Document that the channel-injection helper appends the full channel set

Author: andreiborza

packages/aws-serverless/src/init.ts

@@ -55,8 +55,10 @@ function shouldDisableLayerExtensionForProxy(): boolean {
 // If at some point we need to filter a node integration out for good, we need to make sure to also filter it out there.
 export function getDefaultIntegrations(options: Options): Integration[] {
   const integrations = [...getDefaultIntegrationsWithoutPerformance(), awsIntegration(), awsLambdaIntegration()];
-  // If the app opted into diagnostics-channel injection, swap the OTel `Aws` integration for its
-  // channel-based equivalent (registered in `@sentry/server-utils`). No-op otherwise.
+  // If the app opted into diagnostics-channel injection, the OTel `Aws` integration is swapped for
+  // its channel-based equivalent AND the full channel-integration set is appended (mysql, postgres,
+  // express, ...), giving opted-in apps performance coverage this SDK's defaults otherwise omit.
+  // No-op otherwise.
   return applyDiagnosticsChannelInjectionIntegrations(integrations, options);
 }
 

packages/node/src/sdk/index.ts

@@ -44,14 +44,16 @@ export function getDefaultIntegrations(options: Options): Integration[] {
 
 /**
  * When the app opted into diagnostics-channel injection (via
- * `experimentalUseDiagnosticsChannelInjection()`) AND span recording is enabled, swap the
- * channel-based integrations in place of their OTel equivalents so the two don't both instrument the
- * same library. Otherwise returns `integrations` unchanged.
+ * `experimentalUseDiagnosticsChannelInjection()`) AND span recording is enabled, drop the OTel
+ * integrations that have a channel-based replacement and append the FULL channel-integration set,
+ * so the two never both instrument the same library. Otherwise returns `integrations` unchanged.
  *
- * Every channel-based integration we ship today is a 1:1 replacement for an OTel performance/tracing
- * integration and produces nothing but spans, so this is gated on span recording. Exported so SDKs
- * that build their own default-integration set (e.g. `@sentry/aws-serverless`) can apply the same
- * swap instead of duplicating this logic.
+ * Note the asymmetry: appended channel integrations are not limited to ones whose OTel counterpart
+ * was in `integrations`. For `@sentry/node` that makes no difference (the incoming list carries the
+ * whole OTel performance set), but a caller with a narrower list (e.g. `@sentry/aws-serverless`)
+ * gains channel coverage for libraries it never shipped OTel integrations for. Channel integrations
+ * produce nothing but spans, so this is gated on span recording. Exported so SDKs that build their
+ * own default-integration set can apply the same logic instead of duplicating it.
  */
 export function applyDiagnosticsChannelInjectionIntegrations(
   integrations: Integration[],