Finalize implementation

NEWS.md

@@ -1,5 +1,10 @@
 # tidyselect (development version)
 
+* `eval_select(allow_empty = FALSE)` gains a new argument to yield a better error
+  message in case of empty selection (@olivroy, #327)
+
+* `eval_select(allow_empty = FALSE)` now throws a classed error message (@olivroy, #347).
+
 # tidyselect 1.2.1
 
 * Performance improvements (#337, #338, #339, #341)

R/eval-relocate.R

@@ -89,6 +89,7 @@ eval_relocate <- function(expr,
     allow_empty = allow_empty,
     allow_predicates = allow_predicates,
     type = "relocate",
+    error_arg = NULL, # TODO need to know which to use. can `before_arg` or `after_arg` be passed here?
     error_call = error_call
   )
 
@@ -122,7 +123,8 @@ eval_relocate <- function(expr,
         env = env,
         error_call = error_call,
         allow_predicates = allow_predicates,
-        allow_rename = FALSE
+        allow_rename = FALSE,
+        error_arg = before_arg
       ),
       arg = before_arg,
       error_call = error_call
@@ -143,7 +145,8 @@ eval_relocate <- function(expr,
         env = env,
         error_call = error_call,
         allow_predicates = allow_predicates,
-        allow_rename = FALSE
+        allow_rename = FALSE,
+        error_arg = after_arg
       ),
       arg = after_arg,
       error_call = error_call

R/eval-select.R

@@ -43,7 +43,8 @@
 #'   use predicates (i.e. in `where()`). If `FALSE`, will error if `expr` uses a
 #'   predicate. Will automatically be set to `FALSE` if `data` does not
 #'   support predicates (as determined by [tidyselect_data_has_predicates()]).
-#' @param error_arg Argument name to include in error message.
+#' @param error_arg Argument name to include in error message if `allow_empty = FALSE`.
+#'   Will give a better error message if the selection ends up empty.
 #' @inheritParams rlang::args_dots_empty
 #'
 #' @return A named vector of numeric locations, one for each of the
@@ -104,6 +105,11 @@
 #' # Note that the trick above works because `expr({{ arg }})` is the
 #' # same as `enquo(arg)`.
 #'
+#' # give a better error message if you don't want empty selection
+#' select_not_empty <- function(x, cols) {
+#'   eval_select(expr = enquo(cols), data = x, allow_empty = FALSE, error_arg = "cols")
+#' }
+#' try(select_not_empty(mtcars, cols = starts_with("vs2")))
 #'
 #' # The evaluators return a named vector of locations. Here are
 #' # examples of using these location vectors to implement `select()`

R/eval-walk.R

@@ -131,7 +131,19 @@ ensure_named <- function(pos,
 
 check_empty <- function(x, allow_empty = TRUE, error_arg = NULL, call = caller_env()) {
   if (!allow_empty && length(x) == 0) {
-    cli::cli_abort("Must select at least one item.", call = call)
+    if (is.null(error_arg)) {
+      cli::cli_abort(
+        "Must select at least one item.",
+        call = call,
+        class = "tidyselect:::error_disallowed_empty"
+      )
+    } else {
+      cli::cli_abort(
+        "{.or {.arg {error_arg}}} must select at least one column.",
+        call = call,
+        class = "tidyselect:::error_disallowed_empty"
+        )
+    }
   }
 }
 

R/utils.R

@@ -8,6 +8,7 @@ select_loc <- function(x,
                        allow_rename = TRUE,
                        allow_empty = TRUE,
                        allow_predicates = TRUE,
+                       error_arg = NULL,
                        error_call = current_env()) {
   check_dots_empty()
 
@@ -21,6 +22,7 @@ select_loc <- function(x,
     allow_rename = allow_rename,
     allow_empty = allow_empty,
     allow_predicates = allow_predicates,
+    error_arg = error_arg,
     error_call = error_call
   )
 }

tests/testthat/_snaps/eval-relocate.md

@@ -84,19 +84,19 @@
     Code
       (expect_error(relocate_loc(x, allow_empty = FALSE)))
     Output
-      <error/rlang_error>
+      <error/tidyselect:::error_disallowed_empty>
       Error in `relocate_loc()`:
       ! Must select at least one item.
     Code
       (expect_error(relocate_loc(mtcars, integer(), allow_empty = FALSE)))
     Output
-      <error/rlang_error>
+      <error/tidyselect:::error_disallowed_empty>
       Error in `relocate_loc()`:
       ! Must select at least one item.
     Code
       (expect_error(relocate_loc(mtcars, starts_with("z"), allow_empty = FALSE)))
     Output
-      <error/rlang_error>
+      <error/tidyselect:::error_disallowed_empty>
       Error in `relocate_loc()`:
       ! Must select at least one item.
 

tests/testthat/_snaps/eval-select.md

@@ -66,6 +66,24 @@
       Error in `select_loc()`:
       ! Must select at least one item.
 
+# can forbid empty selections with informative error
+
+    Code
+      select_loc(mtcars, allow_empty = FALSE, error_arg = "cols")
+    Condition
+      Error in `select_loc()`:
+      ! `cols` must select at least one column.
+    Code
+      select_loc(mtcars, integer(), allow_empty = FALSE, error_arg = "x")
+    Condition
+      Error in `select_loc()`:
+      ! `x` must select at least one column.
+    Code
+      select_loc(mtcars, starts_with("z"), allow_empty = FALSE, error_arg = "y")
+    Condition
+      Error in `select_loc()`:
+      ! `y` must select at least one column.
+
 # eval_select() errors mention correct calls
 
     Code

tests/testthat/test-eval-select.R

@@ -105,6 +105,14 @@ test_that("can forbid empty selections", {
   })
 })
 
+test_that("can forbid empty selections with informative error", {
+  expect_snapshot(error = TRUE, {
+    select_loc(mtcars, allow_empty = FALSE,  error_arg = "cols")
+    select_loc(mtcars, integer(), allow_empty = FALSE, error_arg = "x")
+    select_loc(mtcars, starts_with("z"), allow_empty = FALSE, error_arg = "y")
+  })
+})
+
 test_that("eval_select() errors mention correct calls", {
   f <- function() stop("foo")
   expect_snapshot((expect_error(select_loc(mtcars, f()))))