LuaLS / LuaLS/lua-language-server

Infer the type of the returned expression from the return type declaration

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Dominant language
Lua
Stars
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Forks
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Description

The situation:

---@class Test
---@field foo number

---@return Test
local function test()
    return {
        foo = 'this is not a number!',
    }
end

The code passes as valid when in reality the field is assigned a wrong type of value.

Right now the workaround is to do

---@class Test
---@field foo number

---@return Test
local function test()
    ---@type Test
    return {
        foo = 'this is not a number!',
    }
end

which to me feels like belaboring the obvious. Would be great if LuaLS assumed this automatically.

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First steps

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  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 Lua snippet in a local language-server setup and inspect how return type declarations are handled during table type inference. The change is complete when the declared Test return type causes the incorrect string assigned to foo to be diagnosed without an extra @type annotation, while the existing workaround remains valid.

Written by the indexing model from the issue text.

Assessment

Tech stack
lua
Domain
devtools
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
42/100

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