Need check nil: I checked the code for nil and the LSP is still complaining, what am I missing?

[andradei]

[Frityet]

you aren't checking rectangle_region for being nil, you are checking if e has a value. You would need to do

if not rectangle_region then error("my_screenshot error taking screenshot") end

[andradei]

you aren't checking rectangle_region for being nil

But didn't I explicitly do that in

-- vvvvvvvvvvvvvvvvvvvv
if not rectangle_region or rectangle_region == "" then
  -- ...
end

[tomlau10]

The warning is saying that you didn't check nil for rectangle_region when you call rectangle_region:gsub(...) 😅

• you first assign it on the line local rectangle_region, e = proc(slurp_command)
  => rectangle_region maybe nil here I believe
• in your code pattern, you maybe having proc() to return a pair, i.e.
  • (string, nil) or (nil, error)
  • however LuaLS doesn't support mutually-exclusive multi-return yet
    (related discussion: Mutually-exclusive multi-return #3102)
  • it will infer each return value individually => so rectangle_region: string|nil and e: error|nil
• on your gsub() line, you are doing <string|nil>:gsub(...) in the viewpoint of LuaLS
  => missing nil check

---

In the meantime, if you don't want to change the code structure, you may need to use @cast to tell LuaLS that
=> after the iferr(), rectangle_region will not be nil 🤔

local rectangle_region, e = proc(slurp_command)
iferrr(e, "xxx")
---@cast rectangle_region -? # means remove the nil type
-- luals should not complain now

[andradei]

Thank you for such a great explanation!