From 39feee8e3a6fee885aee60672a9dde0dfd08896c Mon Sep 17 00:00:00 2001
From: Binbin <binloveplay1314@qq.com>
Date: Tue, 11 Jan 2022 20:26:13 +0800
Subject: [PATCH] LPOP/RPOP with count against non existing list return null
 array (#10095)

It used to return `$-1` in RESP2, now we will return `*-1`.
This is a bug in redis 6.2 when COUNT was added, the `COUNT`
option was introduced in #8179. Fix #10089.

the documentation of [LPOP](https://redis.io/commands/lpop) says
```
When called without the count argument:
Bulk string reply: the value of the first element, or nil when key does not exist.

When called with the count argument:
Array reply: list of popped elements, or nil when key does not exist.
```
---
 src/t_list.c             |  2 +-
 tests/unit/type/list.tcl | 44 +++++++++++++++++++++++++++++++++-------
 2 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/src/t_list.c b/src/t_list.c
index 460437853..4d74a1665 100644
--- a/src/t_list.c
+++ b/src/t_list.c
@@ -501,7 +501,7 @@ void popGenericCommand(client *c, int where) {
             return;
     }
 
-    robj *o = lookupKeyWriteOrReply(c, c->argv[1], shared.null[c->resp]);
+    robj *o = lookupKeyWriteOrReply(c, c->argv[1], hascount ? shared.nullarray[c->resp]: shared.null[c->resp]);
     if (o == NULL || checkType(c, o, OBJ_LIST))
         return;
 
diff --git a/tests/unit/type/list.tcl b/tests/unit/type/list.tcl
index 31c8c56bb..3981d3f87 100644
--- a/tests/unit/type/list.tcl
+++ b/tests/unit/type/list.tcl
@@ -496,15 +496,45 @@ start_server {
         assert_error "*ERR*range*" {r lpop forbarqaz -123}
     }
 
-    # Make sure we can distinguish between an empty array and a null response
-    r readraw 1
+    proc verify_resp_response {resp response resp2_response resp3_response} {
+        if {$resp == 2} {
+            assert_equal $response $resp2_response
+        } elseif {$resp == 3} {
+            assert_equal $response $resp3_response
+        }
+    }
 
-    test {RPOP/LPOP with the count 0 returns an empty array} {
-        r lpush listcount zero
-        r lpop listcount 0
-    } {*0}
+    foreach resp {3 2} {
+        r hello $resp
 
-    r readraw 0
+        # Make sure we can distinguish between an empty array and a null response
+        r readraw 1
+
+        test "LPOP/RPOP with the count 0 returns an empty array in RESP$resp" {
+            r lpush listcount zero
+            assert_equal {*0} [r lpop listcount 0]
+            assert_equal {*0} [r rpop listcount 0]
+        }
+
+        test "LPOP/RPOP against non existing key in RESP$resp" {
+            r del non_existing_key
+
+            verify_resp_response $resp [r lpop non_existing_key] {$-1} {_}
+            verify_resp_response $resp [r rpop non_existing_key] {$-1} {_}
+        }
+
+        test "LPOP/RPOP with <count> against non existing key in RESP$resp" {
+            r del non_existing_key
+
+            verify_resp_response $resp [r lpop non_existing_key 0] {*-1} {_}
+            verify_resp_response $resp [r lpop non_existing_key 1] {*-1} {_}
+
+            verify_resp_response $resp [r rpop non_existing_key 0] {*-1} {_}
+            verify_resp_response $resp [r rpop non_existing_key 1] {*-1} {_}
+        }
+
+        r readraw 0
+    }
 
     test {Variadic RPUSH/LPUSH} {
         r del mylist