Divert linear regressions with poisson family to poisson_reg()

NEWS.md

@@ -23,6 +23,8 @@
 
 * Aligned `null_model()` with other model types; the model type now has an engine argument that defaults to `"parsnip"` and is checked with the same machinery that checks other model types in the package (#1083).
 
+* If linear regression is requested with a Poisson family, an error will occur and refer the user to `poisson_reg()` (#1219).
+
 ## Bug Fixes
 
 * Make sure that parsnip does not convert ordered factor predictions to be unordered.

R/linear_reg.R

@@ -73,6 +73,27 @@ translate.linear_reg <- function(x, engine = x$engine, ...) {
     # evaluated value for the parameter.
     x$args$penalty <- rlang::eval_tidy(x$args$penalty)
   }
+
+  # ------------------------------------------------------------------------------
+  # We want to avoid folks passing in a poisson family instead of using
+  # poisson_reg(). It's hard to detect this.
+
+  is_fam <- names(x$eng_args) == "family"
+  if (any(is_fam)) {
+    eng_args <- rlang::eval_tidy(x$eng_args[[which(is_fam)]])
+    if (is.function(eng_args)) {
+      eng_args <- try(eng_args(), silent = TRUE)
+    }
+    if (inherits(eng_args, "family")) {
+      eng_args <- eng_args$family
+    }
+    if (eng_args == "poisson") {
+      cli::cli_abort(
+        "A Poisson family was requested for {.fn linear_reg}. Please use
+        {.fn poisson_reg} and the engines in the {.pkg poissonreg} package.",
+        call = rlang::call2("linear_reg"))
+    }
+  }
   x
 }
 

tests/testthat/_snaps/linear_reg.md

@@ -139,3 +139,39 @@
       Error in `fit()`:
       ! `penalty` must be a number larger than or equal to 0 or `NULL`, not the number -1.
 
+# prevent using a Poisson family
+
+    Code
+      linear_reg(penalty = 1) %>% set_engine("glmnet", family = poisson) %>%
+        translate()
+    Condition
+      Error in `linear_reg()`:
+      ! A Poisson family was requested for `linear_reg()`. Please use `poisson_reg()` and the engines in the poissonreg package.
+
+---
+
+    Code
+      linear_reg(penalty = 1) %>% set_engine("glmnet", family = stats::poisson) %>%
+        translate()
+    Condition
+      Error in `linear_reg()`:
+      ! A Poisson family was requested for `linear_reg()`. Please use `poisson_reg()` and the engines in the poissonreg package.
+
+---
+
+    Code
+      linear_reg(penalty = 1) %>% set_engine("glmnet", family = stats::poisson()) %>%
+        translate()
+    Condition
+      Error in `linear_reg()`:
+      ! A Poisson family was requested for `linear_reg()`. Please use `poisson_reg()` and the engines in the poissonreg package.
+
+---
+
+    Code
+      linear_reg(penalty = 1) %>% set_engine("glmnet", family = "poisson") %>%
+        translate()
+    Condition
+      Error in `linear_reg()`:
+      ! A Poisson family was requested for `linear_reg()`. Please use `poisson_reg()` and the engines in the poissonreg package.
+

tests/testthat/test-linear_reg.R

@@ -358,3 +358,31 @@ test_that("check_args() works", {
     }
   )
 })
+
+
+test_that("prevent using a Poisson family", {
+  expect_snapshot(
+    linear_reg(penalty = 1) %>%
+      set_engine("glmnet", family = poisson) %>%
+      translate(),
+    error = TRUE
+  )
+  expect_snapshot(
+    linear_reg(penalty = 1) %>%
+      set_engine("glmnet", family = stats::poisson) %>%
+      translate(),
+    error = TRUE
+  )
+  expect_snapshot(
+    linear_reg(penalty = 1) %>%
+      set_engine("glmnet", family = stats::poisson()) %>%
+      translate(),
+    error = TRUE
+  )
+  expect_snapshot(
+    linear_reg(penalty = 1) %>%
+      set_engine("glmnet", family = "poisson") %>%
+      translate(),
+    error = TRUE
+  )
+})