames, &iter, entry) {
+		if (strmap_contains(side2_dir_renames, entry->key))
+			string_list_append(&duplicated, entry->key);
+	}
+
+	for (i = 0; i < duplicated.nr; i++) {
+		strmap_remove(side1_dir_renames, duplicated.items[i].string, 0);
+		strmap_remove(side2_dir_renames, duplicated.items[i].string, 0);
+	}
+	string_list_clear(&duplicated, 0);
+}
+
+static struct strmap_entry *check_dir_renamed(const char *path,
+					      struct strmap *dir_renames)
+{
+	char *temp = xstrdup(path);
+	char *end;
+	struct strmap_entry *e = NULL;
+
+	while ((end = strrchr(temp, '/'))) {
+		*end = '\0';
+		e = strmap_get_entry(dir_renames, temp);
+		if (e)
+			break;
+	}
+	free(temp);
+	return e;
+}
+
+static void compute_collisions(struct strmap *collisions,
+			       struct strmap *dir_renames,
+			       struct diff_queue_struct *pairs)
+{
+	int i;
+
+	strmap_init_with_options(collisions, NULL, 0);
+	if (strmap_empty(dir_renames))
+		return;
+
+	/*
+	 * 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.
+	 */
+	for (i = 0; i < pairs->nr; ++i) {
+		struct strmap_entry *rename_info;
+		struct collision_info *collision_info;
+		char *new_path;
+		struct diff_filepair *pair = pairs->queue[i];
+
+		if (pair->status != 'A' && pair->status != 'R')
+			continue;
+		rename_info = check_dir_renamed(pair->two->path, dir_renames);
+		if (!rename_info)
+			continue;
+
+		new_path = apply_dir_rename(rename_info, pair->two->path);
+		assert(new_path);
+		collision_info = strmap_get(collisions, new_path);
+		if (collision_info) {
+			free(new_path);
+		} else {
+			collision_info = xcalloc(1,
+						 sizeof(struct collision_info));
+			string_list_init(&collision_info->source_files, 0);
+			strmap_put(collisions, new_path, collision_info);
+		}
+		string_list_insert(&collision_info->source_files,
+				   pair->two->path);
+	}
+}
+
+static char *check_for_directory_rename(struct merge_options *opt,
+					const char *path,
+					unsigned side_index,
+					struct strmap *dir_renames,
+					struct strmap *dir_rename_exclusions,
+					struct strmap *collisions,
+					int *clean_merge)
+{
+	char *new_path = NULL;
+	struct strmap_entry *rename_info;
+	struct strmap_entry *otherinfo = NULL;
+	const char *new_dir;
+
+	if (strmap_empty(dir_renames))
+		return new_path;
+	rename_info = check_dir_renamed(path, dir_renames);
+	if (!rename_info)
+		return new_path;
+	/* old_dir = rename_info->key; */
+	new_dir = rename_info->value;
+
+	/*
+	 * 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 otherinfo 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.
+	 */
+	otherinfo = strmap_get_entry(dir_rename_exclusions, new_dir);
+	if (otherinfo) {
+		path_msg(opt, rename_info->key, 1,
+			 _("WARNING: Avoiding applying %s -> %s rename "
+			   "to %s, because %s itself was renamed."),
+			 rename_info->key, new_dir, path, new_dir);
+		return NULL;
+	}
+
+	new_path = handle_path_level_conflicts(opt, path, side_index,
+					       rename_info, collisions);
+	*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)
+{
+	/*
+	 * The basic idea is to get the conflict_info from opt->priv->paths
+	 * at old path, and insert it into new_path; basically just this:
+	 *     ci = strmap_get(&opt->priv->paths, old_path);
+	 *     strmap_remove(&opt->priv->paths, old_path, 0);
+	 *     strmap_put(&opt->priv->paths, new_path, ci);
+	 * However, there are some factors complicating this:
+	 *     - opt->priv->paths may already have an entry at new_path
+	 *     - Each ci tracks its containing directory, so we need to
+	 *       update that
+	 *     - If another ci has the same containing directory, then
+	 *       the two char*'s MUST point to the same location.  See the
+	 *       comment in struct merged_info.  strcmp equality is not
+	 *       enough; we need pointer equality.
+	 *     - opt->priv->paths must hold the parent directories of any
+	 *       entries that are added.  So, if this directory rename
+	 *       causes entirely new directories, we must recursively add
+	 *       parent directories.
+	 *     - For each parent directory added to opt->priv->paths, we
+	 *       also need to get its parent directory stored in its
+	 *       conflict_info->merged.directory_name with all the same
+	 *       requirements about pointer equality.
+	 */
+	struct string_list dirs_to_insert = STRING_LIST_INIT_NODUP;
+	struct conflict_info *ci, *new_ci;
+	struct strmap_entry *entry;
+	const char *branch_with_new_path, *branch_with_dir_rename;
+	const char *old_path = pair->two->path;
+	const char *parent_name;
+	const char *cur_path;
+	int i, len;
+
+	entry = strmap_get_entry(&opt->priv->paths, old_path);
+	old_path = entry->key;
+	ci = entry->value;
+	VERIFY_CI(ci);
+
+	/* Find parent directories missing from opt->priv->paths */
+	cur_path = new_path;
+	while (1) {
+		/* Find the parent directory of cur_path */
+		char *last_slash = strrchr(cur_path, '/');
+		if (last_slash) {
+			parent_name = xstrndup(cur_path, last_slash - cur_path);
+		} else {
+			parent_name = opt->priv->toplevel_dir;
+			break;
+		}
+
+		/* Look it up in opt->priv->paths */
+		entry = strmap_get_entry(&opt->priv->paths, parent_name);
+		if (entry) {
+			free((char*)parent_name);
+			parent_name = entry->key; /* reuse known pointer */
+			break;
+		}
+
+		/* Record this is one of the directories we need to insert */
+		string_list_append(&dirs_to_insert, parent_name);
+		cur_path = parent_name;
+	}
+
+	/* Traverse dirs_to_insert and insert them into opt->priv->paths */
+	for (i = dirs_to_insert.nr-1; i >= 0; --i) {
+		struct conflict_info *dir_ci;
+		char *cur_dir = dirs_to_insert.items[i].string;
+
+		dir_ci = xcalloc(1, sizeof(*dir_ci));
+
+		dir_ci->merged.directory_name = parent_name;
+		len = strlen(parent_name);
+		/* len+1 because of trailing '/' character */
+		dir_ci->merged.basename_offset = (len > 0 ? len+1 : len);
+		dir_ci->dirmask = ci->filemask;
+		strmap_put(&opt->priv->paths, cur_dir, dir_ci);
+
+		parent_name = cur_dir;
+	}
+
+	/*
+	 * We are removing old_path from opt->priv->paths.  old_path also will
+	 * eventually need to be freed, but it may still be used by e.g.
+	 * ci->pathnames.  So, store it in another string-list for now.
+	 */
+	string_list_append(&opt->priv->paths_to_free, old_path);
+
+	assert(ci->filemask == 2 || ci->filemask == 4);
+	assert(ci->dirmask == 0);
+	strmap_remove(&opt->priv->paths, old_path, 0);
+
+	branch_with_new_path   = (ci->filemask == 2) ? opt->branch1 : opt->branch2;
+	branch_with_dir_rename = (ci->filemask == 2) ? opt->branch2 : opt->branch1;
+
+	/* Now, finally update ci and stick it into opt->priv->paths */
+	ci->merged.directory_name = parent_name;
+	len = strlen(parent_name);
+	ci->merged.basename_offset = (len > 0 ? len+1 : len);
+	new_ci = strmap_get(&opt->priv->paths, new_path);
+	if (!new_ci) {
+		/* Place ci back into opt->priv->paths, but at new_path */
+		strmap_put(&opt->priv->paths, new_path, ci);
+	} else {
+		int index;
+
+		/* A few sanity checks */
+		VERIFY_CI(new_ci);
+		assert(ci->filemask == 2 || ci->filemask == 4);
+		assert((new_ci->filemask & ci->filemask) == 0);
+		assert(!new_ci->merged.clean);
+
+		/* Copy stuff from ci into new_ci */
+		new_ci->filemask |= ci->filemask;
+		if (new_ci->dirmask)
+			new_ci->df_conflict = 1;
+		index = (ci->filemask >> 1);
+		new_ci->pathnames[index] = ci->pathnames[index];
+		new_ci->stages[index].mode = ci->stages[index].mode;
+		oidcpy(&new_ci->stages[index].oid, &ci->stages[index].oid);
+
+		free(ci);
+		ci = new_ci;
+	}
+
+	if (opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_TRUE) {
+		/* Notify user of updated path */
+		if (pair->status == 'A')
+			path_msg(opt, new_path, 1,
+				 _("Path updated: %s added in %s inside a "
+				   "directory that was renamed in %s; moving "
+				   "it to %s."),
+				 old_path, branch_with_new_path,
+				 branch_with_dir_rename, new_path);
+		else
+			path_msg(opt, new_path, 1,
+				 _("Path updated: %s renamed to %s in %s, "
+				   "inside a directory that was renamed in %s; "
+				   "moving it to %s."),
+				 pair->one->path, old_path, branch_with_new_path,
+				 branch_with_dir_rename, new_path);
+	} else {
+		/*
+		 * opt->detect_directory_renames has the value
+		 * MERGE_DIRECTORY_RENAMES_CONFLICT, so mark these as conflicts.
+		 */
+		ci->path_conflict = 1;
+		if (pair->status == 'A')
+			path_msg(opt, new_path, 0,
+				 _("CONFLICT (file location): %s added in %s "
+				   "inside a directory that was renamed in %s, "
+				   "suggesting it should perhaps be moved to "
+				   "%s."),
+				 old_path, branch_with_new_path,
+				 branch_with_dir_rename, new_path);
+		else
+			path_msg(opt, new_path, 0,
+				 _("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."),
+				 pair->one->path, old_path, branch_with_new_path,
+				 branch_with_dir_rename, new_path);
+	}
+
+	/*
+	 * Finally, record the new location.
+	 */
+	pair->two->path = new_path;
+}
+
 /*** Function Grouping: functions related to regular rename detection ***/
 
 static int process_renames(struct merge_options *opt,
@@ -663,12 +1805,28 @@ static int process_renames(struct merge_options *opt,
 		const char *rename_branch = NULL, *delete_branch = NULL;
 
 		old_ent = strmap_get_entry(&opt->priv->paths, pair->one->path);
-		oldpath = old_ent->key;
-		oldinfo = old_ent->value;
-
 		new_ent = strmap_get_entry(&opt->priv->paths, pair->two->path);
-		newpath = new_ent->key;
-		newinfo = new_ent->value;
+		if (old_ent) {
+			oldpath = old_ent->key;
+			oldinfo = old_ent->value;
+		}
+		newpath = pair->two->path;
+		if (new_ent) {
+			newpath = new_ent->key;
+			newinfo = new_ent->value;
+		}
+
+		/*
+		 * If pair->one->path isn't in opt->priv->paths, that means
+		 * that either directory rename detection removed that
+		 * path, or a parent directory of oldpath was resolved and
+		 * we don't even need the rename; in either case, we can
+		 * skip it.  If oldinfo->merged.clean, then the other side
+		 * of history had no changes to oldpath and we don't need
+		 * the rename and can skip it.
+		 */
+		if (!oldinfo || oldinfo->merged.clean)
+			continue;
 
 		/*
 		 * diff_filepairs have copies of pathnames, thus we have to
@@ -949,9 +2107,12 @@ static void detect_regular_renames(struct merge_options *opt,
 	diff_opts.show_rename_progress = opt->show_rename_progress;
 	diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;
 	diff_setup_done(&diff_opts);
+
+	trace2_region_enter("diff", "diffcore_rename", opt->repo);
 	diff_tree_oid(&merge_base->object.oid, &side->object.oid, "",
 		      &diff_opts);
 	diffcore_std(&diff_opts);
+	trace2_region_leave("diff", "diffcore_rename", opt->repo);
 
 	if (diff_opts.needed_rename_limit > renames->needed_limit)
 		renames->needed_limit = diff_opts.needed_rename_limit;
@@ -970,22 +2131,44 @@ static void detect_regular_renames(struct merge_options *opt,
  */
 static int collect_renames(struct merge_options *opt,
 			   struct diff_queue_struct *result,
-			   unsigned side_index)
+			   unsigned side_index,
+			   struct strmap *dir_renames_for_side,
+			   struct strmap *rename_exclusions)
 {
 	int i, clean = 1;
+	struct strmap collisions;
 	struct diff_queue_struct *side_pairs;
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
 	struct rename_info *renames = &opt->priv->renames;
 
 	side_pairs = &renames->pairs[side_index];
+	compute_collisions(&collisions, dir_renames_for_side, side_pairs);
 
 	for (i = 0; i < side_pairs->nr; ++i) {
 		struct diff_filepair *p = side_pairs->queue[i];
+		char *new_path; /* non-NULL only with directory renames */
 
-		if (p->status != 'R') {
+		if (p->status != 'A' && p->status != 'R') {
 			diff_free_filepair(p);
 			continue;
 		}
 
+		new_path = check_for_directory_rename(opt, p->two->path,
+						      side_index,
+						      dir_renames_for_side,
+						      rename_exclusions,
+						      &collisions,
+						      &clean);
+
+		if (p->status != 'R' && !new_path) {
+			diff_free_filepair(p);
+			continue;
+		}
+
+		if (new_path)
+			apply_directory_rename_modifications(opt, p, new_path);
+
 		/*
 		 * p->score comes back from diffcore_rename_extended() with
 		 * the similarity of the renamed file.  The similarity is
@@ -1000,6 +2183,20 @@ static int collect_renames(struct merge_options *opt,
 		result->queue[result->nr++] = p;
 	}
 
+	/* Free each value in the collisions map */
+	strmap_for_each_entry(&collisions, &iter, entry) {
+		struct collision_info *info = entry->value;
+		string_list_clear(&info->source_files, 0);
+	}
+	/*
+	 * In compute_collisions(), we set collisions.strdup_strings to 0
+	 * so that we wouldn't have to make another copy of the new_path
+	 * allocated by apply_dir_rename().  But now that we've used them
+	 * and have no other references to these strings, it is time to
+	 * deallocate them.
+	 */
+	free_strmap_strings(&collisions);
+	strmap_clear(&collisions, 1);
 	return clean;
 }
 
@@ -1010,21 +2207,42 @@ static int detect_and_process_renames(struct merge_options *opt,
 {
 	struct diff_queue_struct combined;
 	struct rename_info *renames = &opt->priv->renames;
-	int s, clean = 1;
+	int need_dir_renames, s, clean = 1;
 
 	memset(&combined, 0, sizeof(combined));
 
+	trace2_region_enter("merge", "regular renames", opt->repo);
 	detect_regular_renames(opt, merge_base, side1, MERGE_SIDE1);
 	detect_regular_renames(opt, merge_base, side2, MERGE_SIDE2);
+	trace2_region_leave("merge", "regular renames", opt->repo);
+
+	trace2_region_enter("merge", "directory renames", opt->repo);
+	need_dir_renames =
+	  !opt->priv->call_depth &&
+	  (opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_TRUE ||
+	   opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_CONFLICT);
+
+	if (need_dir_renames) {
+		get_provisional_directory_renames(opt, MERGE_SIDE1, &clean);
+		get_provisional_directory_renames(opt, MERGE_SIDE2, &clean);
+		handle_directory_level_conflicts(opt);
+	}
 
 	ALLOC_GROW(combined.queue,
 		   renames->pairs[1].nr + renames->pairs[2].nr,
 		   combined.alloc);
-	clean &= collect_renames(opt, &combined, MERGE_SIDE1);
-	clean &= collect_renames(opt, &combined, MERGE_SIDE2);
+	clean &= collect_renames(opt, &combined, MERGE_SIDE1,
+				 &renames->dir_renames[2],
+				 &renames->dir_renames[1]);
+	clean &= collect_renames(opt, &combined, MERGE_SIDE2,
+				 &renames->dir_renames[1],
+				 &renames->dir_renames[2]);
 	QSORT(combined.queue, combined.nr, compare_pairs);
+	trace2_region_leave("merge", "directory renames", opt->repo);
 
+	trace2_region_enter("merge", "process renames", opt->repo);
 	clean &= process_renames(opt, &combined);
+	trace2_region_leave("merge", "process renames", opt->repo);
 
 	/* Free memory for renames->pairs[] and combined */
 	for (s = MERGE_SIDE1; s <= MERGE_SIDE2; s++) {
@@ -1366,6 +2584,8 @@ static void process_entry(struct merge_options *opt,
 			  struct conflict_info *ci,
 			  struct directory_versions *dir_metadata)
 {
+	int df_file_index = 0;
+
 	VERIFY_CI(ci);
 	assert(ci->filemask >= 0 && ci->filemask <= 7);
 	/* ci->match_mask == 7 was handled in collect_merge_info_callback() */
@@ -1380,14 +2600,108 @@ static void process_entry(struct merge_options *opt,
 		assert(ci->df_conflict);
 	}
 
-	if (ci->df_conflict) {
-		die("Not yet implemented.");
+	if (ci->df_conflict && ci->merged.result.mode == 0) {
+		int i;
+
+		/*
+		 * directory no longer in the way, but we do have a file we
+		 * need to place here so we need to clean away the "directory
+		 * merges to nothing" result.
+		 */
+		ci->df_conflict = 0;
+		assert(ci->filemask != 0);
+		ci->merged.clean = 0;
+		ci->merged.is_null = 0;
+		/* and we want to zero out any directory-related entries */
+		ci->match_mask = (ci->match_mask & ~ci->dirmask);
+		ci->dirmask = 0;
+		for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) {
+			if (ci->filemask & (1 << i))
+				continue;
+			ci->stages[i].mode = 0;
+			oidcpy(&ci->stages[i].oid, &null_oid);
+		}
+	} else if (ci->df_conflict && ci->merged.result.mode != 0) {
+		/*
+		 * This started out as a D/F conflict, and the entries in
+		 * the competing directory were not removed by the merge as
+		 * evidenced by write_completed_directory() writing a value
+		 * to ci->merged.result.mode.
+		 */
+		struct conflict_info *new_ci;
+		const char *branch;
+		const char *old_path = path;
+		int i;
+
+		assert(ci->merged.result.mode == S_IFDIR);
+
+		/*
+		 * If filemask is 1, we can just ignore the file as having
+		 * been deleted on both sides.  We do not want to overwrite
+		 * ci->merged.result, since it stores the tree for all the
+		 * files under it.
+		 */
+		if (ci->filemask == 1) {
+			ci->filemask = 0;
+			return;
+		}
+
+		/*
+		 * This file still exists on at least one side, and we want
+		 * the directory to remain here, so we need to move this
+		 * path to some new location.
+		 */
+		new_ci = xcalloc(1, sizeof(*new_ci));
+		/* We don't really want new_ci->merged.result copied, but it'll
+		 * be overwritten below so it doesn't matter.  We also don't
+		 * want any directory mode/oid values copied, but we'll zero
+		 * those out immediately.  We do want the rest of ci copied.
+		 */
+		memcpy(new_ci, ci, sizeof(*ci));
+		new_ci->match_mask = (new_ci->match_mask & ~new_ci->dirmask);
+		new_ci->dirmask = 0;
+		for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) {
+			if (new_ci->filemask & (1 << i))
+				continue;
+			/* zero out any entries related to directories */
+			new_ci->stages[i].mode = 0;
+			oidcpy(&new_ci->stages[i].oid, &null_oid);
+		}
+
+		/*
+		 * Find out which side this file came from; note that we
+		 * cannot just use ci->filemask, because renames could cause
+		 * the filemask to go back to 7.  So we use dirmask, then
+		 * pick the opposite side's index.
+		 */
+		df_file_index = (ci->dirmask & (1 << 1)) ? 2 : 1;
+		branch = (df_file_index == 1) ? opt->branch1 : opt->branch2;
+		path = unique_path(&opt->priv->paths, path, branch);
+		strmap_put(&opt->priv->paths, path, new_ci);
+
+		path_msg(opt, path, 0,
+			 _("CONFLICT (file/directory): directory in the way "
+			   "of %s from %s; moving it to %s instead."),
+			 old_path, branch, path);
+
+		/*
+		 * Zero out the filemask for the old ci.  At this point, ci
+		 * was just an entry for a directory, so we don't need to
+		 * do anything more with it.
+		 */
+		ci->filemask = 0;
+
+		/*
+		 * Now note that we're working on the new entry (path was
+		 * updated above.
+		 */
+		ci = new_ci;
 	}
 
 	/*
 	 * NOTE: Below there is a long switch-like if-elseif-elseif... block
 	 *       which the code goes through even for the df_conflict cases
-	 *       above.  Well, it will once we don't die-not-implemented above.
+	 *       above.
 	 */
 	if (ci->match_mask) {
 		ci->merged.clean = 1;
@@ -1411,21 +2725,142 @@ static void process_entry(struct merge_options *opt,
 	} else if (ci->filemask >= 6 &&
 		   (S_IFMT & ci->stages[1].mode) !=
 		   (S_IFMT & ci->stages[2].mode)) {
-		/*
-		 * Two different items from (file/submodule/symlink)
-		 */
-		die("Not yet implemented.");
+		/* Two different items from (file/submodule/symlink) */
+		if (opt->priv->call_depth) {
+			/* Just use the version from the merge base */
+			ci->merged.clean = 0;
+			oidcpy(&ci->merged.result.oid, &ci->stages[0].oid);
+			ci->merged.result.mode = ci->stages[0].mode;
+			ci->merged.is_null = (ci->merged.result.mode == 0);
+		} else {
+			/* Handle by renaming one or both to separate paths. */
+			unsigned o_mode = ci->stages[0].mode;
+			unsigned a_mode = ci->stages[1].mode;
+			unsigned b_mode = ci->stages[2].mode;
+			struct conflict_info *new_ci;
+			const char *a_path = NULL, *b_path = NULL;
+			int rename_a = 0, rename_b = 0;
+
+			new_ci = xmalloc(sizeof(*new_ci));
+
+			if (S_ISREG(a_mode))
+				rename_a = 1;
+			else if (S_ISREG(b_mode))
+				rename_b = 1;
+			else {
+				rename_a = 1;
+				rename_b = 1;
+			}
+
+			path_msg(opt, path, 0,
+				 _("CONFLICT (distinct types): %s had different "
+				   "types on each side; renamed %s of them so "
+				   "each can be recorded somewhere."),
+				 path,
+				 (rename_a && rename_b) ? _("both") : _("one"));
+
+			ci->merged.clean = 0;
+			memcpy(new_ci, ci, sizeof(*new_ci));
+
+			/* Put b into new_ci, removing a from stages */
+			new_ci->merged.result.mode = ci->stages[2].mode;
+			oidcpy(&new_ci->merged.result.oid, &ci->stages[2].oid);
+			new_ci->stages[1].mode = 0;
+			oidcpy(&new_ci->stages[1].oid, &null_oid);
+			new_ci->filemask = 5;
+			if ((S_IFMT & b_mode) != (S_IFMT & o_mode)) {
+				new_ci->stages[0].mode = 0;
+				oidcpy(&new_ci->stages[0].oid, &null_oid);
+				new_ci->filemask = 4;
+			}
+
+			/* Leave only a in ci, fixing stages. */
+			ci->merged.result.mode = ci->stages[1].mode;
+			oidcpy(&ci->merged.result.oid, &ci->stages[1].oid);
+			ci->stages[2].mode = 0;
+			oidcpy(&ci->stages[2].oid, &null_oid);
+			ci->filemask = 3;
+			if ((S_IFMT & a_mode) != (S_IFMT & o_mode)) {
+				ci->stages[0].mode = 0;
+				oidcpy(&ci->stages[0].oid, &null_oid);
+				ci->filemask = 2;
+			}
+
+			/* Insert entries into opt->priv_paths */
+			assert(rename_a || rename_b);
+			if (rename_a) {
+				a_path = unique_path(&opt->priv->paths,
+						     path, opt->branch1);
+				strmap_put(&opt->priv->paths, a_path, ci);
+			}
+
+			if (rename_b)
+				b_path = unique_path(&opt->priv->paths,
+						     path, opt->branch2);
+			else
+				b_path = path;
+			strmap_put(&opt->priv->paths, b_path, new_ci);
+
+			if (rename_a && rename_b) {
+				strmap_remove(&opt->priv->paths, path, 0);
+				/*
+				 * We removed path from opt->priv->paths.  path
+				 * will also eventually need to be freed, but
+				 * it may still be used by e.g.  ci->pathnames.
+				 * So, store it in another string-list for now.
+				 */
+				string_list_append(&opt->priv->paths_to_free,
+						   path);
+			}
+
+			/*
+			 * Do special handling for b_path since process_entry()
+			 * won't be called on it specially.
+			 */
+			strmap_put(&opt->priv->conflicted, b_path, new_ci);
+			record_entry_for_tree(dir_metadata, b_path,
+					      &new_ci->merged);
+
+			/*
+			 * Remaining code for processing this entry should
+			 * think in terms of processing a_path.
+			 */
+			if (a_path)
+				path = a_path;
+		}
 	} else if (ci->filemask >= 6) {
-		/*
-		 * TODO: Needs a two-way or three-way content merge, but we're
-		 * just being lazy and copying the version from HEAD and
-		 * leaving it as conflicted.
-		 */
-		ci->merged.clean = 0;
-		ci->merged.result.mode = ci->stages[1].mode;
-		oidcpy(&ci->merged.result.oid, &ci->stages[1].oid);
-		/* When we fix above, we'll call handle_content_merge() */
-		(void)handle_content_merge;
+		/* Need a two-way or three-way content merge */
+		struct version_info merged_file;
+		unsigned clean_merge;
+		struct version_info *o = &ci->stages[0];
+		struct version_info *a = &ci->stages[1];
+		struct version_info *b = &ci->stages[2];
+
+		clean_merge = handle_content_merge(opt, path, o, a, b,
+						   ci->pathnames,
+						   opt->priv->call_depth * 2,
+						   &merged_file);
+		ci->merged.clean = clean_merge &&
+				   !ci->df_conflict && !ci->path_conflict;
+		ci->merged.result.mode = merged_file.mode;
+		ci->merged.is_null = (merged_file.mode == 0);
+		oidcpy(&ci->merged.result.oid, &merged_file.oid);
+		if (clean_merge && ci->df_conflict) {
+			assert(df_file_index == 1 || df_file_index == 2);
+			ci->filemask = 1 << df_file_index;
+			ci->stages[df_file_index].mode = merged_file.mode;
+			oidcpy(&ci->stages[df_file_index].oid, &merged_file.oid);
+		}
+		if (!clean_merge) {
+			const char *reason = _("content");
+			if (ci->filemask == 6)
+				reason = _("add/add");
+			if (S_ISGITLINK(merged_file.mode))
+				reason = _("submodule");
+			path_msg(opt, path, 0,
+				 _("CONFLICT (%s): Merge conflict in %s"),
+				 reason, path);
+		}
 	} else if (ci->filemask == 3 || ci->filemask == 5) {
 		/* Modify/delete */
 		const char *modify_branch, *delete_branch;
@@ -1489,20 +2924,30 @@ static void process_entries(struct merge_options *opt,
 						   STRING_LIST_INIT_NODUP,
 						   NULL, 0 };
 
+	trace2_region_enter("merge", "process_entries setup", opt->repo);
 	if (strmap_empty(&opt->priv->paths)) {
 		oidcpy(result_oid, opt->repo->hash_algo->empty_tree);
 		return;
 	}
 
 	/* Hack to pre-allocate plist to the desired size */
+	trace2_region_enter("merge", "plist grow", opt->repo);
 	ALLOC_GROW(plist.items, strmap_get_size(&opt->priv->paths), plist.alloc);
+	trace2_region_leave("merge", "plist grow", opt->repo);
 
 	/* Put every entry from paths into plist, then sort */
+	trace2_region_enter("merge", "plist copy", opt->repo);
 	strmap_for_each_entry(&opt->priv->paths, &iter, e) {
 		string_list_append(&plist, e->key)->util = e->value;
 	}
+	trace2_region_leave("merge", "plist copy", opt->repo);
+
+	trace2_region_enter("merge", "plist special sort", opt->repo);
 	plist.cmp = string_list_df_name_compare;
 	string_list_sort(&plist);
+	trace2_region_leave("merge", "plist special sort", opt->repo);
+
+	trace2_region_leave("merge", "process_entries setup", opt->repo);
 
 	/*
 	 * Iterate over the items in reverse order, so we can handle paths
@@ -1513,6 +2958,7 @@ static void process_entries(struct merge_options *opt,
 	 * (because it allows us to know whether the directory is still in
 	 * the way when it is time to process the file at the same path).
 	 */
+	trace2_region_enter("merge", "processing", opt->repo);
 	for (entry = &plist.items[plist.nr-1]; entry >= plist.items; --entry) {
 		char *path = entry->string;
 		/*
@@ -1531,7 +2977,9 @@ static void process_entries(struct merge_options *opt,
 			process_entry(opt, path, ci, &dir_metadata);
 		}
 	}
+	trace2_region_leave("merge", "processing", opt->repo);
 
+	trace2_region_enter("merge", "process_entries cleanup", opt->repo);
 	if (dir_metadata.offsets.nr != 1 ||
 	    (uintptr_t)dir_metadata.offsets.items[0].util != 0) {
 		printf("dir_metadata.offsets.nr = %d (should be 1)\n",
@@ -1546,6 +2994,7 @@ static void process_entries(struct merge_options *opt,
 	string_list_clear(&plist, 0);
 	string_list_clear(&dir_metadata.versions, 0);
 	string_list_clear(&dir_metadata.offsets, 0);
+	trace2_region_leave("merge", "process_entries cleanup", opt->repo);
 }
 
 /*** Function Grouping: functions related to merge_switch_to_result() ***/
@@ -1704,12 +3153,15 @@ void merge_switch_to_result(struct merge_options *opt,
 	if (result->clean >= 0 && update_worktree_and_index) {
 		struct merge_options_internal *opti = result->priv;
 
+		trace2_region_enter("merge", "checkout", opt->repo);
 		if (checkout(opt, head, result->tree)) {
 			/* failure to function */
 			result->clean = -1;
 			return;
 		}
+		trace2_region_leave("merge", "checkout", opt->repo);
 
+		trace2_region_enter("merge", "record_conflicted", opt->repo);
 		if (record_conflicted_index_entries(opt, opt->repo->index,
 						    &opti->paths,
 						    &opti->conflicted)) {
@@ -1717,6 +3169,7 @@ void merge_switch_to_result(struct merge_options *opt,
 			result->clean = -1;
 			return;
 		}
+		trace2_region_leave("merge", "record_conflicted", opt->repo);
 	}
 
 	if (display_update_msgs) {
@@ -1726,6 +3179,8 @@ void merge_switch_to_result(struct merge_options *opt,
 		struct string_list olist = STRING_LIST_INIT_NODUP;
 		int i;
 
+		trace2_region_enter("merge", "display messages", opt->repo);
+
 		/* Hack to pre-allocate olist to the desired size */
 		ALLOC_GROW(olist.items, strmap_get_size(&opti->output),
 			   olist.alloc);
@@ -1747,6 +3202,8 @@ void merge_switch_to_result(struct merge_options *opt,
 		/* Also include needed rename limit adjustment now */
 		diff_warn_rename_limit("merge.renamelimit",
 				       opti->renames.needed_limit, 0);
+
+		trace2_region_leave("merge", "display messages", opt->repo);
 	}
 
 	merge_finalize(opt, result);
@@ -1784,7 +3241,11 @@ static struct commit *make_virtual_commit(struct repository *repo,
 
 static void merge_start(struct merge_options *opt, struct merge_result *result)
 {
+	struct rename_info *renames;
+	int i;
+
 	/* Sanity checks on opt */
+	trace2_region_enter("merge", "sanity checks", opt->repo);
 	assert(opt->repo);
 
 	assert(opt->branch1 && opt->branch2);
@@ -1811,13 +3272,43 @@ static void merge_start(struct merge_options *opt, struct merge_result *result)
 	assert(opt->obuf.len == 0);
 
 	assert(opt->priv == NULL);
+	if (result->priv) {
+		opt->priv = result->priv;
+		result->priv = NULL;
+		/*
+		 * opt->priv non-NULL means we had results from a previous
+		 * run; do a few sanity checks that user didn't mess with
+		 * it in an obvious fashion.
+		 */
+		assert(opt->priv->call_depth == 0);
+		assert(!opt->priv->toplevel_dir ||
+		       0 == strlen(opt->priv->toplevel_dir));
+	}
+	trace2_region_leave("merge", "sanity checks", opt->repo);
 
 	/* Default to histogram diff.  Actually, just hardcode it...for now. */
 	opt->xdl_opts = DIFF_WITH_ALG(opt, HISTOGRAM_DIFF);
 
 	/* Initialization of opt->priv, our internal merge data */
+	trace2_region_enter("merge", "allocate/init", opt->repo);
+	if (opt->priv) {
+		clear_or_reinit_internal_opts(opt->priv, 1);
+		trace2_region_leave("merge", "allocate/init", opt->repo);
+		return;
+	}
 	opt->priv = xcalloc(1, sizeof(*opt->priv));
 
+	/* Initialization of various renames fields */
+	renames = &opt->priv->renames;
+	for (i = MERGE_SIDE1; i <= MERGE_SIDE2; i++) {
+		strset_init_with_options(&renames->dirs_removed[i],
+					 NULL, 0);
+		strmap_init_with_options(&renames->dir_rename_count[i],
+					 NULL, 1);
+		strmap_init_with_options(&renames->dir_renames[i],
+					 NULL, 0);
+	}
+
 	/*
 	 * Although we initialize opt->priv->paths with strdup_strings=0,
 	 * that's just to avoid making yet another copy of an allocated
@@ -1837,6 +3328,8 @@ static void merge_start(struct merge_options *opt, struct merge_result *result)
 	 * subset of the overall paths that have special output.
 	 */
 	strmap_init(&opt->priv->output);
+
+	trace2_region_leave("merge", "allocate/init", opt->repo);
 }
 
 /*** Function Grouping: merge_incore_*() and their internal variants ***/
@@ -1852,6 +3345,7 @@ static void merge_ort_nonrecursive_internal(struct merge_options *opt,
 {
 	struct object_id working_tree_oid;
 
+	trace2_region_enter("merge", "collect_merge_info", opt->repo);
 	if (collect_merge_info(opt, merge_base, side1, side2) != 0) {
 		/*
 		 * TRANSLATORS: The %s arguments are: 1) tree hash of a merge
@@ -1864,10 +3358,16 @@ static void merge_ort_nonrecursive_internal(struct merge_options *opt,
 		result->clean = -1;
 		return;
 	}
+	trace2_region_leave("merge", "collect_merge_info", opt->repo);
 
+	trace2_region_enter("merge", "renames", opt->repo);
 	result->clean = detect_and_process_renames(opt, merge_base,
 						   side1, side2);
+	trace2_region_leave("merge", "renames", opt->repo);
+
+	trace2_region_enter("merge", "process_entries", opt->repo);
 	process_entries(opt, &working_tree_oid);
+	trace2_region_leave("merge", "process_entries", opt->repo);
 
 	/* Set return values */
 	result->tree = parse_tree_indirect(&working_tree_oid);
@@ -1968,9 +3468,15 @@ void merge_incore_nonrecursive(struct merge_options *opt,
 			       struct tree *side2,
 			       struct merge_result *result)
 {
+	trace2_region_enter("merge", "incore_nonrecursive", opt->repo);
+
+	trace2_region_enter("merge", "merge_start", opt->repo);
 	assert(opt->ancestor != NULL);
 	merge_start(opt, result);
+	trace2_region_leave("merge", "merge_start", opt->repo);
+
 	merge_ort_nonrecursive_internal(opt, merge_base, side1, side2, result);
+	trace2_region_leave("merge", "incore_nonrecursive", opt->repo);
 }
 
 void merge_incore_recursive(struct merge_options *opt,
@@ -1979,9 +3485,15 @@ void merge_incore_recursive(struct merge_options *opt,
 			    struct commit *side2,
 			    struct merge_result *result)
 {
+	trace2_region_enter("merge", "incore_recursive", opt->repo);
+
 	/* We set the ancestor label based on the merge_bases */
 	assert(opt->ancestor == NULL);
 
+	trace2_region_enter("merge", "merge_start", opt->repo);
 	merge_start(opt, result);
+	trace2_region_leave("merge", "merge_start", opt->repo);
+
 	merge_ort_internal(opt, merge_bases, side1, side2, result);
+	trace2_region_leave("merge", "incore_recursive", opt->repo);
 }