IndexStaticFaced::ConfigCheck dispatch silently broken since #888 — staticConfigCheckMap is never populated

[foxspy]

Description

IndexStaticFaced::ConfigCheck (introduced in #888) is supposed to dispatch to per-index StaticConfigCheck implementations to validate (indexType, config) combinations before building. The dispatch has been silently dead since the feature merged: staticConfigCheckMap is never populated for any registered index, so the per-index checks never run.

Root cause is a type mismatch in the SFINAE probe that gates registration:

• IndexStaticFaced::InternalConfigCheck is declared with (const BaseConfig&, const IndexVersion&, std::string&) (include/knowhere/index/index_static.h:134).
• All real StaticConfigCheck implementations take (const Config&, PARAM_TYPE, std::string&) (e.g. src/index/ivf/ivf.cc:138, src/index/hnsw/hnsw.h:94).

PARAM_TYPE is an unscoped enum, and int32_t (IndexVersion) does not implicitly convert to it, so has_static_StaticConfigCheck<...>::value evaluates to false for every index. The if constexpr block in RegisterStaticFunc (index_static.h:114-117) is therefore dead code, staticConfigCheckMap stays empty, and ConfigCheck always falls through to return Status::success at index_static.cc:63.

Expected Behavior

IndexStaticFaced<fp32>::ConfigCheck("IVF_FLAT", version, {"metric_type":"HAMMING","nlist":128}, msg) should return Status::invalid_metric_type (since IVF float indexes only accept L2/IP/COSINE).

Actual Behavior

Returns Status::success. The metric/data-type validation defined in IvfIndexNode::StaticConfigCheck and HnswIndexNode::StaticConfigCheck never executes. Build-time pre-check is a no-op for any caller.

Impact

• All callers (e.g. Milvus pre-build validation) get false-positive success on invalid config combinations. The non-fatal layers downstream still catch most cases at build time, but later and with worse error messages.
• The tests/ut/test_config.cc::checkBuildConfig helper only asserts Status::success, so the bug never surfaced in CI.
• Bug has been silent since enhance: provide a static checking method for index config #888 (2024-10-15).