From 06d94fe7f16e8985878a24332978731439599c4e Mon Sep 17 00:00:00 2001
From: unwox <me@unwox.com>
Date: Mon, 13 Oct 2025 22:25:27 +0600
Subject: fix error handling

---
 lua.go    | 4 +++-
 luajit.go | 4 +++-
 worker.go | 5 ++---
 3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/lua.go b/lua.go
index b6d7027..11eec3e 100644
--- a/lua.go
+++ b/lua.go
@@ -293,12 +293,14 @@ func (l *Lua) GetGlobal(name string) {
 }
 
 func (l *Lua) NewThread(yield func(), resume func() bool) *Lua {
-	return &Lua{
+	newl := &Lua{
 		l: C.lua_newthread(l.l),
 		running: l.running,
 		resume: resume,
 		yield: yield,
 	}
+	newl.PushGoFunction(TracebackHandler)
+	return newl
 }
 
 // TracebackHandler handles stack trace formatting on errors.
diff --git a/luajit.go b/luajit.go
index 2ed3788..0b1fb55 100644
--- a/luajit.go
+++ b/luajit.go
@@ -290,12 +290,14 @@ func (l *Lua) GetGlobal(name string) {
 }
 
 func (l *Lua) NewThread(yield func(), resume func() bool) *Lua {
-	return &Lua{
+	newl := &Lua{
 		l: C.lua_newthread(l.l),
 		running: l.running,
 		resume: resume,
 		yield: yield,
 	}
+	newl.PushGoFunction(TracebackHandler)
+	return newl
 }
 
 // TracebackHandler handles stack trace formatting on errors.
diff --git a/worker.go b/worker.go
index d252708..ea4892a 100644
--- a/worker.go
+++ b/worker.go
@@ -110,7 +110,6 @@ func (w *Worker) Start(argv []string, module map[string]any) error {
 			return err
 		}
 		w.lua.SetGlobal("fennel")
-
 		err = w.lua.LoadAndCall(`
 			debug.traceback = fennel.traceback
 			fennel.install()
@@ -342,12 +341,12 @@ func (w *Worker) Eval(code string) error {
 	w.mu.Lock()
 	defer w.mu.Unlock()
 	if w.evalFn != nil {
+		// FIXME: does this branch pollute stack?
 		w.lua.PushFromRef(*w.evalFn)
 		w.lua.PushString(code)
-		return w.lua.PCall(1, 0, 0)
+		return w.lua.PCall(1, 0, 1)
 	}
 	err := w.lua.LoadAndCall(code)
-	w.lua.Pop(w.lua.StackLen())
 	return err
 }
 
-- 
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