V error with receiver method on interface

[islonely]

Describe the bug

V is giving an error about the parameter to the function not implementing the interface fields. But it's testing for the wrong interface. The fn (mut node Node) append_child(child &Node) is what is giving the error. The compiler is expecting an Element interface there for some reason. Using this instead where fn append_child is invoked does work.

element.children << &Node(&Text{
	name: 'text'
	text: 'Hello, World!'
})

Reproduction Steps

interface Node {
	id string
	name string
mut:
	children []&Node
}

fn (mut node Node) append_child(child &Node) {
	node.children << child
}

interface Element {
	Node
	attributes map[string]string
}

[heap]
struct NodeBase {
	id   string
	name string
mut:
	children []&Node
}

[heap]
struct Text {
	NodeBase
	text string
}

[heap]
struct HTMLBodyElement {
	NodeBase
	attributes map[string]string
}

fn main() {
	mut element := &Element(&HTMLBodyElement{
		name: 'body'
	})
	element.append_child(&Node(&Text{
		name: 'text'
		text: 'Hello, World!'
	}))
	println(element)
}

Expected Behavior

output:

&Element(HTMLBodyElement{
    NodeBase: NodeBase{
        id: ''
        name: 'body'
        children: [&Node(Text{
    NodeBase: NodeBase{
        id: ''
        name: 'text'
        children: []
    }
    text: 'Hello, World!'
})]
    }
    attributes: {}
})

Current Behavior

output:

C:/Users/imado/Documents/test.v:41:23: error: cannot implement interface `Element` with a different interface `&Node`
   39 |         name: 'body'
   40 |     })
   41 |     element.append_child(&Node(&Text{
      |                          ~~~~~~~~~~~~
   42 |         name: 'text'
   43 |         text: 'Hello, World!'
C:/Users/imado/Documents/test.v:41:23: error: `&Node` doesn't implement field `attributes` of interface `Element`
   39 |         name: 'body'
   40 |     })
   41 |     element.append_child(&Node(&Text{
      |                          ~~~~~~~~~~~~
   42 |         name: 'text'
   43 |         text: 'Hello, World!'

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.2 37e5616

Environment details (OS name and version, etc.)

V full version: V 0.4.2 37e5616
OS: windows, Microsoft Windows 11 Pro v22621 64-bit
Processor: 16 cpus, 64bit, little endian, 

getwd: C:\Users\imado\Documents\cyberian_tiger
vexe: C:\Users\imado\v\v.exe
vexe mtime: 2023-10-09 22:29:31

vroot: OK, value: C:\Users\imado\v
VMODULES: OK, value: C:\Users\imado\.vmodules
VTMP: OK, value: C:\Users\imado\AppData\Local\Temp\v_0

Git version: git version 2.33.1.windows.1
Git vroot status: weekly.2023.40.1-50-g37e5616b (9 commit(s) behind V master)
.git/config present: true

CC version: Error: 'cc' is not recognized as an internal or external command,
operable program or batch file.

thirdparty/tcc status: thirdparty-windows-amd64 e90c2620

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[Delta456]

I am not sure if receiver methods should work for interfaces.

[JalonSolov]

I agree. An interface in V is more of a contract than a concrete item.

However, if it shouldn't be allowed, then V should give an error message when you try to create one.

[islonely]

How it works now is that an interface can't implement it's own method, but can have methods on the type itself. https://github.com/vlang/v/blob/master/doc/docs.md#interface-method-definitions

This is not allowed.

interface Dog {
    bark()
}

fn (dog Dog) bark() { ... }

This is allowed.

interface Dog {}

fn (dog Dog) bark() { ... }