deprecate rpart_train() (#1048)

NEWS.md

@@ -1,5 +1,7 @@
 # parsnip (development version)
 
+* `rpart_train()` has been deprecated in favor of using `decision_tree()` with the `"rpart"` engine or `rpart::rpart()` directly (#1044).
+
 * Fixed bug in fitting some model types with the `"spark"` engine (#1045).
 
 * Fixed issues in metadata for the `"brulee"` engine where several arguments were mistakenly protected. (#1050, #1054)

R/decision_tree.R

@@ -138,9 +138,12 @@ check_args.decision_tree <- function(object) {
 
 #' Decision trees via rpart
 #'
-#' `rpart_train` is a wrapper for `rpart()` tree-based models
+#' @description
+#' `rpart_train()` is a wrapper for `rpart()` tree-based models
 #'  where all of the model arguments are in the main function.
 #'
+#'  The function is now deprecated, as parsnip uses `rpart::rpart()` directly.
+#'
 #' @param formula A model formula.
 #' @param data A data frame.
 #' @param cp A non-negative number for complexity parameter. Any split
@@ -166,6 +169,12 @@ check_args.decision_tree <- function(object) {
 #' @export
 rpart_train <-
   function(formula, data, weights = NULL, cp = 0.01, minsplit = 20, maxdepth = 30, ...) {
+    lifecycle::deprecate_warn(
+      "1.2.0",
+      "rpart_train()",
+      details = 'Instead, use `decision_tree(engine = "rpart")` or `rpart::rpart()` directly.'
+    )
+
     bitness <- 8 * .Machine$sizeof.pointer
     if (bitness == 32 & maxdepth > 30)
       maxdepth <- 30

tests/testthat/test_decision_tree.R

@@ -26,6 +26,16 @@ test_that('bad input', {
   expect_snapshot_error(translate(decision_tree(formula = y ~ x)))
 })
 
+test_that('rpart_train is stop-deprecated when it ought to be (#1044)', {
+  skip_on_cran()
+
+  # once this test fails, transition `rpart_train()` to `deprecate_stop()`
+  # and transition this test to fail if `rpart_train()` still exists after a year.
+  if (Sys.Date() > "2025-01-01") {
+    expect_error(rpart_train(mpg ~ ., mtcars))
+  }
+})
+
 # ------------------------------------------------------------------------------
 
 test_that('argument checks for data dimensions', {