Type inference fails when using table function definition, forward-declared type, and typeof() types

[goldenstein64]

This code snippet fails to infer the type of obj.f.

--!strict
local t = {}

function t.f(x: a) end
type a = any

local obj = t
print(obj.f) -- TypeError: Key 'f' not found in table 't'

obj is assumed to be of type typeof(t).

This makes obj.f an *error-type*, and it makes any values it returns an *error-type*, which makes any operations on its returned values an *error-type*, etc.

This snippet only fails in a few orderings of these statements. There are many changes that will make the error disappear, such as:

• defining the function inside the table.

--!strict
local t = {
  f = function(x: a) end
}

type a = any

local obj = t
print(obj.f)

• defining the function without sugar syntax.

--!strict
local t = {}

t.f = function(x: a) end
type a = any

local obj = t
print(obj.f)

• defining the type above the function definition or using a's type directly.

--!strict
local t = {}

type a = any
function t.f(x: a) end

local obj = t
print(obj.f)

--!strict
local t = {}

function t.f(x: any) end

local obj = t
print(obj.f)

• referencing t directly instead of obj.

--!strict
local t = {}

function t.f(x: a) end
type a = any

print(t.f)

• Casting obj's type explicitly.

--!strict
local t = {}

function t.f(x: a) end
type a = any

local obj = t :: { f: (a) -> () }
print(obj.f)

[andyfriesen]

This is fixed in the new solver.