expectContainerField

fn expectContainerField(p: *Parse) !Node.Index {
    _ = p.eatToken(.keyword_comptime);
    const main_token = p.tok_i;
    _ = p.eatTokens(&.{ .identifier, .colon });
    const type_expr = try p.expectTypeExpr();
    const align_expr = try p.parseByteAlign();
    const value_expr = if (p.eatToken(.equal) == null) null else try p.expectExpr();

    if (align_expr == null) {
        return p.addNode(.{
            .tag = .container_field_init,
            .main_token = main_token,
            .data = .{ .node_and_opt_node = .{
                type_expr,
                .fromOptional(value_expr),
            } },
        });
    } else if (value_expr == null) {
        return p.addNode(.{
            .tag = .container_field_align,
            .main_token = main_token,
            .data = .{ .node_and_node = .{
                type_expr,
                align_expr.?,
            } },
        });
    } else {
        return p.addNode(.{
            .tag = .container_field,
            .main_token = main_token,
            .data = .{ .node_and_extra = .{
                type_expr,
                try p.addExtra(Node.ContainerField{
                    .align_expr = align_expr.?,
                    .value_expr = value_expr.?,
                }),
            } },
        });
    }
}