Fix error messages

Author: teunbrand

R/geom-ribbon.R

@@ -145,9 +145,9 @@ GeomRibbon <- ggproto("GeomRibbon", Geom,
       # these to vary
       non_constant <- setdiff(non_constant, c("fill", "alpha"))
     }
-    if (length(non_constant) > 1) {
+    if (length(non_constant) > 0) {
       cli::cli_abort(
-        "Aesthetics can not vary along a ribbon: {.field {.and non_constant}}."
+        "Aesthetics can not vary along a ribbon: {.and {.field {non_constant}}}."
       )
     }
     if (length(aes$fill) > 1 || length(aes$alpha) > 1) {

tests/testthat/_snaps/geom-ribbon.md

@@ -17,7 +17,7 @@
     Problem while converting geom to grob.
     i Error occurred in the 1st layer.
     Caused by error in `draw_group()`:
-    ! Aesthetics can not vary along a ribbon.
+    ! Aesthetics can not vary along a ribbon: linewidth.
 
 ---
 

tests/testthat/test-geom-ribbon.R

@@ -7,7 +7,7 @@ test_that("geom_ribbon() checks the aesthetics", {
     geom_ribbon(aes(y = year, xmin = level - 5, xmax = level + 5), orientation = "x")
   expect_snapshot_error(ggplotGrob(p))
   p <- ggplot(huron) +
-    geom_ribbon(aes(year, ymin = level - 5, ymax = level + 5, fill = year))
+    geom_ribbon(aes(year, ymin = level - 5, ymax = level + 5, linewidth = year))
   expect_snapshot_error(ggplotGrob(p))
 
   expect_snapshot_error(geom_ribbon(aes(year, ymin = level - 5, ymax = level + 5), outline.type = "test"))