From 8d0f057a1bbbd21c2cf3c5e33bf798277b528d94 Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Tue, 24 Feb 2026 15:15:41 +0000
Subject: [PATCH 01/13] tests for trying to construct a parameter set from
 non-param objects

---
 tests/testthat/_snaps/parameters.md | 26 ++++++++++++++++++++++++++
 tests/testthat/test-parameters.R    | 11 +++++++++++
 2 files changed, 37 insertions(+)

diff --git a/tests/testthat/_snaps/parameters.md b/tests/testthat/_snaps/parameters.md
index 1765dcf8..2c993117 100644
--- a/tests/testthat/_snaps/parameters.md
+++ b/tests/testthat/_snaps/parameters.md
@@ -178,3 +178,29 @@
       Error in `parameters()`:
       ! <parameters> objects cannot be created from a tibble.
 
+# parameters() errors with non-param inputs
+
+    Code
+      parameters()
+    Condition
+      Error:
+      ! ! Could not evaluate cli `{}` expression: `x`.
+      Caused by error in `eval(expr, envir = envir)`:
+      ! argument "x" is missing, with no default
+
+---
+
+    Code
+      parameters(mtry(), "min_n")
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
+---
+
+    Code
+      parameters(list(mtry(), "min_n"))
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
diff --git a/tests/testthat/test-parameters.R b/tests/testthat/test-parameters.R
index aef44ab1..8f183c0f 100644
--- a/tests/testthat/test-parameters.R
+++ b/tests/testthat/test-parameters.R
@@ -120,6 +120,17 @@ test_that("parameters.default", {
   expect_snapshot(error = TRUE, parameters(tibble::as_tibble(mtcars)))
 })
 
+test_that("parameters() errors with non-param inputs", {
+  # no input at all
+  expect_snapshot(error = TRUE, parameters())
+
+  # param method
+  expect_snapshot(error = TRUE, parameters(mtry(), "min_n"))
+
+  # list method 
+  expect_snapshot(error = TRUE, parameters(list(mtry(), "min_n")))
+})
+
 # ------------------------------------------------------------------------------
 # `[]`
 

From 8fcdcf7aef457fe2e73d9f141ebd50266f26ee42 Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Tue, 24 Feb 2026 18:43:59 +0000
Subject: [PATCH 02/13] more tests for `grid_regular()` inputs

---
 R/grids.R                      |   1 -
 tests/testthat/_snaps/grids.md | 112 +++++++++++++++++++++++++++++++++
 tests/testthat/test-grids.R    |  40 ++++++++++++
 3 files changed, 152 insertions(+), 1 deletion(-)

diff --git a/R/grids.R b/R/grids.R
index 5b6f28c3..8d981739 100644
--- a/R/grids.R
+++ b/R/grids.R
@@ -68,7 +68,6 @@ grid_regular.parameters <- function(
   original = TRUE,
   filter = NULL
 ) {
-  # test for NA and finalized
   # test for empty ...
   params <- x$object
   names(params) <- x$id
diff --git a/tests/testthat/_snaps/grids.md b/tests/testthat/_snaps/grids.md
index 4264d411..6bcc7e79 100644
--- a/tests/testthat/_snaps/grids.md
+++ b/tests/testthat/_snaps/grids.md
@@ -115,6 +115,118 @@
       Error in `grid_regular()`:
       ! `original` must be `TRUE` or `FALSE`, not the string "yes".
 
+# grid_regular() errors with non-param inputs
+
+    Code
+      grid_regular()
+    Condition
+      Error in `UseMethod()`:
+      ! no applicable method for 'grid_regular' applied to an object of class "NULL"
+
+---
+
+    Code
+      grid_regular(penalty(), "min_n")
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
+---
+
+    Code
+      grid_regular(list())
+    Condition
+      Error in `grid_regular()`:
+      ! At least one parameter object is required.
+
+---
+
+    Code
+      grid_regular(list(penalty(), "min_n"))
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
+# grid_regular.parameters() checks for NA
+
+    Code
+      grid_regular(p)
+    Condition
+      Error in `grid_regular()`:
+      ! This argument must have class <param>: `NA`.
+
+# grid_regular() errors with params containing unknowns
+
+    Code
+      grid_regular(parameters(mtry()))
+    Condition
+      Error in `grid_regular()`:
+      x This argument contains unknowns: `mtry`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_regular(mtry())
+    Condition
+      Error in `grid_regular()`:
+      x This argument contains unknowns: `mtry`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_regular(mtry(), sample_size())
+    Condition
+      Error in `grid_regular()`:
+      x These arguments contain unknowns: `mtry` and `sample_size`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_regular(list(mtry()))
+    Condition
+      Error in `grid_regular()`:
+      x This argument contains unknowns: `mtry`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_regular(list(mtry_custom_name = mtry()))
+    Condition
+      Error in `grid_regular()`:
+      x This argument contains unknowns: `mtry_custom_name`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_regular(list(mtry(), sample_size()))
+    Condition
+      Error in `grid_regular()`:
+      x These arguments contain unknowns: `mtry` and `sample_size`.
+      i See the `dials::finalize()` function.
+
+# grid_regular() errors with duplicate parameter ids
+
+    Code
+      grid_regular(penalty(), penalty())
+    Condition
+      Error in `parameters()`:
+      x `id` must have unique values.
+      i Duplicates: "penalty"
+
+---
+
+    Code
+      grid_regular(list(a = penalty(), a = mtry()))
+    Condition
+      Error in `parameters()`:
+      x `id` must have unique values.
+      i Duplicates: "a"
+
 # new param grid from conventional data frame
 
     Code
diff --git a/tests/testthat/test-grids.R b/tests/testthat/test-grids.R
index 3671df5a..4fa5c10c 100644
--- a/tests/testthat/test-grids.R
+++ b/tests/testthat/test-grids.R
@@ -114,6 +114,46 @@ test_that("grid_regular validates inputs", {
   expect_snapshot(error = TRUE, grid_regular(penalty(), original = "yes"))
 })
 
+test_that("grid_regular() errors with non-param inputs", {
+  # no input at all
+  expect_snapshot(error = TRUE, grid_regular())
+
+  # param method
+  expect_snapshot(error = TRUE, grid_regular(penalty(), "min_n"))
+
+  # list method
+  expect_snapshot(error = TRUE, grid_regular(list()))
+  expect_snapshot(error = TRUE, grid_regular(list(penalty(), "min_n")))
+})
+
+test_that("grid_regular.parameters() checks for NA", {
+  p <- parameters(penalty())
+  p <- update(p, penalty = NA)
+  expect_snapshot(error = TRUE, grid_regular(p))
+})
+
+test_that("grid_regular() errors with params containing unknowns", {
+  # parameters method
+  expect_snapshot(error = TRUE, grid_regular(parameters(mtry())))
+
+  # param method
+  expect_snapshot(error = TRUE, grid_regular(mtry()))
+  expect_snapshot(error = TRUE, grid_regular(mtry(), sample_size()))
+
+  # list method
+  expect_snapshot(error = TRUE, grid_regular(list(mtry())))
+  expect_snapshot(error = TRUE, grid_regular(list(mtry_custom_name = mtry())))
+  expect_snapshot(error = TRUE, grid_regular(list(mtry(), sample_size())))
+})
+
+test_that("grid_regular() errors with duplicate parameter ids", {
+  # param method
+  expect_snapshot(error = TRUE, grid_regular(penalty(), penalty()))
+
+  # list method
+  expect_snapshot(error = TRUE, grid_regular(list(a = penalty(), a = mtry())))
+})
+
 test_that("new param grid from conventional data frame", {
   x <- data.frame(num_comp = 1:3)
 

From d05a345e43a00ad520b0b49089329175bfdd041f Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Tue, 24 Feb 2026 18:59:12 +0000
Subject: [PATCH 03/13] same tests for the other grid functions

---
 R/grids.R                              |   1 -
 R/space_filling.R                      |   1 -
 tests/testthat/_snaps/grids.md         | 112 +++++++++++++++++++++++++
 tests/testthat/_snaps/space_filling.md | 112 +++++++++++++++++++++++++
 tests/testthat/test-grids.R            |  40 +++++++++
 tests/testthat/test-space_filling.R    |  46 ++++++++++
 6 files changed, 310 insertions(+), 2 deletions(-)

diff --git a/R/grids.R b/R/grids.R
index 8d981739..61c89c7a 100644
--- a/R/grids.R
+++ b/R/grids.R
@@ -206,7 +206,6 @@ grid_random.parameters <- function(
   original = TRUE,
   filter = NULL
 ) {
-  # test for NA and finalized
   # test for empty ...
   params <- x$object
   names(params) <- x$id
diff --git a/R/space_filling.R b/R/space_filling.R
index 97f372bc..5d5ba670 100644
--- a/R/space_filling.R
+++ b/R/space_filling.R
@@ -118,7 +118,6 @@ grid_space_filling.parameters <- function(
   iter = 1000,
   original = TRUE
 ) {
-  # test for NA and finalized
   # test for empty ...
   params <- x$object
   names(params) <- x$id
diff --git a/tests/testthat/_snaps/grids.md b/tests/testthat/_snaps/grids.md
index 6bcc7e79..f56f7537 100644
--- a/tests/testthat/_snaps/grids.md
+++ b/tests/testthat/_snaps/grids.md
@@ -91,6 +91,118 @@
       Error in `grid_random()`:
       ! `original` must be `TRUE` or `FALSE`, not the string "yes".
 
+# grid_random() errors with non-param inputs
+
+    Code
+      grid_random()
+    Condition
+      Error in `UseMethod()`:
+      ! no applicable method for 'grid_random' applied to an object of class "NULL"
+
+---
+
+    Code
+      grid_random(penalty(), "min_n")
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
+---
+
+    Code
+      grid_random(list())
+    Condition
+      Error in `grid_random()`:
+      ! At least one parameter object is required.
+
+---
+
+    Code
+      grid_random(list(penalty(), "min_n"))
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
+# grid_random.parameters() checks for NA
+
+    Code
+      grid_random(p)
+    Condition
+      Error in `grid_random()`:
+      ! This argument must have class <param>: `NA`.
+
+# grid_random() errors with params containing unknowns
+
+    Code
+      grid_random(parameters(mtry()))
+    Condition
+      Error in `grid_random()`:
+      x This argument contains unknowns: `mtry`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_random(mtry())
+    Condition
+      Error in `grid_random()`:
+      x This argument contains unknowns: `mtry`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_random(mtry(), sample_size())
+    Condition
+      Error in `grid_random()`:
+      x These arguments contain unknowns: `mtry` and `sample_size`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_random(list(mtry()))
+    Condition
+      Error in `grid_random()`:
+      x This argument contains unknowns: `mtry`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_random(list(mtry_custom_name = mtry()))
+    Condition
+      Error in `grid_random()`:
+      x This argument contains unknowns: `mtry_custom_name`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_random(list(mtry(), sample_size()))
+    Condition
+      Error in `grid_random()`:
+      x These arguments contain unknowns: `mtry` and `sample_size`.
+      i See the `dials::finalize()` function.
+
+# grid_random() errors with duplicate parameter ids
+
+    Code
+      grid_random(penalty(), penalty())
+    Condition
+      Error in `parameters()`:
+      x `id` must have unique values.
+      i Duplicates: "penalty"
+
+---
+
+    Code
+      grid_random(list(a = penalty(), a = mtry()))
+    Condition
+      Error in `parameters()`:
+      x `id` must have unique values.
+      i Duplicates: "a"
+
 # grid_regular validates inputs
 
     Code
diff --git a/tests/testthat/_snaps/space_filling.md b/tests/testthat/_snaps/space_filling.md
index eec6b515..756d908f 100644
--- a/tests/testthat/_snaps/space_filling.md
+++ b/tests/testthat/_snaps/space_filling.md
@@ -113,3 +113,115 @@
       Error in `grid_space_filling()`:
       ! `original` must be `TRUE` or `FALSE`, not the string "yes".
 
+# grid_space_filling() errors with non-param inputs
+
+    Code
+      grid_space_filling()
+    Condition
+      Error in `UseMethod()`:
+      ! no applicable method for 'grid_space_filling' applied to an object of class "NULL"
+
+---
+
+    Code
+      grid_space_filling(penalty(), "min_n")
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
+---
+
+    Code
+      grid_space_filling(list())
+    Condition
+      Error in `grid_space_filling()`:
+      ! At least one parameter object is required.
+
+---
+
+    Code
+      grid_space_filling(list(penalty(), "min_n"))
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
+# grid_space_filling.parameters() checks for NA
+
+    Code
+      grid_space_filling(p)
+    Condition
+      Error in `grid_space_filling()`:
+      ! This argument must have class <param>: `NA`.
+
+# grid_space_filling() errors with params containing unknowns
+
+    Code
+      grid_space_filling(parameters(mtry()))
+    Condition
+      Error in `grid_space_filling()`:
+      x This argument contains unknowns: `mtry`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_space_filling(mtry())
+    Condition
+      Error in `grid_space_filling()`:
+      x This argument contains unknowns: `mtry`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_space_filling(mtry(), sample_size())
+    Condition
+      Error in `grid_space_filling()`:
+      x These arguments contain unknowns: `mtry` and `sample_size`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_space_filling(list(mtry()))
+    Condition
+      Error in `grid_space_filling()`:
+      x This argument contains unknowns: `mtry`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_space_filling(list(mtry_custom_name = mtry()))
+    Condition
+      Error in `grid_space_filling()`:
+      x This argument contains unknowns: `mtry_custom_name`.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      grid_space_filling(list(mtry(), sample_size()))
+    Condition
+      Error in `grid_space_filling()`:
+      x These arguments contain unknowns: `mtry` and `sample_size`.
+      i See the `dials::finalize()` function.
+
+# grid_space_filling() errors with duplicate parameter ids
+
+    Code
+      grid_space_filling(penalty(), penalty())
+    Condition
+      Error in `parameters()`:
+      x `id` must have unique values.
+      i Duplicates: "penalty"
+
+---
+
+    Code
+      grid_space_filling(list(a = penalty(), a = mtry()))
+    Condition
+      Error in `parameters()`:
+      x `id` must have unique values.
+      i Duplicates: "a"
+
diff --git a/tests/testthat/test-grids.R b/tests/testthat/test-grids.R
index 4fa5c10c..7a70ba42 100644
--- a/tests/testthat/test-grids.R
+++ b/tests/testthat/test-grids.R
@@ -108,6 +108,46 @@ test_that("grid_random validates inputs", {
   expect_snapshot(error = TRUE, grid_random(penalty(), original = "yes"))
 })
 
+test_that("grid_random() errors with non-param inputs", {
+  # no input at all
+  expect_snapshot(error = TRUE, grid_random())
+
+  # param method
+  expect_snapshot(error = TRUE, grid_random(penalty(), "min_n"))
+
+  # list method
+  expect_snapshot(error = TRUE, grid_random(list()))
+  expect_snapshot(error = TRUE, grid_random(list(penalty(), "min_n")))
+})
+
+test_that("grid_random.parameters() checks for NA", {
+  p <- parameters(penalty())
+  p <- update(p, penalty = NA)
+  expect_snapshot(error = TRUE, grid_random(p))
+})
+
+test_that("grid_random() errors with params containing unknowns", {
+  # parameters method
+  expect_snapshot(error = TRUE, grid_random(parameters(mtry())))
+
+  # param method
+  expect_snapshot(error = TRUE, grid_random(mtry()))
+  expect_snapshot(error = TRUE, grid_random(mtry(), sample_size()))
+
+  # list method
+  expect_snapshot(error = TRUE, grid_random(list(mtry())))
+  expect_snapshot(error = TRUE, grid_random(list(mtry_custom_name = mtry())))
+  expect_snapshot(error = TRUE, grid_random(list(mtry(), sample_size())))
+})
+
+test_that("grid_random() errors with duplicate parameter ids", {
+  # param method
+  expect_snapshot(error = TRUE, grid_random(penalty(), penalty()))
+
+  # list method
+  expect_snapshot(error = TRUE, grid_random(list(a = penalty(), a = mtry())))
+})
+
 test_that("grid_regular validates inputs", {
   expect_snapshot(error = TRUE, grid_regular(penalty(), levels = "three"))
   expect_snapshot(error = TRUE, grid_regular(penalty(), levels = -1))
diff --git a/tests/testthat/test-space_filling.R b/tests/testthat/test-space_filling.R
index 7323d17b..aed9b70b 100644
--- a/tests/testthat/test-space_filling.R
+++ b/tests/testthat/test-space_filling.R
@@ -342,6 +342,52 @@ test_that("grid_space_filling validates inputs", {
   expect_snapshot(error = TRUE, grid_space_filling(penalty(), original = "yes"))
 })
 
+test_that("grid_space_filling() errors with non-param inputs", {
+  # no input at all
+  expect_snapshot(error = TRUE, grid_space_filling())
+
+  # param method
+  expect_snapshot(error = TRUE, grid_space_filling(penalty(), "min_n"))
+
+  # list method
+  expect_snapshot(error = TRUE, grid_space_filling(list()))
+  expect_snapshot(error = TRUE, grid_space_filling(list(penalty(), "min_n")))
+})
+
+test_that("grid_space_filling.parameters() checks for NA", {
+  p <- parameters(penalty())
+  p <- update(p, penalty = NA)
+  expect_snapshot(error = TRUE, grid_space_filling(p))
+})
+
+test_that("grid_space_filling() errors with params containing unknowns", {
+  # parameters method
+  expect_snapshot(error = TRUE, grid_space_filling(parameters(mtry())))
+
+  # param method
+  expect_snapshot(error = TRUE, grid_space_filling(mtry()))
+  expect_snapshot(error = TRUE, grid_space_filling(mtry(), sample_size()))
+
+  # list method
+  expect_snapshot(error = TRUE, grid_space_filling(list(mtry())))
+  expect_snapshot(
+    error = TRUE,
+    grid_space_filling(list(mtry_custom_name = mtry()))
+  )
+  expect_snapshot(error = TRUE, grid_space_filling(list(mtry(), sample_size())))
+})
+
+test_that("grid_space_filling() errors with duplicate parameter ids", {
+  # param method
+  expect_snapshot(error = TRUE, grid_space_filling(penalty(), penalty()))
+
+  # list method
+  expect_snapshot(
+    error = TRUE,
+    grid_space_filling(list(a = penalty(), a = mtry()))
+  )
+})
+
 test_that("pre-made designs respect the 'original argument", {
   # See issue #409
 

From 4895b392a9e0c0a566e8ac4c37f8f72c82cf0304 Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Tue, 24 Feb 2026 20:04:00 +0000
Subject: [PATCH 04/13] add tests for mixing non-param and param with unknown

---
 tests/testthat/_snaps/grids.md         | 32 ++++++++++++++++++++++++++
 tests/testthat/_snaps/space_filling.md | 16 +++++++++++++
 tests/testthat/test-grids.R            |  4 ++++
 tests/testthat/test-space_filling.R    |  2 ++
 4 files changed, 54 insertions(+)

diff --git a/tests/testthat/_snaps/grids.md b/tests/testthat/_snaps/grids.md
index f56f7537..fe5ff8bc 100644
--- a/tests/testthat/_snaps/grids.md
+++ b/tests/testthat/_snaps/grids.md
@@ -107,6 +107,14 @@
       Error in `parameters()`:
       ! The objects should all be <param> objects.
 
+---
+
+    Code
+      grid_random(mtry(), "min_n")
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
 ---
 
     Code
@@ -123,6 +131,14 @@
       Error in `parameters()`:
       ! The objects should all be <param> objects.
 
+---
+
+    Code
+      grid_random(list(mtry(), "min_n"))
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
 # grid_random.parameters() checks for NA
 
     Code
@@ -243,6 +259,14 @@
       Error in `parameters()`:
       ! The objects should all be <param> objects.
 
+---
+
+    Code
+      grid_regular(mtry(), "min_n")
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
 ---
 
     Code
@@ -259,6 +283,14 @@
       Error in `parameters()`:
       ! The objects should all be <param> objects.
 
+---
+
+    Code
+      grid_regular(list(mtry(), "min_n"))
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
 # grid_regular.parameters() checks for NA
 
     Code
diff --git a/tests/testthat/_snaps/space_filling.md b/tests/testthat/_snaps/space_filling.md
index 756d908f..f26d0803 100644
--- a/tests/testthat/_snaps/space_filling.md
+++ b/tests/testthat/_snaps/space_filling.md
@@ -129,6 +129,14 @@
       Error in `parameters()`:
       ! The objects should all be <param> objects.
 
+---
+
+    Code
+      grid_space_filling(mtry(), "min_n")
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
 ---
 
     Code
@@ -145,6 +153,14 @@
       Error in `parameters()`:
       ! The objects should all be <param> objects.
 
+---
+
+    Code
+      grid_space_filling(list(mtry(), "min_n"))
+    Condition
+      Error in `parameters()`:
+      ! The objects should all be <param> objects.
+
 # grid_space_filling.parameters() checks for NA
 
     Code
diff --git a/tests/testthat/test-grids.R b/tests/testthat/test-grids.R
index 7a70ba42..5199ab0d 100644
--- a/tests/testthat/test-grids.R
+++ b/tests/testthat/test-grids.R
@@ -114,10 +114,12 @@ test_that("grid_random() errors with non-param inputs", {
 
   # param method
   expect_snapshot(error = TRUE, grid_random(penalty(), "min_n"))
+  expect_snapshot(error = TRUE, grid_random(mtry(), "min_n"))
 
   # list method
   expect_snapshot(error = TRUE, grid_random(list()))
   expect_snapshot(error = TRUE, grid_random(list(penalty(), "min_n")))
+  expect_snapshot(error = TRUE, grid_random(list(mtry(), "min_n")))
 })
 
 test_that("grid_random.parameters() checks for NA", {
@@ -160,10 +162,12 @@ test_that("grid_regular() errors with non-param inputs", {
 
   # param method
   expect_snapshot(error = TRUE, grid_regular(penalty(), "min_n"))
+  expect_snapshot(error = TRUE, grid_regular(mtry(), "min_n"))
 
   # list method
   expect_snapshot(error = TRUE, grid_regular(list()))
   expect_snapshot(error = TRUE, grid_regular(list(penalty(), "min_n")))
+  expect_snapshot(error = TRUE, grid_regular(list(mtry(), "min_n")))
 })
 
 test_that("grid_regular.parameters() checks for NA", {
diff --git a/tests/testthat/test-space_filling.R b/tests/testthat/test-space_filling.R
index aed9b70b..06e1b8e9 100644
--- a/tests/testthat/test-space_filling.R
+++ b/tests/testthat/test-space_filling.R
@@ -348,10 +348,12 @@ test_that("grid_space_filling() errors with non-param inputs", {
 
   # param method
   expect_snapshot(error = TRUE, grid_space_filling(penalty(), "min_n"))
+  expect_snapshot(error = TRUE, grid_space_filling(mtry(), "min_n"))
 
   # list method
   expect_snapshot(error = TRUE, grid_space_filling(list()))
   expect_snapshot(error = TRUE, grid_space_filling(list(penalty(), "min_n")))
+  expect_snapshot(error = TRUE, grid_space_filling(list(mtry(), "min_n")))
 })
 
 test_that("grid_space_filling.parameters() checks for NA", {

From dd8a6e43fab97461a1e82add69dbfd478b1eb0ab Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Tue, 7 Apr 2026 10:45:20 +0100
Subject: [PATCH 05/13] add new `check_param()`

---
 R/misc.R                         | 44 ++++++++++++++++++++++++
 tests/testthat/_snaps/misc.md    | 58 ++++++++++++++++++++++++++++++++
 tests/testthat/test-misc.R       | 34 +++++++++++++++++++
 tests/testthat/test-parameters.R |  2 +-
 4 files changed, 137 insertions(+), 1 deletion(-)

diff --git a/R/misc.R b/R/misc.R
index 922ee704..5ad8c0b6 100644
--- a/R/misc.R
+++ b/R/misc.R
@@ -292,3 +292,47 @@ check_unique <- function(x, ..., arg = caller_arg(x), call = caller_env()) {
     call = call
   )
 }
+
+check_param <- function(
+  x,
+  ...,
+  allow_na = FALSE,
+  allow_unknown = FALSE,
+  arg = caller_arg(x),
+  call = caller_env()
+) {
+  check_dots_empty()
+
+  if (allow_na && all(is.na(x))) {
+    return(invisible(NULL))
+  }
+
+  if (inherits(x, "param")) {
+    if (allow_unknown || !has_unknowns(x)) {
+      return(invisible(NULL))
+    }
+
+    cli::cli_abort(
+      c(
+        x = "{.arg {arg}} must be a {.cls param} object without unknowns.",
+        i = "See the {.fn dials::finalize} function."
+      ),
+      call = call
+    )
+  }
+
+  what <- if (allow_unknown) {
+    "a <param> object"
+  } else {
+    "a <param> object without unknowns"
+  }
+
+  stop_input_type(
+    x,
+    what,
+    ...,
+    allow_na = allow_na,
+    arg = arg,
+    call = call
+  )
+}
diff --git a/tests/testthat/_snaps/misc.md b/tests/testthat/_snaps/misc.md
index ee938fab..d2f03fbe 100644
--- a/tests/testthat/_snaps/misc.md
+++ b/tests/testthat/_snaps/misc.md
@@ -212,3 +212,61 @@
       i This is an internal error that was detected in the dials package.
         Please report it at <https://github.com/tidymodels/dials/issues> with a reprex (<https://tidyverse.org/help/>) and the full backtrace.
 
+# check_param() errors for param with unknowns when not allowed
+
+    Code
+      check_param(mtry())
+    Condition
+      Error:
+      x `mtry()` must be a <param> object without unknowns.
+      i See the `dials::finalize()` function.
+
+---
+
+    Code
+      check_param(mtry(), allow_unknown = FALSE)
+    Condition
+      Error:
+      x `mtry()` must be a <param> object without unknowns.
+      i See the `dials::finalize()` function.
+
+# check_param() errors for NA when not allowed
+
+    Code
+      check_param(NA)
+    Condition
+      Error:
+      ! `NA` must be a <param> object without unknowns, not `NA`.
+
+---
+
+    Code
+      check_param(NA, allow_na = FALSE)
+    Condition
+      Error:
+      ! `NA` must be a <param> object without unknowns, not `NA`.
+
+# check_param() errors for non-param objects
+
+    Code
+      check_param("not a param")
+    Condition
+      Error:
+      ! `"not a param"` must be a <param> object without unknowns, not the string "not a param".
+
+# check_param() uses custom arg name
+
+    Code
+      check_param("x", arg = "my_param")
+    Condition
+      Error:
+      ! `my_param` must be a <param> object without unknowns, not the string "x".
+
+# check_param() error mentions NA when allowed
+
+    Code
+      check_param("x", allow_na = TRUE)
+    Condition
+      Error:
+      ! `"x"` must be a <param> object without unknowns or `NA`, not the string "x".
+
diff --git a/tests/testthat/test-misc.R b/tests/testthat/test-misc.R
index 18cec59c..3c06a392 100644
--- a/tests/testthat/test-misc.R
+++ b/tests/testthat/test-misc.R
@@ -119,3 +119,37 @@ test_that("vctrs-helpers-parameters", {
     dials:::df_size(2)
   )
 })
+
+test_that("check_param() passes for valid param objects", {
+  expect_no_error(check_param(penalty()))
+})
+
+test_that("check_param() passes for param with unknowns when allowed", {
+  expect_no_error(check_param(mtry(), allow_unknown = TRUE))
+})
+
+test_that("check_param() errors for param with unknowns when not allowed", {
+  expect_snapshot(error = TRUE, check_param(mtry()))
+  expect_snapshot(error = TRUE, check_param(mtry(), allow_unknown = FALSE))
+})
+
+test_that("check_param() passes for NA when allowed", {
+  expect_no_error(check_param(NA, allow_na = TRUE))
+})
+
+test_that("check_param() errors for NA when not allowed", {
+  expect_snapshot(error = TRUE, check_param(NA))
+  expect_snapshot(error = TRUE, check_param(NA, allow_na = FALSE))
+})
+
+test_that("check_param() errors for non-param objects", {
+  expect_snapshot(error = TRUE, check_param("not a param"))
+})
+
+test_that("check_param() uses custom arg name", {
+  expect_snapshot(error = TRUE, check_param("x", arg = "my_param"))
+})
+
+test_that("check_param() error mentions NA when allowed", {
+  expect_snapshot(error = TRUE, check_param("x", allow_na = TRUE))
+})
diff --git a/tests/testthat/test-parameters.R b/tests/testthat/test-parameters.R
index 8f183c0f..c02f9382 100644
--- a/tests/testthat/test-parameters.R
+++ b/tests/testthat/test-parameters.R
@@ -127,7 +127,7 @@ test_that("parameters() errors with non-param inputs", {
   # param method
   expect_snapshot(error = TRUE, parameters(mtry(), "min_n"))
 
-  # list method 
+  # list method
   expect_snapshot(error = TRUE, parameters(list(mtry(), "min_n")))
 })
 

From fa9be9dc40fd0d910d060d2eff42b5070d2dc70e Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Wed, 8 Apr 2026 10:50:03 +0100
Subject: [PATCH 06/13] use`check_param()` for `parameters()`

---
 R/parameters.R                         | 11 ++++++++---
 tests/testthat/_snaps/grids.md         | 16 ++++++++--------
 tests/testthat/_snaps/parameters.md    |  6 +++---
 tests/testthat/_snaps/space_filling.md |  8 ++++----
 4 files changed, 23 insertions(+), 18 deletions(-)

diff --git a/R/parameters.R b/R/parameters.R
index 03e03a65..82a2aa84 100644
--- a/R/parameters.R
+++ b/R/parameters.R
@@ -44,9 +44,14 @@ parameters.param <- function(x, ...) {
 parameters.list <- function(x, ...) {
   check_dots_empty()
 
-  elem_param <- purrr::map_lgl(x, inherits, "param")
-  if (!all(elem_param)) {
-    cli::cli_abort("The objects should all be {.cls param} objects.")
+  param_names <- names(x)
+  for (i in seq_along(x)) {
+    check_param(
+      x[[i]],
+      allow_na = FALSE,
+      allow_unknown = TRUE,
+      arg = param_names[i] %||% paste("Argument", i)
+    )
   }
   elem_name <- purrr::map_chr(x, \(.x) names(.x$label))
   elem_id <- names(x)
diff --git a/tests/testthat/_snaps/grids.md b/tests/testthat/_snaps/grids.md
index fe5ff8bc..06fe88e7 100644
--- a/tests/testthat/_snaps/grids.md
+++ b/tests/testthat/_snaps/grids.md
@@ -105,7 +105,7 @@
       grid_random(penalty(), "min_n")
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 ---
 
@@ -113,7 +113,7 @@
       grid_random(mtry(), "min_n")
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 ---
 
@@ -129,7 +129,7 @@
       grid_random(list(penalty(), "min_n"))
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 ---
 
@@ -137,7 +137,7 @@
       grid_random(list(mtry(), "min_n"))
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 # grid_random.parameters() checks for NA
 
@@ -257,7 +257,7 @@
       grid_regular(penalty(), "min_n")
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 ---
 
@@ -265,7 +265,7 @@
       grid_regular(mtry(), "min_n")
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 ---
 
@@ -281,7 +281,7 @@
       grid_regular(list(penalty(), "min_n"))
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 ---
 
@@ -289,7 +289,7 @@
       grid_regular(list(mtry(), "min_n"))
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 # grid_regular.parameters() checks for NA
 
diff --git a/tests/testthat/_snaps/parameters.md b/tests/testthat/_snaps/parameters.md
index 2c993117..10723ea9 100644
--- a/tests/testthat/_snaps/parameters.md
+++ b/tests/testthat/_snaps/parameters.md
@@ -67,7 +67,7 @@
       parameters(list(a = mtry, a = penalty()))
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `a` must be a <param> object, not a function.
 
 # updating
 
@@ -194,7 +194,7 @@
       parameters(mtry(), "min_n")
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 ---
 
@@ -202,5 +202,5 @@
       parameters(list(mtry(), "min_n"))
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
diff --git a/tests/testthat/_snaps/space_filling.md b/tests/testthat/_snaps/space_filling.md
index f26d0803..f047499c 100644
--- a/tests/testthat/_snaps/space_filling.md
+++ b/tests/testthat/_snaps/space_filling.md
@@ -127,7 +127,7 @@
       grid_space_filling(penalty(), "min_n")
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 ---
 
@@ -135,7 +135,7 @@
       grid_space_filling(mtry(), "min_n")
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 ---
 
@@ -151,7 +151,7 @@
       grid_space_filling(list(penalty(), "min_n"))
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 ---
 
@@ -159,7 +159,7 @@
       grid_space_filling(list(mtry(), "min_n"))
     Condition
       Error in `parameters()`:
-      ! The objects should all be <param> objects.
+      ! `Argument 2` must be a <param> object, not the string "min_n".
 
 # grid_space_filling.parameters() checks for NA
 

From 359c8dde9b9bf504c8fa30fc8498eeaf120a70e7 Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Wed, 8 Apr 2026 10:53:39 +0100
Subject: [PATCH 07/13] use `check_param()` in `parameters_constr()`

---
 R/parameters.R                      | 37 ++++++++++-------------------
 tests/testthat/_snaps/parameters.md |  4 ++--
 2 files changed, 14 insertions(+), 27 deletions(-)

diff --git a/R/parameters.R b/R/parameters.R
index 82a2aa84..4942abec 100644
--- a/R/parameters.R
+++ b/R/parameters.R
@@ -71,30 +71,6 @@ parameters.list <- function(x, ...) {
   )
 }
 
-param_or_na <- function(x) {
-  inherits(x, "param") || all(is.na(x))
-}
-
-check_list_of_param <- function(x, ..., call = caller_env()) {
-  check_dots_empty()
-  if (!is.list(x)) {
-    cli::cli_abort(
-      "{.arg object} must be a list of {.cls param} objects.",
-      call = call
-    )
-  }
-  is_good_boi <- map_lgl(x, param_or_na)
-  if (!all(is_good_boi)) {
-    offenders <- which(!is_good_boi)
-
-    cli::cli_abort(
-      "{.arg object} elements in the following positions must be {.code NA} or a 
-      {.cls param} object: {offenders}.",
-      call = call
-    )
-  }
-}
-
 #' Construct a new parameter set object
 #'
 #' @param name,id,source,component,component_id Character strings with the same
@@ -125,7 +101,18 @@ parameters_constr <- function(
   check_character(source, call = call)
   check_character(component, call = call)
   check_character(component_id, call = call)
-  check_list_of_param(object, call = call)
+  if (!is.list(object)) {
+    cli::cli_abort("{.arg object} must be a list.", call = call)
+  }
+  for (i in seq_along(object)) {
+    check_param(
+      object[[i]],
+      allow_na = TRUE,
+      allow_unknown = TRUE,
+      arg = paste0("object[[", i, "]]"),
+      call = call
+    )
+  }
 
   n_elements <- lengths(list(name, id, source, component, component_id, object))
   n_elements_unique <- unique(n_elements)
diff --git a/tests/testthat/_snaps/parameters.md b/tests/testthat/_snaps/parameters.md
index 10723ea9..2279d374 100644
--- a/tests/testthat/_snaps/parameters.md
+++ b/tests/testthat/_snaps/parameters.md
@@ -23,7 +23,7 @@
       parameters_constr(ab, ab, ab, ab, ab, object = "not a params list")
     Condition
       Error:
-      ! `object` must be a list of <param> objects.
+      ! `object` must be a list.
 
 ---
 
@@ -32,7 +32,7 @@
       parameters_constr(ab, ab, ab, ab, ab, object = list(penalty(), "not a param"))
     Condition
       Error:
-      ! `object` elements in the following positions must be `NA` or a <param> object: 2.
+      ! `object[[2]]` must be a <param> object or `NA`, not the string "not a param".
 
 ---
 

From db179d8c42d8dcfd25f85a2a8bc862c3b6aae4dd Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Wed, 8 Apr 2026 12:35:05 +0100
Subject: [PATCH 08/13] fine-tune the argument name

---
 R/misc.R       | 10 ++++++++++
 R/parameters.R |  2 +-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/R/misc.R b/R/misc.R
index 5ad8c0b6..17c1cfdf 100644
--- a/R/misc.R
+++ b/R/misc.R
@@ -336,3 +336,13 @@ check_param <- function(
     call = call
   )
 }
+
+param_arg_name <- function(name, x, position) {
+  if (!is.null(name) && nzchar(name)) {
+    return(name)
+  }
+  if (inherits(x, "param")) {
+    return(names(x$label))
+  }
+  paste("Argument", position)
+}
diff --git a/R/parameters.R b/R/parameters.R
index 4942abec..4e96c5e0 100644
--- a/R/parameters.R
+++ b/R/parameters.R
@@ -50,7 +50,7 @@ parameters.list <- function(x, ...) {
       x[[i]],
       allow_na = FALSE,
       allow_unknown = TRUE,
-      arg = param_names[i] %||% paste("Argument", i)
+      arg = param_arg_name(param_names[i], x[[i]], i)
     )
   }
   elem_name <- purrr::map_chr(x, \(.x) names(.x$label))

From 60de7985e9e07e0a6d353bc862a8f58ad7a5d19e Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Wed, 8 Apr 2026 12:36:27 +0100
Subject: [PATCH 09/13] use `check_param()` for grid functions

check early for both parameter class and no unknowns so that we get a better error call than via `parameters()` or `validate_params()` from `make_*()`

check that the dots are empty for #434
---
 R/grids.R                              | 92 ++++++++++++++++++++++++--
 R/space_filling.R                      | 43 +++++++++++-
 tests/testthat/_snaps/aaa_unknown.md   | 34 +++++-----
 tests/testthat/_snaps/grids.md         | 76 +++++++++++----------
 tests/testthat/_snaps/space_filling.md | 38 ++++++-----
 tests/testthat/test-space_filling.R    |  2 +-
 6 files changed, 207 insertions(+), 78 deletions(-)

diff --git a/R/grids.R b/R/grids.R
index 61c89c7a..96400212 100644
--- a/R/grids.R
+++ b/R/grids.R
@@ -68,7 +68,21 @@ grid_regular.parameters <- function(
   original = TRUE,
   filter = NULL
 ) {
-  # test for empty ...
+  check_dots_empty()
+
+  if (nrow(x) == 0) {
+    cli::cli_abort("At least one parameter object is required.")
+  }
+  # check for unknowns
+  for (i in seq_along(x$object)) {
+    check_param(
+      x$object[[i]],
+      allow_na = FALSE,
+      allow_unknown = FALSE,
+      arg = x$id[i]
+    )
+  }
+
   params <- x$object
   names(params) <- x$id
   grd <- make_regular_grid(
@@ -90,6 +104,22 @@ grid_regular.list <- function(
   original = TRUE,
   filter = NULL
 ) {
+  check_dots_empty()
+
+  if (length(x) == 0) {
+    cli::cli_abort("At least one parameter object is required.")
+  }
+  # check for unknowns
+  param_names <- names(x)
+  for (i in seq_along(x)) {
+    check_param(
+      x[[i]],
+      allow_na = FALSE,
+      allow_unknown = FALSE,
+      arg = param_arg_name(param_names[i], x[[i]], i)
+    )
+  }
+
   y <- parameters(x)
   params <- y$object
   names(params) <- y$id
@@ -113,7 +143,19 @@ grid_regular.param <- function(
   original = TRUE,
   filter = NULL
 ) {
-  y <- parameters(list(x, ...))
+  # check for unknowns
+  param_list <- list(x, ...)
+  param_names <- names(param_list)
+  for (i in seq_along(param_list)) {
+    check_param(
+      param_list[[i]],
+      allow_na = FALSE,
+      allow_unknown = FALSE,
+      arg = param_arg_name(param_names[i], param_list[[i]], i)
+    )
+  }
+
+  y <- parameters(param_list)
   params <- y$object
   names(params) <- y$id
   grd <- make_regular_grid(
@@ -206,7 +248,21 @@ grid_random.parameters <- function(
   original = TRUE,
   filter = NULL
 ) {
-  # test for empty ...
+  check_dots_empty()
+
+  if (nrow(x) == 0) {
+    cli::cli_abort("At least one parameter object is required.")
+  }
+  # check for unknowns
+  for (i in seq_along(x$object)) {
+    check_param(
+      x$object[[i]],
+      allow_na = FALSE,
+      allow_unknown = FALSE,
+      arg = x$id[i]
+    )
+  }
+
   params <- x$object
   names(params) <- x$id
   grd <- make_random_grid(
@@ -222,6 +278,22 @@ grid_random.parameters <- function(
 #' @export
 #' @rdname grid_regular
 grid_random.list <- function(x, ..., size = 5, original = TRUE, filter = NULL) {
+  check_dots_empty()
+
+  if (length(x) == 0) {
+    cli::cli_abort("At least one parameter object is required.")
+  }
+  # check for unknowns
+  param_names <- names(x)
+  for (i in seq_along(x)) {
+    check_param(
+      x[[i]],
+      allow_na = FALSE,
+      allow_unknown = FALSE,
+      arg = param_arg_name(param_names[i], x[[i]], i)
+    )
+  }
+
   y <- parameters(x)
   params <- y$object
   names(params) <- y$id
@@ -245,7 +317,19 @@ grid_random.param <- function(
   original = TRUE,
   filter = NULL
 ) {
-  y <- parameters(list(x, ...))
+  param_list <- list(x, ...)
+  # check for unknowns
+  param_names <- names(param_list)
+  for (i in seq_along(param_list)) {
+    check_param(
+      param_list[[i]],
+      allow_na = FALSE,
+      allow_unknown = FALSE,
+      arg = param_arg_name(param_names[i], param_list[[i]], i)
+    )
+  }
+
+  y <- parameters(param_list)
   params <- y$object
   names(params) <- y$id
   grd <- make_random_grid(
diff --git a/R/space_filling.R b/R/space_filling.R
index 5d5ba670..41db0a7b 100644
--- a/R/space_filling.R
+++ b/R/space_filling.R
@@ -118,7 +118,20 @@ grid_space_filling.parameters <- function(
   iter = 1000,
   original = TRUE
 ) {
-  # test for empty ...
+  check_dots_empty()
+
+  if (nrow(x) == 0) {
+    cli::cli_abort("At least one parameter object is required.")
+  }
+  for (i in seq_along(x$object)) {
+    check_param(
+      x$object[[i]],
+      allow_na = FALSE,
+      allow_unknown = FALSE,
+      arg = x$id[i]
+    )
+  }
+
   params <- x$object
   names(params) <- x$id
   grd <- make_sfd(
@@ -144,6 +157,21 @@ grid_space_filling.list <- function(
   iter = 1000,
   original = TRUE
 ) {
+  check_dots_empty()
+
+  if (length(x) == 0) {
+    cli::cli_abort("At least one parameter object is required.")
+  }
+  param_names <- names(x)
+  for (i in seq_along(x)) {
+    check_param(
+      x[[i]],
+      allow_na = FALSE,
+      allow_unknown = FALSE,
+      arg = param_arg_name(param_names[i], x[[i]], i)
+    )
+  }
+
   y <- parameters(x)
   params <- y$object
   names(params) <- y$id
@@ -171,7 +199,18 @@ grid_space_filling.param <- function(
   type = "any",
   original = TRUE
 ) {
-  y <- parameters(list(x, ...))
+  param_list <- list(x, ...)
+  param_names <- names(param_list)
+  for (i in seq_along(param_list)) {
+    check_param(
+      param_list[[i]],
+      allow_na = FALSE,
+      allow_unknown = FALSE,
+      arg = param_arg_name(param_names[i], param_list[[i]], i)
+    )
+  }
+
+  y <- parameters(param_list)
   params <- y$object
   names(params) <- y$id
   grd <- make_sfd(
diff --git a/tests/testthat/_snaps/aaa_unknown.md b/tests/testthat/_snaps/aaa_unknown.md
index b5062524..5ca42269 100644
--- a/tests/testthat/_snaps/aaa_unknown.md
+++ b/tests/testthat/_snaps/aaa_unknown.md
@@ -4,7 +4,7 @@
       grid_regular(p1)
     Condition
       Error in `grid_regular()`:
-      x This argument contains unknowns: `q`.
+      x `q` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -13,7 +13,7 @@
       grid_regular(p2)
     Condition
       Error in `grid_regular()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -22,7 +22,7 @@
       grid_regular(p3)
     Condition
       Error in `grid_regular()`:
-      x These arguments contain unknowns: `mtry` and `q`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -31,7 +31,7 @@
       grid_random(p1)
     Condition
       Error in `grid_random()`:
-      x This argument contains unknowns: `q`.
+      x `q` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -40,7 +40,7 @@
       grid_random(p2)
     Condition
       Error in `grid_random()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -49,7 +49,7 @@
       grid_space_filling(p1, type = "latin_hypercube")
     Condition
       Error in `grid_space_filling()`:
-      x This argument contains unknowns: `q`.
+      x `q` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -58,7 +58,7 @@
       grid_space_filling(p2, type = "latin_hypercube")
     Condition
       Error in `grid_space_filling()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -67,7 +67,7 @@
       grid_space_filling(p1, type = "max_entropy")
     Condition
       Error in `grid_space_filling()`:
-      x This argument contains unknowns: `q`.
+      x `q` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -76,7 +76,7 @@
       grid_space_filling(p2, type = "max_entropy")
     Condition
       Error in `grid_space_filling()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -85,7 +85,7 @@
       grid_regular(min_n(), q = mtry())
     Condition
       Error in `grid_regular()`:
-      x This argument contains unknowns: `q`.
+      x `q` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -94,7 +94,7 @@
       grid_regular(mtry())
     Condition
       Error in `grid_regular()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -103,7 +103,7 @@
       grid_random(min_n(), q = mtry())
     Condition
       Error in `grid_random()`:
-      x This argument contains unknowns: `q`.
+      x `q` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -112,7 +112,7 @@
       grid_random(mtry())
     Condition
       Error in `grid_random()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -121,7 +121,7 @@
       grid_regular(min_n(), q = mtry())
     Condition
       Error in `grid_regular()`:
-      x This argument contains unknowns: `q`.
+      x `q` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -130,7 +130,7 @@
       grid_space_filling(mtry(), type = "latin_hypercube")
     Condition
       Error in `grid_space_filling()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -139,7 +139,7 @@
       grid_space_filling(min_n(), q = mtry(), type = "max_entropy")
     Condition
       Error in `grid_space_filling()`:
-      x This argument contains unknowns: `q`.
+      x `q` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -148,6 +148,6 @@
       grid_space_filling(mtry(), type = "max_entropy")
     Condition
       Error in `grid_space_filling()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
diff --git a/tests/testthat/_snaps/grids.md b/tests/testthat/_snaps/grids.md
index 06fe88e7..07ec9b27 100644
--- a/tests/testthat/_snaps/grids.md
+++ b/tests/testthat/_snaps/grids.md
@@ -104,16 +104,17 @@
     Code
       grid_random(penalty(), "min_n")
     Condition
-      Error in `parameters()`:
-      ! `Argument 2` must be a <param> object, not the string "min_n".
+      Error in `grid_random()`:
+      ! `Argument 2` must be a <param> object without unknowns, not the string "min_n".
 
 ---
 
     Code
       grid_random(mtry(), "min_n")
     Condition
-      Error in `parameters()`:
-      ! `Argument 2` must be a <param> object, not the string "min_n".
+      Error in `grid_random()`:
+      x `mtry` must be a <param> object without unknowns.
+      i See the `dials::finalize()` function.
 
 ---
 
@@ -128,16 +129,17 @@
     Code
       grid_random(list(penalty(), "min_n"))
     Condition
-      Error in `parameters()`:
-      ! `Argument 2` must be a <param> object, not the string "min_n".
+      Error in `grid_random()`:
+      ! `Argument 2` must be a <param> object without unknowns, not the string "min_n".
 
 ---
 
     Code
       grid_random(list(mtry(), "min_n"))
     Condition
-      Error in `parameters()`:
-      ! `Argument 2` must be a <param> object, not the string "min_n".
+      Error in `grid_random()`:
+      x `mtry` must be a <param> object without unknowns.
+      i See the `dials::finalize()` function.
 
 # grid_random.parameters() checks for NA
 
@@ -145,7 +147,7 @@
       grid_random(p)
     Condition
       Error in `grid_random()`:
-      ! This argument must have class <param>: `NA`.
+      ! `penalty` must be a <param> object without unknowns, not `NA`.
 
 # grid_random() errors with params containing unknowns
 
@@ -153,7 +155,7 @@
       grid_random(parameters(mtry()))
     Condition
       Error in `grid_random()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -162,7 +164,7 @@
       grid_random(mtry())
     Condition
       Error in `grid_random()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -171,7 +173,7 @@
       grid_random(mtry(), sample_size())
     Condition
       Error in `grid_random()`:
-      x These arguments contain unknowns: `mtry` and `sample_size`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -180,7 +182,7 @@
       grid_random(list(mtry()))
     Condition
       Error in `grid_random()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -189,7 +191,7 @@
       grid_random(list(mtry_custom_name = mtry()))
     Condition
       Error in `grid_random()`:
-      x This argument contains unknowns: `mtry_custom_name`.
+      x `mtry_custom_name` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -198,7 +200,7 @@
       grid_random(list(mtry(), sample_size()))
     Condition
       Error in `grid_random()`:
-      x These arguments contain unknowns: `mtry` and `sample_size`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 # grid_random() errors with duplicate parameter ids
@@ -215,9 +217,9 @@
     Code
       grid_random(list(a = penalty(), a = mtry()))
     Condition
-      Error in `parameters()`:
-      x `id` must have unique values.
-      i Duplicates: "a"
+      Error in `grid_random()`:
+      x `a` must be a <param> object without unknowns.
+      i See the `dials::finalize()` function.
 
 # grid_regular validates inputs
 
@@ -256,16 +258,17 @@
     Code
       grid_regular(penalty(), "min_n")
     Condition
-      Error in `parameters()`:
-      ! `Argument 2` must be a <param> object, not the string "min_n".
+      Error in `grid_regular()`:
+      ! `Argument 2` must be a <param> object without unknowns, not the string "min_n".
 
 ---
 
     Code
       grid_regular(mtry(), "min_n")
     Condition
-      Error in `parameters()`:
-      ! `Argument 2` must be a <param> object, not the string "min_n".
+      Error in `grid_regular()`:
+      x `mtry` must be a <param> object without unknowns.
+      i See the `dials::finalize()` function.
 
 ---
 
@@ -280,16 +283,17 @@
     Code
       grid_regular(list(penalty(), "min_n"))
     Condition
-      Error in `parameters()`:
-      ! `Argument 2` must be a <param> object, not the string "min_n".
+      Error in `grid_regular()`:
+      ! `Argument 2` must be a <param> object without unknowns, not the string "min_n".
 
 ---
 
     Code
       grid_regular(list(mtry(), "min_n"))
     Condition
-      Error in `parameters()`:
-      ! `Argument 2` must be a <param> object, not the string "min_n".
+      Error in `grid_regular()`:
+      x `mtry` must be a <param> object without unknowns.
+      i See the `dials::finalize()` function.
 
 # grid_regular.parameters() checks for NA
 
@@ -297,7 +301,7 @@
       grid_regular(p)
     Condition
       Error in `grid_regular()`:
-      ! This argument must have class <param>: `NA`.
+      ! `penalty` must be a <param> object without unknowns, not `NA`.
 
 # grid_regular() errors with params containing unknowns
 
@@ -305,7 +309,7 @@
       grid_regular(parameters(mtry()))
     Condition
       Error in `grid_regular()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -314,7 +318,7 @@
       grid_regular(mtry())
     Condition
       Error in `grid_regular()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -323,7 +327,7 @@
       grid_regular(mtry(), sample_size())
     Condition
       Error in `grid_regular()`:
-      x These arguments contain unknowns: `mtry` and `sample_size`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -332,7 +336,7 @@
       grid_regular(list(mtry()))
     Condition
       Error in `grid_regular()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -341,7 +345,7 @@
       grid_regular(list(mtry_custom_name = mtry()))
     Condition
       Error in `grid_regular()`:
-      x This argument contains unknowns: `mtry_custom_name`.
+      x `mtry_custom_name` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -350,7 +354,7 @@
       grid_regular(list(mtry(), sample_size()))
     Condition
       Error in `grid_regular()`:
-      x These arguments contain unknowns: `mtry` and `sample_size`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 # grid_regular() errors with duplicate parameter ids
@@ -367,9 +371,9 @@
     Code
       grid_regular(list(a = penalty(), a = mtry()))
     Condition
-      Error in `parameters()`:
-      x `id` must have unique values.
-      i Duplicates: "a"
+      Error in `grid_regular()`:
+      x `a` must be a <param> object without unknowns.
+      i See the `dials::finalize()` function.
 
 # new param grid from conventional data frame
 
diff --git a/tests/testthat/_snaps/space_filling.md b/tests/testthat/_snaps/space_filling.md
index f047499c..dca7a9ab 100644
--- a/tests/testthat/_snaps/space_filling.md
+++ b/tests/testthat/_snaps/space_filling.md
@@ -126,16 +126,17 @@
     Code
       grid_space_filling(penalty(), "min_n")
     Condition
-      Error in `parameters()`:
-      ! `Argument 2` must be a <param> object, not the string "min_n".
+      Error in `grid_space_filling()`:
+      ! `Argument 2` must be a <param> object without unknowns, not the string "min_n".
 
 ---
 
     Code
       grid_space_filling(mtry(), "min_n")
     Condition
-      Error in `parameters()`:
-      ! `Argument 2` must be a <param> object, not the string "min_n".
+      Error in `grid_space_filling()`:
+      x `mtry` must be a <param> object without unknowns.
+      i See the `dials::finalize()` function.
 
 ---
 
@@ -150,16 +151,17 @@
     Code
       grid_space_filling(list(penalty(), "min_n"))
     Condition
-      Error in `parameters()`:
-      ! `Argument 2` must be a <param> object, not the string "min_n".
+      Error in `grid_space_filling()`:
+      ! `Argument 2` must be a <param> object without unknowns, not the string "min_n".
 
 ---
 
     Code
       grid_space_filling(list(mtry(), "min_n"))
     Condition
-      Error in `parameters()`:
-      ! `Argument 2` must be a <param> object, not the string "min_n".
+      Error in `grid_space_filling()`:
+      x `mtry` must be a <param> object without unknowns.
+      i See the `dials::finalize()` function.
 
 # grid_space_filling.parameters() checks for NA
 
@@ -167,7 +169,7 @@
       grid_space_filling(p)
     Condition
       Error in `grid_space_filling()`:
-      ! This argument must have class <param>: `NA`.
+      ! `penalty` must be a <param> object without unknowns, not `NA`.
 
 # grid_space_filling() errors with params containing unknowns
 
@@ -175,7 +177,7 @@
       grid_space_filling(parameters(mtry()))
     Condition
       Error in `grid_space_filling()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -184,7 +186,7 @@
       grid_space_filling(mtry())
     Condition
       Error in `grid_space_filling()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -193,7 +195,7 @@
       grid_space_filling(mtry(), sample_size())
     Condition
       Error in `grid_space_filling()`:
-      x These arguments contain unknowns: `mtry` and `sample_size`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -202,7 +204,7 @@
       grid_space_filling(list(mtry()))
     Condition
       Error in `grid_space_filling()`:
-      x This argument contains unknowns: `mtry`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -211,7 +213,7 @@
       grid_space_filling(list(mtry_custom_name = mtry()))
     Condition
       Error in `grid_space_filling()`:
-      x This argument contains unknowns: `mtry_custom_name`.
+      x `mtry_custom_name` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -220,7 +222,7 @@
       grid_space_filling(list(mtry(), sample_size()))
     Condition
       Error in `grid_space_filling()`:
-      x These arguments contain unknowns: `mtry` and `sample_size`.
+      x `mtry` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 # grid_space_filling() errors with duplicate parameter ids
@@ -237,7 +239,7 @@
     Code
       grid_space_filling(list(a = penalty(), a = mtry()))
     Condition
-      Error in `parameters()`:
-      x `id` must have unique values.
-      i Duplicates: "a"
+      Error in `grid_space_filling()`:
+      x `a` must be a <param> object without unknowns.
+      i See the `dials::finalize()` function.
 
diff --git a/tests/testthat/test-space_filling.R b/tests/testthat/test-space_filling.R
index 06e1b8e9..c13b6efb 100644
--- a/tests/testthat/test-space_filling.R
+++ b/tests/testthat/test-space_filling.R
@@ -151,7 +151,7 @@ test_that("sfd package designs AE", {
   dials_2_any <- grid_space_filling(prm, size = size, type = "any")
   sfd_2_any <- sfd::get_design(2, num_points = size, type = "any")
 
-  dials_2_ae <- grid_space_filling(prm, size = size, method = "audze_eglais")
+  dials_2_ae <- grid_space_filling(prm, size = size, type = "audze_eglais")
   sfd_2_ae <- sfd::get_design(2, num_points = size, type = "audze_eglais")
   names(sfd_2_ae) <- prm$id
   for (i in 1:2) {

From b63727834c50226fdbc340d006649c5b60317904 Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Wed, 8 Apr 2026 13:34:42 +0100
Subject: [PATCH 10/13] Remove now unnecessary checks

`validate_params()` can be removed when the user-facing `grid_max_entropy()` and `grid_latin_hypercube()` are removed and `make_max_entropy_grid()` and `make_latin_hypercube_grid()` don't need `validate_params()` anymore
---
 R/grids.R         | 4 ++--
 R/space_filling.R | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/R/grids.R b/R/grids.R
index 96400212..052a9c30 100644
--- a/R/grids.R
+++ b/R/grids.R
@@ -177,7 +177,7 @@ make_regular_grid <- function(
 ) {
   check_levels(levels, call = call)
   check_bool(original, call = call)
-  validate_params(..., call = call)
+
   filter_quo <- enquo(filter)
   param_quos <- quos(...)
   params <- map(param_quos, eval_tidy)
@@ -351,7 +351,7 @@ make_random_grid <- function(
 ) {
   check_number_whole(size, min = 1, call = call)
   check_bool(original, call = call)
-  validate_params(..., call = call)
+
   filter_quo <- enquo(filter)
   param_quos <- quos(...)
   params <- map(param_quos, eval_tidy)
diff --git a/R/space_filling.R b/R/space_filling.R
index 41db0a7b..e5f4a655 100644
--- a/R/space_filling.R
+++ b/R/space_filling.R
@@ -253,7 +253,7 @@ make_sfd <- function(
   check_number_whole(iter, min = 1, call = call)
   check_bool(original, call = call)
   type <- rlang::arg_match(type, sfd_types)
-  validate_params(..., call = call)
+
   param_quos <- quos(...)
   params <- map(param_quos, eval_tidy)
   p <- length(params)

From 82eb4f925392683115f5bde6679eb627c80b6d5d Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Wed, 8 Apr 2026 13:44:58 +0100
Subject: [PATCH 11/13] update tests

mainly to test for duplicate names again as intended
---
 tests/testthat/_snaps/grids.md | 20 ++++++++++----------
 tests/testthat/test-grids.R    |  9 ++++++---
 2 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/tests/testthat/_snaps/grids.md b/tests/testthat/_snaps/grids.md
index 07ec9b27..9ebb1360 100644
--- a/tests/testthat/_snaps/grids.md
+++ b/tests/testthat/_snaps/grids.md
@@ -215,11 +215,11 @@
 ---
 
     Code
-      grid_random(list(a = penalty(), a = mtry()))
+      grid_random(list(a = penalty(), a = penalty()))
     Condition
-      Error in `grid_random()`:
-      x `a` must be a <param> object without unknowns.
-      i See the `dials::finalize()` function.
+      Error in `parameters()`:
+      x `id` must have unique values.
+      i Duplicates: "a"
 
 # grid_regular validates inputs
 
@@ -324,10 +324,10 @@
 ---
 
     Code
-      grid_regular(mtry(), sample_size())
+      grid_regular(penalty(), sample_size())
     Condition
       Error in `grid_regular()`:
-      x `mtry` must be a <param> object without unknowns.
+      x `sample_size` must be a <param> object without unknowns.
       i See the `dials::finalize()` function.
 
 ---
@@ -369,11 +369,11 @@
 ---
 
     Code
-      grid_regular(list(a = penalty(), a = mtry()))
+      grid_regular(list(a = penalty(), a = penalty()))
     Condition
-      Error in `grid_regular()`:
-      x `a` must be a <param> object without unknowns.
-      i See the `dials::finalize()` function.
+      Error in `parameters()`:
+      x `id` must have unique values.
+      i Duplicates: "a"
 
 # new param grid from conventional data frame
 
diff --git a/tests/testthat/test-grids.R b/tests/testthat/test-grids.R
index 5199ab0d..743a42f8 100644
--- a/tests/testthat/test-grids.R
+++ b/tests/testthat/test-grids.R
@@ -147,7 +147,7 @@ test_that("grid_random() errors with duplicate parameter ids", {
   expect_snapshot(error = TRUE, grid_random(penalty(), penalty()))
 
   # list method
-  expect_snapshot(error = TRUE, grid_random(list(a = penalty(), a = mtry())))
+  expect_snapshot(error = TRUE, grid_random(list(a = penalty(), a = penalty())))
 })
 
 test_that("grid_regular validates inputs", {
@@ -182,7 +182,7 @@ test_that("grid_regular() errors with params containing unknowns", {
 
   # param method
   expect_snapshot(error = TRUE, grid_regular(mtry()))
-  expect_snapshot(error = TRUE, grid_regular(mtry(), sample_size()))
+  expect_snapshot(error = TRUE, grid_regular(penalty(), sample_size()))
 
   # list method
   expect_snapshot(error = TRUE, grid_regular(list(mtry())))
@@ -195,7 +195,10 @@ test_that("grid_regular() errors with duplicate parameter ids", {
   expect_snapshot(error = TRUE, grid_regular(penalty(), penalty()))
 
   # list method
-  expect_snapshot(error = TRUE, grid_regular(list(a = penalty(), a = mtry())))
+  expect_snapshot(
+    error = TRUE,
+    grid_regular(list(a = penalty(), a = penalty()))
+  )
 })
 
 test_that("new param grid from conventional data frame", {

From b077f1b99415908a8934cad927e6044f8c824002 Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Wed, 8 Apr 2026 14:17:10 +0100
Subject: [PATCH 12/13] Improve error for `parameters()` without inputs

---
 R/parameters.R                      | 5 +++++
 tests/testthat/_snaps/parameters.md | 6 ++----
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/R/parameters.R b/R/parameters.R
index 4e96c5e0..44b89cfa 100644
--- a/R/parameters.R
+++ b/R/parameters.R
@@ -25,6 +25,11 @@ parameters <- function(x, ...) {
 #' @export
 #' @rdname parameters
 parameters.default <- function(x, ...) {
+  if (missing(x)) {
+    cli::cli_abort(
+      "No input provided. Please supply at least one parameter object."
+    )
+  }
   cli::cli_abort(
     "{.cls parameters} objects cannot be created from {.obj_type_friendly {x}}."
   )
diff --git a/tests/testthat/_snaps/parameters.md b/tests/testthat/_snaps/parameters.md
index 2279d374..1668b1eb 100644
--- a/tests/testthat/_snaps/parameters.md
+++ b/tests/testthat/_snaps/parameters.md
@@ -183,10 +183,8 @@
     Code
       parameters()
     Condition
-      Error:
-      ! ! Could not evaluate cli `{}` expression: `x`.
-      Caused by error in `eval(expr, envir = envir)`:
-      ! argument "x" is missing, with no default
+      Error in `parameters()`:
+      ! No input provided. Please supply at least one parameter object.
 
 ---
 

From 5b4f2bafbe6c676fd5626b26f3e25a21a2ad4abc Mon Sep 17 00:00:00 2001
From: Hannah Frick <hannah@posit.co>
Date: Wed, 8 Apr 2026 15:31:54 +0100
Subject: [PATCH 13/13] Update NEWS

---
 NEWS.md | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index b9e49d5c..3269ec02 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -4,6 +4,9 @@
 
 * Parameters were added for the `tab_pfn` model: `num_estimators()`, `softmax_temperature()`, `balance_probabilities()`, `average_before_softmax()`, and `training_set_limit()`.
 
+* `parameters()` and the `grid_*()` functions give more information in the error message when non-parameter objects are passed in (#437).
+
+
 # dials 1.4.2
 
 * `prop_terms()` is a new parameter object used for recipes that do supervised feature selection (#395).