cgen error with gcc, but not with tcc, for a program, printing an incomplete typedef C struct

[spytheman]

V doctor:

V full version: V 0.4.4 a36c693
OS: linux, Ubuntu 20.04.6 LTS
Processor: 4 cpus, 64bit, little endian, Intel(R) Core(TM) i3-3225 CPU @ 3.30GHz

getwd: /space/v/oo
vexe: /space/v/oo/v
vexe mtime: 2024-03-18 09:30:45

vroot: OK, value: /space/v/oo
VMODULES: OK, value: /home/delian/.vmodules
VTMP: OK, value: /tmp/v_1000

Git version: git version 2.42.0
Git vroot status: weekly.2024.12
.git/config present: true

CC version: cc (Ubuntu 10.5.0-1ubuntu1~20.04) 10.5.0
thirdparty/tcc status: thirdparty-linux-amd64 40e5cbb5

What did you do?
v -g -o vdbg cmd/v && vdbg y.v

#include <X11/Xlib.h>

@[typedef]
pub struct C.Display {}
// fn (d &C.Display) str() string { return 'C.Display{}' }

fn main() {
    x := unsafe { &C.Display( malloc(1024) ) }
    println(x)
}

What did you expect to see?

A compiled program, but with gcc. It does compile with tcc.

What did you see instead?
With tcc, which is OK:

&C.Display{}

With gcc, there is an error:

#0 11:35:51 ᛋ master /v/oo❱v -cc gcc run y.v
==================
/tmp/v_1000/y.01HS8ENRJ7YKPB6BXD22QC67E8.tmp.c:2129:35: error: parameter 1 (‘it’) has incomplete type
 2129 | static string Display_str(Display it) { return indent_Display_str(it, 0);}
      |                           ~~~~~~~~^~
/tmp/v_1000/y.01HS8ENRJ7YKPB6BXD22QC67E8.tmp.c: In function ‘Display_str’:
/tmp/v_1000/y.01HS8ENRJ7YKPB6BXD22QC67E8.tmp.c:2129:67: error: type of formal parameter 1 is incomplete
 2129 | static string Display_str(Display it) { return indent_Display_str(it, 0);}
      |                                                                   ^~
/tmp/v_1000/y.01HS8ENRJ7YKPB6BXD22QC67E8.tmp.c: At top level:
/tmp/v_1000/y.01HS8ENRJ7YKPB6BXD22QC67E8.tmp.c:2135:42: error: parameter 1 (‘it’) has incomplete type
 2135 | static string indent_Display_str(Display it, int indent_count) {
      |                                  ~~~~~~~~^~
/tmp/v_1000/y.01HS8ENRJ7YKPB6BXD22QC67E8.tmp.c: In function ‘main__main’:
...
==================
(Use `v -cg` to print the entire error message)

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[spytheman]

A possible solution is to change the autogenerated C struct str() method from:
static string Display_str(Display it) { return indent_Display_str(it, 0);}
to:
static string Display_str(Display *it) { return indent_Display_str(it, 0);}

i.e. pass Display to it as a pointer, which is valid, even for incomplete C struct types.

[spytheman]

Note that vlib/clipboard/x11/clipboard.c.v line 23, has a workaround for that bug (in c29b64e), and without it, stuff like this, does not work with clang or gcc, since V structs in wrappers, often contain C struct fields, and the generation for auto string methods is recursive:

import clipboard
c := clipboard.new()
println(c)