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Add diagnostics_channel TracingChannel support by logaretm · Pull Request #3624 · brianc/node-postgres

@logaretm @claude 

Enables instrumentation libraries (OpenTelemetry, etc.) to subscribe to
structured events without monkey-patching. Uses TracingChannel for async
context propagation and plain channels for simple events.

Channels:
- pg:query (TracingChannel) — query lifecycle with result enrichment
- pg:connection (TracingChannel) — client connect lifecycle
- pg:pool:connect (TracingChannel) — pool checkout lifecycle
- pg:pool:release (plain) — client released back to pool
- pg:pool:remove (plain) — client removed from pool

All instrumentation is guarded by hasSubscribers for zero overhead when
unused. Gracefully degrades to no-ops on Node < 19.9 or non-Node
environments.

Closes brianc#3619

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

AI review requested due to automatic review settings

March 5, 2026 17:40

@logaretm @claude 

TracingChannel is not available on Node 18 LTS. Skip the tracing-dependent
tests gracefully instead of failing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

@logaretm

This was referenced

Mar 12, 2026 
Node 18 backported TracingChannel but without the aggregated
`hasSubscribers` getter (it returns `undefined` instead of a boolean).
Raw truthiness checks treat `undefined` as "no subscribers" which
silently disables tracing on Node 18.

Replace all `channel.hasSubscribers` guards with `shouldTrace(channel)`
which checks `hasSubscribers !== false` — treating `undefined` (Node 18)
as "might have subscribers, trace unconditionally" and `false` (Node 20+)
as "definitely no subscribers, skip".

Also removes the now-unnecessary test skip logic since TracingChannel
does exist on Node 18.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Node 18 backported TracingChannel but with a buggy implementation —
unsubscribing and resubscribing to the same channel crashes internally
(`_subscribers` becomes undefined). Node 16 has no TracingChannel at all.

Gate tests on `hasStableTracingChannel` which checks both that
`dc.tracingChannel` exists AND that the aggregated `hasSubscribers`
getter returns a boolean (only true on Node 19.9+/20.5+).

TracingChannel tests: skipped on Node 16/18, run on Node 20+
Plain channel tests (release/remove): run on all versions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
…omise type

tracePromise wraps the result in a native Promise, which breaks
clients configured with a custom Promise implementation (e.g. bluebird).
Switch to traceCallback inside the user's this._Promise constructor
so the returned promise type is always correct.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

This was referenced

Mar 17, 2026