C codegen: nested `or` blocks emit invalid C (`*(T*) _t.data = ;`) when outer call result is discarded

[quaesitor-scientiam]

V version

V 0.5.1 1510663 on Windows 11, MSVC backend (-cc msvc).

Description

When a function returning !T (T non-void) is called as a statement (return value discarded) with an or { ... } block whose tail expression is itself an or block on a !void call, the C generator emits an assignment with an empty right-hand side:

*(T*) _t.data = ;

MSVC rejects this with error C2059: syntax error: ';'.

Minimal reproduction

module main

struct Item {
	id int
}

fn get_item() !Item {
	return Item{id: 1}
}

fn do_void() ! {
	return error('boom')
}

fn main() {
	get_item() or {
		do_void() or {
			println('inner: ${err}')
		}
	}
}

Build:

v -cc msvc -keepc repro.v

Result:

repro.exe.tmp.c(8373): error C2059: syntax error: ';'
builder error: msvc error

Generated C (excerpt)

VV_LOC void main__main(void) {
    _result_main__Item _t1 = main__get_item();
    if (_t1.is_error) {
        IError err = _t1.err;
        _result_void _t2 = main__do_void();
        if (_t2.is_error) {
            IError err = _t2.err;
            builtin__println(...);
        ;
        }

        *(main__Item*) _t1.data = ;   // <-- invalid C, empty RHS
    }

 ;
}

The compiler appears to treat the inner or block (a !void expression used as a statement) as a value expression yielding Item, then emits the standard "store the or-block's value into _t1.data" assignment with no RHS because there is no value.

Expected behavior

Either:

1. No assignment should be emitted at all, since the outer call's result is discarded (the call is used as a statement); the or block exists only for side-effecting error handling, or
2. A V-level error/warning should reject the program if codegen cannot lower it.

Workarounds

Any of these compile and behave correctly:

• Use the if x := call() { } else { } form on the outer call instead of or { ... }.
• Extract the inner do_void() or { ... } into a helper function so the outer or block does not end with a nested or expression.
• Add a non-or trailing statement inside the outer or block (e.g. return, continue, or another non-or call).

Notes

• Reproduces on all three C backends I tested (Windows 11):
  • -cc msvc → error C2059: syntax error: ';'
  • -cc tcc → error: identifier expected
  • -cc gcc → error: expected expression before ';' token
• Triggered specifically by nesting — a single-level or { do_void() or { ... } } is the smallest shape that hits it. A non-or tail in the outer block (e.g. or { do_void() or { ... }; return }) avoids the bug.

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