diff --git a/unpack-trees.c b/unpack-trees.c
index c659af67c62..f5294194aa1 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -66,8 +66,8 @@ static const char *unpack_plumbing_errors[NB_UNPACK_TREES_WARNING_TYPES] = {
 };
 
 #define ERRORMSG(o,type) \
-	( ((o) && (o)->msgs[(type)]) \
-	  ? ((o)->msgs[(type)])      \
+	( ((o) && (o)->internal.msgs[(type)]) \
+	  ? ((o)->internal.msgs[(type)])      \
 	  : (unpack_plumbing_errors[(type)]) )
 
 static const char *super_prefixed(const char *path, const char *super_prefix)
@@ -108,10 +108,10 @@ void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
 				  const char *cmd)
 {
 	int i;
-	const char **msgs = opts->msgs;
+	const char **msgs = opts->internal.msgs;
 	const char *msg;
 
-	strvec_init(&opts->msgs_to_free);
+	strvec_init(&opts->internal.msgs_to_free);
 
 	if (!strcmp(cmd, "checkout"))
 		msg = advice_enabled(ADVICE_COMMIT_BEFORE_MERGE)
@@ -129,7 +129,7 @@ void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
 			  "Please commit your changes or stash them before you %s.")
 		      : _("Your local changes to the following files would be overwritten by %s:\n%%s");
 	msgs[ERROR_WOULD_OVERWRITE] = msgs[ERROR_NOT_UPTODATE_FILE] =
-		strvec_pushf(&opts->msgs_to_free, msg, cmd, cmd);
+		strvec_pushf(&opts->internal.msgs_to_free, msg, cmd, cmd);
 
 	msgs[ERROR_NOT_UPTODATE_DIR] =
 		_("Updating the following directories would lose untracked files in them:\n%s");
@@ -153,7 +153,7 @@ void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
 			  "Please move or remove them before you %s.")
 		      : _("The following untracked working tree files would be removed by %s:\n%%s");
 	msgs[ERROR_WOULD_LOSE_UNTRACKED_REMOVED] =
-		strvec_pushf(&opts->msgs_to_free, msg, cmd, cmd);
+		strvec_pushf(&opts->internal.msgs_to_free, msg, cmd, cmd);
 
 	if (!strcmp(cmd, "checkout"))
 		msg = advice_enabled(ADVICE_COMMIT_BEFORE_MERGE)
@@ -171,7 +171,7 @@ void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
 			  "Please move or remove them before you %s.")
 		      : _("The following untracked working tree files would be overwritten by %s:\n%%s");
 	msgs[ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN] =
-		strvec_pushf(&opts->msgs_to_free, msg, cmd, cmd);
+		strvec_pushf(&opts->internal.msgs_to_free, msg, cmd, cmd);
 
 	/*
 	 * Special case: ERROR_BIND_OVERLAP refers to a pair of paths, we
@@ -189,16 +189,16 @@ void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
 	msgs[WARNING_SPARSE_ORPHANED_NOT_OVERWRITTEN] =
 		_("The following paths were already present and thus not updated despite sparse patterns:\n%s");
 
-	opts->show_all_errors = 1;
+	opts->internal.show_all_errors = 1;
 	/* rejected paths may not have a static buffer */
-	for (i = 0; i < ARRAY_SIZE(opts->unpack_rejects); i++)
-		opts->unpack_rejects[i].strdup_strings = 1;
+	for (i = 0; i < ARRAY_SIZE(opts->internal.unpack_rejects); i++)
+		opts->internal.unpack_rejects[i].strdup_strings = 1;
 }
 
 void clear_unpack_trees_porcelain(struct unpack_trees_options *opts)
 {
-	strvec_clear(&opts->msgs_to_free);
-	memset(opts->msgs, 0, sizeof(opts->msgs));
+	strvec_clear(&opts->internal.msgs_to_free);
+	memset(opts->internal.msgs, 0, sizeof(opts->internal.msgs));
 }
 
 static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
@@ -210,7 +210,7 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 		set |= CE_WT_REMOVE;
 
 	ce->ce_flags = (ce->ce_flags & ~clear) | set;
-	return add_index_entry(&o->result, ce,
+	return add_index_entry(&o->internal.result, ce,
 			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
@@ -218,7 +218,7 @@ static void add_entry(struct unpack_trees_options *o,
 		      const struct cache_entry *ce,
 		      unsigned int set, unsigned int clear)
 {
-	do_add_entry(o, dup_cache_entry(ce, &o->result), set, clear);
+	do_add_entry(o, dup_cache_entry(ce, &o->internal.result), set, clear);
 }
 
 /*
@@ -233,7 +233,7 @@ static int add_rejected_path(struct unpack_trees_options *o,
 	if (o->quiet)
 		return -1;
 
-	if (!o->show_all_errors)
+	if (!o->internal.show_all_errors)
 		return error(ERRORMSG(o, e), super_prefixed(path,
 							    o->super_prefix));
 
@@ -241,7 +241,7 @@ static int add_rejected_path(struct unpack_trees_options *o,
 	 * Otherwise, insert in a list for future display by
 	 * display_(error|warning)_msgs()
 	 */
-	string_list_append(&o->unpack_rejects[e], path);
+	string_list_append(&o->internal.unpack_rejects[e], path);
 	return -1;
 }
 
@@ -253,7 +253,7 @@ static void display_error_msgs(struct unpack_trees_options *o)
 	int e;
 	unsigned error_displayed = 0;
 	for (e = 0; e < NB_UNPACK_TREES_ERROR_TYPES; e++) {
-		struct string_list *rejects = &o->unpack_rejects[e];
+		struct string_list *rejects = &o->internal.unpack_rejects[e];
 
 		if (rejects->nr > 0) {
 			int i;
@@ -281,7 +281,7 @@ static void display_warning_msgs(struct unpack_trees_options *o)
 	unsigned warning_displayed = 0;
 	for (e = NB_UNPACK_TREES_ERROR_TYPES + 1;
 	     e < NB_UNPACK_TREES_WARNING_TYPES; e++) {
-		struct string_list *rejects = &o->unpack_rejects[e];
+		struct string_list *rejects = &o->internal.unpack_rejects[e];
 
 		if (rejects->nr > 0) {
 			int i;
@@ -600,13 +600,14 @@ static void mark_ce_used(struct cache_entry *ce, struct unpack_trees_options *o)
 {
 	ce->ce_flags |= CE_UNPACKED;
 
-	if (o->cache_bottom < o->src_index->cache_nr &&
-	    o->src_index->cache[o->cache_bottom] == ce) {
-		int bottom = o->cache_bottom;
+	if (o->internal.cache_bottom < o->src_index->cache_nr &&
+	    o->src_index->cache[o->internal.cache_bottom] == ce) {
+		int bottom = o->internal.cache_bottom;
+
 		while (bottom < o->src_index->cache_nr &&
 		       o->src_index->cache[bottom]->ce_flags & CE_UNPACKED)
 			bottom++;
-		o->cache_bottom = bottom;
+		o->internal.cache_bottom = bottom;
 	}
 }
 
@@ -652,7 +653,7 @@ static void mark_ce_used_same_name(struct cache_entry *ce,
 static struct cache_entry *next_cache_entry(struct unpack_trees_options *o)
 {
 	const struct index_state *index = o->src_index;
-	int pos = o->cache_bottom;
+	int pos = o->internal.cache_bottom;
 
 	while (pos < index->cache_nr) {
 		struct cache_entry *ce = index->cache[pos];
@@ -711,7 +712,7 @@ static void restore_cache_bottom(struct traverse_info *info, int bottom)
 
 	if (o->diff_index_cached)
 		return;
-	o->cache_bottom = bottom;
+	o->internal.cache_bottom = bottom;
 }
 
 static int switch_cache_bottom(struct traverse_info *info)
@@ -721,13 +722,13 @@ static int switch_cache_bottom(struct traverse_info *info)
 
 	if (o->diff_index_cached)
 		return 0;
-	ret = o->cache_bottom;
+	ret = o->internal.cache_bottom;
 	pos = find_cache_pos(info->prev, info->name, info->namelen);
 
 	if (pos < -1)
-		o->cache_bottom = -2 - pos;
+		o->internal.cache_bottom = -2 - pos;
 	else if (pos < 0)
-		o->cache_bottom = o->src_index->cache_nr;
+		o->internal.cache_bottom = o->src_index->cache_nr;
 	return ret;
 }
 
@@ -873,9 +874,9 @@ static int traverse_trees_recursive(int n, unsigned long dirmask,
 		 * save and restore cache_bottom anyway to not miss
 		 * unprocessed entries before 'pos'.
 		 */
-		bottom = o->cache_bottom;
+		bottom = o->internal.cache_bottom;
 		ret = traverse_by_cache_tree(pos, nr_entries, n, info);
-		o->cache_bottom = bottom;
+		o->internal.cache_bottom = bottom;
 		return ret;
 	}
 
@@ -1212,7 +1213,7 @@ static int unpack_single_entry(int n, unsigned long mask,
 		 * cache entry from the index aware logic.
 		 */
 		src[i + o->merge] = create_ce_entry(info, names + i, stage,
-						    &o->result, o->merge,
+						    &o->internal.result, o->merge,
 						    bit & dirmask);
 	}
 
@@ -1237,7 +1238,7 @@ static int unpack_single_entry(int n, unsigned long mask,
 
 static int unpack_failed(struct unpack_trees_options *o, const char *message)
 {
-	discard_index(&o->result);
+	discard_index(&o->internal.result);
 	if (!o->quiet && !o->exiting_early) {
 		if (message)
 			return error("%s", message);
@@ -1260,7 +1261,7 @@ static int find_cache_pos(struct traverse_info *info,
 	struct index_state *index = o->src_index;
 	int pfxlen = info->pathlen;
 
-	for (pos = o->cache_bottom; pos < index->cache_nr; pos++) {
+	for (pos = o->internal.cache_bottom; pos < index->cache_nr; pos++) {
 		const struct cache_entry *ce = index->cache[pos];
 		const char *ce_name, *ce_slash;
 		int cmp, ce_len;
@@ -1271,8 +1272,8 @@ static int find_cache_pos(struct traverse_info *info,
 			 * we can never match it; don't check it
 			 * again.
 			 */
-			if (pos == o->cache_bottom)
-				++o->cache_bottom;
+			if (pos == o->internal.cache_bottom)
+				++o->internal.cache_bottom;
 			continue;
 		}
 		if (!ce_in_traverse_path(ce, info)) {
@@ -1450,7 +1451,7 @@ static int unpack_sparse_callback(int n, unsigned long mask, unsigned long dirma
 	 */
 	if (!is_null_oid(&names[0].oid)) {
 		src[0] = create_ce_entry(info, &names[0], 0,
-					&o->result, 1,
+					&o->internal.result, 1,
 					dirmask & (1ul << 0));
 		src[0]->ce_flags |= (CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE);
 	}
@@ -1560,7 +1561,7 @@ static int unpack_callback(int n, unsigned long mask, unsigned long dirmask, str
 				 * in 'mark_ce_used()'
 				 */
 				if (!src[0] || !S_ISSPARSEDIR(src[0]->ce_mode))
-					o->cache_bottom += matches;
+					o->internal.cache_bottom += matches;
 				return mask;
 			}
 		}
@@ -1907,37 +1908,37 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 		populate_from_existing_patterns(o, &pl);
 	}
 
-	index_state_init(&o->result, o->src_index->repo);
-	o->result.initialized = 1;
-	o->result.timestamp.sec = o->src_index->timestamp.sec;
-	o->result.timestamp.nsec = o->src_index->timestamp.nsec;
-	o->result.version = o->src_index->version;
+	index_state_init(&o->internal.result, o->src_index->repo);
+	o->internal.result.initialized = 1;
+	o->internal.result.timestamp.sec = o->src_index->timestamp.sec;
+	o->internal.result.timestamp.nsec = o->src_index->timestamp.nsec;
+	o->internal.result.version = o->src_index->version;
 	if (!o->src_index->split_index) {
-		o->result.split_index = NULL;
+		o->internal.result.split_index = NULL;
 	} else if (o->src_index == o->dst_index) {
 		/*
 		 * o->dst_index (and thus o->src_index) will be discarded
-		 * and overwritten with o->result at the end of this function,
+		 * and overwritten with o->internal.result at the end of this function,
 		 * so just use src_index's split_index to avoid having to
 		 * create a new one.
 		 */
-		o->result.split_index = o->src_index->split_index;
-		o->result.split_index->refcount++;
+		o->internal.result.split_index = o->src_index->split_index;
+		o->internal.result.split_index->refcount++;
 	} else {
-		o->result.split_index = init_split_index(&o->result);
+		o->internal.result.split_index = init_split_index(&o->internal.result);
 	}
-	oidcpy(&o->result.oid, &o->src_index->oid);
+	oidcpy(&o->internal.result.oid, &o->src_index->oid);
 	o->merge_size = len;
 	mark_all_ce_unused(o->src_index);
 
-	o->result.fsmonitor_last_update =
+	o->internal.result.fsmonitor_last_update =
 		xstrdup_or_null(o->src_index->fsmonitor_last_update);
-	o->result.fsmonitor_has_run_once = o->src_index->fsmonitor_has_run_once;
+	o->internal.result.fsmonitor_has_run_once = o->src_index->fsmonitor_has_run_once;
 
 	if (!o->src_index->initialized &&
 	    !repo->settings.command_requires_full_index &&
-	    is_sparse_index_allowed(&o->result, 0))
-		o->result.sparse_index = 1;
+	    is_sparse_index_allowed(&o->internal.result, 0))
+		o->internal.result.sparse_index = 1;
 
 	/*
 	 * Sparse checkout loop #1: set NEW_SKIP_WORKTREE on existing entries
@@ -1957,7 +1958,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 		setup_traverse_info(&info, prefix);
 		info.fn = unpack_callback;
 		info.data = o;
-		info.show_all_errors = o->show_all_errors;
+		info.show_all_errors = o->internal.show_all_errors;
 		info.pathspec = o->pathspec;
 
 		if (o->prefix) {
@@ -1998,7 +1999,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 	}
 	mark_all_ce_unused(o->src_index);
 
-	if (o->trivial_merges_only && o->nontrivial_merge) {
+	if (o->trivial_merges_only && o->internal.nontrivial_merge) {
 		ret = unpack_failed(o, "Merge requires file-level merging");
 		goto done;
 	}
@@ -2009,13 +2010,13 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 		 * If they will have NEW_SKIP_WORKTREE, also set CE_SKIP_WORKTREE
 		 * so apply_sparse_checkout() won't attempt to remove it from worktree
 		 */
-		mark_new_skip_worktree(o->internal.pl, &o->result,
+		mark_new_skip_worktree(o->internal.pl, &o->internal.result,
 				       CE_ADDED, CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE,
 				       o->verbose_update);
 
 		ret = 0;
-		for (i = 0; i < o->result.cache_nr; i++) {
-			struct cache_entry *ce = o->result.cache[i];
+		for (i = 0; i < o->internal.result.cache_nr; i++) {
+			struct cache_entry *ce = o->internal.result.cache[i];
 
 			/*
 			 * Entries marked with CE_ADDED in merged_entry() do not have
@@ -2029,7 +2030,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 			    verify_absent(ce, WARNING_SPARSE_ORPHANED_NOT_OVERWRITTEN, o))
 				ret = 1;
 
-			if (apply_sparse_checkout(&o->result, ce, o))
+			if (apply_sparse_checkout(&o->internal.result, ce, o))
 				ret = 1;
 		}
 		if (ret == 1) {
@@ -2037,30 +2038,30 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 			 * Inability to sparsify or de-sparsify individual
 			 * paths is not an error, but just a warning.
 			 */
-			if (o->show_all_errors)
+			if (o->internal.show_all_errors)
 				display_warning_msgs(o);
 			ret = 0;
 		}
 	}
 
-	ret = check_updates(o, &o->result) ? (-2) : 0;
+	ret = check_updates(o, &o->internal.result) ? (-2) : 0;
 	if (o->dst_index) {
-		move_index_extensions(&o->result, o->src_index);
+		move_index_extensions(&o->internal.result, o->src_index);
 		if (!ret) {
 			if (git_env_bool("GIT_TEST_CHECK_CACHE_TREE", 0))
-				cache_tree_verify(the_repository, &o->result);
+				cache_tree_verify(the_repository, &o->internal.result);
 			if (!o->skip_cache_tree_update &&
-			    !cache_tree_fully_valid(o->result.cache_tree))
-				cache_tree_update(&o->result,
+			    !cache_tree_fully_valid(o->internal.result.cache_tree))
+				cache_tree_update(&o->internal.result,
 						  WRITE_TREE_SILENT |
 						  WRITE_TREE_REPAIR);
 		}
 
-		o->result.updated_workdir = 1;
+		o->internal.result.updated_workdir = 1;
 		discard_index(o->dst_index);
-		*o->dst_index = o->result;
+		*o->dst_index = o->internal.result;
 	} else {
-		discard_index(&o->result);
+		discard_index(&o->internal.result);
 	}
 	o->src_index = NULL;
 
@@ -2076,7 +2077,7 @@ done:
 	return ret;
 
 return_failed:
-	if (o->show_all_errors)
+	if (o->internal.show_all_errors)
 		display_error_msgs(o);
 	mark_all_ce_unused(o->src_index);
 	ret = unpack_failed(o, NULL);
@@ -2099,9 +2100,9 @@ enum update_sparsity_result update_sparsity(struct unpack_trees_options *o,
 	unsigned old_show_all_errors;
 	int free_pattern_list = 0;
 
-	old_show_all_errors = o->show_all_errors;
-	o->show_all_errors = 1;
-	index_state_init(&o->result, o->src_index->repo);
+	old_show_all_errors = o->internal.show_all_errors;
+	o->internal.show_all_errors = 1;
+	index_state_init(&o->internal.result, o->src_index->repo);
 
 	/* Sanity checks */
 	if (!o->update || o->index_only || o->skip_sparse_checkout)
@@ -2148,7 +2149,7 @@ enum update_sparsity_result update_sparsity(struct unpack_trees_options *o,
 		ret = UPDATE_SPARSITY_WORKTREE_UPDATE_FAILURES;
 
 	display_warning_msgs(o);
-	o->show_all_errors = old_show_all_errors;
+	o->internal.show_all_errors = old_show_all_errors;
 	if (free_pattern_list) {
 		clear_pattern_list(pl);
 		free(pl);
@@ -2248,15 +2249,15 @@ static int verify_uptodate_sparse(const struct cache_entry *ce,
 }
 
 /*
- * TODO: We should actually invalidate o->result, not src_index [1].
+ * TODO: We should actually invalidate o->internal.result, not src_index [1].
  * But since cache tree and untracked cache both are not copied to
- * o->result until unpacking is complete, we invalidate them on
+ * o->internal.result until unpacking is complete, we invalidate them on
  * src_index instead with the assumption that they will be copied to
  * dst_index at the end.
  *
  * [1] src_index->cache_tree is also used in unpack_callback() so if
- * we invalidate o->result, we need to update it to use
- * o->result.cache_tree as well.
+ * we invalidate o->internal.result, we need to update it to use
+ * o->internal.result.cache_tree as well.
  */
 static void invalidate_ce_path(const struct cache_entry *ce,
 			       struct unpack_trees_options *o)
@@ -2424,7 +2425,7 @@ static int check_ok_to_remove(const char *name, int len, int dtype,
 	 * delete this path, which is in a subdirectory that
 	 * is being replaced with a blob.
 	 */
-	result = index_file_exists(&o->result, name, len, 0);
+	result = index_file_exists(&o->internal.result, name, len, 0);
 	if (result) {
 		if (result->ce_flags & CE_REMOVE)
 			return 0;
@@ -2525,7 +2526,7 @@ static int merged_entry(const struct cache_entry *ce,
 			struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
-	struct cache_entry *merge = dup_cache_entry(ce, &o->result);
+	struct cache_entry *merge = dup_cache_entry(ce, &o->internal.result);
 
 	if (!old) {
 		/*
@@ -2620,7 +2621,7 @@ static int merged_sparse_dir(const struct cache_entry * const *src, int n,
 	setup_traverse_info(&info, src[0]->name);
 	info.fn = unpack_sparse_callback;
 	info.data = o;
-	info.show_all_errors = o->show_all_errors;
+	info.show_all_errors = o->internal.show_all_errors;
 	info.pathspec = o->pathspec;
 
 	/* Get the tree descriptors of the sparse directory in each of the merging trees */
@@ -2838,7 +2839,7 @@ int threeway_merge(const struct cache_entry * const *stages,
 			return -1;
 	}
 
-	o->nontrivial_merge = 1;
+	o->internal.nontrivial_merge = 1;
 
 	/* #2, #3, #4, #6, #7, #9, #10, #11. */
 	count = 0;
diff --git a/unpack-trees.h b/unpack-trees.h
index 5c1a9314a06..0335c89bc75 100644
--- a/unpack-trees.h
+++ b/unpack-trees.h
@@ -59,7 +59,6 @@ struct unpack_trees_options {
 		     preserve_ignored,
 		     clone,
 		     index_only,
-		     nontrivial_merge,
 		     trivial_merges_only,
 		     verbose_update,
 		     aggressive,
@@ -70,22 +69,13 @@ struct unpack_trees_options {
 		     skip_sparse_checkout,
 		     quiet,
 		     exiting_early,
-		     show_all_errors,
 		     dry_run,
 		     skip_cache_tree_update;
 	enum unpack_trees_reset_type reset;
 	const char *prefix;
 	const char *super_prefix;
-	int cache_bottom;
 	struct pathspec *pathspec;
 	merge_fn_t fn;
-	const char *msgs[NB_UNPACK_TREES_WARNING_TYPES];
-	struct strvec msgs_to_free;
-	/*
-	 * Store error messages in an array, each case
-	 * corresponding to a error message type
-	 */
-	struct string_list unpack_rejects[NB_UNPACK_TREES_WARNING_TYPES];
 
 	int head_idx;
 	int merge_size;
@@ -95,11 +85,25 @@ struct unpack_trees_options {
 
 	struct index_state *dst_index;
 	struct index_state *src_index;
-	struct index_state result;
 
 	struct checkout_metadata meta;
 
 	struct unpack_trees_options_internal {
+		unsigned int nontrivial_merge,
+			     show_all_errors;
+
+		int cache_bottom;
+		const char *msgs[NB_UNPACK_TREES_WARNING_TYPES];
+		struct strvec msgs_to_free;
+
+		/*
+		 * Store error messages in an array, each case
+		 * corresponding to a error message type
+		 */
+		struct string_list unpack_rejects[NB_UNPACK_TREES_WARNING_TYPES];
+
+		struct index_state result;
+
 		struct pattern_list *pl;
 		struct dir_struct *dir;
 	} internal;
