Fix issue 1546, fill aesthetic does not show in the legend guide for stat_summary

NEWS.md

@@ -265,6 +265,9 @@ up correct aspect ratio, and draws a graticule.
   (@davharris #1951). It also orders by the `x` aesthetic, making it easier 
   to pass pre-computed values without manual ordering (@izahn, #2028).
   It also now knows it has `ymin` and `ymax` aesthetics (#1939).
+
+* Fixed legend-drawing bug when using `geom_smooth()` with stats other than
+  `stat_smooth()` (@clauswilke, #1546).
 
 * `geom_tile()` now once again interprets `width` and `height` correctly 
   (@malcolmbarrett, #2510)

R/geom-smooth.r

@@ -87,12 +87,12 @@ geom_smooth <- function(mapping = NULL, data = NULL,
 
   params <- list(
     na.rm = na.rm,
+    se = se,
     ...
   )
   if (identical(stat, "smooth")) {
     params$method <- method
     params$formula <- formula
-    params$se <- se
   }
 
   layer(
@@ -115,11 +115,19 @@ GeomSmooth <- ggproto("GeomSmooth", Geom,
   setup_data = function(data, params) {
     GeomLine$setup_data(data, params)
   },
-  draw_group = function(data, panel_params, coord) {
+
+  # The `se` argument is set to false here to make sure drawing the
+  # geom and drawing the legend is in synch. If the geom is used by a
+  # stat that doesn't set the `se` argument then `se` will be missing
+  # and the legend key won't be drawn. With `se = FALSE` here the
+  # ribbon won't be drawn either in that case, keeping the overall
+  # behavior predictable and sensible. The user will realize that they
+  # need to set `se = TRUE` to obtain the ribbon and the legend key.
+  draw_group = function(data, panel_params, coord, se = FALSE) {
     ribbon <- transform(data, colour = NA)
     path <- transform(data, alpha = NA)
 
-    has_ribbon <- !is.null(data$ymax) && !is.null(data$ymin)
+    has_ribbon <- se && !is.null(data$ymax) && !is.null(data$ymin)
 
     gList(
       if (has_ribbon) GeomRibbon$draw_group(ribbon, panel_params, coord),

tests/testthat/test-function-args.r

@@ -13,7 +13,7 @@ test_that("geom_xxx and GeomXxx$draw arg defaults match", {
   # These aren't actually geoms, or need special parameters and can't be tested this way.
   geom_fun_names <- setdiff(
     geom_fun_names,
-    c("geom_map", "geom_sf", "geom_column", "annotation_custom", "annotation_map",
+    c("geom_map", "geom_sf", "geom_smooth", "geom_column", "annotation_custom", "annotation_map",
       "annotation_raster", "annotation_id")
   )
 

tests/testthat/test-geom-smooth.R

@@ -8,3 +8,21 @@ test_that("Data is ordered by x", {
 
   expect_equal(layer_data(ps)[c("x", "y")], df[order(df$x), ])
 })
+
+# Visual tests ------------------------------------------------------------
+
+test_that("geom_smooth() works with alternative stats", {
+  df <- data.frame(x = c(1, 1, 2, 2, 1, 1, 2, 2),
+                   y = c(1, 2, 2, 3, 2, 3, 1, 2),
+                   fill = c(rep("A", 4), rep("B", 4)))
+
+  expect_doppelganger("ribbon turned on in geom_smooth", {
+    ggplot(df, aes(x, y, color = fill, fill = fill)) +
+      geom_smooth(stat = "summary") # ribbon on by default
+  })
+
+  expect_doppelganger("ribbon turned off in geom_smooth", {
+    ggplot(df, aes(x, y, color = fill, fill = fill)) +
+      geom_smooth(stat = "summary", se = FALSE) # ribbon is turned off via `se = FALSE`
+  })
+})