Fix cryptic error messages caused by missing aesthetics (#2754)

Fixes #2637 ; Fixes #2706

Author: Dana Paige Seidel

NEWS.md

@@ -1,5 +1,8 @@
 # ggplot2 3.0.0.9000
 
+*   All `geom_*()` now display an informative error message when required 
+    aesthetics are missing (@dpseidel, #2637 and #2706).
+
 *   `sec_axis()` and `dup_axis()` now return appropriate breaks for the secondary
     axis when applied to log transformed scales (@dpseidel, #2729).
 

R/layer.r

@@ -283,15 +283,14 @@ Layer <- ggproto("Layer", NULL,
 
   compute_geom_1 = function(self, data) {
     if (empty(data)) return(data.frame())
-    data <- self$geom$setup_data(data, c(self$geom_params, self$aes_params))
 
     check_required_aesthetics(
       self$geom$required_aes,
       c(names(data), names(self$aes_params)),
       snake_class(self$geom)
     )
 
-    data
+    self$geom$setup_data(data, c(self$geom_params, self$aes_params))
   },
 
   compute_position = function(self, data, layout) {

tests/testthat/test-layer.r

@@ -26,6 +26,18 @@ test_that("column vectors are allowed (#2609)", {
   expect_is(layer_data(p), "data.frame")
 })
 
+test_that("missing aesthetics trigger informative error", {
+  df <- data.frame(x = 1:10)
+  expect_error(
+    ggplot_build(ggplot(df) + geom_line()),
+    "requires the following missing aesthetics:"
+  )
+  expect_error(
+    ggplot_build(ggplot(df) + geom_col()),
+    "requires the following missing aesthetics:"
+  )
+})
+
 # Data extraction ---------------------------------------------------------
 
 test_that("layer_data returns a data.frame", {