Generic fntype error

[kbkpbot]

Describe the bug

When define a generic fntype, it has some bug.

Reproduction Steps

sort.v :

module main

type FnSortCB[T] = fn (const_a T, const_b T) int

fn sort[T](arr []T, sort_cb FnSortCB) []T {
	return arr
}

fn sort2[T](arr []T, sort_cb fn (const_a T, const_b T) int) []T {
	return arr
}

fn my_cmp(a int, b int) int {
	if a == b {
		return 0
	}
	if a < b {
		return 1
	}
	return -1
}

fn main() {
	mut a := [123,553,223,126,883,257]
	
	x := sort(a, my_cmp)	// if change to `sort2`, that can be compiled.
	println(x)
}

Expected Behavior

compile ok

Current Behavior

~/v/sort$ v sort.v
sort.v:26:15: error: cannot use `fn (int, int) int` as `fn (voidptr, voidptr) int` in argument 2 to `sort`
   24 |     mut a := [123,553,223,126,883,257]
   25 |
   26 |     x := sort(a, my_cmp)
      |                  ~~~~~~
   27 |     println(x)
   28 | }
Details: `FnSortCB`'s expected argument `const_a` to be a pointer, but the passed argument `a` is NOT a pointer

Possible Solution

use sort2 instead of sort

Additional Information/Context

No response

V version

V 0.4.9 9fc8352

Environment details (OS name and version, etc.)

V full version	V 0.4.9 9fc8352
OS	linux, Ubuntu 24.04.1 LTS
Processor	8 cpus, 64bit, little endian, Intel(R) Core(TM) i7-9700 CPU @ 3.00GHz
Memory	0.58GB/15.51GB
V executable	/media/HD/github/kbkpbot/v/v
V last modified time	2025-01-08 12:09:42
V home dir	OK, value: /media/HD/github/kbkpbot/v
VMODULES	OK, value: /home/mars/.vmodules
VTMP	OK, value: /tmp/v_1000
Current working dir	OK, value: /home/mars/v/sort
Git version	git version 2.43.0
V git status	weekly.2025.1-12-g9fc83526 (29 commit(s) behind V master)
.git/config present	true
cc version	cc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
gcc version	gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
clang version	Ubuntu clang version 18.1.3 (1ubuntu1)
tcc version	tcc version 0.9.28rc 2024-07-31 HEAD@1cee0908 (x86_64 Linux)
tcc git status	thirdparty-linux-amd64 0134e9b9
emcc version	N/A
glibc version	ldd (Ubuntu GLIBC 2.39-0ubuntu8.3) 2.39

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[huly-for-github]

Connected to Huly®: V_0.6-21883

[kbkpbot]

By replaceing FnSortCB with FnSort, will create a different error?

module main

type FnSort[T] = fn (const_a T, const_b T) int

fn sort[T](arr []T, sort_cb FnSort) []T {
        return arr
}

fn sort2[T](arr []T, sort_cb fn (const_a T, const_b T) int) []T {
        return arr
}

fn my_cmp(a int, b int) int {
        if a == b {
                return 0
        }
        if a < b {
                return 1
        }
        return -1
}

fn main() {
        mut a := [123,553,223,126,883,257]

        x := sort(a, my_cmp)    // if change to `sort2`, that can be compiled.
        println(x)
}

error message:

sort2.v:26:15: error: cannot use `fn (int, int) int` as `fn (T, T) int` in argument 2 to `sort`

[kbkpbot]

I found the error has something related to vlib/builtin/cfns_wrapper.c.v, in this file,

type FnSortCB = fn (const_a voidptr, const_b voidptr) int

It should conflict with my FnSortCB type definition.

So I think the checker should be improved to check this case, by issue an error message "duplicate definition"

[felipensp]

We have a checker error here. Because your code should be:
fn sort[T](arr []T, sort_cb FnSort[T]) []T {

As the alias is a generic one, it must receive the [T] there. As we do in the following case:

type Foo[T] = Struct[T] | int

struct Bar {
	a Foo // error: `Foo` type is generic sumtype, must specify the generic type names, e.g. Foo[T], Foo[int]
}