From 2bcaad46e11cd25dbe3b3c1bd0851862b627edad Mon Sep 17 00:00:00 2001
From: Barak Amar <barak.amar@gmail.com>
Date: Tue, 25 Aug 2026 11:51:42 +0300
Subject: [PATCH] Convert non-error panics to errors in protect

protect() asserted that every recovered value is an error, but the VM
panics with plain strings in many places (panic("unreachable"),
panic("XMove not implemented yet"), the "expected opcode" invariants in
the bytecode interpreter). Any of those turned into a second panic -
"interface conversion: string is not error" - crashing the host and
losing the original message.

Pass real errors through unchanged and wrap anything else with
fmt.Errorf, so a protected call always returns an error.
---
 stack.go   | 10 ++++++++--
 vm_test.go |  9 +++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/stack.go b/stack.go
index 2570a54..3f45799 100644
--- a/stack.go
+++ b/stack.go
@@ -1,6 +1,9 @@
 package lua
 
-import "log"
+import (
+	"fmt"
+	"log"
+)
 
 func (l *State) push(v value) {
 	l.stack[l.top] = v
@@ -406,7 +409,10 @@ func (l *State) protect(f func()) (err error) {
 	nestedGoCallCount, protectFunction := l.nestedGoCallCount, l.protectFunction
 	l.protectFunction = func() {
 		if e := recover(); e != nil {
-			err = e.(error)
+			var ok bool
+			if err, ok = e.(error); !ok {
+				err = fmt.Errorf("%v", e)
+			}
 			l.nestedGoCallCount, l.protectFunction = nestedGoCallCount, protectFunction
 		}
 	}
diff --git a/vm_test.go b/vm_test.go
index e78570c..df385ba 100644
--- a/vm_test.go
+++ b/vm_test.go
@@ -351,6 +351,15 @@ func TestErrorf(t *testing.T) {
 	}
 }
 
+func TestPanicWithString(t *testing.T) {
+	l := NewState()
+	OpenLibraries(l)
+	LoadString(l, "debug.gethook()")
+	if err := l.ProtectedCall(0, 0, 0); err == nil {
+		t.Fatal("expected an error, got none")
+	}
+}
+
 func TestPairsSplit(t *testing.T) {
 	testString(t, `
 	local t = {}