new compiler: `json.decode(...)!` in `main` generates invalid C

[davlgd]

Describe the bug

With the new compiler, calling json.decode with ! in main generates C that does not compile. The old compiler handles it fine. (I know json is deprecated in favour of json2, but it is still in vlib.)

Reproduction Steps

import json

struct Person {
	name string
}

fn main() {
	p := json.decode(Person, '{"name":"a"}')!
	println(p.name)
}

v -new-compiler run main.v

Expected Behavior

a

Current Behavior

The C compiler fails:

error: use of undeclared identifier 'Optional_main__Person'
error: use of undeclared identifier '__or_opt_0'

V version

V 0.5.2 4af2cb4 (-new-compiler). The old compiler I compare with is what -old-compiler runs, the V 0.5.2 release (7647ce1).

Environment details (OS name and version, etc.)

macOS 26.6, arm64, Apple clang 21

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