From affd4e432ee299d22be95314bcc72a9347f586fb 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 | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/tablelib.go b/tablelib.go
index f3f46070..02474311 100644
--- a/tablelib.go
+++ b/tablelib.go
@@ -66,19 +66,18 @@ func tableConcat(L *LState) int {
 		L.Push(emptyLString)
 		return 1
 	}
-	//TODO should flushing?
-	retbottom := L.GetTop()
+	result := ""
 	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)
+		result += LVAsString(v)
 		if i != j {
-			L.Push(sep)
+			result += LVAsString(sep)
 		}
 	}
-	L.Push(stringConcat(L, L.GetTop()-retbottom, L.reg.Top()-1))
+	L.Push(LString(result))
 	return 1
 }