// `xx <pack>[i]` erased to a protocol-typed local.
//
// Erasing a single comptime-pack element to a protocol scalar routes through
// buildProtocolErasure. A pack index is a comptime rvalue (a pack has no
// runtime storage — `sources[i]` resolves to the call-site arg, which only
// gets storage when lowered as a value), so the erasure must heap-copy the
// materialized element rather than take its address.
//
// Regression (issue 0135): `xx sources[0]` used to lower the bare pack as a
// value and error with "pack 'sources' has no runtime value".

#import "modules/std.sx";

VL :: protocol(T: Type) { get :: () -> T; }
IntCell :: struct { v: i64; }
impl VL(i64) for IntCell { get :: (self: *IntCell) -> i64 => self.v; }

first :: (..sources: VL) -> i64 {
    x : VL(i64) = xx sources[0];   // erase element 0 to VL(i64)
    return x.get();
}

main :: () -> i32 {
    print("{}\n", first(IntCell.{ v = 7 }));                       // 7
    print("{}\n", first(IntCell.{ v = 42 }, IntCell.{ v = 99 }));  // 42 (element 0)
    0
}