fix title_spec() for vectorized input

NEWS.md

@@ -1,5 +1,9 @@
 # ggplot2 (development version)
 
+* `element_text()` now issues a warning when vectorized arguments are provided, as in
+  `colour = c("red", "green", "blue")`. Such use is discouraged and not officially supported
+   (@clauswilke, #3492).
+
 * stacking text when calculating the labels and the y axis with
   `stat_summary()` now works (@ikosmidis, #2709)
 

R/margins.R

@@ -71,8 +71,8 @@ title_spec <- function(label, x, y, hjust, vjust, angle, gp = gpar(),
   # Use trigonometry to calculate grobheight and width for rotated grobs. This is only
   # exactly correct when vjust = 1. We need to take the absolute value so we don't make
   # the grob smaller when it's flipped over.
-  text_height <- unit(1, "grobheight", text_grob) + abs(cos(angle / 180 * pi)) * descent
-  text_width <- unit(1, "grobwidth", text_grob) + abs(sin(angle / 180 * pi)) * descent
+  text_height <- unit(1, "grobheight", text_grob) + abs(cos(angle[1] / 180 * pi)) * descent
+  text_width <- unit(1, "grobwidth", text_grob) + abs(sin(angle[1] / 180 * pi)) * descent
 
   if (isTRUE(debug)) {
     children <- gList(
@@ -333,29 +333,36 @@ rotate_just <- function(angle, hjust, vjust) {
   list(hjust = hnew, vjust = vnew)
 }
 descent_cache <- new.env(parent = emptyenv())
+# Important: This function is not vectorized. Do not use to look up multiple
+# font descents at once.
 font_descent <- function(family = "", face = "plain", size = 12, cex = 1) {
   cur_dev <- names(grDevices::dev.cur())
+  if (cur_dev == "null device") {
+    cache <- FALSE   # don't cache if no device open
+  } else {
+    cache <- TRUE
+  }
   key <- paste0(cur_dev, ':', family, ':', face, ":", size, ":", cex)
-  descents <- lapply(key, function(k) {
-    descent <- descent_cache[[k]]
-
-    if (is.null(descent)) {
-      descent <- convertHeight(grobDescent(textGrob(
-        label = "gjpqyQ",
-        gp = gpar(
-          fontsize = size,
-          cex = cex,
-          fontfamily = family,
-          fontface = face
-        )
-      )), 'inches')
-      descent_cache[[k]] <- descent
+  # we only look up the first result; this function is not vectorized
+  key <- key[1]
+
+  descent <- descent_cache[[key]]
+
+  if (is.null(descent)) {
+    descent <- convertHeight(grobDescent(textGrob(
+      label = "gjpqyQ",
+      gp = gpar(
+        fontsize = size,
+        cex = cex,
+        fontfamily = family,
+        fontface = face
+      )
+    )), 'inches')
+
+    if (cache) {
+      descent_cache[[key]] <- descent
     }
-    descent
-  })
-  if (length(descents) == 1) {
-    descents[[1]]
-  } else {
-    do.call(unit.c, descents)
   }
+
+  descent
 }

R/theme-elements.r

@@ -112,6 +112,20 @@ element_text <- function(family = NULL, face = NULL, colour = NULL,
   color = NULL, margin = NULL, debug = NULL, inherit.blank = FALSE) {
 
   if (!is.null(color))  colour <- color
+
+  n <- max(
+    length(family), length(face), length(colour), length(size),
+    length(hjust), length(vjust), length(angle), length(lineheight)
+  )
+  if (n > 1) {
+    warning(
+      "Vectorized input to `element_text()` is not officially supported.\n",
+      "Results may be unexpected or may change in future versions of ggplot2.",
+      call. = FALSE
+    )
+  }
+
+
   structure(
     list(family = family, face = face, colour = colour, size = size,
       hjust = hjust, vjust = vjust, angle = angle, lineheight = lineheight,