Global in one file affects diagnostics in another

How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

Which OS are you using?

Windows

What is the issue affecting?

Diagnostics/Syntax Checking

Expected Behaviour

If I have 1.lua:

function Main()
    foobar = 1
end

and 2.lua:

function Main()
    print(foobar)
end

in the same workspace/directory.

I would expect 2.lua to show foobar as undefined (unless I explicitly require 1.lua)

Actual Behaviour

No error is shown.

Additional Notes

This might be a pecularity of how I'm using lua (each file defines a separate plugin) but I would be surprised if this is an uncommon usage pattern. At the very least there should be a way to configure the behaviour.

Also - I'd be curious to understand the thinking behind the existing behaviour?

Reproduce the example in the Visual Studio Code extension with 1.lua and 2.lua in the same workspace, then trace how the language server shares globals between files. Determine how explicit require usage should affect diagnostics and whether a configuration option is needed. Done means 2.lua reports foobar as undefined unless 1.lua is explicitly required.