zero-range limits in binned scale

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* `scale_*_binned()` handles zero-range limits more gracefully (@teunbrand, 
+  #5066)
 * Binned scales are now compatible with `trans = "date"` and `trans = "time"` 
   (@teunbrand, #4217).
 * `ggsave()` warns when multiple `filename`s are given, and only writes to the
@@ -12,7 +14,7 @@
   (@teunbrand based on @clauswilke's suggestion #5051).
 * Fixed a regression in `Coord$train_panel_guides()` where names of guides were 
   dropped (@maxsutton, #5063)
-  
+
 # ggplot2 3.4.0
 This is a minor release focusing on tightening up the internals and ironing out
 some inconsistencies in the API. The biggest change is the addition of the 

R/scale-.r

@@ -1021,16 +1021,22 @@ ScaleBinned <- ggproto("ScaleBinned", Scale,
       x <- self$rescale(self$oob(x, range = limits), limits)
       breaks <- self$rescale(breaks, limits)
 
-      x_binned <- cut(x, breaks,
-        labels = FALSE,
-        include.lowest = TRUE,
-        right = self$right
-      )
+      if (length(breaks) > 1) {
+        x_binned <- cut(x, breaks,
+          labels = FALSE,
+          include.lowest = TRUE,
+          right = self$right
+        )
+        midpoints <- breaks[-1] - diff(breaks) / 2
+      } else {
+        x_binned  <- 1L
+        midpoints <- 0.5
+      }
 
       if (!is.null(self$palette.cache)) {
         pal <- self$palette.cache
       } else {
-        pal <- self$palette(breaks[-1] - diff(breaks) / 2)
+        pal <- self$palette(midpoints)
         self$palette.cache <- pal
       }