defined c functions do not warn if param is of name `interface`

[dy-tea]

Describe the bug

Compile the included code on linux, you will need wayland-client installed.

Reproduction Steps

#flag linux -I/usr/include
#flag linux -lwayland-client
#include <wayland-client-protocol.h>
#include <wayland-util.h>

pub struct C.wl_interface {
pub:
	name         &char
	version      int
	method_count int
	// methods &C.wl_message
	event_count int
	// events  &C.wl_message
}

pub struct C.wl_registry {}
fn C.wl_registry_bind(wl_registry &C.wl_registry, name u32, interface &C.wl_interface, version u32) voidptr

fn main() {
	registry := C.wl_registry{}
	bound := C.wl_registry_bind(&registry, u32(0), 0, u32(0))
}

Expected Behavior

Should recognize that the function wl_registry_bind takes 4 parameters.

Current Behavior

test.v:21:2: warning: unused variable: `bound`
   19 | fn main() {
   20 |     registry := C.wl_registry{}
   21 |     bound := C.wl_registry_bind(&registry, u32(0), 0, u32(0))
      |     ~~~~~
   22 | }
test.v:21:13: error: expected 5 arguments, but got 4
   19 | fn main() {
   20 |     registry := C.wl_registry{}
   21 |     bound := C.wl_registry_bind(&registry, u32(0), 0, u32(0))
      |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   22 | }
Details: have (&C.wl_registry, u32, int literal, u32)
         want (&C.wl_registry, u32, main.interface, &C.wl_interface, u32)

Possible Solution

We are getting an extra type called main.interface which is suspicious. Not sure what the cause is.

Additional Information/Context

No response

V version

V 0.4.12 b052af8

Environment details (OS name and version, etc.)

V full version	V 0.4.12 2a121047627b93badb74be8332ca2ea63a0bdb5d.b052af8
OS	linux, "CachyOS"
Processor	16 cpus, 64bit, little endian, AMD Ryzen 7 5700G with Radeon Graphics
Memory	5.41GB/13.55GB
V executable	/home/dylan/Repos/v/v
V last modified time	2025-11-27 15:34:00
V home dir	OK, value: /home/dylan/Repos/v
VMODULES	OK, value: /home/dylan/.vmodules
VTMP	OK, value: /tmp/v_1000
Current working dir	OK, value: /home/dylan
Git version	git version 2.52.0
V git status	weekly.2025.47-74-g64078cfb
.git/config present	true
cc version	cc (GCC) 15.2.1 20251112
gcc version	gcc (GCC) 15.2.1 20251112
clang version	clang version 21.1.6
tcc version	tcc version 0.9.28rc 2025-02-13 HEAD@f8bd136d (x86_64 Linux)
tcc git status	thirdparty-linux-amd64 696c1d84
emcc version	N/A
glibc version	ldd (GNU libc) 2.42

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[dy-tea]

Same happens if we explicitly pass the interface:

test.v:24:13: error: expected 5 arguments, but got 4
   22 |        c'name', 0, 1, 1
   23 |     }
   24 |     bound := C.wl_registry_bind(&registry, u32(0), &iface, u32(0))
      |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   25 | }
Details: have (&C.wl_registry, u32, &C.wl_interface, u32)
         want (&C.wl_registry, u32, main.interface, &C.wl_interface, u32)

[dy-tea]

Never mind, the actual issue is there is that the variable is called interface which is a keyword. There is no warning for this.