Two Rule Suggestions: multiple returns in function calls / table definitions and string concatenation

multiple returns in function calls / table definitions

local a = { "one", "two", "three" }
local b = { unpack(a), "four" }
local c = { "four", unpack(a) }
print(#b) -- 2
print(#c) -- 4

unpack's behavior is quite unintuitive; when the output is not in the last position of a table definition, only the first element is actually included in the new table. (In fact, this not only applies to unpack, but to every function that returns multiple values – only happens most often with unpack that will people will notice, I assume.)

see explainer in the docs: https://www.lua.org/manual/5.3/manual.html#3.4

I think a diagnostic that reminds one of such cases would be very useful, since it's a common gotcha in lua.

string concatenation

print("foo" + "bar")

Common mistake to not use .. for string concatenation. Even though I am used to lua, it still happens to me all the time after coming back from writing in a different language. A diagnostic here would be useful. (And I am actually a bit surprised that there isn't one yet.)

Inizia con la sezione del manuale di Lua 5.3 collegata nell’issue, prestando particolare attenzione alle regole dei valori restituiti multipli illustrate dagli esempi con le tabelle. Individua poi i punti di ingresso della diagnostica del language server per le espressioni con valori restituiti multipli nelle definizioni di tabelle e per l’uso di + con stringhe. Il lavoro è completato quando entrambi gli esempi producono diagnostica utile senza segnalare erroneamente codice Lua valido.