lua, overriding bizhawk-reserved variables

[mugg91]

confirmed in 1.11.7 and 1.11.8.2

Not sure if this is something you'll look into but here goes.
I had a script active and was editing/saving it while refreshing over and over. At one point I declared

bit=7

and from that point on, when the script needed to use bit.check or bit.clear, it would crash saying that "bit" is a number value. This would persist even after deleting the offending line (it persists through refreshes). But it fixes itself when closing and reopening the lua client. (Only took me half an hour to figure that out)

There might be more issues related to this one (what happens when overriding other bizhawk-reserved variables such as "userdata", "emu", "client" etc.?)

This is also somewhat related to an issue where two different scripts could override each other's values. But I'm not sure if that issue still exists.

[zeromus]

the lua philosophy is you can build it yourself, and you should. you can build a script which protects all built-in symbols. look for guidance in more general lua resources on the web

I'm quite sure the "issue" where two different scripts can stomp on each other still exists. Whether you think this is an "issue" depends on whether you prefer your scripts to collaborate or run in isolation.

[iamgreaser]

This might work for your case:

if not global_traps_locked then
    local realg=_G
    local newg=setmetatable({}, {
        __index=function(t,k)
            return realg[k]
        end,
        __newindex=function(t,k,v)
            if realg[k] then
                error("attempted to assign to global variable `"..k.."`")
            else
                rawset(t,k,v)
            end
        end,
    })
    realg.global_traps_locked = true
    setfenv(0, newg)
end

[adelikat]

I'm going to classify this as a "won't fix". There might be hacks we can do to prevent you from clobbering things. But there is a certain level of expertise expected when scripting for an emulator. And I think this can be safely classified as a thing for the user to avoid. We combat it with having more unlikely names for libraries such as bizstring. In the case of bit I can see how it is more likely to be inadvertent but I think once you know, you know to simply avoid it.