Override default density method (#5358)

tests/testthat/helper-density.R

@@ -0,0 +1,21 @@
+
+# In R devel from 4.3.0 onwards, the density calculation has slightly changed,
+# which affects visual snapshots that use a density calculation, like
+# `geom_violin()` and `geom_density()`.
+# See https://developer.r-project.org/blosxom.cgi/R-devel/NEWS/2023/05/03#n2023-05-03
+#
+# It has a backwards compatibility argument called 'old.coords' that can be used
+# to perform the classic density calculation, which means we can stably use
+# visual tests in R devel.
+#
+# Since that argument is not available in older versions, we have to use the
+# following workaround. Here, we conditionally override the default
+# density method to use `old.coords = TRUE`.
+if ("old.coords" %in% names(formals(stats::density.default))) {
+  registerS3method(
+    "density", "default",
+    function(..., old.coords = TRUE) {
+      stats::density.default(..., old.coords = old.coords)
+    }
+  )
+}