error informatively with bad object in set_* functions

NAMESPACE

@@ -57,8 +57,11 @@ S3method(req_pkgs,model_fit)
 S3method(req_pkgs,model_spec)
 S3method(required_pkgs,model_fit)
 S3method(required_pkgs,model_spec)
+S3method(set_args,default)
 S3method(set_args,model_spec)
+S3method(set_engine,default)
 S3method(set_engine,model_spec)
+S3method(set_mode,default)
 S3method(set_mode,model_spec)
 S3method(tidy,"_LiblineaR")
 S3method(tidy,"_elnet")

R/aaa_models.R

@@ -92,6 +92,22 @@ set_env_val <- function(name, value) {
 
 # ------------------------------------------------------------------------------
 
+error_set_object <- function(object, func) {
+  msg <-
+    "`{func}()` expected a model specification to be supplied to the \
+     `object` argument, but received a(n) `{class(object)[1]}` object."
+
+  if (inherits(object, "function") &&
+      isTRUE(environment(object)$.packageName == "parsnip")) {
+    msg <- c(
+      msg,
+      "i" = "Did you mistakenly pass `model_function` rather than `model_function()`?"
+    )
+  }
+
+  cli::cli_abort(msg, call = call2(func))
+}
+
 check_eng_val <- function(eng) {
   if (rlang::is_missing(eng) || length(eng) != 1 || !is.character(eng))
     rlang::abort("Please supply a character string for an engine name (e.g. `'lm'`)")

R/arguments.R

@@ -77,6 +77,13 @@ set_args.model_spec <- function(object, ...) {
   )
 }
 
+#' @export
+set_args.default <- function(object,...) {
+  error_set_object(object, func = "set_args")
+
+  invisible(FALSE)
+}
+
 #' @rdname set_args
 #' @export
 set_mode <- function(object, mode) {
@@ -95,6 +102,13 @@ set_mode.model_spec <- function(object, mode) {
   object
 }
 
+#' @export
+set_mode.default <- function(object, mode) {
+  error_set_object(object, func = "set_mode")
+
+  invisible(FALSE)
+}
+
 # ------------------------------------------------------------------------------
 
 maybe_eval <- function(x) {

R/engines.R

@@ -136,6 +136,13 @@ set_engine.model_spec <- function(object, engine, ...) {
   )
 }
 
+#' @export
+set_engine.default <- function(object, engine, ...) {
+  error_set_object(object, func = "set_engine")
+
+  invisible(FALSE)
+}
+
 #' Display currently available engines for a model
 #'
 #' The possible engines for a model can depend on what packages are loaded.

tests/testthat/_snaps/args_and_modes.md

@@ -3,14 +3,58 @@
     Code
       set_mode(mtcars, "regression")
     Condition
-      Error in `UseMethod()`:
-      ! no applicable method for 'set_mode' applied to an object of class "data.frame"
+      Error in `set_mode()`:
+      ! `set_mode()` expected a model specification to be supplied to the `object` argument, but received a(n) `data.frame` object.
 
 ---
 
     Code
       set_args(mtcars, blah = "blah")
     Condition
-      Error in `UseMethod()`:
-      ! no applicable method for 'set_args' applied to an object of class "data.frame"
+      Error in `set_args()`:
+      ! `set_args()` expected a model specification to be supplied to the `object` argument, but received a(n) `data.frame` object.
+
+---
+
+    Code
+      bag_tree %>% set_mode("classification")
+    Condition
+      Error in `set_mode()`:
+      ! `set_mode()` expected a model specification to be supplied to the `object` argument, but received a(n) `function` object.
+      i Did you mistakenly pass `model_function` rather than `model_function()`?
+
+---
+
+    Code
+      bag_tree %>% set_engine("rpart")
+    Condition
+      Error in `set_engine()`:
+      ! `set_engine()` expected a model specification to be supplied to the `object` argument, but received a(n) `function` object.
+      i Did you mistakenly pass `model_function` rather than `model_function()`?
+
+---
+
+    Code
+      bag_tree %>% set_args(boop = "bop")
+    Condition
+      Error in `set_args()`:
+      ! `set_args()` expected a model specification to be supplied to the `object` argument, but received a(n) `function` object.
+      i Did you mistakenly pass `model_function` rather than `model_function()`?
+
+---
+
+    Code
+      1L %>% set_args(mode = "classification")
+    Condition
+      Error in `set_args()`:
+      ! `set_args()` expected a model specification to be supplied to the `object` argument, but received a(n) `integer` object.
+
+---
+
+    Code
+      bag_tree %>% set_mode("classification")
+    Condition
+      Error in `set_mode()`:
+      ! `set_mode()` expected a model specification to be supplied to the `object` argument, but received a(n) `function` object.
+      i Did you mistakenly pass `model_function` rather than `model_function()`?
 

tests/testthat/_snaps/misc.md

@@ -19,6 +19,6 @@
     Code
       set_engine(mtcars, "rpart")
     Condition
-      Error in `UseMethod()`:
-      ! no applicable method for 'set_engine' applied to an object of class "data.frame"
+      Error in `set_engine()`:
+      ! `set_engine()` expected a model specification to be supplied to the `object` argument, but received a(n) `data.frame` object.
 

tests/testthat/test_args_and_modes.R

@@ -109,5 +109,28 @@ test_that("set_* functions error when input isn't model_spec", {
   expect_snapshot(error = TRUE,
                   set_args(mtcars, blah = "blah")
   )
+
+  expect_snapshot(error = TRUE,
+                  bag_tree %>% set_mode("classification")
+  )
+
+  expect_snapshot(error = TRUE,
+                  bag_tree %>% set_engine("rpart")
+  )
+
+  expect_snapshot(error = TRUE,
+                  bag_tree %>% set_args(boop = "bop")
+  )
+
+  # won't raise "info" part of error if not a parsnip-namespaced function
+  # not a function
+  expect_snapshot(error = TRUE,
+                  1L %>% set_args(mode = "classification")
+  )
+
+  # not from parsnip
+  expect_snapshot(error = TRUE,
+                  bag_tree %>% set_mode("classification")
+  )
 })