[PATCH] box: fix autoincrement for json path indexes

[Vladimir Davydov <vdavydov.dev@gmail.com>]

The autoincrement code was written when there were no nested field.
Now, it isn't enough to just skip to the autoincrement field - we also
need to descend deeper if key_part->path is set.

Note, the code expects the nested field to be present and set to NULL.
That is, if field path is [1].a.b, the tuple must have all intermediate
fields set: {{a = {b = box.NULL}}} (usage of box.NULL is mandatory to
create a tuple like that in Lua).

Closes #4210
---
 src/box/request.c          | 10 +++++++++-
 test/box/sequence.result   | 32 ++++++++++++++++++++++++++++++++
 test/box/sequence.test.lua | 12 ++++++++++++
 3 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/src/box/request.c b/src/box/request.c
index 9d3287f9..041a8d54 100644
--- a/src/box/request.c
+++ b/src/box/request.c
@@ -163,7 +163,8 @@ request_handle_sequence(struct request *request, struct space *space)
 	const char *data = request->tuple;
 	const char *data_end = request->tuple_end;
 	int len = mp_decode_array(&data);
-	int fieldno = pk->def->key_def->parts[space->sequence_part].fieldno;
+	struct key_part *part = &pk->def->key_def->parts[space->sequence_part];
+	int fieldno = part->fieldno;
 	if (unlikely(len < fieldno + 1))
 		return 0;
 
@@ -174,6 +175,13 @@ request_handle_sequence(struct request *request, struct space *space)
 		} while (--fieldno > 0);
 	}
 
+	if (part->path != NULL) {
+		tuple_go_to_path(&key, part->path, part->path_len,
+				 MULTIKEY_NONE);
+		if (key == NULL)
+			return 0; /* field not found */
+	}
+
 	int64_t value;
 	if (mp_typeof(*key) == MP_NIL) {
 		/*
diff --git a/test/box/sequence.result b/test/box/sequence.result
index 8a7c349c..3cac4dc9 100644
--- a/test/box/sequence.result
+++ b/test/box/sequence.result
@@ -2033,3 +2033,35 @@ s:insert{'d', box.NULL, 1001}
 s:drop()
 ---
 ...
+--
+-- gh-4210: using sequence with a json path key part.
+--
+s = box.schema.space.create('test')
+---
+...
+_ = s:create_index('pk', {parts = {{'[1].a.b[1]', 'unsigned'}}, sequence = true})
+---
+...
+s:replace{} -- error
+---
+- error: Tuple field [1]["a"]["b"][1] required by space format is missing
+...
+s:replace{{c = {}}} -- error
+---
+- error: Tuple field [1]["a"]["b"][1] required by space format is missing
+...
+s:replace{{a = {c = {}}}} -- error
+---
+- error: Tuple field [1]["a"]["b"][1] required by space format is missing
+...
+s:replace{{a = {b = {}}}} -- error
+---
+- error: Tuple field [1]["a"]["b"][1] required by space format is missing
+...
+s:replace{{a = {b = {box.NULL}}}} -- ok
+---
+- [{'a': {'b': [1]}}]
+...
+s:drop()
+---
+...
diff --git a/test/box/sequence.test.lua b/test/box/sequence.test.lua
index d931a94e..c39f1d41 100644
--- a/test/box/sequence.test.lua
+++ b/test/box/sequence.test.lua
@@ -685,3 +685,15 @@ s.index.pk.sequence_id == sequence_id
 s:insert{'d', 1000, 1000}
 s:insert{'d', box.NULL, 1001}
 s:drop()
+
+--
+-- gh-4210: using sequence with a json path key part.
+--
+s = box.schema.space.create('test')
+_ = s:create_index('pk', {parts = {{'[1].a.b[1]', 'unsigned'}}, sequence = true})
+s:replace{} -- error
+s:replace{{c = {}}} -- error
+s:replace{{a = {c = {}}}} -- error
+s:replace{{a = {b = {}}}} -- error
+s:replace{{a = {b = {box.NULL}}}} -- ok
+s:drop()
-- 
2.11.0