Type checking does not work at all with `` (backtick) literals

How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

Which OS are you using?

Windows

What is the issue affecting?

Type Checking

Expected Behaviour

A = 1
B = 2
---@type `A`
local foo = A -- this should be fine
---@type `A`
local bar = B -- but this should give a type error
---@type `A`
local baz = 1 -- ideally, so should this (because you didn't use the literal name "A")

---@type `A`|string
local var = A -- this should be fine

Actual Behaviour

A = 1
B = 2
---@type `A`
local foo = -- A is correctly the only autocomplete suggestion
---@type `A`
local bar = 3 -- but this does not give any type error

---@param a `A`
function f(a) end
local baz = f("Hello") -- nor does this

---@type `A`|string
local var = A --[[Cannot assign `integer` to `string|`A``.
- `integer` cannot match `string|`A``
- Type `integer` cannot match `string`
- Type `number` cannot match `string`
Lua Diagnostics.(assign-type-mismatch)
]]

Reproduction steps

1. Extension version v3.9.3

Additional Notes

This is important for things like

A = 1
B = 2
---@alias Enum `A`|`B`

("enums" without tables) to be type checked, like in the "Literal Custom Type" example of https://luals.github.io/wiki/annotations/#alias

I experimented for a bit trying to fix the problem, but I can't quite find where the problem lies. All I know is that the backtick literals aren't being interpreted as types for the purposes of type checking.

In any case, here are some tests for test/diagnostics/assign-type-mismatch.lua to make sure it's fixed:

TEST [[
local A = "Hello"
local B = 2

---@type `A`
local x = A

---@type `B`
local y = B
]]

TEST [[
local A = "Hello"

---@alias myLiteralAliases `A` | integer

---@type myLiteralAliases
local x = A

---@type myLiteralAliases
local y = 3
]]

TEST [[
local B = 2

---@alias myLiteralAliases `B` | string

---@type myLiteralAliases
local x = B

---@type myLiteralAliases
local y = "Hello"
]]

TEST [[
local A = "Hello"
local B = 2

---@alias myLiteralAliases `A`|`B`

---@type myLiteralAliases
--local x = A

---@type myLiteralAliases
--local y = B
]]

TEST [[
local A = "Hello"
local B = "World"

---@alias myLiteralAliases `A`|`B`

---@type myLiteralAliases
--local <!x!> = 1

---@type myLiteralAliases
--local <!y!> = "A"
]]

TEST [[
local A = 1
local B = 2

---@alias myLiteralAliases `A`|`B`

---@type myLiteralAliases
--local <!x!> = "A"
]]

and if we want to disallow the value (only allowing the actual symbol):

TEST [[
local A = "Hello"

---@type `A`
local <!x!> = "Hello"
]]

TEST [[
local A = "Hello"

---@alias myLiteralAliases `A` | integer

---@type myLiteralAliases
local <!x!> = "Hello"
]]

TEST [[
local A = "Hello"
local B = "World"

---@alias myLiteralAliases `A`|`B`

---@type myLiteralAliases
local <!x!> = "Hello"
]]

Bắt đầu với các trường hợp tái hiện trong test/diagnostics/assign-type-mismatch.lua và chạy bài kiểm tra chẩn đoán đó. Truy vết cách các literal dấu backtick được xử lý khi kiểm tra kiểu, sau đó làm cho các phép gán hợp lệ và không hợp lệ được liệt kê tạo ra các chẩn đoán như mong đợi, bao gồm cả các bí danh literal.