Use .sql$foo(x, y) to make it clear that you're calling the SQL
foo() function, not the R foo() function. This also makes it easier to
reduce R CMD check notes in packages; just import .sql from dbplyr with
e.g. @importFrom dbplyr .sql.
Note that .sql itself does nothing and is just NULL; it is automatically
removed when dbplyr translates your R code to SQL.
Examples
library(dplyr, warn.conflicts = FALSE)
db <- lazy_frame(x = 1, y = 2)
db |> mutate(z = .sql$CUMULATIVE_SUM(x, 1))
#> <SQL>
#> SELECT "df".*, CUMULATIVE_SUM("x", 1.0) AS "z"
#> FROM "df"