LuaLS / LuaLS/lua-language-server

Generics in nested functions don't work for some annotations unless there are no arguments passed

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Lua
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Description

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?

Annotations

Expected Behaviour

passing an argument should have no effect, and the types of nested functions should be resolved correctly
some examples:

---@generic T
---@param arg T
---@return fun(): fun(): T
local function POOL1(arg) return function() return function() return arg end end end -- implementing the function makes no difference for the typing
local func1 = POOL1(5.2) -- type is `fun(): fun(): number`
local func2 = func1(4) -- type should be `fun(): number`, instead it's `fun(): <T>` with an unresolved generic
---@class POOL2<T>: { EnumerateActive: fun():(T, fun():T)) }
---@type POOL2<number>
local headerPool = {}
local number, func = headerPool:EnumerateActive()
-- number type is `number`
-- func type should be `fun(): number`, instead it's `fun(): <T>` with an unresolved generic
---@alias POOL3<T> fun(arg: number): T, (fun():T)
---@type POOL3<number>
local getPool
local number, func = getPool(3)
-- number type is `number`
-- func type should be `fun(): number`, instead it's `fun(): <T>` with an unresolved generic

all 3 examples work fine if you don't pass any argument

Actual Behaviour

when an argument is passed to the outer function, the inner function doesn't have the generic resolved
image
if no arguments are passed (i.e. headerPool.EnumerateActive()), then they are resolved properly
the type of the argument makes no difference, and annotating the function as accepting an argument also makes no difference

interestingly, when hovering over the function itself, the tooltip does show the correctly resolved types
image

Reproduction steps

copy the provided snippets, and check which types the variables resolve to

Additional Notes

Tested on both VSCode and Jetbrains IDEs
The example is contrived, my real usecase is to annotate an object pool class, that allows you to acquire objects of a given (generic) type, and allows iterating over them.

I know this has worked in a past version, though I don't remember how long ago that was (several weeks or months most likely)

Log File

No response

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the three provided Lua annotation examples and inspect how nested generic types are resolved when the outer function receives an argument. Compare the inferred types with the no-argument cases and the expected hover results. Done means all three examples resolve their inner functions to the concrete type, such as number, while preserving the existing correct behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
lua
Domain
devtools
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
48/100

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