@operator add customization for first operand?

[SeanTheBuilder1]

How are you using the lua-language-server?

NeoVim

Which OS are you using?

Linux

What is the issue affecting?

Annotations

Expected Behaviour

I expected it would work like this

---@class Vector3
---@field x number
---@field y number
---@field z number
---@operator add(Vector, Vector3): Vector3 # Vector3 + Vector3
---@operator add(number, Vector3): Vector3 # number + Vector3
---@operator add(Vector3, number): Vector3 # Vector3 + number
Vector3 = {}

Actual Behaviour

But instead it is like this

---@class Vector3
---@field x number
---@field y number
---@field z number
---@operator add(Vector): Vector3 # Vector3 + Vector3
---@operator add(number, Vector3): Vector3 # this is impossible as far as I know
---@operator add(number): Vector3 # Vector3 + number
Vector3 = {}

Reproduction steps

copy paste 'Expected Behaviour code'
displays " ')' expected "

Additional Notes

I am asking if the impossible case is actually possible and that it is only undocumented or something. I expected the binary operators to take two parameters instead of just one. Thank you.

Log File

No response

[tomlau10]

From lua-users wiki, these kinds of mathematic operators will check metatables on both side (the left value first, then the right).
http://lua-users.org/wiki/MetatableEvents

• __add - Addition. When writing "myTable + object" or "object + myTable", if myTable's metatable has an __add key pointing to a function, that function is invoked (passing the left and right operands in order) and the return value used.
  • ''If both operands are tables, the left table is checked before the right table for the presence of an __add metaevent.

With a bit of digging in LuaLS codebase, I think this functionality can be added here:

lua-language-server/script/vm/operator.lua

Lines 302 to 306 in 26a7b69

	local node = vm.runOperator(binaryMap[op], source[1], source[2])
	if node then
	vm.setNode(source, node)
	return
	end

• After running once using source[1], source[2], if no matched result found, we can run it again using source[2], source[1]

local node = vm.runOperator(binaryMap[op], source[1], source[2])
if not node and op == '+' then
    -- interchangeable for '+'
    node = vm.runOperator(binaryMap[op], source[2], source[1])
end
if node then
    vm.setNode(source, node)
    return
end

---

I tested this and it works 👀

---@class Vector3
---@field x number
---@field y number
---@field z number
---@operator add(Vector3): Vector3 # Vector3 + Vector3
---@operator add(number): Vector3 # Vector3 + number | number + Vector3
Vector3 = {}

local a = 1 + Vector3
local b = 1.1 + Vector3
local c = (1*2+3) + Vector3

local x ---@type number
local d = x + Vector3

-- a, b, c, d are all inferred as `Vector3`

Note that the above demo code I only check for + operator, and from the lua user wiki, this interchangeable logic applies to: __add, __sub, __mul, __div, __mod, __pow, __concat. I suggest @SeanTheBuilder1 can try to work on this and open a PR after testing 👍

[SeanTheBuilder1]

This is an interesting find and I find it a good enough workaround for now while #1371 is still being worked on for the asymmetric operations. Added that with that preliminary code snippet would make the LSP in line with the actual behavior of lua code.

[SeanTheBuilder1]

whoops misclick i apologize

[tomlau10]

I have never thought of an asymmetric __add ... what could be a possible use case for that 😂 ?

[SeanTheBuilder1]

Good day, yeah I couldn't think of a practical one either but that might be an edge case for the future. Technically you could do that with a C binding where it returns a different type when it detects if it was the left or right operand. But that might be too weird, after all I'm just trying to have parity with a library I'm interfacing which has support for scalars on the left operand and so far I can't find a case which breaks symmetry.