cgen: C nested structs do not work

[dy-tea]

Describe the bug

C structs that contain other structs directly within them with a variable name are not usable in V.

Reproduction Steps

Create a new v project with the following files:

// test.h
#ifndef TEST_H
#define TEST_H

typedef struct {
      struct {
               int x;
       } inner;
} outer;

#endif

// main.v
#flag -I @VMODROOT
#include "test.h"

struct C.outer {
	inner struct {
		x int
	}
}

struct Outer {
	inner struct {
		val int
	}
}

fn main() {
	_ = Outer{}
	_ = C.outer{}
}

Expected Behavior

Should compile.
You are not able to set x at all, even during instantiation of the struct, it should be either set to 0 or produce an error that it is unset (once supported).

Current Behavior

The code will compile with the _ = C.outer{} line removed but will not when it is present, in that case it will output given v -cg -show-c-output .:

======== Output of the C Compiler (/home/dylan/Repos/v/thirdparty/tcc/tcc.exe) ========
/tmp/v_1000/vbug.01JH6NX3SPVX8Z0C171VAPM0PE.tmp.c:2027: error: initialization of incomplete type
=======================================================================================
======== Output of the C Compiler (cc) ========
/tmp/v_1000/vbug.01JH6NX3SPVX8Z0C171VAPM0PE.tmp.c: In function ‘main__main’:
/tmp/v_1000/vbug.01JH6NX3SPVX8Z0C171VAPM0PE.tmp.c:2027:17: error: variable ‘_’ has initializer but incomplete type
 2027 |         {struct outer _ = ((struct outer){.inner = (main___VAnonStruct1){
      |                 ^~~~~
/tmp/v_1000/vbug.01JH6NX3SPVX8Z0C171VAPM0PE.tmp.c:2027:44: error: ‘struct outer’ has no member named ‘inner’
 2027 |         {struct outer _ = ((struct outer){.inner = (main___VAnonStruct1){
      |                                            ^~~~~
/tmp/v_1000/vbug.01JH6NX3SPVX8Z0C171VAPM0PE.tmp.c:2027:52: warning: excess elements in struct initializer
 2027 |         {struct outer _ = ((struct outer){.inner = (main___VAnonStruct1){
      |                                                    ^
/tmp/v_1000/vbug.01JH6NX3SPVX8Z0C171VAPM0PE.tmp.c:2027:52: note: (near initialization for ‘(anonymous)’)
/tmp/v_1000/vbug.01JH6NX3SPVX8Z0C171VAPM0PE.tmp.c:2027:42: error: invalid use of undefined type ‘struct outer’
 2027 |         {struct outer _ = ((struct outer){.inner = (main___VAnonStruct1){
      |                                          ^
/tmp/v_1000/vbug.01JH6NX3SPVX8Z0C171VAPM0PE.tmp.c:2027:23: error: storage size of ‘_’ isn’t known
 2027 |         {struct outer _ = ((struct outer){.inner = (main___VAnonStruct1){
      |                       ^
===============================================

Possible Solution

No response

Additional Information/Context

Working on my project https://github.com/dy-tea/vompositor, I noticed that nested structs were generating invalid eq functions during cgen. I have not been able to reproduce this issue outside that codebase so far but noticed this issue while attempting to reproduce it.

V version

V 0.4.9 ba9d358

Environment details (OS name and version, etc.)

|V full version      |V 0.4.9 de3b184.ba9d358
|:-------------------|:-------------------
|OS                  |linux, "CachyOS"
|Processor           |12 cpus, 64bit, little endian, 13th Gen Intel(R) Core(TM) i5-1335U
|Memory              |3.79GB/15.31GB
|                    |
|V executable        |/home/dylan/Repos/v/v
|V last modified time|2025-01-09 22:52:24
|                    |
|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/Repos/vbug
|                    |
|Git version         |git version 2.47.1
|V git status        |weekly.2025.1-25-gba9d358d
|.git/config present |true
|                    |
|cc version          |cc (GCC) 14.2.1 20240910
|gcc version         |gcc (GCC) 14.2.1 20240910
|clang version       |clang version 18.1.8
|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 (GNU libc) 2.40

Note

You can use the 👍 reaction to increase the issue's priority for developers.

Please note that only the 👍 reaction to the issue itself counts as a vote.
Other reactions and those to comments will not be taken into account.

_{Huly®: V_0.6-21851}