Bug with 0-col data frames in vec_order_info() affecting vec_rank()

[DavisVaughan]

From tidyverse/dplyr#6899

> vctrs::vec_rank(data.frame(row.names = 1:10))
 [1] 2037149796 1075052658          0          0          0  470093824 2037149796 1075052658          0          0

Probably from

> vctrs:::vec_order_info(data.frame(row.names = 1:10))
[[1]]
 [1]  1  2  3  4  5  6  7  8  9 10

[[2]]
integer(0)

[[3]]
[1] 0

Where the 2nd slot is supposed to hold the group sizes?

I think the 2nd slot should just hold a 10? i.e. all rows are the same? Not 100% sure but seems consistent with our treatment of 0 col data frames in vec_equal() and elsewhere

[DavisVaughan]

Probably need to do something like "push group size equivalent to data frame size" in this 0 column special case here

vctrs/src/order.c

Lines 3971 to 3975 in e88a3e2

	// Special case no columns
	if (n_cols == 0) {
	init_order(p_order);
	return;
	}

i.e. groups_size_maybe_push(size, p_group_infos);