fix: Pick log message from merging object in Pino instrumentation

lib/instrumentation/pino/pino.js

@@ -15,6 +15,7 @@ const {
 } = require('../../util/application-logging')
 const semver = require('semver')
 
+// eslint-disable-next-line sonarjs/cognitive-complexity
 module.exports = function instrument(shim, tools) {
   const pinoVersion = shim.pkgVersion
 
@@ -50,13 +51,21 @@ module.exports = function instrument(shim, tools) {
     return function wrappedAsJson() {
       const args = shim.argsToArray.apply(shim, arguments)
       const level = this?.levels?.labels?.[args[2]]
+      // Pino log methods accept a singular object (a merging object) that can
+      // have a `msg` property for the log message. In such cases, we need to
+      // update that log property instead of the second parameter.
+      const useMergeObj = args[1] === undefined && Object.hasOwn(args[0], 'msg')
 
       if (isMetricsEnabled(config)) {
         incrementLoggingLinesMetrics(level, metrics)
       }
 
       if (isLocalDecoratingEnabled(config)) {
-        args[1] += agent.getNRLinkingMetadata()
+        if (useMergeObj === true) {
+          args[0].msg += agent.getNRLinkingMetadata()
+        } else {
+          args[1] += agent.getNRLinkingMetadata()
+        }
       }
 
       /**
@@ -69,7 +78,7 @@ module.exports = function instrument(shim, tools) {
       if (isLogForwardingEnabled(config, agent)) {
         const chindings = this[symbols.chindingsSym]
         const formatLogLine = reformatLogLine({
-          msg: args[1],
+          msg: useMergeObj === true ? args[0].msg : args[1],
           logLine,
           agent,
           chindings,

test/versioned/pino/pino.tap.js

@@ -83,14 +83,28 @@ tap.test('Pino instrumentation', (t) => {
     const message = 'pino decorating test'
     helper.runInTransaction(agent, 'pino-test', async () => {
       logger.info(message)
-      const line = await once(stream, 'data')
+      let line = await once(stream, 'data')
       originalMsgAssertion({
         t,
         includeLocalDecorating: true,
         hostname: agent.config.getHostnameSafe(),
         logLine: line
       })
       t.same(agent.logs.getEvents(), [], 'should not add any logs to log aggregator')
+
+      // Verify that merging object only logs get decorated:
+      logger.info({ msg: message })
+      line = await once(stream, 'data')
+      console.log(line)
+      t.equal(line.msg.startsWith(`${message} NR-LINKING|test-guid`), true)
+      originalMsgAssertion({
+        t,
+        includeLocalDecorating: true,
+        hostname: agent.config.getHostnameSafe(),
+        logLine: line
+      })
+      t.same(agent.logs.getEvents(), [], 'should not add any logs to log aggregator')
+
       t.end()
     })
   })
@@ -375,4 +389,19 @@ tap.test('Pino instrumentation', (t) => {
       })
     })
   })
+
+  t.test('should honor msg key in merging object (issue 2410)', async (t) => {
+    t.context.config = setupAgent(t.context, { application_logging: { enabled: true } })
+    const { agent, config, pino } = t.context
+    const localStream = sink()
+    const localLogger = pino({ base: undefined }, localStream)
+    const message = 'pino unit test'
+    const level = 'info'
+    localLogger[level]({ msg: message })
+    await once(localStream, 'data')
+    t.equal(agent.logs.getEvents().length, 1, 'should have 1 log in aggregator')
+    const formattedLine = agent.logs.getEvents()[0]()
+    t.validateAnnotations({ line: formattedLine, message, level, config })
+    t.end()
+  })
 })