try to load dependencies on fit_members

DESCRIPTION

@@ -53,6 +53,7 @@ Suggests:
     rmarkdown,
     nnet,
     kernlab,
+    mockr,
     h2o,
     SuperLearner
 Config/Needs/website: 

R/fit_members.R

@@ -69,6 +69,7 @@
 #' @export
 fit_members <- function(model_stack, ...) {
   check_model_stack(model_stack)
+  check_for_required_packages(model_stack)
 
   dat <- model_stack[["train"]]
 
@@ -221,3 +222,59 @@ check_model_stack <- function(model_stack) {
     check_inherits(model_stack, "model_stack")
   }
 }
+
+# given a model stack, find the packages required to fit members and predict 
+# on new values, and error if any of them are not loaded
+check_for_required_packages <- function(x) {
+  # for dispatch to required_pkgs.workflow when model
+  # is loaded in a fresh environment
+  suppressPackageStartupMessages(requireNamespace("workflows"))
+
+  pkgs <-
+    purrr::map(
+      x$model_defs,
+      parsnip::required_pkgs
+    ) %>%
+    unlist() %>%
+    unique()
+
+  installed <- purrr::map_lgl(
+    pkgs,
+    is_installed_
+  )
+
+  if (any(!installed)) {
+    error_needs_install(pkgs, installed)
+  }
+
+  purrr::map(
+    pkgs,
+    ~suppressPackageStartupMessages(requireNamespace(.x, quietly = TRUE))
+  )
+
+  invisible(TRUE)
+}
+
+# takes in a vector of package names and a logical vector giving
+# whether or not each is installed
+error_needs_install <- function(pkgs, installed) {
+  plural <- sum(!installed) != 1
+
+  last_sep <- if (sum(!installed) == 2) {"` and `"} else {"`, and `"}
+
+  need_install <- paste0(
+    "`",
+    glue::glue_collapse(pkgs[!installed], sep = "`, `", last = last_sep),
+    "`"
+  )
+
+  glue_stop(
+    "The following package{if (plural) 's' else ''} ",
+    "need{if (plural) '' else 's'} to be installed before ",
+    "fitting members: {need_install}"
+  )
+}
+
+is_installed_ <- function(pkg) {
+  rlang::is_installed(pkg)
+}

tests/testthat/_snaps/fit_members.md

@@ -0,0 +1,16 @@
+# fit_members checks for required packages
+
+    The following package needs to be installed before fitting members: `a`
+
+---
+
+    The following packages need to be installed before fitting members: `a` and `b`
+
+---
+
+    The following packages need to be installed before fitting members: `a`, `b`, and `c`
+
+---
+
+    The following packages need to be installed before fitting members: `recipes`, `parsnip`, and `kernlab`
+

tests/testthat/test_fit_members.R

@@ -18,7 +18,6 @@ library(kernlab)
 skip_if_not_installed("nnet")
 library(nnet)
 
-
 test_that("basic fit_members works", {
   skip_on_cran()
 
@@ -121,3 +120,36 @@ test_that("fit_members errors informatively with a bad model_stack arg", {
     "`model_stack` have already been fitted and need not"
   )
 })
+
+test_that("fit_members checks for required packages", {
+  skip_on_cran()
+
+  skip_if_not_installed("mockr")
+
+  library(mockr)
+
+  # check pluralization of error
+  expect_snapshot_error(error_needs_install(letters[1], rep(FALSE, 1)))
+  expect_snapshot_error(error_needs_install(letters[1:2], rep(FALSE, 2)))
+  expect_snapshot_error(error_needs_install(letters[1:3], rep(FALSE, 3)))
+
+  # loads dependency when it's installed but not loaded
+  unloadNamespace("kernlab")
+
+  expect_s3_class(
+    st_reg_1_ %>%
+      fit_members(),
+    "model_stack"
+  )
+
+  expect_true(isNamespaceLoaded("kernlab"))
+
+  # errors informatively when it's not installed
+  mockr::with_mock(
+    is_installed_ = function(x) {FALSE},
+    {expect_snapshot_error(
+        st_reg_1_ %>%
+          fit_members()
+    )}
+  )
+})