Fix for position_dodge(preserve = "single") with location based data (

#6000)

* fallback for location based data

* Warn when x/xmin are absent

R/position-dodge.R

@@ -106,6 +106,11 @@ PositionDodge <- ggproto("PositionDodge", Position,
   reverse = NULL,
   setup_params = function(self, data) {
     flipped_aes <- has_flipped_aes(data, default = self$orientation == "y")
+    check_required_aesthetics(
+      if (flipped_aes) "y|ymin" else "x|xmin",
+      names(data), snake_class(self)
+    )
+
     data <- flip_data(data, flipped_aes)
     if (is.null(data$xmin) && is.null(data$xmax) && is.null(self$width)) {
       cli::cli_warn(c(
@@ -117,8 +122,10 @@ PositionDodge <- ggproto("PositionDodge", Position,
     if (identical(self$preserve, "total")) {
       n <- NULL
     } else {
-      n <- vec_unique(data[c("group", "PANEL", "xmin")])
-      n <- vec_group_id(n[c("PANEL", "xmin")])
+      data$xmin <- data$xmin %||% data$x
+      cols <- intersect(colnames(data), c("group", "PANEL", "xmin"))
+      n <- vec_unique(data[cols])
+      n <- vec_group_id(n[setdiff(cols, "group")])
       n <- max(tabulate(n, attr(n, "n")))
     }
 

tests/testthat/test-position_dodge.R

@@ -37,3 +37,19 @@ test_that("position_dodge() can reverse the dodge order", {
   ld <- get_layer_data(p + geom_col(position = position_dodge(reverse = FALSE)))
   expect_equal(ld$label[order(ld$x)], c("A", "A", "B", "B", "C"))
 })
+
+test_that("position_dodge warns about missing required aesthetics", {
+
+  # Bit of a contrived geom to not have a required 'x' aesthetic
+  GeomDummy <- ggproto(NULL, GeomPoint, required_aes = NULL, optional_aes = "x")
+
+  p <- ggplot(mtcars, aes(cyl, disp, colour = factor(vs))) +
+    layer(
+      geom = GeomDummy,
+      stat = "identity",
+      position = position_dodge(width = 0.5),
+      mapping = aes(x = NULL)
+    )
+
+  expect_error(ggplot_build(p), "requires the following missing aesthetics")
+})