allow inheritance of geom elements

Author: teunbrand

R/geom-.R

@@ -133,7 +133,7 @@ Geom <- ggproto("Geom",
     # Fill in missing aesthetics with their defaults
     missing_aes <- setdiff(names(default_aes), names(data))
     default_aes <- default_aes[missing_aes]
-    themed_defaults <- eval_from_theme(default_aes, theme)
+    themed_defaults <- eval_from_theme(default_aes, theme, class(self))
     default_aes[names(themed_defaults)] <- themed_defaults
 
     # Mark staged/scaled defaults as modifier (#6135)
@@ -243,13 +243,33 @@ Geom <- ggproto("Geom",
 #' @rdname is_tests
 is.geom <- function(x) inherits(x, "Geom")
 
-eval_from_theme <- function(aesthetics, theme) {
+eval_from_theme <- function(aesthetics, theme, class = NULL) {
   themed <- is_themed_aes(aesthetics)
   if (!any(themed)) {
     return(aesthetics)
   }
-  settings <- calc_element("geom", theme) %||% .default_geom_element
-  lapply(aesthetics[themed], eval_tidy, data = settings)
+
+  element <- calc_element("geom", theme) %||% .default_geom_element
+  class <- setdiff(class, c("Geom", "ggproto", "gg"))
+
+  if (length(class) > 0) {
+
+    # CamelCase to dot.case
+    class <- gsub("([A-Za-z])([A-Z])([a-z])", "\\1.\\2\\3", class)
+    class <- gsub("([a-z])([A-Z])", "\\1.\\2", class)
+    class <- to_lower_ascii(class)
+
+    class <- class[class %in% names(theme)]
+
+    # Inherit up to parent geom class
+    if (length(class) > 0) {
+      for (cls in rev(class)) {
+        element <- combine_elements(theme[[cls]], element)
+      }
+    }
+  }
+
+  lapply(aesthetics[themed], eval_tidy, data = element)
 }
 
 #' Graphical units