@field private in @meta file triggers warning even when accessed within the same class

[Mayron]

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

When defining a class in a ---@meta file with @field private annotations, the Lua language server warns about accessing those private fields even when they are accessed within the implementation of the same class (just in a separate file). This makes private fields effectively unusable if you're organizing types in meta files.

The language server should not warn about access to @field private fields when they are accessed within the implementation of the class they belong to, even if that implementation is in a separate file.

I think this is by design rather than a bug, so maybe this is a feature request?

Actual Behaviour

Even though I'm accessing the private field in the implementation of that class, I see a warning:

Reproduction steps

1. In types.lua (meta file)

---@meta

---@class (exact) ModuleMixin
---@field private __loaded boolean
---@field Load fun(self)
---@field IsLoaded fun(self): boolean
---@field Init fun(self)

2. ModuleMixin.lua (implementation)

---@type SmartChat.ModuleMixin
local ModuleMixin = {}

function ModuleMixin:Init()
  self.__loaded = false  -- <-- LuaLS warns that __loaded is private
end

Additional Notes

I use a @meta file to separate type annotations from implementation, which is common in larger projects. This issue makes it difficult to use private meaningfully unless everything is co-located in the same file, which defeats the purpose of a metadata/type declaration file.

Would it be possible to make private refer to "the class definition context" rather than "the file only"?

Thanks!

Log File

No response

[tomlau10]

IIUC, the problem is because you used @type annotation

• this makes the local ModuleMixin become a typed variable (or an instance variable?) instead of a class variable
• if you use ---@class ModuleMixin then it will work correctly 🤔

---@class ModuleMixin
local ModuleMixin = {}

function ModuleMixin:Init()
    self.__loaded = false  -- no more warning
end

---

but this has a side effect

I noticed that you used the (exact) class feature, which will warn if you try to inject any field/method that are not predefined. But after you used ---@class in you implementation, seems it will not warn you about method injection ... 😕

---@class ModuleMixin
local ModuleMixin = {}

function ModuleMixin:Init()
    self.__loaded = false  -- no more warning
end

function ModuleMixin:custom()   --> no `inject-field` warning for this
    self.x = 1  --> this will still warn `inject-field` as expected
end

[Mayron]

@tomlau10 thank you! I was just thinking about this as a solution. I wasn't sure if having @class twice in the meta file and implementation file was a bad practice, or if whatever analyser VS Code uses would think there were duplicate classes but this seems to work. Brilliant! 👍

[Mayron]

I guess this issue can be closed, but it might be worth updating the docs (unless I missed this) for the meta or annotation sections to clarify this. Unless, this isn't how meta files are supposed to work and I'm doing it wrong lol

[Mayron]

I noticed that you used the (exact) class feature, which will warn if you try to inject any field/method that are not predefined. But after you used ---@class in you implementation, seems it will not warn you about method injection ... 😕

Yea, I noticed this too. I had to disable a few warnings in the metafile to also let me define the methods in a table rather than by using @field (so that I could describe the method with additional annotation) but the exact annotation didn't like this.

---@diagnostic disable: duplicate-index, inject-field

---@class (exact) ModuleMixin
---@field private __loaded boolean
---@field private __name string
---@field private __localizedName string
---@field private __enabled boolean
---@field private __callbacks ModuleCallbacks
local ModuleMixin = {
  ---@param config ModuleConfig
  Init = function(self, config) end;
  ---@param enabled boolean
  SetEnabled = function(self, enabled) end;
  ---@return boolean
  IsEnabled = function(self) end;
  Load = function (self) end;
  ---@return boolean
  IsLoaded = function (self) end;
};

[CppCXY]

Another better approach is to allow both meta files and actual files to define the same class, with one serving as the actual implementation and the other as annotations

[tomlau10]

I wasn't sure if having @class twice in the meta file and implementation file was a bad practice

In LuaLS @class can be used multiple times. This is similar to the partial class concept of C# where you can break down the definition of a very large class into multiple files. My team employed this annotation pattern in our project 👀 .

Unless, this isn't how meta files are supposed to work and I'm doing it wrong lol

I am not sure if defining class/method signature in a meta file then use it to enforce the implementation is the intended way to use the annotation 😕. AFAIK, meta file is used to define header of a library, whether it is a 3rd party library or a c library, that you cannot write annotation to. (that's why you need a meta file).

Of course I can understand what you want to achieve here, that you want to separate the annotation and the actual code as much as possible. It's good that you found a way to workaround it. 😂

---

Okay back to your last reply/question: https://github.com/LuaLS/lua-language-server/issues/3211#issuecomment-3008185862

At first I think that you don't need to define methods in a table, you can just write them as method in your meta file

---@meta

---@class ModuleConfig
---@class ModuleCallbacks

---@class (exact) ModuleMixin
---@field private __loaded boolean
---@field private __name string
---@field private __localizedName string
---@field private __enabled boolean
---@field private __callbacks ModuleCallbacks
local ModuleMixin = {}

---@param config ModuleConfig
function ModuleMixin:Init(config) end

---@param enabled boolean
function ModuleMixin:SetEnabled(enabled) end

---@return boolean
function ModuleMixin:IsEnabled() end

function ModuleMixin:Load() end

---@return boolean
function ModuleMixin:IsLoaded() end

⚠ but after that I noticed the dilemma here ...

• if in the meta file, these methods are defined outside the table then in the ModuleMixin.lua (implementation) you will get duplicate-set-field warnings 🤦
• that's because you really "defined" the same named methods for the same class twice and this warning will only go away if you use @type instead of @class, which is an optimization done by me: https://github.com/LuaLS/lua-language-server/pull/2859/commits/d2df7788d526960a427698fe66c73c2831dd2730 (before that pr, you will get duplicate-set-field no matter you use @class or @type for the namespace variable)
• however if you use @type there, then we will be back to the starting point ... the self.__loaded = true will throw invisible warning again 😇

I just found a hack ?! 🤯

As you may have found out, @class for the same class can actually be defined multiple times. So I just tried to define the exact attribute in another @class annotation Wow, seems it works

• type.lua

---@meta

---@class ModuleConfig
---@class ModuleCallbacks

---@class ModuleMixin
---@field private __loaded boolean
---@field private __name string
---@field private __localizedName string
---@field private __enabled boolean
---@field private __callbacks ModuleCallbacks
local ModuleMixin = {
    ---@param config ModuleConfig
    Init = function(self, config) end;
    ---@param enabled boolean
    SetEnabled = function(self, enabled) end;
    ---@return boolean
    IsEnabled = function(self) end;
    Load = function (self) end;
    ---@return boolean
    IsLoaded = function (self) end;
};

---@class (exact) ModuleMixin
-- now mark this class as exact class

=> then you don't need the ---@diagnostic disable: duplicate-index, inject-field 😄

[tomlau10]

🤯 🤯 I think I found a solution (an optimization / a fix to be accurate) for the duplicate-set-field warnings issues

• if the def node is inside a meta file => it should not take part in the duplicate-set-field diagnostics => because it is most probably just a defined interface https://github.com/LuaLS/lua-language-server/blob/32fec3cc99af8b9a1e45c2455a8c3bd0d3e38f66/script/core/diagnostics/duplicate-set-field.lua#L52-L60
• add the following

            if vm.isMetaFile(guide.getUri(def)) then
                -- def node is inside meta file, this should be treated as interface only
                goto CONTINUE
            end

• now if the same named class method is originally defined in a meta file, it will not be considered as duplicate-set-field but if you define the same named class method twice, both outside of meta files => they will still trigger duplicate set field as usual

---

With this fix, one can just write the interface using usual class:method style. No more duplicate-set-field in ModuleMixin:Init under main.lua 🥳