Because upvalues are resolved at compile time. They're not free names.
Sadly, this means that this patch really doesn't do much more for you than strict.lua aside from being able to control which blocks it applies to.
/s/ Adam
Why upvalues cause no error?
local b="upvalue"
function test()
local print=print
do <erroronfreename>
print("b=",b) -- wtf? no error
end
end
test()
пн, 22 июл. 2019 г. в 10:40, pocomane <pocomane_7a@pocomane.com>:
>
> I attach a patch for the last lua revision on github [1]. It changes the "Global by default" policy to a "No default" one. This is done only in specifically marked go/end blocks. In particular:
>
> - It adds an <erroronfreename> attribute
> - It allows do/end block to have attributes
> - In a do/end block with an <erroronfreename> attribute, a free name raises a compile time error instead of being translated to _ENV.name
>
> It is just a very minimal proof of concept (e.g. there is no check of which attribute is valid for each statement), however the patch lets you to write:
>
> ```
> -- toplevel works as usual
> print("ok")
>
> -- clean do block works as usual
> do
> print("ok")
> end
>
> -- a marked do block "Hides" the "Globals"
> do <erroronfreename>
> _ENV.print("ok") -- ok: _ENV is an upvalue
> print("BAD") -- error: "print" is a free name in a protected block
> end
>
> -- nested block inherits the attribute
> do <erroronfreename>
> do
> print("BAD")
> end
> end
> ```
>
> Initially, I thought it could be useful to protect against typos, e.g. wrapping the whole script with:
>
> ```
> -- copy all the needed globals into locals, e.g.
> local print = print
> do <erroronfreename>
> -- ... whole script ...
> end
> ```
>
> But this pattern has some issue, for example to change a global value you have to write `_ENV.name = val`, and a typo in "name" is still not catched. (Obviously you can use static.lua, but, as observed in another thread, sometimes runtime-checks may be problematic).
>
> pocomane
>
> [1] https://github.com/lua/lua/commit/1fb4d539254b67e7e35ed698250c66d1edff0e08
>
