parseAsmOutputItem

fn parseAsmOutputItem(p: *Parse) !?Node.Index {
    _ = p.eatToken(.l_bracket) orelse return null;
    const identifier = try p.expectToken(.identifier);
    _ = try p.expectToken(.r_bracket);
    _ = try p.expectToken(.string_literal);
    _ = try p.expectToken(.l_paren);
    const type_expr: Node.OptionalIndex = blk: {
        if (p.eatToken(.arrow)) |_| {
            break :blk .fromOptional(try p.expectTypeExpr());
        } else {
            _ = try p.expectToken(.identifier);
            break :blk .none;
        }
    };
    const rparen = try p.expectToken(.r_paren);
    return try p.addNode(.{
        .tag = .asm_output,
        .main_token = identifier,
        .data = .{ .opt_node_and_token = .{
            type_expr,
            rparen,
        } },
    });
}