xpcall with error in error handler returns (nil, nil)

[mzki]

You must post issues only here. Questions, ideas must be posted in discussions.

• GopherLua is a Lua5.1 implementation. You should be familiar with Lua programming language. Have you read Lua 5.1 reference manual carefully?
• GopherLua is a Lua5.1 implementation. In Lua, to keep it simple, it is more important to remove functionalities rather than to add functionalities unlike other languages . If you are going to introduce some new cool functionalities into the GopherLua code base and the functionalities can be implemented by existing APIs, It should be implemented as a library.

Please answer the following before submitting your issue:

1. What version of GopherLua are you using? : 2b3f02d
2. What version of Go are you using? : go version go1.19.12 linux/amd64
3. What operating system and processor architecture are you using? : See 2.
4. What did you do? :
5. What did you expect to see? :
   xpcall with error in error handler returns (false, error-object).

/ # lua
Lua 5.1.5  Copyright (C) 1994-2012 Lua.org, PUC-Rio
> ok, msg = xpcall(function() error("fn") end, function(err) error("handler") end)
> print(ok, msg)
false   error in error handling
> function test()
>>   xpcall(function() error("fn") end, function(err) error("handler") end)
>>   error("expected to reach this")
>> end
> test()
stdin:3: expected to reach this
stack traceback:
        [C]: in function 'error'
        stdin:3: in function 'test'
        stdin:1: in main chunk
        [C]: ?
>

6. What did you see instead? :
   xpcall with error in error handler returns (nil, nil).
   In addition, xpcall exits current function scope and interpreter does not execute next line.

/workspaces/gopher-lua/cmd/glua# ./glua 
GopherLua 0.1 Copyright (C) 2015 -2017 Yusuke Inuzuka
> ok, msg = xpcall(function() error("fn") end, function(err) error("handler") end)
> print(ok, msg)
nil     nil
> function test()
>>   xpcall(function() error("fn") end, function(err) error("handler") end)
>>   error("expected to reach this")
>> end
> test()
> 

Although the behavior of xpcall with error in error handler is not well described in the reference, but it is better to be compatible with CLua5.1 behavior.