vars() was only needed for the scoped verbs, which have been superseded
by the use of across() in an existing verb. See vignette("colwise") for
details.
This helper is intended to provide equivalent semantics to
select(). It is used for instance in scoped summarising and
mutating verbs (mutate_at() and summarise_at()).
Note that verbs accepting a vars() specification also accept a
numeric vector of positions or a character vector of column names.
vars(...)<tidy-select> Variables to include/exclude
in mutate/summarise. You can use same specifications as in select().
If missing, defaults to all non-grouping variables.
all_vars() and any_vars() for other quoting
functions that you can use with scoped verbs.