Fix labeller to pass .default for lookups (#4031) (#4032)

* Fix labeller to pass .default for lookups (#4031)

Pass .default to as_labeller even when margin_labeller is null, such as
when using named arguements for a lookup table.

* Correct style, and add line to NEWS.md

* Move NEWS bullet into dev version section

Co-authored-by: Kara Woo <[email protected]>

Author: waltersom

NEWS.md

@@ -1,5 +1,8 @@
 # ggplot2 (development version)
 
+* Fixed a bug in `labeller()` so that `.default` is passed to `as_labeller()`
+  when labellers are specified by naming faceting variables. (@waltersom, #4031)
+
 # ggplot2 3.3.2
 This is a small release focusing on fixing regressions introduced in 3.3.1.
 

R/labeller.r

@@ -437,7 +437,7 @@ labeller <- function(..., .rows = NULL, .cols = NULL,
     }
 
     if (is.null(margin_labeller)) {
-      labellers <- lapply(dots, as_labeller)
+      labellers <- lapply(dots, as_labeller, default = .default)
     } else {
       margin_labeller <- as_labeller(margin_labeller, default = .default,
                                      multi_line = .multi_line)