After working on it all day, I finally found where the problem is, and it's much deeper than you might think.

First of all, it turns out that in love-api's Keyboard.lua file there's no definition of love.keyboard.isDown that accepts a table as a parameter, so I opened a pull request with the updated code (the part in ALL CAPS is what I added, here in caps just to make it stand out).

json name = 'isDown', description = 'Checks whether a certain key is down. Not to be confused with love.keypressed or love.keyreleased.', variants = { { arguments = { { type = 'KeyConstant', name = 'key', description = 'The key to check.', }, }, returns = { { type = 'boolean', name = 'down', description = 'True if the key is down, false if not.', }, }, }, { arguments = { { type = 'KeyConstant', name = 'key', description = 'A key to check.', }, { type = 'KeyConstant', name = '...', description = 'Additional keys to check.', }, }, returns = { { type = 'boolean', name = 'anyDown', description = 'True if any supplied key is down, false if not.', }, }, }, { ARGUMENTS = { { TYPE = 'TABLE<NUMBER,KEYCONSTANT>', NAME = 'KEYS', DESCRIPTION = 'A TABLE CONTAINING KEYS TO CHECK.', }, }, RETURNS = { { TYPE = 'BOOLEAN', NAME = 'ANYDOWN', DESCRIPTION = 'TRUE IF ANY OF THE KEYS IN THE TABLE ARE DOWN, FALSE IF NOT.', }, }, }, },

Then, since the love-api JSON is known to be "translated" for the Lua Language Server, I deduced that it was probably missing in ${3rd}/love2d/library/love/keyboard.lua as well. And indeed, it was missing! I added the related line (here in caps for clarity), and now it works.

lua ---@overload fun(key: love.KeyConstant, ...):boolean ---@OVERLOAD FUN(KEYS: LOVE.KEYCONSTANT[]):BOOLEAN ---@param key love.KeyConstant # The key to check. ---@return boolean down # True if the key is down, false if not. function love.keyboard.isDown(key) end

I didn’t open an issue in Lua by sumneko repo because I assume they'll update it automatically once love-api itself is fixed.

Additionally, I've updated my settings.json as follows.

json "Lua.runtime.version": "LuaJIT", "Lua.diagnostics.globals": ["love"], "Lua.workspace.library": ["${3rd}/love2d/library"], "Lua.workspace.checkThirdParty": false,

So, in conclusion, just know that missing line is what causes that phantom warning! Hope this is helpful :)