Merge branch 'en/merge-path-collision'

Updates for corner cases in merge-recursive.

* en/merge-path-collision:
  t6036: avoid non-portable "cp -a"
  merge-recursive: combine error handling
  t6036, t6043: increase code coverage for file collision handling
  merge-recursive: improve rename/rename(1to2)/add[/add] handling
  merge-recursive: use handle_file_collision for add/add conflicts
  merge-recursive: improve handling for rename/rename(2to1) conflicts
  merge-recursive: fix rename/add conflict handling
  merge-recursive: new function for better colliding conflict resolutions
  merge-recursive: increase marker length with depth of recursion
  t6036, t6042: testcases for rename collision of already conflicting files
  t6042: add tests for consistency in file collision conflict handling

6 files changed, 1149 insertions, 292 deletions

diff --git a/ll-merge.c b/ll-merge.c
index 3c8fb917e9..5b8d46aede 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -384,7 +384,9 @@ int ll_merge(mmbuffer_t *result_buf,
 	if (opts->virtual_ancestor) {
 		if (driver->recursive)
 			driver = find_ll_merge_driver(driver->recursive);
-		marker_size += 2;
+	}
+	if (opts->extra_marker_size) {
+		marker_size += opts->extra_marker_size;
 	}
 	return driver->fn(driver, result_buf, path, ancestor, ancestor_label,
 			  ours, our_label, theirs, their_label,
diff --git a/ll-merge.h b/ll-merge.h
index 6c6e22e40d..b9e2af1c88 100644
--- a/ll-merge.h
+++ b/ll-merge.h
@@ -13,6 +13,7 @@ struct ll_merge_options {
 	unsigned virtual_ancestor : 1;
 	unsigned variant : 2;	/* favor ours, favor theirs, or union merge */
 	unsigned renormalize : 1;
+	unsigned extra_marker_size;
 	long xdl_opts;
 };
 
diff --git a/merge-recursive.c b/merge-recursive.c
index acc2f64a4e..ecf8db0b71 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -186,6 +186,7 @@ static int oid_eq(const struct object_id *a, const struct object_id *b)
 enum rename_type {
 	RENAME_NORMAL = 0,
 	RENAME_VIA_DIR,
+	RENAME_ADD,
 	RENAME_DELETE,
 	RENAME_ONE_FILE_TO_ONE,
 	RENAME_ONE_FILE_TO_TWO,
@@ -228,6 +229,7 @@ static inline void setup_rename_conflict_info(enum rename_type rename_type,
 					      struct stage_data *src_entry1,
 					      struct stage_data *src_entry2)
 {
+	int ostage1 = 0, ostage2;
 	struct rename_conflict_info *ci;
 
 	/*
@@ -264,18 +266,22 @@ static inline void setup_rename_conflict_info(enum rename_type rename_type,
 		dst_entry2->rename_conflict_info = ci;
 	}
 
-	if (rename_type == RENAME_TWO_FILES_TO_ONE) {
-		/*
-		 * For each rename, there could have been
-		 * modifications on the side of history where that
-		 * file was not renamed.
-		 */
-		int ostage1 = o->branch1 == branch1 ? 3 : 2;
-		int ostage2 = ostage1 ^ 1;
+	/*
+	 * For each rename, there could have been
+	 * modifications on the side of history where that
+	 * file was not renamed.
+	 */
+	if (rename_type == RENAME_ADD ||
+	    rename_type == RENAME_TWO_FILES_TO_ONE) {
+		ostage1 = o->branch1 == branch1 ? 3 : 2;
 
 		ci->ren1_other.path = pair1->one->path;
 		oidcpy(&ci->ren1_other.oid, &src_entry1->stages[ostage1].oid);
 		ci->ren1_other.mode = src_entry1->stages[ostage1].mode;
+	}
+
+	if (rename_type == RENAME_TWO_FILES_TO_ONE) {
+		ostage2 = ostage1 ^ 1;
 
 		ci->ren2_other.path = pair2->one->path;
 		oidcpy(&ci->ren2_other.oid, &src_entry2->stages[ostage2].oid);
@@ -690,27 +696,6 @@ static int update_stages(struct merge_options *opt, const char *path,
 	return 0;
 }
 
-static int update_stages_for_stage_data(struct merge_options *opt,
-					const char *path,
-					const struct stage_data *stage_data)
-{
-	struct diff_filespec o, a, b;
-
-	o.mode = stage_data->stages[1].mode;
-	oidcpy(&o.oid, &stage_data->stages[1].oid);
-
-	a.mode = stage_data->stages[2].mode;
-	oidcpy(&a.oid, &stage_data->stages[2].oid);
-
-	b.mode = stage_data->stages[3].mode;
-	oidcpy(&b.oid, &stage_data->stages[3].oid);
-
-	return update_stages(opt, path,
-			     is_null_oid(&o.oid) ? NULL : &o,
-			     is_null_oid(&a.oid) ? NULL : &a,
-			     is_null_oid(&b.oid) ? NULL : &b);
-}
-
 static void update_entry(struct stage_data *entry,
 			 struct diff_filespec *o,
 			 struct diff_filespec *a,
@@ -1058,7 +1043,8 @@ static int merge_3way(struct merge_options *o,
 		      const struct diff_filespec *a,
 		      const struct diff_filespec *b,
 		      const char *branch1,
-		      const char *branch2)
+		      const char *branch2,
+		      const int extra_marker_size)
 {
 	mmfile_t orig, src1, src2;
 	struct ll_merge_options ll_opts = {0};
@@ -1066,6 +1052,7 @@ static int merge_3way(struct merge_options *o,
 	int merge_status;
 
 	ll_opts.renormalize = o->renormalize;
+	ll_opts.extra_marker_size = extra_marker_size;
 	ll_opts.xdl_opts = o->xdl_opts;
 
 	if (o->call_depth) {
@@ -1301,6 +1288,7 @@ static int merge_mode_and_contents(struct merge_options *o,
 				   const char *filename,
 				   const char *branch1,
 				   const char *branch2,
+				   const int extra_marker_size,
 				   struct merge_file_info *result)
 {
 	if (o->branch1 != branch1) {
@@ -1311,7 +1299,8 @@ static int merge_mode_and_contents(struct merge_options *o,
 		 */
 		return merge_mode_and_contents(o, one, b, a,
 					       filename,
-					       branch2, branch1, result);
+					       branch2, branch1,
+					       extra_marker_size, result);
 	}
 
 	result->merge = 0;
@@ -1352,7 +1341,8 @@ static int merge_mode_and_contents(struct merge_options *o,
 			int ret = 0, merge_status;
 
 			merge_status = merge_3way(o, &result_buf, one, a, b,
-						  branch1, branch2);
+						  branch1, branch2,
+						  extra_marker_size);
 
 			if ((merge_status < 0) || !result_buf.ptr)
 				ret = err(o, _("Failed to execute internal merge"));
@@ -1555,80 +1545,203 @@ static struct diff_filespec *filespec_from_entry(struct diff_filespec *target,
 	return target;
 }
 
-static int handle_file(struct merge_options *o,
-			struct diff_filespec *rename,
-			int stage,
-			struct rename_conflict_info *ci)
+static int handle_file_collision(struct merge_options *o,
+				 const char *collide_path,
+				 const char *prev_path1,
+				 const char *prev_path2,
+				 const char *branch1, const char *branch2,
+				 const struct object_id *a_oid,
+				 unsigned int a_mode,
+				 const struct object_id *b_oid,
+				 unsigned int b_mode)
 {
-	char *dst_name = rename->path;
-	struct stage_data *dst_entry;
-	const char *cur_branch, *other_branch;
-	struct diff_filespec other;
-	struct diff_filespec *add;
-	int ret;
+	struct merge_file_info mfi;
+	struct diff_filespec null, a, b;
+	char *alt_path = NULL;
+	const char *update_path = collide_path;
 
-	if (stage == 2) {
-		dst_entry = ci->dst_entry1;
-		cur_branch = ci->branch1;
-		other_branch = ci->branch2;
-	} else {
-		dst_entry = ci->dst_entry2;
-		cur_branch = ci->branch2;
-		other_branch = ci->branch1;
+	/*
+	 * 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 == o->branch1.  So, simply
+	 * flip arguments around if we don't have that.
+	 */
+	if (branch1 != o->branch1) {
+		return handle_file_collision(o, collide_path,
+					     prev_path2, prev_path1,
+					     branch2, branch1,
+					     b_oid, b_mode,
+					     a_oid, a_mode);
 	}
 
-	add = filespec_from_entry(&other, dst_entry, stage ^ 1);
-	if (add) {
-		int ren_src_was_dirty = was_dirty(o, rename->path);
-		char *add_name = unique_path(o, rename->path, other_branch);
-		if (update_file(o, 0, &add->oid, add->mode, add_name))
-			return -1;
+	/*
+	 * In the recursive case, we just opt to undo renames
+	 */
+	if (o->call_depth && (prev_path1 || prev_path2)) {
+		/* Put first file (a_oid, a_mode) in its original spot */
+		if (prev_path1) {
+			if (update_file(o, 1, a_oid, a_mode, prev_path1))
+				return -1;
+		} else {
+			if (update_file(o, 1, a_oid, a_mode, collide_path))
+				return -1;
+		}
 
-		if (ren_src_was_dirty) {
-			output(o, 1, _("Refusing to lose dirty file at %s"),
-			       rename->path);
+		/* Put second file (b_oid, b_mode) in its original spot */
+		if (prev_path2) {
+			if (update_file(o, 1, b_oid, b_mode, prev_path2))
+				return -1;
+		} else {
+			if (update_file(o, 1, b_oid, b_mode, collide_path))
+				return -1;
 		}
+
+		/* Don't leave something at collision path if unrenaming both */
+		if (prev_path1 && prev_path2)
+			remove_file(o, 1, collide_path, 0);
+
+		return 0;
+	}
+
+	/* Remove rename sources if rename/add or rename/rename(2to1) */
+	if (prev_path1)
+		remove_file(o, 1, prev_path1,
+			    o->call_depth || would_lose_untracked(prev_path1));
+	if (prev_path2)
+		remove_file(o, 1, prev_path2,
+			    o->call_depth || would_lose_untracked(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(o, collide_path)) {
+		output(o, 1, _("Refusing to lose dirty file at %s"),
+		       collide_path);
+		update_path = alt_path = unique_path(o, collide_path, "merged");
+	} else if (would_lose_untracked(collide_path)) {
 		/*
-		 * Because the double negatives somehow keep confusing me...
-		 *    1) update_wd iff !ren_src_was_dirty.
-		 *    2) no_wd iff !update_wd
-		 *    3) so, no_wd == !!ren_src_was_dirty == ren_src_was_dirty
+		 * 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.
 		 */
-		remove_file(o, 0, rename->path, ren_src_was_dirty);
-		dst_name = unique_path(o, rename->path, cur_branch);
+		output(o, 1, _("Refusing to lose untracked file at "
+			       "%s, even though it's in the way."),
+		       collide_path);
+		update_path = alt_path = unique_path(o, collide_path, "merged");
 	} else {
-		if (dir_in_way(rename->path, !o->call_depth, 0)) {
-			dst_name = unique_path(o, rename->path, cur_branch);
-			output(o, 1, _("%s is a directory in %s adding as %s instead"),
-			       rename->path, other_branch, dst_name);
-		} else if (!o->call_depth &&
-			   would_lose_untracked(rename->path)) {
-			dst_name = unique_path(o, rename->path, cur_branch);
-			output(o, 1, _("Refusing to lose untracked file at %s; "
-				       "adding as %s instead"),
-			       rename->path, dst_name);
-		}
+		/*
+		 * 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(o, 0, collide_path, 0);
 	}
-	if ((ret = update_file(o, 0, &rename->oid, rename->mode, dst_name)))
-		; /* fall through, do allow dst_name to be released */
-	else if (stage == 2)
-		ret = update_stages(o, rename->path, NULL, rename, add);
-	else
-		ret = update_stages(o, rename->path, NULL, add, rename);
 
-	if (dst_name != rename->path)
-		free(dst_name);
+	/* Store things in diff_filespecs for functions that need it */
+	memset(&a, 0, sizeof(struct diff_filespec));
+	memset(&b, 0, sizeof(struct diff_filespec));
+	null.path = a.path = b.path = (char *)collide_path;
+	oidcpy(&null.oid, &null_oid);
+	null.mode = 0;
+	oidcpy(&a.oid, a_oid);
+	a.mode = a_mode;
+	a.oid_valid = 1;
+	oidcpy(&b.oid, b_oid);
+	b.mode = b_mode;
+	b.oid_valid = 1;
 
-	return ret;
+	if (merge_mode_and_contents(o, &null, &a, &b, collide_path,
+				    branch1, branch2, o->call_depth * 2, &mfi))
+		return -1;
+	mfi.clean &= !alt_path;
+	if (update_file(o, mfi.clean, &mfi.oid, mfi.mode, update_path))
+		return -1;
+	if (!mfi.clean && !o->call_depth &&
+	    update_stages(o, 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 *o,
+			     struct rename_conflict_info *ci)
+{
+	/* a was renamed to c, and a separate c was added. */
+	struct diff_filespec *a = ci->pair1->one;
+	struct diff_filespec *c = ci->pair1->two;
+	char *path = c->path;
+	char *prev_path_desc;
+	struct merge_file_info mfi;
+
+	int other_stage = (ci->branch1 == o->branch1 ? 3 : 2);
+
+	output(o, 1, _("CONFLICT (rename/add): "
+	       "Rename %s->%s in %s.  Added %s in %s"),
+	       a->path, c->path, ci->branch1,
+	       c->path, ci->branch2);
+
+	prev_path_desc = xstrfmt("version of %s from %s", path, a->path);
+	if (merge_mode_and_contents(o, a, c, &ci->ren1_other, prev_path_desc,
+				    o->branch1, o->branch2,
+				    1 + o->call_depth * 2, &mfi))
+		return -1;
+	free(prev_path_desc);
+
+	return handle_file_collision(o,
+				     c->path, a->path, NULL,
+				     ci->branch1, ci->branch2,
+				     &mfi.oid, mfi.mode,
+				     &ci->dst_entry1->stages[other_stage].oid,
+				     ci->dst_entry1->stages[other_stage].mode);
+}
+
+static char *find_path_for_conflict(struct merge_options *o,
+				    const char *path,
+				    const char *branch1,
+				    const char *branch2)
+{
+	char *new_path = NULL;
+	if (dir_in_way(path, !o->call_depth, 0)) {
+		new_path = unique_path(o, path, branch1);
+		output(o, 1, _("%s is a directory in %s adding "
+			       "as %s instead"),
+		       path, branch2, new_path);
+	} else if (would_lose_untracked(path)) {
+		new_path = unique_path(o, path, branch1);
+		output(o, 1, _("Refusing to lose untracked file"
+			       " at %s; adding as %s instead"),
+		       path, new_path);
+	}
+
+	return new_path;
 }
 
 static int handle_rename_rename_1to2(struct merge_options *o,
 				     struct rename_conflict_info *ci)
 {
 	/* One file was renamed in both branches, but to different names. */
+	struct merge_file_info mfi;
+	struct diff_filespec other;
+	struct diff_filespec *add;
 	struct diff_filespec *one = ci->pair1->one;
 	struct diff_filespec *a = ci->pair1->two;
 	struct diff_filespec *b = ci->pair2->two;
+	char *path_desc;
 
 	output(o, 1, _("CONFLICT (rename/rename): "
 	       "Rename \"%s\"->\"%s\" in branch \"%s\" "
@@ -1636,14 +1749,16 @@ static int handle_rename_rename_1to2(struct merge_options *o,
 	       one->path, a->path, ci->branch1,
 	       one->path, b->path, ci->branch2,
 	       o->call_depth ? _(" (left unresolved)") : "");
-	if (o->call_depth) {
-		struct merge_file_info mfi;
-		struct diff_filespec other;
-		struct diff_filespec *add;
-		if (merge_mode_and_contents(o, one, a, b, one->path,
-					    ci->branch1, ci->branch2, &mfi))
-			return -1;
 
+	path_desc = xstrfmt("%s and %s, both renamed from %s",
+			    a->path, b->path, one->path);
+	if (merge_mode_and_contents(o, one, a, b, path_desc,
+				    ci->branch1, ci->branch2,
+				    o->call_depth * 2, &mfi))
+		return -1;
+	free(path_desc);
+
+	if (o->call_depth) {
 		/*
 		 * FIXME: For rename/add-source conflicts (if we could detect
 		 * such), this is wrong.  We should instead find a unique
@@ -1675,8 +1790,50 @@ static int handle_rename_rename_1to2(struct merge_options *o,
 		}
 		else
 			remove_file_from_cache(b->path);
-	} else if (handle_file(o, a, 2, ci) || handle_file(o, b, 3, ci))
-		return -1;
+	} else {
+		/*
+		 * 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 = filespec_from_entry(&other, ci->dst_entry1, 2 ^ 1);
+		if (add) {
+			if (handle_file_collision(o, a->path,
+						  NULL, NULL,
+						  ci->branch1, ci->branch2,
+						  &mfi.oid, mfi.mode,
+						  &add->oid, add->mode) < 0)
+				return -1;
+		} else {
+			char *new_path = find_path_for_conflict(o, a->path,
+								ci->branch1,
+								ci->branch2);
+			if (update_file(o, 0, &mfi.oid, mfi.mode, new_path ? new_path : a->path))
+				return -1;
+			free(new_path);
+			if (update_stages(o, a->path, NULL, a, NULL))
+				return -1;
+		}
+
+		add = filespec_from_entry(&other, ci->dst_entry2, 3 ^ 1);
+		if (add) {
+			if (handle_file_collision(o, b->path,
+						  NULL, NULL,
+						  ci->branch1, ci->branch2,
+						  &add->oid, add->mode,
+						  &mfi.oid, mfi.mode) < 0)
+				return -1;
+		} else {
+			char *new_path = find_path_for_conflict(o, b->path,
+								ci->branch2,
+								ci->branch1);
+			if (update_file(o, 0, &mfi.oid, mfi.mode, new_path ? new_path : b->path))
+				return -1;
+			free(new_path);
+			if (update_stages(o, b->path, NULL, NULL, b))
+				return -1;
+		}
+	}
 
 	return 0;
 }
@@ -1694,7 +1851,6 @@ static int handle_rename_rename_2to1(struct merge_options *o,
 	char *path_side_2_desc;
 	struct merge_file_info mfi_c1;
 	struct merge_file_info mfi_c2;
-	int ret;
 
 	output(o, 1, _("CONFLICT (rename/rename): "
 	       "Rename %s->%s in %s. "
@@ -1702,79 +1858,22 @@ static int handle_rename_rename_2to1(struct merge_options *o,
 	       a->path, c1->path, ci->branch1,
 	       b->path, c2->path, ci->branch2);
 
-	remove_file(o, 1, a->path, o->call_depth || would_lose_untracked(a->path));
-	remove_file(o, 1, b->path, o->call_depth || would_lose_untracked(b->path));
-
 	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);
 	if (merge_mode_and_contents(o, a, c1, &ci->ren1_other, path_side_1_desc,
-				    o->branch1, o->branch2, &mfi_c1) ||
+				    o->branch1, o->branch2,
+				    1 + o->call_depth * 2, &mfi_c1) ||
 	    merge_mode_and_contents(o, b, &ci->ren2_other, c2, path_side_2_desc,
-				    o->branch1, o->branch2, &mfi_c2))
+				    o->branch1, o->branch2,
+				    1 + o->call_depth * 2, &mfi_c2))
 		return -1;
 	free(path_side_1_desc);
 	free(path_side_2_desc);
 
-	if (o->call_depth) {
-		/*
-		 * If mfi_c1.clean && mfi_c2.clean, then it might make
-		 * sense to do a two-way merge of those results.  But, I
-		 * think in all cases, it makes sense to have the virtual
-		 * merge base just undo the renames; they can be detected
-		 * again later for the non-recursive merge.
-		 */
-		remove_file(o, 0, path, 0);
-		ret = update_file(o, 0, &mfi_c1.oid, mfi_c1.mode, a->path);
-		if (!ret)
-			ret = update_file(o, 0, &mfi_c2.oid, mfi_c2.mode,
-					  b->path);
-	} else {
-		char *new_path1 = unique_path(o, path, ci->branch1);
-		char *new_path2 = unique_path(o, path, ci->branch2);
-		output(o, 1, _("Renaming %s to %s and %s to %s instead"),
-		       a->path, new_path1, b->path, new_path2);
-		if (was_dirty(o, path))
-			output(o, 1, _("Refusing to lose dirty file at %s"),
-			       path);
-		else if (would_lose_untracked(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(o, 1, _("Refusing to lose untracked file at "
-				       "%s, even though it's in the way."),
-			       path);
-		else
-			remove_file(o, 0, path, 0);
-		ret = update_file(o, 0, &mfi_c1.oid, mfi_c1.mode, new_path1);
-		if (!ret)
-			ret = update_file(o, 0, &mfi_c2.oid, mfi_c2.mode,
-					  new_path2);
-		/*
-		 * unpack_trees() actually populates the index for us for
-		 * "normal" rename/rename(2to1) situtations so that the
-		 * correct entries are at the higher stages, which would
-		 * make the call below to update_stages_for_stage_data
-		 * unnecessary.  However, if either of the renames came
-		 * from a directory rename, then unpack_trees() will not
-		 * have gotten the right data loaded into the index, so we
-		 * need to do so now.  (While it'd be tempting to move this
-		 * call to update_stages_for_stage_data() to
-		 * apply_directory_rename_modifications(), that would break
-		 * our intermediate calls to would_lose_untracked() since
-		 * those rely on the current in-memory index.  See also the
-		 * big "NOTE" in update_stages()).
-		 */
-		if (update_stages_for_stage_data(o, path, ci->dst_entry1))
-			ret = -1;
-
-		free(new_path2);
-		free(new_path1);
-	}
-
-	return ret;
+	return handle_file_collision(o, path, a->path, b->path,
+				     ci->branch1, ci->branch2,
+				     &mfi_c1.oid, mfi_c1.mode,
+				     &mfi_c2.oid, mfi_c2.mode);
 }
 
 /*
@@ -2732,47 +2831,23 @@ static int process_renames(struct merge_options *o,
 						      0  /* update_wd    */))
 					clean_merge = -1;
 			} else if (!oid_eq(&dst_other.oid, &null_oid)) {
-				clean_merge = 0;
-				try_merge = 1;
-				output(o, 1, _("CONFLICT (rename/add): Rename %s->%s in %s. "
-				       "%s added in %s"),
-				       ren1_src, ren1_dst, branch1,
-				       ren1_dst, branch2);
-				if (o->call_depth) {
-					struct merge_file_info mfi;
-					struct diff_filespec one, a, b;
-
-					oidcpy(&one.oid, &null_oid);
-					one.mode = 0;
-					one.path = ren1->pair->two->path;
-
-					oidcpy(&a.oid, &ren1->pair->two->oid);
-					a.mode = ren1->pair->two->mode;
-					a.path = one.path;
-
-					oidcpy(&b.oid, &dst_other.oid);
-					b.mode = dst_other.mode;
-					b.path = one.path;
-
-					if (merge_mode_and_contents(o, &one, &a, &b, ren1_dst,
-								    branch1, branch2,
-								    &mfi)) {
-						clean_merge = -1;
-						goto cleanup_and_return;
-					}
-					output(o, 1, _("Adding merged %s"), ren1_dst);
-					if (update_file(o, 0, &mfi.oid,
-							mfi.mode, ren1_dst))
-						clean_merge = -1;
-					try_merge = 0;
-				} else {
-					char *new_path = unique_path(o, ren1_dst, branch2);
-					output(o, 1, _("Adding as %s instead"), new_path);
-					if (update_file(o, 0, &dst_other.oid,
-							dst_other.mode, new_path))
-						clean_merge = -1;
-					free(new_path);
-				}
+				/*
+				 * 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,
+							   ren1->pair,
+							   NULL,
+							   branch1,
+							   branch2,
+							   ren1->dst_entry,
+							   NULL,
+							   o,
+							   ren1->src_entry,
+							   NULL);
 			} else
 				try_merge = 1;
 
@@ -3053,7 +3128,8 @@ static int handle_content_merge(struct merge_options *o,
 			df_conflict_remains = 1;
 	}
 	if (merge_mode_and_contents(o, &one, &a, &b, path,
-				    o->branch1, o->branch2, &mfi))
+				    o->branch1, o->branch2,
+				    o->call_depth * 2, &mfi))
 		return -1;
 
 	/*
@@ -3183,6 +3259,15 @@ static int process_entry(struct merge_options *o,
 						  conflict_info->branch2))
 				clean_merge = -1;
 			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(o, conflict_info);
+			break;
 		case RENAME_DELETE:
 			clean_merge = 0;
 			if (handle_rename_delete(o,
@@ -3197,9 +3282,14 @@ static int process_entry(struct merge_options *o,
 				clean_merge = -1;
 			break;
 		case RENAME_TWO_FILES_TO_ONE:
-			clean_merge = 0;
-			if (handle_rename_rename_2to1(o, conflict_info))
-				clean_merge = -1;
+			/*
+			 * 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(o,
+								conflict_info);
 			break;
 		default:
 			entry->processed = 0;
@@ -3267,14 +3357,27 @@ static int process_entry(struct merge_options *o,
 				clean_merge = -1;
 		}
 	} else if (a_oid && b_oid) {
-		/* Case C: Added in both (check for same permissions) and */
-		/* case D: Modified in both, but differently. */
-		int is_dirty = 0; /* unpack_trees would have bailed if dirty */
-		clean_merge = handle_content_merge(o, path, is_dirty,
-						   o_oid, o_mode,
-						   a_oid, a_mode,
-						   b_oid, b_mode,
-						   NULL);
+		if (!o_oid) {
+			/* Case C: Added in both (check for same permissions) */
+			output(o, 1,
+			       _("CONFLICT (add/add): Merge conflict in %s"),
+			       path);
+			clean_merge = handle_file_collision(o,
+							    path, NULL, NULL,
+							    o->branch1,
+							    o->branch2,
+							    a_oid, a_mode,
+							    b_oid, b_mode);
+		} else {
+			/* case D: Modified in both, but differently. */
+			int is_dirty = 0; /* unpack_trees would have bailed if dirty */
+			clean_merge = handle_content_merge(o, path,
+							   is_dirty,
+							   o_oid, o_mode,
+							   a_oid, a_mode,
+							   b_oid, b_mode,
+							   NULL);
+		}
 	} else if (!o_oid && !a_oid && !b_oid) {
 		/*
 		 * this entry was deleted altogether. a_mode == 0 means
diff --git a/t/t6036-recursive-corner-cases.sh b/t/t6036-recursive-corner-cases.sh
index e1cef58f2a..d23b948f27 100755
--- a/t/t6036-recursive-corner-cases.sh
+++ b/t/t6036-recursive-corner-cases.sh
@@ -64,15 +64,12 @@ test_expect_success 'merge simple rename+criss-cross with no modifications' '
 		git ls-files -u >out &&
 		test_line_count = 2 out &&
 		git ls-files -o >out &&
-		test_line_count = 3 out &&
+		test_line_count = 1 out &&
 
 		git rev-parse >expect       \
-			L2:three   R2:three \
 			L2:three   R2:three &&
 		git rev-parse   >actual     \
 			:2:three   :3:three &&
-		git hash-object >>actual    \
-			three~HEAD three~R2^0 &&
 		test_cmp expect actual
 	)
 '
@@ -140,15 +137,12 @@ test_expect_success 'merge criss-cross + rename merges with basic modification'
 		git ls-files -u >out &&
 		test_line_count = 2 out &&
 		git ls-files -o >out &&
-		test_line_count = 3 out &&
+		test_line_count = 1 out &&
 
 		git rev-parse >expect       \
-			L2:three   R2:three \
 			L2:three   R2:three &&
 		git rev-parse   >actual     \
 			:2:three   :3:three &&
-		git hash-object >>actual    \
-			three~HEAD three~R2^0 &&
 		test_cmp expect actual
 	)
 '
@@ -185,7 +179,7 @@ test_expect_success 'setup differently handled merges of rename/add conflict' '
 		git branch B &&
 		git checkout -b C &&
 		echo 10 >>a &&
-		echo "other content" >>new_a &&
+		test_write_lines 0 1 2 3 4 5 6 7 foobar >new_a &&
 		git add a new_a &&
 		test_tick && git commit -m C &&
 
@@ -195,14 +189,14 @@ test_expect_success 'setup differently handled merges of rename/add conflict' '
 
 		git checkout B^0 &&
 		test_must_fail git merge C &&
-		git clean -f &&
+		git show :2:new_a >new_a &&
+		git add new_a &&
 		test_tick && git commit -m D &&
 		git tag D &&
 
 		git checkout C^0 &&
 		test_must_fail git merge B &&
-		rm new_a~HEAD new_a &&
-		printf "Incorrectly merged content" >>new_a &&
+		test_write_lines 0 1 2 3 4 5 6 7 bad_merge >new_a &&
 		git add -u &&
 		test_tick && git commit -m E &&
 		git tag E
@@ -225,21 +219,74 @@ test_expect_success 'git detects differently handled merges conflict' '
 		test_line_count = 1 out &&
 
 		git rev-parse >expect       \
-			D:new_a  E:new_a &&
+			C:new_a  D:new_a  E:new_a &&
 		git rev-parse   >actual     \
-			:2:new_a :3:new_a &&
+			:1:new_a :2:new_a :3:new_a &&
 		test_cmp expect actual &&
 
-		git cat-file -p C:new_a >ours &&
-		git cat-file -p B:new_a >theirs &&
+		# Test that the two-way merge in new_a is as expected
+		git cat-file -p D:new_a >ours &&
+		git cat-file -p E:new_a >theirs &&
 		>empty &&
 		test_must_fail git merge-file \
-			-L "Temporary merge branch 1" \
+			-L "HEAD" \
 			-L "" \
-			-L "Temporary merge branch 2" \
+			-L "E^0" \
 			ours empty theirs &&
 		sed -e "s/^\([<=>]\)/\1\1\1/" ours >expect &&
-		git cat-file -p :1:new_a >actual &&
+		git hash-object new_a >actual &&
+		git hash-object ours  >expect &&
+		test_cmp expect actual
+	)
+'
+
+# Repeat the above testcase with precisely the same setup, other than with
+# the two merge bases having different orderings of commit timestamps so
+# that they are reversed in the order they are provided to merge-recursive,
+# so that we can improve code coverage.
+test_expect_success 'git detects differently handled merges conflict, swapped' '
+	(
+		cd rename-add &&
+
+		# Difference #1: Do cleanup from previous testrun
+		git reset --hard &&
+		git clean -fdqx &&
+
+		# Difference #2: Change commit timestamps
+		btime=$(git log --no-walk --date=raw --format=%cd B | awk "{print \$1}") &&
+		ctime=$(git log --no-walk --date=raw --format=%cd C | awk "{print \$1}") &&
+		newctime=$(($btime+1)) &&
+		git fast-export --no-data --all | sed -e s/$ctime/$newctime/ | git fast-import --force --quiet &&
+		# End of differences; rest is copy-paste of last test
+
+		git checkout D^0 &&
+		test_must_fail git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 3 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		git rev-parse >expect       \
+			C:new_a  D:new_a  E:new_a &&
+		git rev-parse   >actual     \
+			:1:new_a :2:new_a :3:new_a &&
+		test_cmp expect actual &&
+
+		# Test that the two-way merge in new_a is as expected
+		git cat-file -p D:new_a >ours &&
+		git cat-file -p E:new_a >theirs &&
+		>empty &&
+		test_must_fail git merge-file \
+			-L "HEAD" \
+			-L "" \
+			-L "E^0" \
+			ours empty theirs &&
+		sed -e "s/^\([<=>]\)/\1\1\1/" ours >expect &&
+		git hash-object new_a >actual &&
+		git hash-object ours  >expect &&
 		test_cmp expect actual
 	)
 '
@@ -1402,4 +1449,349 @@ test_expect_failure 'check conflicting modes for regular file' '
 	)
 '
 
+# Setup:
+#          L1---L2
+#         /  \ /  \
+#   master    X    ?
+#         \  / \  /
+#          R1---R2
+#
+# Where:
+#   master has two files, named 'b' and 'a'
+#   branches L1 and R1 both modify each of the two files in conflicting ways
+#
+#   L2 is a merge of R1 into L1; more on it later.
+#   R2 is a merge of L1 into R1; more on it later.
+#
+#   X is an auto-generated merge-base used when merging L2 and R2.
+#   since X is a merge of L1 and R1, it has conflicting versions of each file
+#
+#   More about L2 and R2:
+#     - both resolve the conflicts in 'b' and 'a' differently
+#     - L2 renames 'b' to 'm'
+#     - R2 renames 'a' to 'm'
+#
+#   In the end, in file 'm' we have four different conflicting files (from
+#   two versions of 'b' and two of 'a').  In addition, if
+#   merge.conflictstyle is diff3, then the base version also has
+#   conflict markers of its own, leading to a total of three levels of
+#   conflict markers.  This is a pretty weird corner case, but we just want
+#   to ensure that we handle it as well as practical.
+
+test_expect_success 'setup nested conflicts' '
+	test_create_repo nested_conflicts &&
+	(
+		cd nested_conflicts &&
+
+		# Create some related files now
+		for i in $(test_seq 1 10)
+		do
+			echo Random base content line $i
+		done >initial &&
+
+		cp initial b_L1 &&
+		cp initial b_R1 &&
+		cp initial b_L2 &&
+		cp initial b_R2 &&
+		cp initial a_L1 &&
+		cp initial a_R1 &&
+		cp initial a_L2 &&
+		cp initial a_R2 &&
+
+		test_write_lines b b_L1 >>b_L1 &&
+		test_write_lines b b_R1 >>b_R1 &&
+		test_write_lines b b_L2 >>b_L2 &&
+		test_write_lines b b_R2 >>b_R2 &&
+		test_write_lines a a_L1 >>a_L1 &&
+		test_write_lines a a_R1 >>a_R1 &&
+		test_write_lines a a_L2 >>a_L2 &&
+		test_write_lines a a_R2 >>a_R2 &&
+
+		# Setup original commit (or merge-base), consisting of
+		# files named "b" and "a"
+		cp initial b &&
+		cp initial a &&
+		echo b >>b &&
+		echo a >>a &&
+		git add b a &&
+		test_tick && git commit -m initial &&
+
+		git branch L &&
+		git branch R &&
+
+		# Handle the left side
+		git checkout L &&
+		mv -f b_L1 b &&
+		mv -f a_L1 a &&
+		git add b a &&
+		test_tick && git commit -m "version L1 of files" &&
+		git tag L1 &&
+
+		# Handle the right side
+		git checkout R &&
+		mv -f b_R1 b &&
+		mv -f a_R1 a &&
+		git add b a &&
+		test_tick && git commit -m "verson R1 of files" &&
+		git tag R1 &&
+
+		# Create first merge on left side
+		git checkout L &&
+		test_must_fail git merge R1 &&
+		mv -f b_L2 b &&
+		mv -f a_L2 a &&
+		git add b a &&
+		git mv b m &&
+		test_tick && git commit -m "left merge, rename b->m" &&
+		git tag L2 &&
+
+		# Create first merge on right side
+		git checkout R &&
+		test_must_fail git merge L1 &&
+		mv -f b_R2 b &&
+		mv -f a_R2 a &&
+		git add b a &&
+		git mv a m &&
+		test_tick && git commit -m "right merge, rename a->m" &&
+		git tag R2
+	)
+'
+
+test_expect_success 'check nested conflicts' '
+	(
+		cd nested_conflicts &&
+
+		git clean -f &&
+		git checkout L2^0 &&
+
+		# Merge must fail; there is a conflict
+		test_must_fail git -c merge.conflictstyle=diff3 merge -s recursive R2^0 &&
+
+		# Make sure the index has the right number of entries
+		git ls-files -s >out &&
+		test_line_count = 2 out &&
+		git ls-files -u >out &&
+		test_line_count = 2 out &&
+		# Ensure we have the correct number of untracked files
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		# Create a and b from virtual merge base X
+		git cat-file -p master:a >base &&
+		git cat-file -p L1:a >ours &&
+		git cat-file -p R1:a >theirs &&
+		test_must_fail git merge-file --diff3 \
+			-L "Temporary merge branch 1" \
+			-L "merged common ancestors"  \
+			-L "Temporary merge branch 2" \
+			ours  \
+			base  \
+			theirs &&
+		sed -e "s/^\([<|=>]\)/\1\1/" ours >vmb_a &&
+
+		git cat-file -p master:b >base &&
+		git cat-file -p L1:b >ours &&
+		git cat-file -p R1:b >theirs &&
+		test_must_fail git merge-file --diff3 \
+			-L "Temporary merge branch 1" \
+			-L "merged common ancestors"  \
+			-L "Temporary merge branch 2" \
+			ours  \
+			base  \
+			theirs &&
+		sed -e "s/^\([<|=>]\)/\1\1/" ours >vmb_b &&
+
+		# Compare :2:m to expected values
+		git cat-file -p L2:m >ours &&
+		git cat-file -p R2:b >theirs &&
+		test_must_fail git merge-file --diff3  \
+			-L "HEAD:m"                    \
+			-L "merged common ancestors:b" \
+			-L "R2^0:b"                    \
+			ours                           \
+			vmb_b                          \
+			theirs                         &&
+		sed -e "s/^\([<|=>]\)/\1\1/" ours >m_stage_2 &&
+		git cat-file -p :2:m >actual &&
+		test_cmp m_stage_2 actual &&
+
+		# Compare :3:m to expected values
+		git cat-file -p L2:a >ours &&
+		git cat-file -p R2:m >theirs &&
+		test_must_fail git merge-file --diff3  \
+			-L "HEAD:a"                    \
+			-L "merged common ancestors:a" \
+			-L "R2^0:m"                    \
+			ours                           \
+			vmb_a                          \
+			theirs                         &&
+		sed -e "s/^\([<|=>]\)/\1\1/" ours >m_stage_3 &&
+		git cat-file -p :3:m >actual &&
+		test_cmp m_stage_3 actual &&
+
+		# Compare m to expected contents
+		>empty &&
+		cp m_stage_2 expected_final_m &&
+		test_must_fail git merge-file --diff3 \
+			-L "HEAD"                     \
+			-L "merged common ancestors"  \
+			-L "R2^0"                     \
+			expected_final_m              \
+			empty                         \
+			m_stage_3                     &&
+		test_cmp expected_final_m m
+	)
+'
+
+# Setup:
+#          L1---L2---L3
+#         /  \ /  \ /  \
+#   master    X1   X2   ?
+#         \  / \  / \  /
+#          R1---R2---R3
+#
+# Where:
+#   master has one file named 'content'
+#   branches L1 and R1 both modify each of the two files in conflicting ways
+#
+#   L<n> (n>1) is a merge of R<n-1> into L<n-1>
+#   R<n> (n>1) is a merge of L<n-1> into R<n-1>
+#   L<n> and R<n> resolve the conflicts differently.
+#
+#   X<n> is an auto-generated merge-base used when merging L<n+1> and R<n+1>.
+#   By construction, X1 has conflict markers due to conflicting versions.
+#   X2, due to using merge.conflictstyle=3, has nested conflict markers.
+#
+#   So, merging R3 into L3 using merge.conflictstyle=3 should show the
+#   nested conflict markers from X2 in the base version -- that means we
+#   have three levels of conflict markers.  Can we distinguish all three?
+
+test_expect_success 'setup virtual merge base with nested conflicts' '
+	test_create_repo virtual_merge_base_has_nested_conflicts &&
+	(
+		cd virtual_merge_base_has_nested_conflicts &&
+
+		# Create some related files now
+		for i in $(test_seq 1 10)
+		do
+			echo Random base content line $i
+		done >content &&
+
+		# Setup original commit
+		git add content &&
+		test_tick && git commit -m initial &&
+
+		git branch L &&
+		git branch R &&
+
+		# Create L1
+		git checkout L &&
+		echo left >>content &&
+		git add content &&
+		test_tick && git commit -m "version L1 of content" &&
+		git tag L1 &&
+
+		# Create R1
+		git checkout R &&
+		echo right >>content &&
+		git add content &&
+		test_tick && git commit -m "verson R1 of content" &&
+		git tag R1 &&
+
+		# Create L2
+		git checkout L &&
+		test_must_fail git -c merge.conflictstyle=diff3 merge R1 &&
+		git checkout L1 content &&
+		test_tick && git commit -m "version L2 of content" &&
+		git tag L2 &&
+
+		# Create R2
+		git checkout R &&
+		test_must_fail git -c merge.conflictstyle=diff3 merge L1 &&
+		git checkout R1 content &&
+		test_tick && git commit -m "version R2 of content" &&
+		git tag R2 &&
+
+		# Create L3
+		git checkout L &&
+		test_must_fail git -c merge.conflictstyle=diff3 merge R2 &&
+		git checkout L1 content &&
+		test_tick && git commit -m "version L3 of content" &&
+		git tag L3 &&
+
+		# Create R3
+		git checkout R &&
+		test_must_fail git -c merge.conflictstyle=diff3 merge L2 &&
+		git checkout R1 content &&
+		test_tick && git commit -m "version R3 of content" &&
+		git tag R3
+	)
+'
+
+test_expect_success 'check virtual merge base with nested conflicts' '
+	(
+		cd virtual_merge_base_has_nested_conflicts &&
+
+		git checkout L3^0 &&
+
+		# Merge must fail; there is a conflict
+		test_must_fail git -c merge.conflictstyle=diff3 merge -s recursive R3^0 &&
+
+		# Make sure the index has the right number of entries
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 3 out &&
+		# Ensure we have the correct number of untracked files
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		# Compare :[23]:content to expected values
+		git rev-parse L1:content R1:content >expect &&
+		git rev-parse :2:content :3:content >actual &&
+		test_cmp expect actual &&
+
+		# Imitate X1 merge base, except without long enough conflict
+		# markers because a subsequent sed will modify them.  Put
+		# result into vmb.
+		git cat-file -p master:content >base &&
+		git cat-file -p L:content >left &&
+		git cat-file -p R:content >right &&
+		cp left merged-once &&
+		test_must_fail git merge-file --diff3 \
+			-L "Temporary merge branch 1" \
+			-L "merged common ancestors"  \
+			-L "Temporary merge branch 2" \
+			merged-once \
+			base        \
+			right       &&
+		sed -e "s/^\([<|=>]\)/\1\1\1/" merged-once >vmb &&
+
+		# Imitate X2 merge base, overwriting vmb.  Note that we
+		# extend both sets of conflict markers to make them longer
+		# with the sed command.
+		cp left merged-twice &&
+		test_must_fail git merge-file --diff3 \
+			-L "Temporary merge branch 1" \
+			-L "merged common ancestors"  \
+			-L "Temporary merge branch 2" \
+			merged-twice \
+			vmb          \
+			right        &&
+		sed -e "s/^\([<|=>]\)/\1\1\1/" merged-twice >vmb &&
+
+		# Compare :1:content to expected value
+		git cat-file -p :1:content >actual &&
+		test_cmp vmb actual &&
+
+		# Determine expected content in final outer merge, compare to
+		# what the merge generated.
+		cp -f left expect &&
+		test_must_fail git merge-file --diff3                      \
+			-L "HEAD"  -L "merged common ancestors"  -L "R3^0" \
+			expect     vmb                           right     &&
+		test_cmp expect content
+	)
+'
+
 test_done
diff --git a/t/t6042-merge-rename-corner-cases.sh b/t/t6042-merge-rename-corner-cases.sh
index b97aca7fa2..7cc34e7579 100755
--- a/t/t6042-merge-rename-corner-cases.sh
+++ b/t/t6042-merge-rename-corner-cases.sh
@@ -464,17 +464,28 @@ test_expect_success 'handle rename/rename (2to1) conflict correctly' '
 		git ls-files -u c >out &&
 		test_line_count = 2 out &&
 		git ls-files -o >out &&
-		test_line_count = 3 out &&
+		test_line_count = 1 out &&
 
 		test_path_is_missing a &&
 		test_path_is_missing b &&
-		test_path_is_file c~HEAD &&
-		test_path_is_file c~C^0 &&
 
-		git rev-parse >expect   \
-			C:a     B:b     &&
-		git hash-object >actual \
-			c~HEAD  c~C^0   &&
+		git rev-parse >expect  \
+			C:a     B:b    &&
+		git rev-parse >actual  \
+			:2:c    :3:c   &&
+		test_cmp expect actual &&
+
+		# Test that the two-way merge in new_a is as expected
+		git cat-file -p :2:c >>ours &&
+		git cat-file -p :3:c >>theirs &&
+		>empty &&
+		test_must_fail git merge-file \
+			-L "HEAD" \
+			-L "" \
+			-L "C^0" \
+			ours empty theirs &&
+		git hash-object c >actual &&
+		git hash-object ours >expect &&
 		test_cmp expect actual
 	)
 '
@@ -673,7 +684,7 @@ test_expect_success 'rename/rename/add-dest merge still knows about conflicting
 		git ls-files -u c >out &&
 		test_line_count = 2 out &&
 		git ls-files -o >out &&
-		test_line_count = 5 out &&
+		test_line_count = 1 out &&
 
 		git rev-parse >expect               \
 			A:a   C:b   B:b   C:c   B:c &&
@@ -681,14 +692,27 @@ test_expect_success 'rename/rename/add-dest merge still knows about conflicting
 			:1:a  :2:b  :3:b  :2:c  :3:c &&
 		test_cmp expect actual &&
 
-		git rev-parse >expect               \
-			C:c     B:c     C:b     B:b &&
-		git hash-object >actual                \
-			c~HEAD  c~B\^0  b~HEAD  b~B\^0 &&
-		test_cmp expect actual &&
+		# Record some contents for re-doing merges
+		git cat-file -p A:a >stuff &&
+		git cat-file -p C:b >important_info &&
+		git cat-file -p B:c >precious_data &&
+		>empty &&
 
-		test_path_is_missing b &&
-		test_path_is_missing c
+		# Test the merge in b
+		test_must_fail git merge-file \
+			-L "HEAD" \
+			-L "" \
+			-L "B^0" \
+			important_info empty stuff &&
+		test_cmp important_info b &&
+
+		# Test the merge in c
+		test_must_fail git merge-file \
+			-L "HEAD" \
+			-L "" \
+			-L "B^0" \
+			stuff empty precious_data &&
+		test_cmp stuff c
 	)
 '
 
@@ -937,4 +961,283 @@ test_expect_failure 'mod6-check: chains of rename/rename(1to2) and rename/rename
 	)
 '
 
+test_conflicts_with_adds_and_renames() {
+	sideL=$1
+	sideR=$2
+
+	# Setup:
+	#          L
+	#         / \
+	#   master   ?
+	#         \ /
+	#          R
+	#
+	# Where:
+	#   Both L and R have files named 'three' which collide.  Each of
+	#   the colliding files could have been involved in a rename, in
+	#   which case there was a file named 'one' or 'two' that was
+	#   modified on the opposite side of history and renamed into the
+	#   collision on this side of history.
+	#
+	# Questions:
+	#   1) The index should contain both a stage 2 and stage 3 entry
+	#      for the colliding file.  Does it?
+	#   2) When renames are involved, the content merges are clean, so
+	#      the index should reflect the content merges, not merely the
+	#      version of the colliding file from the prior commit.  Does
+	#      it?
+	#   3) There should be a file in the worktree named 'three'
+	#      containing the two-way merged contents of the content-merged
+	#      versions of 'three' from each of the two colliding
+	#      files.  Is it present?
+	#   4) There should not be any three~* files in the working
+	#      tree
+	test_expect_success "setup simple $sideL/$sideR conflict" '
+		test_create_repo simple_${sideL}_${sideR} &&
+		(
+			cd simple_${sideL}_${sideR} &&
+
+			# Create some related files now
+			for i in $(test_seq 1 10)
+			do
+				echo Random base content line $i
+			done >file_v1 &&
+			cp file_v1 file_v2 &&
+			echo modification >>file_v2 &&
+
+			cp file_v1 file_v3 &&
+			echo more stuff >>file_v3 &&
+			cp file_v3 file_v4 &&
+			echo yet more stuff >>file_v4 &&
+
+			# Use a tag to record both these files for simple
+			# access, and clean out these untracked files
+			git tag file_v1 $(git hash-object -w file_v1) &&
+			git tag file_v2 $(git hash-object -w file_v2) &&
+			git tag file_v3 $(git hash-object -w file_v3) &&
+			git tag file_v4 $(git hash-object -w file_v4) &&
+			git clean -f &&
+
+			# Setup original commit (or merge-base), consisting of
+			# files named "one" and "two" if renames were involved.
+			touch irrelevant_file &&
+			git add irrelevant_file &&
+			if [ $sideL = "rename" ]
+			then
+				git show file_v1 >one &&
+				git add one
+			fi &&
+			if [ $sideR = "rename" ]
+			then
+				git show file_v3 >two &&
+				git add two
+			fi &&
+			test_tick && git commit -m initial &&
+
+			git branch L &&
+			git branch R &&
+
+			# Handle the left side
+			git checkout L &&
+			if [ $sideL = "rename" ]
+			then
+				git mv one three
+			else
+				git show file_v2 >three &&
+				git add three
+			fi &&
+			if [ $sideR = "rename" ]
+			then
+				git show file_v4 >two &&
+				git add two
+			fi &&
+			test_tick && git commit -m L &&
+
+			# Handle the right side
+			git checkout R &&
+			if [ $sideL = "rename" ]
+			then
+				git show file_v2 >one &&
+				git add one
+			fi &&
+			if [ $sideR = "rename" ]
+			then
+				git mv two three
+			else
+				git show file_v4 >three &&
+				git add three
+			fi &&
+			test_tick && git commit -m R
+		)
+	'
+
+	test_expect_success "check simple $sideL/$sideR conflict" '
+		(
+			cd simple_${sideL}_${sideR} &&
+
+			git checkout L^0 &&
+
+			# Merge must fail; there is a conflict
+			test_must_fail git merge -s recursive R^0 &&
+
+			# Make sure the index has the right number of entries
+			git ls-files -s >out &&
+			test_line_count = 3 out &&
+			git ls-files -u >out &&
+			test_line_count = 2 out &&
+			# Ensure we have the correct number of untracked files
+			git ls-files -o >out &&
+			test_line_count = 1 out &&
+
+			# Nothing should have touched irrelevant_file
+			git rev-parse >actual      \
+				:0:irrelevant_file \
+				:2:three           \
+				:3:three           &&
+			git rev-parse >expected        \
+				master:irrelevant_file \
+				file_v2                \
+				file_v4                &&
+			test_cmp expected actual &&
+
+			# Make sure we have the correct merged contents for
+			# three
+			git show file_v1 >expected &&
+			cat <<-\EOF >>expected &&
+			<<<<<<< HEAD
+			modification
+			=======
+			more stuff
+			yet more stuff
+			>>>>>>> R^0
+			EOF
+
+			test_cmp expected three
+		)
+	'
+}
+
+test_conflicts_with_adds_and_renames rename rename
+test_conflicts_with_adds_and_renames rename add
+test_conflicts_with_adds_and_renames add    rename
+test_conflicts_with_adds_and_renames add    add
+
+# Setup:
+#          L
+#         / \
+#   master   ?
+#         \ /
+#          R
+#
+# Where:
+#   master has two files, named 'one' and 'two'.
+#   branches L and R both modify 'one', in conflicting ways.
+#   branches L and R both modify 'two', in conflicting ways.
+#   branch L also renames 'one' to 'three'.
+#   branch R also renames 'two' to 'three'.
+#
+#   So, we have four different conflicting files that all end up at path
+#   'three'.
+test_expect_success 'setup nested conflicts from rename/rename(2to1)' '
+	test_create_repo nested_conflicts_from_rename_rename &&
+	(
+		cd nested_conflicts_from_rename_rename &&
+
+		# Create some related files now
+		for i in $(test_seq 1 10)
+		do
+			echo Random base content line $i
+		done >file_v1 &&
+
+		cp file_v1 file_v2 &&
+		cp file_v1 file_v3 &&
+		cp file_v1 file_v4 &&
+		cp file_v1 file_v5 &&
+		cp file_v1 file_v6 &&
+
+		echo one  >>file_v1 &&
+		echo uno  >>file_v2 &&
+		echo eins >>file_v3 &&
+
+		echo two  >>file_v4 &&
+		echo dos  >>file_v5 &&
+		echo zwei >>file_v6 &&
+
+		# Setup original commit (or merge-base), consisting of
+		# files named "one" and "two".
+		mv file_v1 one &&
+		mv file_v4 two &&
+		git add one two &&
+		test_tick && git commit -m english &&
+
+		git branch L &&
+		git branch R &&
+
+		# Handle the left side
+		git checkout L &&
+		git mv one three &&
+		mv -f file_v2 three &&
+		mv -f file_v5 two &&
+		git add two three &&
+		test_tick && git commit -m spanish &&
+
+		# Handle the right side
+		git checkout R &&
+		git mv two three &&
+		mv -f file_v3 one &&
+		mv -f file_v6 three &&
+		git add one three &&
+		test_tick && git commit -m german
+	)
+'
+
+test_expect_success 'check nested conflicts from rename/rename(2to1)' '
+	(
+		cd nested_conflicts_from_rename_rename &&
+
+		git checkout L^0 &&
+
+		# Merge must fail; there is a conflict
+		test_must_fail git merge -s recursive R^0 &&
+
+		# Make sure the index has the right number of entries
+		git ls-files -s >out &&
+		test_line_count = 2 out &&
+		git ls-files -u >out &&
+		test_line_count = 2 out &&
+		# Ensure we have the correct number of untracked files
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		# Compare :2:three to expected values
+		git cat-file -p master:one >base &&
+		git cat-file -p L:three >ours &&
+		git cat-file -p R:one >theirs &&
+		test_must_fail git merge-file    \
+			-L "HEAD:three"  -L ""  -L "R^0:one" \
+			ours             base   theirs &&
+		sed -e "s/^\([<=>]\)/\1\1/" ours >L-three &&
+		git cat-file -p :2:three >expect &&
+		test_cmp expect L-three &&
+
+		# Compare :2:three to expected values
+		git cat-file -p master:two >base &&
+		git cat-file -p L:two >ours &&
+		git cat-file -p R:three >theirs &&
+		test_must_fail git merge-file    \
+			-L "HEAD:two"  -L ""  -L "R^0:three" \
+			ours           base   theirs &&
+		sed -e "s/^\([<=>]\)/\1\1/" ours >R-three &&
+		git cat-file -p :3:three >expect &&
+		test_cmp expect R-three &&
+
+		# Compare three to expected contents
+		>empty &&
+		test_must_fail git merge-file    \
+			-L "HEAD"  -L ""  -L "R^0" \
+			L-three    empty  R-three &&
+		test_cmp three L-three
+	)
+'
+
 test_done
diff --git a/t/t6043-merge-rename-directories.sh b/t/t6043-merge-rename-directories.sh
index 4a71f17edd..62c564707b 100755
--- a/t/t6043-merge-rename-directories.sh
+++ b/t/t6043-merge-rename-directories.sh
@@ -278,7 +278,7 @@ test_expect_success '1d-check: Directory renames cause a rename/rename(2to1) con
 		git ls-files -u >out &&
 		test_line_count = 2 out &&
 		git ls-files -o >out &&
-		test_line_count = 3 out &&
+		test_line_count = 1 out &&
 
 		git rev-parse >actual \
 			:0:x/b :0:x/c :0:x/d :0:x/e :0:x/m :0:x/n &&
@@ -293,15 +293,16 @@ test_expect_success '1d-check: Directory renames cause a rename/rename(2to1) con
 			 A:y/wham  B:z/wham &&
 		test_cmp expect actual &&
 
-		test_path_is_missing x/wham &&
-		test_path_is_file x/wham~HEAD &&
-		test_path_is_file x/wham~B^0 &&
-
-		git hash-object >actual \
-			x/wham~HEAD x/wham~B^0 &&
-		git rev-parse >expect \
-			A:y/wham    B:z/wham &&
-		test_cmp expect actual
+		# Test that the two-way merge in x/wham is as expected
+		git cat-file -p :2:x/wham >expect &&
+		git cat-file -p :3:x/wham >other &&
+		>empty &&
+		test_must_fail git merge-file \
+			-L "HEAD" \
+			-L "" \
+			-L "B^0" \
+			expect empty other &&
+		test_cmp expect x/wham
 	)
 '
 
@@ -1077,7 +1078,7 @@ test_expect_success '5c-check: Transitive rename would cause rename/rename/renam
 		git ls-files -u >out &&
 		test_line_count = 6 out &&
 		git ls-files -o >out &&
-		test_line_count = 3 out &&
+		test_line_count = 1 out &&
 
 		git rev-parse >actual \
 			:0:y/b :0:y/c :0:y/e &&
@@ -1093,9 +1094,9 @@ test_expect_success '5c-check: Transitive rename would cause rename/rename/renam
 		test_cmp expect actual &&
 
 		git hash-object >actual \
-			w/d~HEAD w/d~B^0 z/d &&
+			z/d &&
 		git rev-parse >expect \
-			O:x/d    B:w/d   O:x/d &&
+			O:x/d &&
 		test_cmp expect actual &&
 		test_path_is_missing x/d &&
 		test_path_is_file y/d &&
@@ -1670,7 +1671,7 @@ test_expect_success '7b-check: rename/rename(2to1), but only due to transitive r
 		git ls-files -u >out &&
 		test_line_count = 2 out &&
 		git ls-files -o >out &&
-		test_line_count = 3 out &&
+		test_line_count = 1 out &&
 
 		git rev-parse >actual \
 			:0:y/b :0:y/c :2:y/d :3:y/d &&
@@ -1678,15 +1679,16 @@ test_expect_success '7b-check: rename/rename(2to1), but only due to transitive r
 			 O:z/b  O:z/c  O:w/d  O:x/d &&
 		test_cmp expect actual &&
 
-		test_path_is_missing y/d &&
-		test_path_is_file y/d~HEAD &&
-		test_path_is_file y/d~B^0 &&
-
-		git hash-object >actual \
-			y/d~HEAD y/d~B^0 &&
-		git rev-parse >expect \
-			O:w/d    O:x/d &&
-		test_cmp expect actual
+		# Test that the two-way merge in y/d is as expected
+		git cat-file -p :2:y/d >expect &&
+		git cat-file -p :3:y/d >other &&
+		>empty &&
+		test_must_fail git merge-file \
+			-L "HEAD" \
+			-L "" \
+			-L "B^0" \
+			expect empty other &&
+		test_cmp expect y/d
 	)
 '
 
@@ -3161,11 +3163,48 @@ test_expect_success '10c-check: Overwrite untracked with dir rename/rename(1to2)
 	)
 '
 
+test_expect_success '10c-check: Overwrite untracked with dir rename/rename(1to2), other direction' '
+	(
+		cd 10c &&
+
+		git reset --hard &&
+		git clean -fdqx &&
+
+		git checkout B^0 &&
+		mkdir y &&
+		echo important >y/c &&
+
+		test_must_fail git merge -s recursive A^0 >out 2>err &&
+		test_i18ngrep "CONFLICT (rename/rename)" out &&
+		test_i18ngrep "Refusing to lose untracked file at y/c; adding as y/c~HEAD instead" out &&
+
+		git ls-files -s >out &&
+		test_line_count = 6 out &&
+		git ls-files -u >out &&
+		test_line_count = 3 out &&
+		git ls-files -o >out &&
+		test_line_count = 3 out &&
+
+		git rev-parse >actual \
+			:0:y/a :0:y/b :0:x/d :1:x/c :3:w/c :2:y/c &&
+		git rev-parse >expect \
+			 O:z/a  O:z/b  O:x/d  O:x/c  O:x/c  O:x/c &&
+		test_cmp expect actual &&
+
+		git hash-object y/c~HEAD >actual &&
+		git rev-parse O:x/c >expect &&
+		test_cmp expect actual &&
+
+		echo important >expect &&
+		test_cmp expect y/c
+	)
+'
+
 # Testcase 10d, Delete untracked w/ dir rename/rename(2to1)
 #   Commit O: z/{a,b,c_1},        x/{d,e,f_2}
 #   Commit A: y/{a,b},            x/{d,e,f_2,wham_1} + untracked y/wham
 #   Commit B: z/{a,b,c_1,wham_2}, y/{d,e}
-#   Expected: Failed Merge; y/{a,b,d,e} + untracked y/{wham,wham~B^0,wham~HEAD}+
+#   Expected: Failed Merge; y/{a,b,d,e} + untracked y/{wham,wham~merged}+
 #             CONFLICT(rename/rename) z/c_1 vs x/f_2 -> y/wham
 #             ERROR_MSG(Refusing to lose untracked file at y/wham)
 
@@ -3219,7 +3258,7 @@ test_expect_success '10d-check: Delete untracked with dir rename/rename(2to1)' '
 		git ls-files -u >out &&
 		test_line_count = 2 out &&
 		git ls-files -o >out &&
-		test_line_count = 4 out &&
+		test_line_count = 3 out &&
 
 		git rev-parse >actual \
 			:0:y/a :0:y/b :0:y/d :0:y/e :2:y/wham :3:y/wham &&
@@ -3232,11 +3271,16 @@ test_expect_success '10d-check: Delete untracked with dir rename/rename(2to1)' '
 		echo important >expect &&
 		test_cmp expect y/wham &&
 
-		git hash-object >actual \
-			y/wham~B^0 y/wham~HEAD &&
-		git rev-parse >expect \
-			O:x/f      O:z/c &&
-		test_cmp expect actual
+		# Test that the two-way merge in y/wham~merged is as expected
+		git cat-file -p :2:y/wham >expect &&
+		git cat-file -p :3:y/wham >other &&
+		>empty &&
+		test_must_fail git merge-file \
+			-L "HEAD" \
+			-L "" \
+			-L "B^0" \
+			expect empty other &&
+		test_cmp expect y/wham~merged
 	)
 '
 
@@ -3665,7 +3709,7 @@ test_expect_success '11e-check: Avoid deleting not-uptodate with dir rename/rena
 		git ls-files -u >out &&
 		test_line_count = 4 out &&
 		git ls-files -o >out &&
-		test_line_count = 4 out &&
+		test_line_count = 3 out &&
 
 		echo different >expected &&
 		echo mods >>expected &&
@@ -3677,11 +3721,17 @@ test_expect_success '11e-check: Avoid deleting not-uptodate with dir rename/rena
 			 O:z/a  O:z/b  O:x/d  O:x/c  O:x/c  A:y/c  O:x/c &&
 		test_cmp expect actual &&
 
-		git hash-object >actual \
-			y/c~B^0 y/c~HEAD &&
-		git rev-parse >expect \
-			O:x/c   A:y/c &&
-		test_cmp expect actual
+		# See if y/c~merged has expected contents; requires manually
+		# doing the expected file merge
+		git cat-file -p A:y/c >c1 &&
+		git cat-file -p B:z/c >c2 &&
+		>empty &&
+		test_must_fail git merge-file \
+			-L "HEAD" \
+			-L "" \
+			-L "B^0" \
+			c1 empty c2 &&
+		test_cmp c1 y/c~merged
 	)
 '
 
@@ -3689,7 +3739,7 @@ test_expect_success '11e-check: Avoid deleting not-uptodate with dir rename/rena
 #   Commit O: z/{a,b},        x/{c_1,d_2}
 #   Commit A: y/{a,b,wham_1}, x/d_2, except y/wham has uncommitted mods
 #   Commit B: z/{a,b,wham_2}, x/c_1
-#   Expected: Failed Merge; y/{a,b} + untracked y/{wham~B^0,wham~B^HEAD} +
+#   Expected: Failed Merge; y/{a,b} + untracked y/{wham~merged} +
 #             y/wham with dirty changes from before merge +
 #             CONFLICT(rename/rename) x/c vs x/d -> y/wham
 #             ERROR_MSG(Refusing to lose dirty file at y/wham)
@@ -3741,24 +3791,30 @@ test_expect_success '11f-check: Avoid deleting not-uptodate with dir rename/rena
 		git ls-files -u >out &&
 		test_line_count = 2 out &&
 		git ls-files -o >out &&
-		test_line_count = 4 out &&
+		test_line_count = 3 out &&
 
 		test_seq 1 10 >expected &&
 		echo important >>expected &&
 		test_cmp expected y/wham &&
 
 		test_must_fail git rev-parse :1:y/wham &&
-		git hash-object >actual \
-			y/wham~B^0 y/wham~HEAD &&
-		git rev-parse >expect \
-			O:x/d      O:x/c &&
-		test_cmp expect actual &&
 
 		git rev-parse >actual \
 			:0:y/a :0:y/b :2:y/wham :3:y/wham &&
 		git rev-parse >expect \
 			 O:z/a  O:z/b  O:x/c     O:x/d &&
-		test_cmp expect actual
+		test_cmp expect actual &&
+
+		# Test that the two-way merge in y/wham~merged is as expected
+		git cat-file -p :2:y/wham >expect &&
+		git cat-file -p :3:y/wham >other &&
+		>empty &&
+		test_must_fail git merge-file \
+			-L "HEAD" \
+			-L "" \
+			-L "B^0" \
+			expect empty other &&
+		test_cmp expect y/wham~merged
 	)
 '