Enable horizontal margins on (sub)title/caption (#5545)

* enable x-margins

* add news bullet

Author: teunbrand

NEWS.md

@@ -1,5 +1,8 @@
 # ggplot2 (development version)
 
+* The plot's title, subtitle and caption now obey horizontal text margins
+  (#5533).
+
 * New `guide_axis_stack()` to combine other axis guides on top of one another.
 
 * New `guide_custom()` function for drawing custom graphical objects (grobs)

R/plot-build.R

@@ -265,15 +265,24 @@ ggplot_gtable.ggplot_built <- function(data) {
   }
 
   # Title
-  title <- element_render(theme, "plot.title", plot$labels$title, margin_y = TRUE)
+  title <- element_render(
+    theme, "plot.title", plot$labels$title,
+    margin_y = TRUE, margin_x = TRUE
+  )
   title_height <- grobHeight(title)
 
   # Subtitle
-  subtitle <- element_render(theme, "plot.subtitle", plot$labels$subtitle, margin_y = TRUE)
+  subtitle <- element_render(
+    theme, "plot.subtitle", plot$labels$subtitle,
+    margin_y = TRUE, margin_x = TRUE
+  )
   subtitle_height <- grobHeight(subtitle)
 
   # whole plot annotation
-  caption <- element_render(theme, "plot.caption", plot$labels$caption, margin_y = TRUE)
+  caption <- element_render(
+    theme, "plot.caption", plot$labels$caption,
+    margin_y = TRUE, margin_x = TRUE
+  )
   caption_height <- grobHeight(caption)
 
   # positioning of title and subtitle is governed by plot.title.position