From 03f1fa176dae9b56d067d36912cff3f13de5d593 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Sun, 19 Mar 2023 20:27:30 +0100
Subject: [PATCH] Better message in facetted_pos_scales #91

---
 R/facetted_pos_scales.R                      | 15 ++++++++++++++-
 tests/testthat/_snaps/facetted_pos_scales.md |  8 ++++++++
 tests/testthat/test-facetted_pos_scales.R    | 14 ++++++--------
 3 files changed, 28 insertions(+), 9 deletions(-)
 create mode 100644 tests/testthat/_snaps/facetted_pos_scales.md

diff --git a/R/facetted_pos_scales.R b/R/facetted_pos_scales.R
index 34d8042..c0c8bd5 100644
--- a/R/facetted_pos_scales.R
+++ b/R/facetted_pos_scales.R
@@ -89,7 +89,20 @@ facetted_pos_scales <- function(x = NULL, y = NULL) {
   x_test <- check_facetted_scale(x, "x")
   y_test <- check_facetted_scale(y, "y")
   if (!(x_test & y_test)) {
-    stop("Invalid facetted scale specifications.")
+    if (!x_test & !y_test) {
+      arg  <- "The {.arg x} and {.arg y} arguments "
+      type <- "appropriate"
+    } else if (!x_test) {
+      arg  <- "The {.arg x} argument "
+      type <- "{.field x}"
+    } else {
+      arg  <- "The {.arg y} argument "
+      type <- "{.field y}"
+    }
+    cli::cli_abort(paste0(
+      arg, "should be {.val NULL}, or a list of formulas and/or ",
+      "position scales with the ", type, " aesthetic."
+    ))
   }
 
   x <- validate_facetted_scale(x, "x")
diff --git a/tests/testthat/_snaps/facetted_pos_scales.md b/tests/testthat/_snaps/facetted_pos_scales.md
new file mode 100644
index 0000000..0a70edb
--- /dev/null
+++ b/tests/testthat/_snaps/facetted_pos_scales.md
@@ -0,0 +1,8 @@
+# facetted_pos_scales warns about invalid scales
+
+    The `x` argument should be "NULL", or a list of formulas and/or position scales with the x aesthetic.
+
+---
+
+    The `y` argument should be "NULL", or a list of formulas and/or position scales with the y aesthetic.
+
diff --git a/tests/testthat/test-facetted_pos_scales.R b/tests/testthat/test-facetted_pos_scales.R
index bdf3570..70449f2 100644
--- a/tests/testthat/test-facetted_pos_scales.R
+++ b/tests/testthat/test-facetted_pos_scales.R
@@ -346,16 +346,14 @@ test_that("facetted_pos_scales can handle date scales", {
 test_that("facetted_pos_scales warns about invalid scales", {
 
   # Nonsensical input
-  test <- substitute(facetted_pos_scales(y = list(
-    NULL, scale_y_continuous(), "nonsense")
-  ))
-  expect_error(eval(test), "Invalid facetted scale")
+  expect_snapshot_error(
+    facetted_pos_scales(x = list(NULL, scale_x_continuous(), "nonsense"))
+  )
 
   # Incompatible aesthetics (x-scale to y-argument)
-  test <- substitute(facetted_pos_scales(y = list(
-    NULL, scale_x_continuous()
-  )))
-  expect_error(eval(test), "Invalid facetted scale")
+  expect_snapshot_error(
+    facetted_pos_scales(y = list(NULL, scale_x_continuous()))
+  )
 })
 
 test_that("facetted_pos_scales warns about invalid scales in formulas", {