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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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:
```lua
---@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(): ` with an unresolved generic
```

```lua
---@class POOL2: { EnumerateActive: fun():(T, fun():T)) }
---@type POOL2
local headerPool = {}
local number, func = headerPool:EnumerateActive()
-- number type is `number`
-- func type should be `fun(): number`, instead it's `fun(): ` with an unresolved generic
```

```lua
---@alias POOL3 fun(arg: number): T, (fun():T)
---@type POOL3
local getPool
local number, func = getPool(3)
-- number type is `number`
-- func type should be `fun(): number`, instead it's `fun(): ` 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](https://github.com/user-attachments/assets/b06780fd-deb6-418c-b23b-ff3788d891ac)
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](https://github.com/user-attachments/assets/08f1a903-7655-4dea-a551-80838c8a4154)

### 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

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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