Lifting the return value of a callback to the return value of the parent caller

[benniekiss]

I was wondering if it's possible to annotate a function so that the return value is that of a provided callback.

Something like this:

---@alias callback<T> fun(): T...

---@class Foo: table
Foo = {}

---@generic T
---
---@param callback callback<T>
---
---@return T...
function Foo:exec(callback) end

fizz, buzz = Foo:exec(function ()
    return "fizz", true
end)

baz, biz = Foo:exec(function () return "baz" end)

In VS Code, at least, this does not give me the expected warnings:

The non-variadic version works as I would expect, except for the fact that in baz, biz = ..., biz is typed as string. I would expect nil, since the return is only one value. This is also an issue with the variadic version.

---@alias callback<T> fun(): T

---@class Foo: table
Foo = {}

---@generic T
---
---@param callback callback<T>
---
---@return T
function Foo:exec(callback) end

fizz, buzz = Foo:exec(function ()
    return "fizz", true
end)

baz, biz = Foo:exec(function () return "baz" end)

[CppCXY]

donot use alias

---@generic T
---
---@param callback fun(): T...
---
---@return T...
function Foo:exec(callback) end

fizz, buzz = Foo:exec(function ()
    return "fizz", true
end)

[benniekiss]

While I would like to use the alias, as I re-use the signature in a number of places, this works for me at the moment.