Make sure that expressions are reencoded as expressions when collapsed (#4418)

Author: thomasp85

NEWS.md

@@ -1,5 +1,9 @@
 # ggplot2 (development version)
 
+
+* Fix bug in `labeller()` where parsing was turned off if `.multiline = FALSE`
+  (@thomasp85, #4084)
+  
 * Fix a bug in `qplot()` when supplying `c(NA, NA)` as axis limits 
   (@thomasp85, #4027)
 

R/labeller.r

@@ -88,8 +88,13 @@
 NULL
 
 collapse_labels_lines <- function(labels) {
+  is_exp <- vapply(labels, function(l) length(l) > 0 && is.expression(l[[1]]), logical(1))
   out <- do.call("Map", c(list(paste, sep = ", "), labels))
-  list(unname(unlist(out)))
+  label <- list(unname(unlist(out)))
+  if (all(is_exp)) {
+    label <- lapply(label, function(l) list(parse(text = paste0("list(", l, ")"))))
+  }
+  label
 }
 
 #' @rdname labellers