Type Narrow Exact Strings

Another feature suggestion 😅

It would be useful to be able to type-narrow exact strings.

For example:

---@alias TestTable {test_group_a: {test_field_1: string, test_field_2: string}, test_group_b: {test_field_1: string, test_field_3: string}}

---@type "test_group_a" | "test_group_b"
local test

if test == "test_group_a" then
	---@type TestTable
	local test_table
	test1 = test_table[test].test_field_1
end

When we do if test == "test_group_a" then it would be nice if the type of test narrowed to test_group_a (which can then be used to successfully index test_table. As it is now there is no type narrowing so the inferred type of test1 is unknown when it should be string.

El ejemplo de Lua del issue es el único punto de entrada proporcionado; úsalo para reproducir los tipos actuales de test y test1. Se considera terminado cuando una comprobación de igualdad contra "test_group_a" restringe test lo suficiente como para indexar TestTable e inferir test1 como string, incluida la cobertura del caso mostrado.