From 86450838feb7e73cc33c84c94e73acb3df840681 Mon Sep 17 00:00:00 2001
From: Steve Willoughby <swilloughby@newrelic.com>
Date: Thu, 5 Sep 2024 12:16:34 -0700
Subject: [PATCH] Fix handling of panic(nil)

---
 v3/newrelic/internal_txn.go | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/v3/newrelic/internal_txn.go b/v3/newrelic/internal_txn.go
index 32060485b..545083ca9 100644
--- a/v3/newrelic/internal_txn.go
+++ b/v3/newrelic/internal_txn.go
@@ -10,6 +10,7 @@ import (
 	"net/http"
 	"net/url"
 	"reflect"
+	"runtime"
 	"runtime/debug"
 	"sync"
 	"time"
@@ -445,11 +446,16 @@ func (thd *thread) End(recovered interface{}) error {
 
 	txn.finished = true
 
-	if nil != recovered {
-		e := txnErrorFromPanic(time.Now(), recovered)
-		e.Stack = getStackTrace()
-		thd.noticeErrorInternal(e, nil, false)
-		log.Println(string(debug.Stack()))
+	// It used to be the case that panic(nil) would cause recover() to return nil,
+	// which we test for here. However, that is no longer the case, hence the extra
+	// check at this point to stop panic(nil) from propagating here. (as of Go 1.21)
+	if recovered != nil {
+		if _, isNilPanic := recovered.(*runtime.PanicNilError); !isNilPanic {
+			e := txnErrorFromPanic(time.Now(), recovered)
+			e.Stack = getStackTrace()
+			thd.noticeErrorInternal(e, nil, false)
+			log.Println(string(debug.Stack()))
+		}
 	}
 
 	txn.markEnd(time.Now(), thd.thread)
@@ -542,9 +548,12 @@ func (thd *thread) End(recovered interface{}) error {
 	}
 
 	// Note that if a consumer uses `panic(nil)`, the panic will not
-	// propagate.
-	if nil != recovered {
-		panic(recovered)
+	// propagate.  Update: well, not anymore. Go now returns an actual
+	// non-nil value in this case.
+	if recovered != nil {
+		if _, isNilPanic := recovered.(*runtime.PanicNilError); !isNilPanic {
+			panic(recovered)
+		}
 	}
 
 	return nil