across() doesn't work within group_by()

[Alternikaner]

The behaviour reported with regards to tidyselect-type variables in #518 seems to persist for masking types. (Likely related: #525; #534)

library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union
con <- DBI::dbConnect(RSQLite::SQLite(), dbname = ":memory:")

copy_to(con, nycflights13::flights, "flights",
        temporary = FALSE, 
        indexes = list(
          c("year", "month", "day"), 
          "carrier", 
          "tailnum",
          "dest"
        )
)

flights_db <- tbl(con, "flights")

group_cols <- c("year", "month") 

# Desired result
nycflights13::flights %>%
 group_by(across(all_of(group_cols))) %>%
 summarise(NumFlights = n(), 
           MeanDist   = mean(distance)
          )
#> `summarise()` regrouping output by 'year' (override with `.groups` argument)
#> # A tibble: 12 x 4
#> # Groups:   year [1]
#>     year month NumFlights MeanDist
#>    <int> <int>      <int>    <dbl>
#>  1  2013     1      27004    1007.
#>  2  2013     2      24951    1001.
#>  3  2013     3      28834    1012.
#>  4  2013     4      28330    1039.
#>  5  2013     5      28796    1041.
#>  6  2013     6      28243    1057.
#>  7  2013     7      29425    1059.
#>  8  2013     8      29327    1062.
#>  9  2013     9      27574    1041.
#> 10  2013    10      28889    1039.
#> 11  2013    11      27268    1050.
#> 12  2013    12      28135    1065.

# Fails with db connection
flights_db %>%
 group_by(across(all_of(group_cols))) %>%
  summarise(NumFlights = n(), 
            MeanDist   = mean(distance)
           )
#> Error: Unsupported `.fns` for dbplyr::across()

[hadley]

Somewhat more minimal reprex:

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

df <- memdb_frame(x = 1:5, y = 1:5)
df %>% group_by(across(everything()))
#> Error: Unsupported `.fns` for dbplyr::across()

^{Created on 2021-01-21 by the reprex package (v0.3.0.9001)}