Fix COMMAND GETKEYS for PFMERGE with no source keys (#14942)

PFMERGE's second key spec (source keys) produces an empty range when
called with only a dest key (e.g. PFMERGE dest). getKeysUsingKeySpecs
treats that as invalid_spec, which discards all previously found keys
and returns an error. Add pfmergeGetKeys as a getkeys callback so the
command correctly falls back to it when key specs fail on the edge case.

src/commands.def

@@ -11839,7 +11839,7 @@ struct COMMAND_STRUCT redisCommandTable[] = {
 {MAKE_CMD("pfadd","Adds elements to a HyperLogLog key. Creates the key if it doesn't exist.","O(1) to add every element.","2.8.9",CMD_DOC_NONE,NULL,NULL,"hyperloglog",COMMAND_GROUP_HYPERLOGLOG,PFADD_History,0,PFADD_Tips,0,pfaddCommand,-2,CMD_WRITE|CMD_DENYOOM|CMD_FAST,ACL_CATEGORY_HYPERLOGLOG,PFADD_Keyspecs,1,NULL,2),.args=PFADD_Args},
 {MAKE_CMD("pfcount","Returns the approximated cardinality of the set(s) observed by the HyperLogLog key(s).","O(1) with a very small average constant time when called with a single key. O(N) with N being the number of keys, and much bigger constant times, when called with multiple keys.","2.8.9",CMD_DOC_NONE,NULL,NULL,"hyperloglog",COMMAND_GROUP_HYPERLOGLOG,PFCOUNT_History,0,PFCOUNT_Tips,0,pfcountCommand,-2,CMD_READONLY|CMD_MAY_REPLICATE,ACL_CATEGORY_HYPERLOGLOG,PFCOUNT_Keyspecs,1,NULL,1),.args=PFCOUNT_Args},
 {MAKE_CMD("pfdebug","Internal commands for debugging HyperLogLog values.","N/A","2.8.9",CMD_DOC_SYSCMD,NULL,NULL,"hyperloglog",COMMAND_GROUP_HYPERLOGLOG,PFDEBUG_History,0,PFDEBUG_Tips,0,pfdebugCommand,3,CMD_WRITE|CMD_DENYOOM|CMD_ADMIN,ACL_CATEGORY_HYPERLOGLOG,PFDEBUG_Keyspecs,1,NULL,2),.args=PFDEBUG_Args},
-{MAKE_CMD("pfmerge","Merges one or more HyperLogLog values into a single key.","O(N) to merge N HyperLogLogs, but with high constant times.","2.8.9",CMD_DOC_NONE,NULL,NULL,"hyperloglog",COMMAND_GROUP_HYPERLOGLOG,PFMERGE_History,0,PFMERGE_Tips,0,pfmergeCommand,-2,CMD_WRITE|CMD_DENYOOM,ACL_CATEGORY_HYPERLOGLOG,PFMERGE_Keyspecs,2,NULL,2),.args=PFMERGE_Args},
+{MAKE_CMD("pfmerge","Merges one or more HyperLogLog values into a single key.","O(N) to merge N HyperLogLogs, but with high constant times.","2.8.9",CMD_DOC_NONE,NULL,NULL,"hyperloglog",COMMAND_GROUP_HYPERLOGLOG,PFMERGE_History,0,PFMERGE_Tips,0,pfmergeCommand,-2,CMD_WRITE|CMD_DENYOOM,ACL_CATEGORY_HYPERLOGLOG,PFMERGE_Keyspecs,2,pfmergeGetKeys,2),.args=PFMERGE_Args},
 {MAKE_CMD("pfselftest","An internal command for testing HyperLogLog values.","N/A","2.8.9",CMD_DOC_SYSCMD,NULL,NULL,"hyperloglog",COMMAND_GROUP_HYPERLOGLOG,PFSELFTEST_History,0,PFSELFTEST_Tips,0,pfselftestCommand,1,CMD_ADMIN,ACL_CATEGORY_HYPERLOGLOG,PFSELFTEST_Keyspecs,0,NULL,0)},
 /* list */
 {MAKE_CMD("blmove","Pops an element from a list, pushes it to another list and returns it. Blocks until an element is available otherwise. Deletes the list if the last element was moved.","O(1)","6.2.0",CMD_DOC_NONE,NULL,NULL,"list",COMMAND_GROUP_LIST,BLMOVE_History,0,BLMOVE_Tips,0,blmoveCommand,6,CMD_WRITE|CMD_DENYOOM|CMD_BLOCKING,ACL_CATEGORY_LIST,BLMOVE_Keyspecs,2,NULL,5),.args=BLMOVE_Args},

src/commands/pfmerge.json

@@ -6,6 +6,7 @@
         "since": "2.8.9",
         "arity": -2,
         "function": "pfmergeCommand",
+        "get_keys_function": "pfmergeGetKeys",
         "command_flags": [
             "WRITE",
             "DENYOOM"

src/db.c

@@ -3674,6 +3674,29 @@ int sortGetKeys(struct redisCommand *cmd, robj **argv, int argc, getKeysResult *
     return result->numkeys;
 }
 
+int pfmergeGetKeys(struct redisCommand *cmd, robj **argv, int argc, getKeysResult *result) {
+    int i, numkeys;
+    keyReference *keys;
+    UNUSED(cmd);
+    UNUSED(argv);
+
+    numkeys = argc - 1; /* destkey + all sourcekeys */
+    keys = getKeysPrepareResult(result, numkeys);
+
+    /* destkey at argv[1] */
+    keys[0].pos = 1;
+    keys[0].flags = CMD_KEY_RW | CMD_KEY_ACCESS | CMD_KEY_INSERT;
+
+    /* sourcekeys at argv[2..argc-1], may be zero */
+    for (i = 2; i < argc; i++) {
+        keys[i - 1].pos = i;
+        keys[i - 1].flags = CMD_KEY_RO | CMD_KEY_ACCESS;
+    }
+
+    result->numkeys = numkeys;
+    return result->numkeys;
+}
+
 /* This command declares incomplete keys, so the flags are correctly set for this function */
 int migrateGetKeys(struct redisCommand *cmd, robj **argv, int argc, getKeysResult *result) {
     int i, j, num, first;

src/server.h

@@ -4026,6 +4026,7 @@ int zunionInterDiffStoreGetKeys(struct redisCommand *cmd,robj **argv, int argc,
 int evalGetKeys(struct redisCommand *cmd, robj **argv, int argc, getKeysResult *result);
 int functionGetKeys(struct redisCommand *cmd, robj **argv, int argc, getKeysResult *result);
 int sortGetKeys(struct redisCommand *cmd, robj **argv, int argc, getKeysResult *result);
+int pfmergeGetKeys(struct redisCommand *cmd, robj **argv, int argc, getKeysResult *result);
 int sortROGetKeys(struct redisCommand *cmd, robj **argv, int argc, getKeysResult *result);
 int migrateGetKeys(struct redisCommand *cmd, robj **argv, int argc, getKeysResult *result);
 int georadiusGetKeys(struct redisCommand *cmd, robj **argv, int argc, getKeysResult *result);

tests/unit/introspection-2.tcl

@@ -189,6 +189,17 @@ start_server {tags {"introspection"}} {
         assert_equal {key1 key2} [r command getkeys lcs key1 key2]
     }
 
+    test {COMMAND GETKEYS PFMERGE with and without source keys} {
+        # dest + sources: both key specs yield keys
+        assert_equal {dest src1 src2} [r command getkeys PFMERGE dest src1 src2]
+
+        # dest only, no source keys: spec[1] yields empty range (last < first).
+        # Without pfmergeGetKeys this returned "Invalid arguments" because
+        # getKeysUsingKeySpecs treated the empty range as invalid_spec,
+        # discarding the dest key found by spec[0].
+        assert_equal {dest} [r command getkeys PFMERGE dest]
+    }
+
     test {COMMAND GETKEYS MORE THAN 256 KEYS} {
         set all_keys [list]
         set numkeys 260