[0.16.36] stack trace missing from some Lua errors

[Therax]

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/c local a = 42 game.print(a[1])

Result:

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Cannot execute command. Error: [string "local a = 42 game.print(a[1])"]:1: attempt to index local 'a' (a number value)

All is well so far. Now try:

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/c local a = {42} game.print(next(a,2)[1])

Result:

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Cannot execute command. Error: invalid key to 'next'

Note that there is no source code listed, and no line number (:1: in the previous example). It looks like there is some case where the Lua message handler isn't being set up properly to capture the debug.traceback.

This is reproduceable in mod script code, which can make tracking down certain types of bugs difficult. Derived from mod bug report here where no traceback was displayed or logged.

[Rseding91]

Thanks for the report however there's not much we can do about that.

Those kinds of errors are handled on the Lua side and by the time Factorio error handling knows about the error the stack information is long gone.

[Therax]

Thanks for the report however there's not much we can do about that.

Those kinds of errors are handled on the Lua side and by the time Factorio error handling knows about the error the stack information is long gone.

The standard interpreter seems to handle it just fine via luaL_traceback and lua_pcall():

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Lua 5.2.4  Copyright (C) 1994-2015 Lua.org, PUC-Rio
> function a() next({}, 0) end function b() a() end function c() b() end c()
invalid key to 'next'
stack traceback:
        [C]: in function 'next'
        stdin:1: in function 'a'
        stdin:1: in function 'b'
        stdin:1: in function 'c'
        stdin:1: in main chunk
        [C]: in ?

And Factorio does it correctly for other types of errors. What's different?