Skip registering Hazelcast meters when statistics are not enabled

[jewoodev]

Summary

Follow-up to gh-5402, gh-5409, and gh-7562 for HazelcastCacheMetrics. See gh-5066.

When a Hazelcast IMap is bound without statistics enabled, the registered meters silently report zero, which is hard to diagnose. This change mirrors the JCache pattern from gh-7562: detect the stats-disabled state via MapConfig#isStatisticsEnabled(), log a warning explaining how to enable statistics, and skip registering the stats-dependent meters (cache.size, cache.gets, cache.puts, cache.entries, cache.entry.memory, cache.partition.gets, the near-cache gauges, and the cache.gets.latency/cache.puts.latency/cache.removals.latency timers). cache.size is included because it reads LocalMapStats#getOwnedEntryCount(), which is meaningless once statistics are disabled.

HazelcastCacheMetrics accesses the cache through reflection via HazelcastIMapAdapter, so the new check is added as a reflection chain on the same adapter: AbstractDistributedObject#getNodeEngine → NodeEngine#getConfig → Config#getMapConfig(name) → MapConfig#isStatisticsEnabled. The first two classes are internal types whose package changed between Hazelcast 3.x (com.hazelcast.spi) and 4.x+ (com.hazelcast.spi.impl), so the adapter tries both variants in the same resolveOneOf style that the existing IMap/LocalMapStats/NearCacheStats resolution already uses. The check was verified against Hazelcast 5.3.8, the pinned optionalApi version. If any class or method in the chain cannot be resolved, or the chain throws at runtime, this assumes statistics are enabled to avoid a false-positive warning. This also keeps existing mock-based callers unaffected.

Status of other cache binders

• Caffeine — already handled in Log a warning when instrumenting a cache that is not recording stats in CaffeineCacheMetrics #5402 and Skip registering Caffeine meters when statistics are not enabled #5409.
• JCache — handled in Skip registering JCache meters when statistics are not enabled #7562.
• Hazelcast — covered by this change. Together with Skip registering JCache meters when statistics are not enabled #7562, this closes Log a warning when instrumenting a cache that is not recording stats #5066. Since Skip registering JCache meters when statistics are not enabled #7562 is still open, this PR intentionally avoids a Closes trailer so that whichever of the two PRs merges last can carry it (or so a maintainer can close Log a warning when instrumenting a cache that is not recording stats #5066 manually once both are in).
• EhCache 2 — EhCache 2.5+ has statistics always on, so the check is unnecessary.
• Guava — Guava does not expose a public API to detect whether recordStats() was called. The upstream request (Provide API to see if a cache records statistics google/guava#7381) was closed in 2024 with no plans to add cache features.

Testing

• New test HazelcastCacheMetricsTest#doNotReportMetricsWhenStatisticsAreDisabled registers a MapConfig with statistics disabled at instance startup, binds metrics to that IMap, and asserts both the warning is emitted and that cache.size, cache.gets, cache.puts, cache.entries, cache.entry.memory, cache.partition.gets, and the three latency timers are not registered. This is also what exercises the reflection chain on Hazelcast 5.3.8 end-to-end — the existing tests use default (enabled) statistics, where the chain returning true is indistinguishable from the fail-safe fallback.
• Existing tests continue to pass without changes: they bind a Hazelcast IMap with default (enabled) statistics, so meters register as before.
• ./gradlew :micrometer-core:check passes locally.

[shakuzen]

Thanks for the PR. We'll follow-up once we start merging things for 1.18