LuaLS / LuaLS/lua-language-server
[Feature Request] Intersection types
Nobody has claimed this yet.
- Dominant language
- Lua
- Stars
- 4.4k
- Forks
- 442
- PR merge metrics
- No merged PRs in 30d
Description
I apologize if this request has been reported before, I couldn't find any.
It would be great to be able to explicitly differentiate between union types and intersection types
e.g.
--- @class A
local a = {foo = 1}
--- @class B
local b = {bar = "hello"}
--- @param aOrB A | B
--- @param aAndB A & B
local function someFunc(aOrB, aAndB) end
someFunc(a, a) -- no warning, but 2nd argument should give a warning
--- @param a A
local function someOtherFunc(a) end
--- @type A | B -- would prefer to use A & B and not have any warnings
local aAndB = {foo = 1, bar = "hello"}
someOtherFunc(aAndB) -- Cannot assign `A|B` to parameter `A`. - `B` cannot match `A` - Type `B` cannot match `A` Lua Diagnostics. (param-type-mismatch)
While it's possible to use an explicit class with inheritance as a workaround, this is not always viable, especially when using dynamic types with generics
--- @class C: A, B
local c = {foo = 1, bar = "hello"}
someOtherFunc(aAndB) -- no warning
-- not viable when using something like this
--- @generic T1, T2
--- @param tbl1 T1
--- @param tbl2 T2
--- @return T1 | T2 -- would like to use T1 & T2 instead to avoid the warnings
local function merge(tbl1, tbl2) end
someOtherFunc(merge(a, b)) -- Cannot assign `A|B` to parameter `A`. - `B` cannot match `A` - Type `B` cannot match `A` Lua Diagnostics. (param-type-mismatch)
The suggested syntax A & B for intersection types and A | B for union types matches several other languages, such as TypeScript and PHP.
Edit: another workaround is to enable luals.github.io/wiki/settings#typeweakunioncheck. This has its own downsides, but may be helpful for people trying to avoid the param-type-mismatch warnings
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
No implementation files or tests are named. Start by tracing how Lua annotations represent unions and how the param-type-mismatch diagnostic handles them, then compare behavior with the A & B, A | B, and generic merge examples; done means intersection annotations avoid the demonstrated false warnings while unions retain their current checks.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- lua
- Domain
- developer-experience, tooling
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100