instantiate generics using the passed functions

[georgiy-belyanin]

This patch adds simple type level matching for the doc functions and signatures allowing to instantiate generics based on the passed functions.

The following code demonstrates a generic type instantiated by this feature.

---@param a number
---@return string
local function tostr(a)
    return tostring(a)
end

---@generic T, U
---@param x T
---@param f fun(x: T): U
---@return U
local function apply(x, f)
    return f(x)
end

--"a" is inferred as a string.
a = apply(3, tostr)

[georgiy-belyanin]

I hope the solution is acceptable as a temporary one.

I've a problematic scenario that's hard to deal with.
It'd nice to support the following annotation instantiation allowing really complex calls.

---@generic K, V
---@class fun.table_iterator<K, V>
table_iterator_methods = {}

---@generic K, V, W
---@param self fun.table_iterator<K, V>
---@param f fun(a: V): W
---@return fun.table_iterator<K, W>
function table_iterator_methods.map(self, f) end

---@type fun(a:string, b:string): number
local process = function(a, b)
    return tostring(b)
end

---@type fun.table_iterator<string, string>
local a = {}
-- The  `fun.table_iterator<string, number>` type is not inferred.
-- It's `fun.table_iterator<string, unknown>` instead.
local b = a:map(process)

It's impossible yet to infer the type of b. It happens due to the fact indexing a generic class relies on the fact it's possible to instantiate the type of the call only by instantiating the object generics.

Thus, currently the algorithm works in this steps.

a:map
* Infer type of A (fun.table_iterator<string, string>)
* Try to infer the type of A.map substituting `K` and `V` (and not substituting the arguments) 
* Got something like `fun(self, fun(a: string): unknown): fun.table_iterator<string, unknown>`.

Please, let me now if this is wrong or not.

[CppCXY]

I think it might be better if you write it this way.

[CppCXY]

Generic functions are best defined this way, but there are currently some bugs that I will try to fix.

[CppCXY]

I have fixed the issue with the generics, you can try the most reasonable way to write it again.

[georgiy-belyanin]

Thank you for an explanation and for working in it.

I've changed the return type of process to table and it works strangely. I'd appreciate if you check the scenario out when you have enough time. The type W is infered the same as K.

---@class fun.table_iterator<K, V>
table_iterator_methods = {}

---@generic W
---@param f fun(a: any): W
---@return fun.table_iterator<K, W>
function table_iterator_methods:map(f) end

---@param a string
---@param b number
---@return table
local function process(a, b)
    return {}
end

---@type fun.table_iterator<string, number>
local a = {}

-- b is fun.table_iterator<string, string>, not
-- fun.table_iterator<string, table>
local b = a:map(process)

The behavior is the same if you define process using local process = function ... syntax:

---@param a string
---@param b number
---@return table
local process = function(a, b)
    return {}
end

The syntax suggested by me also ends up with unknown type.

[CppCXY]

Thank you for an explanation and for working in it.

I've changed the return type of process to table and it works strangely. I'd appreciate if you check the scenario out when you have enough time. The type W is infered the same as K.

---@class fun.table_iterator<K, V>
table_iterator_methods = {}

---@generic W
---@param f fun(a: any): W
---@return fun.table_iterator<K, W>
function table_iterator_methods:map(f) end

---@param a string
---@param b number
---@return table
local function process(a, b)
    return {}
end

---@type fun.table_iterator<string, number>
local a = {}

-- b is fun.table_iterator<string, string>, not
-- fun.table_iterator<string, table>
local b = a:map(process)

The behavior is the same if you define process using local process = function ... syntax:

---@param a string
---@param b number
---@return table
local process = function(a, b)
    return {}
end

The syntax suggested by me also ends up with unknown type.

I roughly understand why — there are two generic parameters from different sources here, both numbered 0. I might need to change the generics to an enum type. I'll fix this after I wake up.

[CppCXY]

I have fix this issue, please try again

[georgiy-belyanin]

It now works properly. Thank you very much.