cgen error, when calling a generic function in a $for v in dc.variants { if dc is v { block

[spytheman]

V version: V 0.4.9 d2b30df, press to see full `v doctor` output

V full version	V 0.4.9 f23ae9a.d2b30df
OS	linux, Ubuntu 20.04.6 LTS
Processor	4 cpus, 64bit, little endian, Intel(R) Core(TM) i3-3225 CPU @ 3.30GHz
Memory	1.77GB/15.05GB
V executable	/home/delian/code/v/v
V last modified time	2025-01-12 16:55:08
V home dir	OK, value: /home/delian/code/v
VMODULES	OK, value: /home/delian/.vmodules
VTMP	OK, value: /tmp/v_1000
Current working dir	OK, value: /home/delian/code/v
Git version	git version 2.47.1
V git status	weekly.2025.1-41-g89d405ec
.git/config present	true
cc version	cc (Ubuntu 10.5.0-1ubuntu1~20.04) 10.5.0
gcc version	gcc (Ubuntu 10.5.0-1ubuntu1~20.04) 10.5.0
clang version	clang version 10.0.0-4ubuntu1
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 (Ubuntu GLIBC 2.31-0ubuntu9.16) 2.31

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

pub type DesiredCapabilities = FireFox | Edge

struct FireFox {
	browser_name          string = 'firefox'
	accept_insecure_certs bool   = true
	moz_debugger_address  bool   = true
}

struct Edge {
	browser_name string = 'MicrosoftEdge'
}

fn struct_values[T](s T) map[string]string {
	mut res := map[string]string{}
	$if T is $struct {
		$for field in T.fields {
			res[field.name] = s.$(field.name).str()
		}
	}
	return res
}

fn useit(dc DesiredCapabilities) {
	$for v in dc.variants {
		if dc is v {
			$if v is $struct {
				result := struct_values(dc)
				dump(result)
			}
		}
	}
}

fn main() {
	useit(Edge{})	
}

What did you see?

================== C compilation error (from tcc): ==============
cc: /tmp/v_1000/xx.01JHF178SRTVZ4YE60ZY8B8XZ6.tmp.c:7178: error: cannot convert 'struct main__FireFox' to 'struct main__Edge'
=================================================================
(You can pass `-cg`, or `-show-c-output` as well, to print all the C error messages).

What did you expect to see?

a compiled program

Note: the generated C code around the error, looks like this:

        /* variant 0 */ {
            v.typ = 103;
            if ((dc)._typ == 103) {
                #if 1
                {
                    Map_string_string result = main__struct_values_T_main__Edge((*dc._main__FireFox));
                     _v_dump_expr_Map_string_string(_SLIT("xx.v"), 28, _SLIT("result"), result);
                }
                #endif
            }
        }

i.e. V chose to use the main__struct_values_T_main__Edge variant for the generic function, even though the value was of type main__FireFox .

Note

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[spytheman]

Using this:

fn useit[T](dc T) {
    $if T is $sumtype {
        $for v in T.variants {
            if dc is v {
                dump( struct_values(dc) )
            }
        }
    }
}

fn main() {
    useit(DesiredCapabilities(Edge{}))
}

it compiles fine

[spytheman]

[huly-for-github]

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