desc() checks the number of arguments.

[eutwt]

Currently if you pass two arguments to desc as in desc(a, b), it is converted to a - b by dt_squash_call. This PR adds a check to error if more than one argument is provided.

A similar issue was fixed in dplyr: tidyverse/dplyr#5929

Before this PR:

library(dplyr, warn.conflicts = FALSE)
library(dtplyr, warn.conflicts = FALSE)

dt <- lazy_dt(data.frame(a = rep(1:2, each = 2), b = 1:4))

dt %>% 
  arrange(desc(a, b))
#> Source: local data table [4 x 2]
#> Call:   `_DT1`[order(a - b)]
#> 
#>       a     b
#>   <int> <int>
#> 1     2     4
#> 2     1     2
#> 3     2     3
#> 4     1     1
#> 
#> # Use as.data.table()/as.data.frame()/as_tibble() to access results

^{Created on 2021-08-22 by the reprex package (v2.0.1)}

After this PR:

library(dplyr, warn.conflicts = FALSE)
library(dtplyr, warn.conflicts = FALSE)

dt <- lazy_dt(data.frame(a = rep(1:2, each = 2), b = 1:4))

dt %>% 
  arrange(desc(a, b))
#> Error: `desc()` expects exactly one argument.

^{Created on 2021-08-22 by the reprex package (v2.0.1)}

[hadley]

Looks good — can you please add a bullet to the top of NEWS.md? It should briefly describe the change and end with (@yourname, #issuenumber).

[eutwt]

This is fixing a bug in a feature which has not yet been in any release, and the feature itself already has a bullet. Should I still add a new one?

[eutwt]

I went ahead and added one, but can also revert the commit, either way. Not sure what the convention is.

[hadley]

Oh, support for desc() is new in this release? In that case, no bullet is necessary. Sorry!

[eutwt]

Yep, new this release. Reverted the news commit

[hadley]

Thanks!