Confusing errors when printing a C struct

[jrfondren]

Describe the bug

v generates C code with _str functions that fail with "incomplete type" errors if a C struct is printed, and this isn't communicated well by v's error message.

Reproduction Steps

Try to compile this example program

struct C.example { }

fn main() {
        println(C.example{})
}

Expected Behavior

An error from v about not being able to print the struct.

Current Behavior

$ v -o example example.c.v
tcc.exe: arm64-gen.c:351: arm64_ldrs: Assertion `0' failed.
...
==================
(Use `v -cg` to print the entire error message)

builder error: 
==================
C error. This should never happen.

$ v example.c.v && LANG=C gcc example.c
...
example.c:2050:50: error: parameter 1 ('it') has incomplete type
 2050 | static string struct__example_str(struct example it) { return indent_struct__example_str(it, 0);}
...

Possible Solution

No response

Additional Information/Context

This error can reasonably happen when println() is used in placeholder code to ensure a variable is used:

#flag -lwayland-client
#include <wayland-client.h>

struct C.wl_display { }
fn C.wl_display_connect(&char) &C.wl_display

fn main() {
        mut wl := C.wl_display_connect(unsafe { nil })
        println('this works so far')
}

This prints a warning as the variable wl is used. I added a println(wl) to silence that for the moment and the strange error had me thinking I had some worse problem.

V version

V 0.4.2 5c37c31

Environment details (OS name and version, etc.)

OS: linux
Processor: 4 cpus, 64bit, little endian, aarch64
CC version: cc (GCC) 12.1.0
thirdparty/tcc status: thirdparty-linux-aarch64 dd547903

Note

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[ArtemkaKun]

You have arm64 processor. Do you have PC or you run it from Termux?

[jrfondren]

I have an ARM Linux laptop, from pine64.com. V runs out of the box on the provided Arch image.

[Delta456]

On x84-64

==================
/tmp/v_1000/file.13233380909043727445.tmp.c:12655: error: too many initializers
...
==================
(Use `v -cg` to print the entire error message)

builder error: 
==================
C error. This should never happen.

This is a compiler bug, please report it using `v bug file.v`.

https://github.com/vlang/v/issues/new/choose

You can also use #help on Discord: https://discord.gg/vlang

[felipensp]

Can you try again with a newer version?