feat(commands): ZSet 6.2+ additions (ZRANGESTORE, ZDIFF, ZUNION, ZINTER, ZINTERCARD, ZMSCORE, ZRANDMEMBER, ZMPOP)

[TinDang97]

Summary

Moon ships the core zset command set but is missing the non-STORE aggregation variants and several Redis 6.2 / 7.0 additions. Most application code has workarounds via ZINTERSTORE/ZUNIONSTORE + temp keys, but modern clients (redis-py, ioredis, go-redis) call the inline versions directly.

Missing commands

• ZRANGESTORE dst src min max [BYSCORE|BYLEX] [REV] [LIMIT o c]
• ZDIFF numkeys key [key ...] [WITHSCORES]
• ZDIFFSTORE dst numkeys key [key ...]
• ZUNION numkeys key [key ...] [WEIGHTS ...] [AGGREGATE ...] [WITHSCORES]
• ZINTER numkeys key [key ...] [WEIGHTS ...] [AGGREGATE ...] [WITHSCORES]
• ZINTERCARD numkeys key [key ...] [LIMIT limit]
• ZMSCORE key member [member ...]
• ZRANDMEMBER key [count [WITHSCORES]]
• ZMPOP numkeys key [key ...] MIN|MAX [COUNT count]

Design notes

• ZINTER/ZUNION/ZDIFF are *STORE logic minus the final write — refactor existing storage handlers to return a Vec<(Bytes, f64)> that either gets written or serialized to the response.
• ZRANDMEMBER with count ≥ 0: unique sampling (Fisher-Yates over skiplist). Count < 0: with replacement. Match Redis distribution exactly (consistency tests will catch drift).
• ZMPOP shares plumbing with LMPOP (feat(commands): list/hash/set convenience variants (LPUSHX/RPUSHX/LMPOP/HRANDFIELD/SMOVE/SINTERCARD) #60).
• Watch the aggregate aliasing rules for AGGREGATE MIN/MAX/SUM — easy to get wrong for weighted cases.

Acceptance criteria

• Consistency test for each command with at least: single key, multi-key, empty key, WITHSCORES, WEIGHTS where applicable.
• No allocation regressions on the existing ZINTERSTORE/ZUNIONSTORE paths.

References

• Redis source: src/t_zset.c

[pilotspacex-byte]

Closing — implemented in commit fff223b9 (PR #66, closing #62): all 8
commands (ZRANGESTORE, ZDIFF, ZUNION, ZINTER, ZINTERCARD, ZMSCORE,
ZRANDMEMBER, ZMPOP) are wired via dispatch arms in src/command/mod.rs and
implemented in src/command/sorted_set/sorted_set_read.rs +
sorted_set_write.rs, with metadata entries in src/command/metadata.rs.

Reopen if a specific subcommand or edge case is found broken.

Author: Tin Dang tindang.ht97@gmail.com