cgen: Function types with fixed-length arrays sometimes not translating properly in submodules

[sukus21]

Describe the bug

When declaring function types in submodules, C code generation sometimes doesn't work out properly, when trying to declare the type in the V type definitions section. I cannot get this to happen in the main module, but is easily reproducible in a submodule.

Funnily enough, if I remove the result from the return types of the functions, I get a different C-compiler error.

Reproduction Steps

// File: ./main.v

module main

import not_main

fn main() {
	not_main.function()!
}

// File: ./not_main/faulty.v

module not_main

pub fn function() ! {
	callback_consumer(callback_fn)!
}

type CallbackType = fn() ![4]u8

fn callback_consumer(callback CallbackType) ! {
	callback()!
}

fn callback_fn() ![4]u8 {
	return [u8(1), 2, 3, 255]!
}

Bonus bug: If you remove all the result indicators, you get a whole different set of errors.

Expected Behavior

I expect the program to compile

Current Behavior

Output when compiling WITH result types:

v . -show-c-output
======== Output of the C Compiler (/home/sukus/v/thirdparty/tcc/tcc.exe) ========
/tmp/v_1000/bruh.01K9K36M83HT1EHS0XCBXYC524.tmp.c:660: error: identifier expected
=================================================================================
======== Output of the C Compiler (cc) ========
/tmp/v_1000/bruh.01K9K36M83HT1EHS0XCBXYC524.tmp.c:660:38: error: expected declaration specifiers or ‘...’ before ‘*’ token
  660 | typedef _v__result_Array_fixed_u8_4 (*not_main__CallbackType)();
      |                                      ^
===============================================

Output when compiling WITHOUT result types:

v . -show-c-output
======== Output of the C Compiler (/home/sukus/v/thirdparty/tcc/tcc.exe) ========
/tmp/v_1000/bruh.01K9K3AKQD81KSBV7NJFRQBBJN.tmp.c:4589: error: lvalue expected
=================================================================================
======== Output of the C Compiler (cc) ========
/tmp/v_1000/bruh.01K9K3AKQD81KSBV7NJFRQBBJN.tmp.c:896:60: error: ‘callback’ declared as function returning an array
  896 | VV_LOC void not_main__callback_consumer(Array_fixed_u8_4 (*callback)());
      |                                                            ^~~~~~~~
/tmp/v_1000/bruh.01K9K3AKQD81KSBV7NJFRQBBJN.tmp.c:4588:60: error: ‘callback’ declared as function returning an array
 4588 | VV_LOC void not_main__callback_consumer(Array_fixed_u8_4 (*callback)(void)) {
      |                                                            ^~~~~~~~
/tmp/v_1000/bruh.01K9K3AKQD81KSBV7NJFRQBBJN.tmp.c: In function ‘not_main__callback_consumer’:
/tmp/v_1000/bruh.01K9K3AKQD81KSBV7NJFRQBBJN.tmp.c:4589:19: error: request for member ‘ret_arr’ in something not a structure or union
 4589 |         callback().ret_arr;
      |                   ^
===============================================

Possible Solution

I experimented a bit and found a potential solution to the issue when compiling WITH result types. However, I don't know if this is the correct solution, and have not looked that far into how the V -> C compilation pipeline works, so it might be a long shot: https://github.com/sukus21/v/commit/3f1c6fb9f767ad604f086f9a4b234554a1443b51

Additional Information/Context

No response

V version

V 0.4.12 af62364

Environment details (OS name and version, etc.)

|V full version      |V 0.4.12 af62364a29312a09f76aa9ad3f734790e534c162
|:-------------------|:-------------------
|OS                  |linux, Debian GNU/Linux 12 (bookworm) (VM)
|Processor           |2 cpus, 64bit, little endian, Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GHz
|Memory              |1.09GB/2.02GB
|                    |
|V executable        |/home/admin/v/v
|V last modified time|2025-11-09 00:25:30
|                    |
|V home dir          |OK, value: /home/admin/v
|VMODULES            |OK, value: .vmodules
|VTMP                |OK, value: /tmp/v_0
|Current working dir |OK, value: /home/admin/playground
|                    |
|Git version         |git version 2.39.5
|V git status        |N/A
|.git/config present |true
|                    |
|cc version          |cc (Debian 12.2.0-14+deb12u1) 12.2.0
|gcc version         |gcc (Debian 12.2.0-14+deb12u1) 12.2.0
|clang version       |Debian clang version 14.0.6
|tcc version         |tcc version 0.9.28rc 2025-02-13 HEAD@f8bd136d (x86_64 Linux)
|tcc git status      |Error: fatal: detected dubious ownership in repository at '/home/admin/v/thirdparty/tcc'
To add an exception for this directory, call:

	git config --global --add safe.directory /home/admin/v/thirdparty/tcc
 Error: fatal: detected dubious ownership in repository at '/home/admin/v/thirdparty/tcc'
To add an exception for this directory, call:

	git config --global --add safe.directory /home/admin/v/thirdparty/tcc

|emcc version        |N/A
|glibc version       |ldd (Debian GLIBC 2.36-9+deb12u10) 2.36

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[dy-tea]

Yeah your provided fix appears to work for the error version. I will look into the non-error version.