Add documentation topic for tidyselect arguments (#365)

NEWS.md

@@ -4,6 +4,13 @@
 
 * `eval_select()` now fails when data has duplicate names and a character vector is provided as input (#346).
 
+* New `args_tidy_select` documentation topic. Use the following tags to document tidyselect arguments in your functions:
+
+  ```r
+  #' @param ... <[`tidy-select`][tidyselect::args_tidy_select]> *doc*
+  #' @param sel <[`tidy-select`][tidyselect::args_tidy_select]> *doc*
+  ```
+
 * `eval_select()` and `eval_relocate()` gain a new `error_arg` argument that can be specified to throw a better error message when `allow_empty = FALSE`  or `allow_rename = FALSE` (@olivroy, #327).
 
 * `vars_pull()` now also warns when using `.data` (#335). Please

R/doc-tidy-selection.R

@@ -0,0 +1,35 @@
+#' Argument type: tidy-select
+#'
+#' @description
+#' This page describes the `<tidy-select>` argument modifier which indicates
+#' the argument supports **tidy selections**. Tidy selection provides a concise
+#' dialect of R for selecting variables based on their names or properties.
+#'
+#' Tidy selection is a variant of tidy evaluation. This means that inside
+#' functions tidy-select arguments require special attention, as described in
+#' the *Indirection* section below. If you've never heard of tidy evaluation
+#' before, start with `vignette("programming")`.
+#'
+#'
+#' # Overview of selection features
+#'
+#' ```{r, child = "man/rmd/overview.Rmd"}
+#' ```
+#'
+#'
+#' # Indirection
+#'
+#' There are two main cases:
+#'
+#' *   If you want the user to supply a character vector of column names, use `all_of()`
+#'     or `any_of()`, depending on whether or not you want unknown variable
+#'     names to cause an error, e.g. `select(df, all_of(vars))`,
+#'     `select(df, !any_of(vars))`.
+#'
+#' *   If you want the user to supply a tidyselect specification in
+#'     a function argument, embrace the function argument, e.g.
+#'     `select(df, {{ vars }})`.
+#'
+#' @keywords internal
+#' @name args_tidy_select
+NULL

man/rmd/overview.Rmd

@@ -1,26 +1,35 @@
+Tidyverse selections implement a dialect of R where operators make
+it easy to select variables:
 
-tidyselect implements a DSL for selecting variables. It provides helpers
-for selecting variables:
-
-- `var1:var10`: variables lying between `var1` on the left and `var10` on the right.
-* [`starts_with("a")`][tidyselect::starts_with]: names that start with `"a"`.
-* [`ends_with("z")`][tidyselect::ends_with]: names that end with `"z"`.
-* [`contains("b")`][tidyselect::contains]: names that contain `"b"`.
-* [`matches("x.y")`][tidyselect::matches]: names that match regular expression `x.y`.
-* [`num_range(x, 1:4)`][tidyselect::num_range]: names following the pattern, `x1`, `x2`, ..., `x4`.
-* [`all_of(vars)`][tidyselect::all_of]/[`any_of(vars)`][tidyselect::any_of()]: 
-  matches names stored in the character vector `vars`. `all_of(vars)` will
-  error if the variables aren't present; `any_of(var)` will match just the
-  variables that exist.
-* [`everything()`][tidyselect::everything]: all variables.
-* [`last_col()`][tidyselect::last_col]: furthest column on the right.
-* [`where(is.numeric)`][tidyselect::where]: all variables where
-  `is.numeric()` returns `TRUE`.
-
-As well as operators for combining those selections:
-
-- `!selection`: only variables that don't match `selection`.
-- `selection1 & selection2`: only variables included in both `selection1` and `selection2`.
-- `selection1 | selection2`: all variables that match either `selection1` or `selection2`.
-
-When writing code inside packages you can substitute `"var"` for `var` to avoid `R CMD check` notes. 
+- `:` for selecting a range of consecutive variables.
+- `!` for taking the complement of a set of variables.
+- `&` and `|` for selecting the intersection or the union of two
+  sets of variables.
+- `c()` for combining selections.
+
+In addition, you can use __selection helpers__. Some helpers select specific
+columns:
+
+* [`everything()`][tidyselect::everything]: Matches all variables.
+* [`last_col()`][tidyselect::last_col]: Select last variable, possibly with an offset.
+
+Other helpers select variables by matching patterns in their names:
+
+* [`starts_with()`][tidyselect::starts_with]: Starts with a prefix.
+* [`ends_with()`][tidyselect::ends_with()]: Ends with a suffix.
+* [`contains()`][tidyselect::contains()]: Contains a literal string.
+* [`matches()`][tidyselect::matches()]: Matches a regular expression.
+* [`num_range()`][tidyselect::num_range()]: Matches a numerical range like x01, x02, x03.
+
+Or from external variables stored in a character vector:
+
+* [`all_of()`][tidyselect::all_of()]: Matches variable names in a character vector. All
+  names must be present, otherwise an out-of-bounds error is
+  thrown.
+* [`any_of()`][tidyselect::any_of()]: Same as `all_of()`, except that no error is thrown
+  for names that don't exist.
+
+Or using a predicate function:
+
+* [`where()`][tidyselect::where()]: Applies a function to all variables and selects those
+  for which the function returns `TRUE`.