@@ -941,9 +941,8 @@ static int save_untracked_files(struct stash_info *info, struct strbuf *msg,
 {
 	int ret = 0;
 	struct strbuf untracked_msg = STRBUF_INIT;
-	struct strbuf out = STRBUF_INIT;
 	struct child_process cp_upd_index = CHILD_PROCESS_INIT;
-	struct child_process cp_write_tree = CHILD_PROCESS_INIT;
+	struct index_state istate = { NULL };
 
 	cp_upd_index.git_cmd = 1;
 	argv_array_pushl(&cp_upd_index.args, "update-index", "-z", "--add",

@@ -957,15 +956,11 @@ static int save_untracked_files(struct stash_info *info, struct strbuf *msg,
 		goto done;
 	}
 
-	cp_write_tree.git_cmd = 1;
-	argv_array_push(&cp_write_tree.args, "write-tree");
-	argv_array_pushf(&cp_write_tree.env_array, "GIT_INDEX_FILE=%s",
-			 stash_index_path.buf);
-	if (pipe_command(&cp_write_tree, NULL, 0, &out, 0,NULL, 0)) {
+	if (write_index_as_tree(&info->u_tree, &istate, stash_index_path.buf, 0,
+				NULL)) {
 		ret = -1;
 		goto done;
 	}
-	get_oid_hex(out.buf, &info->u_tree);
 
 	if (commit_tree(untracked_msg.buf, untracked_msg.len,
 			&info->u_tree, NULL, &info->u_commit, NULL, NULL)) {

@@ -974,8 +969,8 @@ static int save_untracked_files(struct stash_info *info, struct strbuf *msg,
 	}
 
 done:
+	discard_index(&istate);
 	strbuf_release(&untracked_msg);
-	strbuf_release(&out);
 	remove_path(stash_index_path.buf);
 	return ret;
 }

@@ -984,11 +979,10 @@ static int stash_patch(struct stash_info *info, struct pathspec ps,
 		       struct strbuf *out_patch, int quiet)
 {
 	int ret = 0;
-	struct strbuf out = STRBUF_INIT;
 	struct child_process cp_read_tree = CHILD_PROCESS_INIT;
 	struct child_process cp_add_i = CHILD_PROCESS_INIT;
-	struct child_process cp_write_tree = CHILD_PROCESS_INIT;
 	struct child_process cp_diff_tree = CHILD_PROCESS_INIT;
+	struct index_state istate = { NULL };
 
 	remove_path(stash_index_path.buf);
 

@@ -1014,17 +1008,12 @@ static int stash_patch(struct stash_info *info, struct pathspec ps,
 	}
 
 	/* State of the working tree. */
-	cp_write_tree.git_cmd = 1;
-	argv_array_push(&cp_write_tree.args, "write-tree");
-	argv_array_pushf(&cp_write_tree.env_array, "GIT_INDEX_FILE=%s",
-			 stash_index_path.buf);
-	if (pipe_command(&cp_write_tree, NULL, 0, &out, 0,NULL, 0)) {
+	if (write_index_as_tree(&info->w_tree, &istate, stash_index_path.buf, 0,
+				NULL)) {
 		ret = -1;
 		goto done;
 	}
 
-	get_oid_hex(out.buf, &info->w_tree);
-
 	cp_diff_tree.git_cmd = 1;
 	argv_array_pushl(&cp_diff_tree.args, "diff-tree", "-p", "HEAD",
 			 oid_to_hex(&info->w_tree), "--", NULL);

@@ -1040,7 +1029,7 @@ static int stash_patch(struct stash_info *info, struct pathspec ps,
 	}
 
 done:
-	strbuf_release(&out);
+	discard_index(&istate);
 	remove_path(stash_index_path.buf);
 	return ret;
 }

@@ -1050,9 +1039,8 @@ static int stash_working_tree(struct stash_info *info, struct pathspec ps)
 	int ret = 0;
 	struct rev_info rev;
 	struct child_process cp_upd_index = CHILD_PROCESS_INIT;
-	struct child_process cp_write_tree = CHILD_PROCESS_INIT;
-	struct strbuf out = STRBUF_INIT;
 	struct strbuf diff_output = STRBUF_INIT;
+	struct index_state istate = { NULL };
 
 	set_alternate_index_output(stash_index_path.buf);
 	if (reset_tree(&info->i_tree, 0, 0)) {

@@ -1091,20 +1079,15 @@ static int stash_working_tree(struct stash_info *info, struct pathspec ps)
 		goto done;
 	}
 
-	cp_write_tree.git_cmd = 1;
-	argv_array_push(&cp_write_tree.args, "write-tree");
-	argv_array_pushf(&cp_write_tree.env_array, "GIT_INDEX_FILE=%s",
-			 stash_index_path.buf);
-	if (pipe_command(&cp_write_tree, NULL, 0, &out, 0,NULL, 0)) {
+	if (write_index_as_tree(&info->w_tree, &istate, stash_index_path.buf, 0,
+				NULL)) {
 		ret = -1;
 		goto done;
 	}
 
-	get_oid_hex(out.buf, &info->w_tree);
-
 done:
+	discard_index(&istate);
 	UNLEAK(rev);
-	strbuf_release(&out);
 	object_array_clear(&rev.pending);
 	strbuf_release(&diff_output);
 	remove_path(stash_index_path.buf);