From 44ded6ac52347ed10925a99876dd9e9beaa6ed74 Mon Sep 17 00:00:00 2001
From: Thierry Fournier <thierry.f.78@gmail.com>
Date: Wed, 26 Feb 2025 10:24:52 +0100
Subject: [PATCH] fix: stack overflow in table.concat function

The previous implementation of tableConcat was pushing all values and
separators onto the Lua stack before concatenating them, which caused
stack overflow with large tables.

This fix changes the implementation to build the result string
incrementally rather than pushing all values onto the stack first,
preventing stack overflow with large tables.

Example that would previously fail but now works correctly:
```
package main

import "github.com/yuin/gopher-lua"

func main() {
	var L *lua.LState
	var err error

	L = lua.NewState()
	defer L.Close()

	err = L.DoString(`
		local t = {}
		for i = 1, 10000 do
			t[i] = tostring(i)
		end
		local s = table.concat(t, ',')
	`)
	if err != nil {
		println(err.Error())
	}
}
```
---
 tablelib.go | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/tablelib.go b/tablelib.go
index f3f46070..f175c696 100644
--- a/tablelib.go
+++ b/tablelib.go
@@ -2,6 +2,7 @@ package lua
 
 import (
 	"sort"
+	"strings"
 )
 
 func OpenTable(L *LState) int {
@@ -66,19 +67,18 @@ func tableConcat(L *LState) int {
 		L.Push(emptyLString)
 		return 1
 	}
-	//TODO should flushing?
-	retbottom := L.GetTop()
+	var sb strings.Builder
 	for ; i <= j; i++ {
 		v := tbl.RawGetInt(i)
 		if !LVCanConvToString(v) {
 			L.RaiseError("invalid value (%s) at index %d in table for concat", v.Type().String(), i)
 		}
-		L.Push(v)
+		sb.WriteString(LVAsString(v))
 		if i != j {
-			L.Push(sep)
+			sb.WriteString(LVAsString(sep))
 		}
 	}
-	L.Push(stringConcat(L, L.GetTop()-retbottom, L.reg.Top()-1))
+	L.Push(LString(sb.String()))
 	return 1
 }