Compiler error when using a concrete type (bool) in a function type parameter within a generic interface method signature

[iperov]

Describe the bug

The V compiler reports an error:
error: generic type name 'bool' is not mentioned in interface 'IProp_r'

when defining a method in a generic interface that uses a function type (fn(...)) where one of the parameter types is a concrete type (bool) not related to the interface's generic parameter [T].

This appears to be incorrect behavior, as the concrete type bool is not intended to be a generic parameter — it should be treated as a fixed type in the signature, similar to how concrete types are allowed in generic struct fields or non-generic functions.

Reproduction Steps

pub type Action[A, B] = fn(v1 A, v2 B)

pub interface IProp_r[T]
{
	listen_state(action Action[T, bool])	 // error: generic type name `bool` is not mentioned in interface `IProp_r`
}

fn main(){
}

Expected Behavior

compiling without errors

Current Behavior

error

generic type name bool is not mentioned in interface IProp_r

Possible Solution

No response

Additional Information/Context

The same code compiles fine in golang.

package main

type Action[A any, B any] func(v1 A, v2 B)

type IProp_r[T any] interface {
	ListenState(action Action[T, bool])
}

func main() {
}

V version

V 0.4.12 087a1c2

Environment details (OS name and version, etc.)

V full version	V 0.4.12 26305ec.087a1c2
OS	windows, Microsoft Windows 10 Pro 19045 64-bit
Processor	8 cpus, 64bit, little endian, Intel(R) Core(TM) i7-9700K CPU @ 3.60GHz
Memory	51.21GB/63.94GB
V executable	C:\PORTABLE\DEVELOP\V\VProject_internal\v\v.exe
V last modified time	2025-12-30 13:33:04
V home dir	OK, value: C:\PORTABLE\DEVELOP\V\VProject_internal\v
VMODULES	OK, value: C:\PORTABLE\DEVELOP\V\VProject_internal_z\u.vmodules
VTMP	OK, value: C:\PORTABLE\DEVELOP\V\VProject_internal_z\t\v_0
Current working dir	OK, value: C:\PORTABLE\DEVELOP\V\VProject\master
Git version	git version 2.50.1.windows.1
V git status	weekly.2025.01-2-g087a1c23
.git/config present	true
cc version	N/A
gcc version	gcc (MinGW-W64 x86_64-ucrt-posix-seh, built by Brecht Sanders, r4) 15.2.0
clang version	N/A
msvc version	N/A
tcc version	tcc version 0.9.27 (x86_64 Windows)
tcc git status	N/A
emcc version	N/A
glibc version	N/A

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