cgen error for program using $for variant in i.variants { in a .str() method of a sumtype

[spytheman]

V doctor:

V full version: V 0.4.8 aeaf607.273adcc
OS: linux, Ubuntu 20.04.6 LTS
Processor: 4 cpus, 64bit, little endian, Intel(R) Core(TM) i3-3225 CPU @ 3.30GHz

getwd: /home/delian/code/v/qbe
vexe: /home/delian/code/v/v
vexe mtime: 2024-11-27 17:05:43

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

env VFLAGS: "-skip-unused"

Git version: git version 2.46.0
Git vroot status: weekly.2024.48-13-g273adcc3
.git/config present: true

CC version: cc (Ubuntu 10.5.0-1ubuntu1~20.04) 10.5.0
emcc version: N/A
thirdparty/tcc status: thirdparty-linux-amd64 0134e9b9

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

struct Add { x f32 y f32}
struct Sub { x f32 y f32}

fn (o Add) str() string { return 'Add ${o.x} ${o.y}' }
fn (o Sub) str() string { return 'Sub ${o.x} ${o.y}' }

pub type Instr = Add | Sub

pub fn (i Instr) str() string {
    $for variant in i.variants {
        if i is variant {
            return i.str()
        }
    }
    return ''
}							

fn main() {
	i1 := Instr(Add{1,2})
	println(i1)
	i2 := Instr(Sub{3,4})
	println(i2)
}

What did you expect to see?

a compiled program, with -skip-unused

What did you see instead?

================== C compilation error (from tcc): ==============
cc: /tmp/v_1000/a.01JDQC0JRVTZ1RR7M5J6AJ5V3W.tmp.c:5682: warning: implicit declaration of function 'main__Add_str'
cc: /tmp/v_1000/a.01JDQC0JRVTZ1RR7M5J6AJ5V3W.tmp.c:5682: error: cannot convert 'int' to 'struct string'
=================================================================
(You can pass `-cg`, or `-show-c-output` as well, to print all the C error messages).

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_0.6-21434}

[spytheman]

Note, that using @[markused] for each .str() method of the variants makes it compile with -skip-unused . So does not using -skip-unused at all.

[spytheman]

Another variation also errors at cgen (with autogenerated .str() methods for the variants):

struct Add { x f32 y f32}
struct Sub { x f32 y f32}

pub type Instr = Add | Sub

pub fn (i Instr) str() string {
    $for variant in i.variants {
        if i is variant {
            return i.str()
        }
    }
    return ''
}

fn main() {
        i1 := Instr(Add{1,2})
        println(i1)
        i2 := Instr(Sub{3,4})
        println(i2)
}

[spytheman]

Not sure why it did not close, but it does work after 2325b1b (#22994).