🐛 Deal with empty radial axes

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* `coord_radial()` now displays no axis instead of throwing an error when
+  a scale has no breaks (@teunbrand, #6271).
 * `geom_ribbon()` now appropriately warns about, and removes, missing values 
   (@teunbrand, #6243).
 * `guide_*()` can now accept two inside legend theme elements:

R/coord-radial.R

@@ -250,11 +250,18 @@ CoordRadial <- ggproto("CoordRadial", Coord,
     names(gdefs) <- aesthetics
 
     # Train theta guide
-    for (t in intersect(c("theta", "theta.sec"), aesthetics[!empty])) {
-      gdefs[[t]] <- guides[[t]]$train(gdefs[[t]], panel_params[[t]])
-      gdefs[[t]] <- guides[[t]]$transform(gdefs[[t]], self, panel_params)
-      gdefs[[t]] <- guides[[t]]$get_layer_key(gdefs[[t]], layers)
-    }
+    t <- intersect(c("theta", "theta.sec"), aesthetics[!empty])
+    gdefs[t] <- Map(
+      function(guide, guide_param, scale) {
+        guide_param$theme_suffix <- "theta"
+        guide_param <- guide$train(guide_param, scale)
+        guide_param <- guide$transform(guide_param, self, panel_params)
+        guide_param <- guide$get_layer_key(guide_param, layers)
+      },
+      guide = guides[t],
+      guide_param = gdefs[t],
+      scale = panel_params[t]
+    )
 
     if (!isFALSE(self$r_axis_inside)) {
       # For radial axis, we need to pretend that rotation starts at 0 and
@@ -269,17 +276,18 @@ CoordRadial <- ggproto("CoordRadial", Coord,
     temp <- modify_list(panel_params, mod)
 
     # Train radial guide
-    for (r in intersect(c("r", "r.sec"), aesthetics[!empty])) {
-      gdefs[[r]] <- guides[[r]]$train(gdefs[[r]], panel_params[[r]])
-      gdefs[[r]] <- guides[[r]]$transform(gdefs[[r]], self, temp) # Use temp
-      gdefs[[r]] <- guides[[r]]$get_layer_key(gdefs[[r]], layers)
-    }
-
-    # Set theme suffixes
-    gdefs$theta$theme_suffix     <- "theta"
-    gdefs$theta.sec$theme_suffix <- "theta"
-    gdefs$r$theme_suffix         <- "r"
-    gdefs$r.sec$theme_suffix     <- "r"
+    r <- intersect(c("r", "r.sec"), aesthetics[!empty])
+    gdefs[r] <- Map(
+      function(guide, guide_param, scale) {
+        guide_param$theme_suffix <- "r"
+        guide_param <- guide$train(guide_param, scale)
+        guide_param <- guide$transform(guide_param, self, temp)
+        guide_param <- guide$get_layer_key(guide_param, layers)
+      },
+      guide = guides[r],
+      guide_param = gdefs[r],
+      scale = panel_params[r]
+    )
 
     panel_params$guides$update_params(gdefs)
     panel_params

R/guide-axis-theta.R

@@ -63,22 +63,26 @@ GuideAxisTheta <- ggproto(
 
   transform = function(params, coord, panel_params) {
 
-    opposite_var <- setdiff(c("x", "y"), params$aesthetic)
-    opposite_value <- switch(params$position, top = , right = , theta.sec = -Inf, Inf)
-    if (is.unsorted(panel_params$inner_radius %||% NA)) {
-      opposite_value <- -opposite_value
-    }
-    if (nrow(params$key) > 0) {
-      params$key[[opposite_var]] <- opposite_value
-    }
-    if (nrow(params$decor) > 0) {
-      params$decor[[opposite_var]] <- opposite_value
+    position <- params$position
+
+    if (!is.null(position)) {
+      opposite_var <- setdiff(c("x", "y"), params$aesthetic)
+      opposite_value <- switch(position, top = , right = , theta.sec = -Inf, Inf)
+      if (is.unsorted(panel_params$inner_radius %||% NA)) {
+        opposite_value <- -opposite_value
+      }
+      if (nrow(params$key) > 0) {
+        params$key[[opposite_var]] <- opposite_value
+      }
+      if (nrow(params$decor) > 0) {
+        params$decor[[opposite_var]] <- opposite_value
+      }
     }
 
     params <- GuideAxis$transform(params, coord, panel_params)
 
     key <- params$key
-    n <- nrow(key)
+    n <- vec_size(key)
     if (n < 1) {
       return(params)
     }

R/guides-.R

@@ -526,7 +526,7 @@ Guides <- ggproto(
       coord <- coord %||% default_inside_position %||% just
 
       groups$justs[[i]] <- just
-      groups$coord[[i]] <- coord
+      groups$coords[[i]] <- coord
     }
 
     groups <- vec_group_loc(vec_slice(groups, keep))
@@ -541,10 +541,10 @@ Guides <- ggproto(
     # prepare output
     for (i in vec_seq_along(groups)) {
       adjust <- NULL
-      position <- groups$key$position[i]
+      position <- groups$key$positions[i]
       if (position == "inside") {
         adjust <- theme(
-          legend.position.inside = groups$key$coord[[i]],
+          legend.position.inside = groups$key$coords[[i]],
           legend.justification.inside = groups$key$justs[[i]]
         )
       }

tests/testthat/test-coord-polar.R

@@ -197,6 +197,18 @@ test_that("radial coords can be reversed", {
   expect_equal(as.numeric(fwd$y), rev(as.numeric(rev$y)))
 })
 
+test_that("coord_radial can deal with empty breaks (#6271)", {
+  p <- ggplot_build(
+    ggplot(mtcars, aes(mpg, disp)) +
+      geom_point() +
+      coord_radial() +
+      scale_x_continuous(breaks = numeric()) +
+      scale_y_continuous(breaks = numeric())
+  )
+  guides <- p$layout$panel_params[[1]]$guides$guides
+  is_none <- vapply(guides, inherits, logical(1), what = "GuideNone")
+  expect_true(all(is_none))
+})
 
 # Visual tests ------------------------------------------------------------