Union type parameter causes "param-type-mismatch" warning

[ArmoredPony]

Here is the code that causes warning:

function add_month(time)
  local dt = os.date('*t', time)
  dt.month = dt.month + 1
  return os.time(dt)
end

And the warning itself:

The code seems to be working. Apparently, the extension understands that the type of dt variable is either string or osdate. It also knows that os.date function takes ostime as an argument:

It assumes that dt is a string and raises the warning but ignores the fact that it's also an osdate. Is this a bug or am I missing something?

[carsakiller]

This is due to os.date returning either a string or table. It may be possible to provide an overload so that unless *t is provided as the first parameter, the return type is string... but that may not be possible right now.

In the meantime, you can @cast the return of os.date to a different type:

local valueIKnowIsOsDate = os.date("*t", time);
---@cast valueIKnowIsOsDate osdate

[ArmoredPony]

Ah, so I have to specify the exact type that belongs to this union. That makes sense I guess, thank you.