Warn about infinite geom_spoke(radius) (#6678)

* warn for infinite radius values

* add news bullet

Author: teunbrand

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* Using infinite `radius` aesthetic in `geom_spoke()` now throws a warning 
+  (#6671)
 * Scales and guides specified by a string can now use package name prefixes to
   indicate a namespace wherein to look for the scale/guide. For example, one can
   use `scale_x_continuous(guide = "legendry::axis_base")` (@teunbrand, #4705).

R/geom-spoke.R

@@ -8,6 +8,10 @@ GeomSpoke <- ggproto(
     data$radius <- data$radius %||% params$radius
     data$angle <- data$angle %||% params$angle
 
+    if (any(is.infinite(data$radius))) {
+      cli::cli_warn("Infinite {.field radius} values are unreliable.")
+    }
+
     transform(data,
               xend = x + cos(angle) * radius,
               yend = y + sin(angle) * radius

tests/testthat/_snaps/geom-spoke.md

@@ -0,0 +1,4 @@
+# geom_spoke warns about infinite radius (#6671)
+
+    Infinite radius values are unreliable.
+

tests/testthat/test-geom-spoke.R

@@ -0,0 +1,4 @@
+test_that("geom_spoke warns about infinite radius (#6671)", {
+  p <- ggplot() + geom_spoke(aes(0, 0, angle = pi / 4, radius = Inf))
+  expect_snapshot_warning(ggplot_build(p))
+})