Fix COMMAND GETKEYS on EVAL without keys (#9733)

Add new no-mandatory-keys flag to support COMMAND GETKEYS of commands
which have no mandatory keys.

In the past we would have got this error:
```
127.0.0.1:6379> command getkeys eval "return 1" 0
(error) ERR Invalid arguments specified for command
```

src/module.c

@@ -803,6 +803,7 @@ int64_t commandFlagsFromString(char *s) {
         else if (!strcasecmp(t,"may-replicate")) flags |= CMD_MAY_REPLICATE;
         else if (!strcasecmp(t,"getkeys-api")) flags |= CMD_MODULE_GETKEYS;
         else if (!strcasecmp(t,"no-cluster")) flags |= CMD_MODULE_NO_CLUSTER;
+        else if (!strcasecmp(t,"no-mandatory-keys")) flags |= CMD_NO_MANDATORY_KEYS;
         else break;
     }
     sdsfreesplitres(tokens,count);
@@ -891,6 +892,7 @@ RedisModuleCommandProxy *moduleCreateCommandProxy(RedisModuleCtx *ctx, const cha
  *                     to authenticate a client.
  * * **"may-replicate"**: This command may generate replication traffic, even
  *                        though it's not a write command.
+ * * **"no-mandatory-keys"**: All the keys this command may take are optional
  *
  * The last three parameters specify which arguments of the new command are
  * Redis keys. See https://redis.io/commands/command for more information.

src/server.c

@@ -175,6 +175,8 @@ struct redisServer server; /* Server global state */
  *
  * sentinel-only: This command is present only when in sentinel mode.
  *
+ * no-mandatory-keys: This key arguments for this command are optional.
+ *
  * The following additional flags are only used in order to put commands
  * in a specific ACL category. Commands can have multiple ACL categories.
  * See redis.conf for the exact meaning of each.
@@ -1751,28 +1753,28 @@ struct redisCommand redisCommandTable[] = {
      * as opposed to after.
       */
     {"eval",evalCommand,-3,
-     "no-script no-monitor may-replicate @scripting",
+     "no-script no-monitor may-replicate no-mandatory-keys @scripting",
      {{"read write", /* We pass both read and write because these flag are worst-case-scenario */
        KSPEC_BS_INDEX,.bs.index={2},
        KSPEC_FK_KEYNUM,.fk.keynum={0,1,1}}},
      evalGetKeys},
 
     {"eval_ro",evalRoCommand,-3,
-     "no-script no-monitor @scripting",
+     "no-script no-monitor no-mandatory-keys @scripting",
      {{"read",
        KSPEC_BS_INDEX,.bs.index={2},
        KSPEC_FK_KEYNUM,.fk.keynum={0,1,1}}},
      evalGetKeys},
 
     {"evalsha",evalShaCommand,-3,
-     "no-script no-monitor may-replicate @scripting",
+     "no-script no-monitor may-replicate no-mandatory-keys @scripting",
      {{"read write", /* We pass both read and write because these flag are worst-case-scenario */
        KSPEC_BS_INDEX,.bs.index={2},
        KSPEC_FK_KEYNUM,.fk.keynum={0,1,1}}},
      evalGetKeys},
 
     {"evalsha_ro",evalShaRoCommand,-3,
-     "no-script no-monitor @scripting",
+     "no-script no-monitor no-mandatory-keys @scripting",
      {{"read",
        KSPEC_BS_INDEX,.bs.index={2},
        KSPEC_FK_KEYNUM,.fk.keynum={0,1,1}}},
@@ -4510,6 +4512,8 @@ void parseCommandFlags(struct redisCommand *c, char *strflags) {
         } else if (!strcasecmp(flag,"only-sentinel")) {
             c->flags |= CMD_SENTINEL; /* Obviously it's s sentinel command */
             c->flags |= CMD_ONLY_SENTINEL;
+        } else if (!strcasecmp(flag,"no-mandatory-keys")) {
+            c->flags |= CMD_NO_MANDATORY_KEYS;
         } else {
             /* Parse ACL categories here if the flag name starts with @. */
             uint64_t catflag;
@@ -5906,7 +5910,11 @@ void getKeysSubcommand(client *c) {
     }
 
     if (!getKeysFromCommand(cmd,c->argv+2,c->argc-2,&result)) {
-        addReplyError(c,"Invalid arguments specified for command");
+        if (cmd->flags & CMD_NO_MANDATORY_KEYS) {
+            addReplyArrayLen(c,0);
+        } else {
+            addReplyError(c,"Invalid arguments specified for command");
+        }
     } else {
         addReplyArrayLen(c,result.numkeys);
         for (j = 0; j < result.numkeys; j++) addReplyBulk(c,c->argv[result.keys[j]+2]);

src/server.h

@@ -236,6 +236,7 @@ extern int configOOMScoreAdjValuesDefaults[CONFIG_OOM_COUNT];
 
 #define CMD_SENTINEL (1ULL<<40)        /* "sentinel" flag */
 #define CMD_ONLY_SENTINEL (1ULL<<41)   /* "only-sentinel" flag */
+#define CMD_NO_MANDATORY_KEYS (1ULL<<42)   /* "no-mandatory-keys" flag */
 
 /* AOF states */
 #define AOF_OFF 0             /* AOF is off */

tests/unit/introspection-2.tcl

@@ -89,6 +89,14 @@ start_server {tags {"introspection"}} {
         assert_equal {key} [r command getkeys xgroup create key groupname $]
     }
 
+    test {COMMAND GETKEYS EVAL with keys} {
+        assert_equal {key} [r command getkeys eval "return 1" 1 key]
+    }
+
+    test {COMMAND GETKEYS EVAL without keys} {
+        assert_equal {} [r command getkeys eval "return 1" 0]
+    }
+
     test "COMMAND LIST FILTERBY ACLCAT" {
         set reply [r command list filterby aclcat hyperloglog]
         assert_equal [lsort $reply] {pfadd pfcount pfdebug pfmerge pfselftest}