catch errors when constructor needs arguments

Author: teunbrand

R/layer.R

@@ -471,7 +471,16 @@ validate_subclass <- function(x, subclass,
   name <- snakeize(name)
   obj <- find_global(name, env = env, mode = "function")
   if (is.function(obj)) {
-    obj <- obj()
+    obj <- try_fetch(
+      obj(),
+      error = function(cnd) {
+        # replace `obj()` call with name of actual constructor
+        cnd$call <- call(name)
+        cli::cli_abort(
+          "Failed to retrieve a {.cls {subclass}} object from {.fn {name}}.",
+          parent = cnd, call = call
+        )
+      })
   }
   # Position constructors return classes directly
   if (inherits(obj, subclass)) {

tests/testthat/_snaps/layer.md

@@ -27,6 +27,12 @@
 
     `environment()` must be either a string or a <geom> object, not an environment.
 
+---
+
+    Failed to retrieve a <Geom> object from `geom_foo()`.
+    Caused by error in `geom_foo()`:
+    ! This function is unconstructable.
+
 # unknown params create warning
 
     Ignoring unknown parameters: `blah`

tests/testthat/test-layer.R

@@ -10,6 +10,9 @@ test_that("layer() checks its input", {
 
   expect_snapshot_error(validate_subclass("test", "geom"))
   expect_snapshot_error(validate_subclass(environment(), "geom"))
+
+  geom_foo <- function(...) stop("This function is unconstructable.")
+  expect_snapshot_error(layer("foo", "identity", position = "identity"))
 })
 
 test_that("aesthetics go in aes_params", {