fix: stack overflow in table.concat function

[thierry-f-78]

Fix: Stack Overflow in table.concat Function

This PR fixes a stack overflow issue in the table.concat function when working with large tables.

Problem

The previous implementation of tableConcat pushed all values and separators onto the Lua stack before concatenating them. This approach caused stack overflow errors when dealing with large tables.

Solution

This fix changes the implementation to build the result string incrementally rather than pushing all values onto the stack first. Instead of accumulating items on the stack, we now:

• Build the string directly by appending each value
• Add separators between values as needed
• Push only the final result string to the stack

Testing

The fix has been verified with large tables that previously caused stack overflow. For example, this test case 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())
        }
}

This example would previously fail with a stack overflow error but now executes successfully.

[tul]

Worth considering go lang string builder? https://pkg.go.dev/strings#Builder ?

[thierry-f-78]

Sorry for the late reply, I missed the notification!

Thanks for the suggestion! Indeed, strings.Builder would be more efficient for string construction, especially with large tables. I'll update the code to use strings.Builder instead of simple concatenation.