Restore axis line when breaks = NULL.

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* Fixed regression in axes where `breaks = NULL` caused the axes to disappear
+  instead of just rendering the axis line (@teunbrand, #5816).
 * `geom_point()` can be dodged vertically by using 
   `position_dodge(..., orientation = "y")` (@teunbrand, #5809).
 * Fixed bug where `na.value` was incorrectly mapped to non-`NA` values 

R/guide-axis-theta.R

@@ -74,17 +74,22 @@ GuideAxisTheta <- ggproto(
 
   transform = function(params, coord, panel_params) {
 
-    opposite <- setdiff(c("x", "y"), params$aesthetic)
-    params$key[[opposite]] <- switch(params$position,
-                                     theta.sec = -Inf,
-                                     top = -Inf,
-                                     right = -Inf,
-                                     Inf)
+    if (nrow(params$key) > 0) {
+      opposite <- setdiff(c("x", "y"), params$aesthetic)
+      params$key[[opposite]] <- switch(params$position,
+                                       theta.sec = -Inf,
+                                       top = -Inf,
+                                       right = -Inf,
+                                       Inf)
+    }
 
     params <- GuideAxis$transform(params, coord, panel_params)
 
     key <- params$key
     n <- nrow(key)
+    if (n < 1) {
+      return(params)
+    }
 
     if (!("theta" %in% names(key))) {
       # We likely have a linear coord, so we match the text angles to
@@ -242,6 +247,12 @@ GuideAxisTheta <- ggproto(
     grobTree(major, minor, name = "ticks")
   },
 
+  draw_early_exit = function(self, params, elements) {
+    line <- self$build_decor(decor = params$decor, elements = elements,
+                             params = params)
+    gTree(children = gList(line), offset = unit(0, "cm"))
+  },
+
   measure_grobs = function(grobs, params, elements) {
     # As this guide is expected to be placed in the interior of coord_radial,
     # we don't need to measure grob sizes nor arrange the layout.

R/guide-axis.R

@@ -115,6 +115,9 @@ GuideAxis <- ggproto(
 
   extract_key = function(scale, aesthetic, minor.ticks = FALSE, ...) {
     major <- Guide$extract_key(scale, aesthetic, ...)
+    if (is.null(major) && is.null(scale$scale$get_breaks())) {
+      major <- data_frame0()
+    }
     if (!minor.ticks) {
       return(major)
     }
@@ -147,10 +150,11 @@ GuideAxis <- ggproto(
   extract_decor = function(scale, aesthetic, position, key, cap = "none", ...) {
 
     value <- c(-Inf, Inf)
-    if (cap %in% c("both", "upper")) {
+    has_key <- !(is.null(key) || nrow(key) < 1)
+    if (cap %in% c("both", "upper") && has_key) {
       value[2] <- max(key[[aesthetic]])
     }
-    if (cap %in% c("both", "lower")) {
+    if (cap %in% c("both", "lower") && has_key) {
       value[1] <- min(key[[aesthetic]])
     }
 
@@ -166,26 +170,32 @@ GuideAxis <- ggproto(
   transform = function(self, params, coord, panel_params) {
     key <- params$key
     position <- params$position
-
-    if (is.null(position) || nrow(key) == 0) {
-      return(params)
+    check <- FALSE
+
+    if (!(is.null(position) || nrow(key) == 0)) {
+      check <- TRUE
+      aesthetics <- names(key)[!grepl("^\\.", names(key))]
+      if (!all(c("x", "y") %in% aesthetics)) {
+        other_aesthetic <- setdiff(c("x", "y"), aesthetics)
+        override_value <- if (position %in% c("bottom", "left")) -Inf else Inf
+        key[[other_aesthetic]] <- override_value
+      }
+      key <- coord$transform(key, panel_params)
+      params$key <- key
     }
 
-    aesthetics <- names(key)[!grepl("^\\.", names(key))]
-    if (!all(c("x", "y") %in% aesthetics)) {
-      other_aesthetic <- setdiff(c("x", "y"), aesthetics)
-      override_value <- if (position %in% c("bottom", "left")) -Inf else Inf
-      key[[other_aesthetic]] <- override_value
-    }
-    key <- coord$transform(key, panel_params)
-    params$key <- key
+    if (!is.null(params$decor)) {
+      params$decor <- coord_munch(coord, params$decor, panel_params)
 
-    params$decor <- coord_munch(coord, params$decor, panel_params)
+      if (!coord$is_linear()) {
+        # For non-linear coords, we hardcode the opposite position
+        params$decor$x <- switch(position, left = 1, right = 0, params$decor$x)
+        params$decor$y <- switch(position, top = 0, bottom = 1, params$decor$y)
+      }
+    }
 
-    if (!coord$is_linear()) {
-      # For non-linear coords, we hardcode the opposite position
-      params$decor$x <- switch(position, left = 1, right = 0, params$decor$x)
-      params$decor$y <- switch(position, top = 0, bottom = 1, params$decor$y)
+    if (!check) {
+      return(params)
     }
 
     # Ported over from `warn_for_position_guide`