Warn that cropping is disabled if pdfcrop or ghostscript are not found.

NEWS.md

@@ -15,6 +15,7 @@ rmarkdown 2.7
 
 - Do not force `options(htmltools.preserve.raw = TRUE)` when this option has been set, otherwise it is impossible for other packages to turn this option off, e.g., yihui/xaringan#293.
 
+- `knitr_options_pdf()` will now throw a warning when `fig_crop = TRUE` but is disabled because required tools `pdfcrop` and/or `ghostscript` are missing (thanks, @netique, #2016).
 
 rmarkdown 2.6
 ================================================================================

R/output_format.R

@@ -262,7 +262,7 @@ knitr_options_pdf <- function(fig_width,
   knit_hooks <- NULL
 
   # apply cropping if requested and we have pdfcrop and ghostscript
-  crop <- fig_crop && find_program("pdfcrop") != '' && tools::find_gs_cmd() != ''
+  crop <- fig_crop && has_crop_tools()
   if (crop) {
     knit_hooks = list(crop = knitr::hook_pdfcrop)
     opts_chunk$crop = TRUE

R/util.R

@@ -312,6 +312,21 @@ find_program <- function(program) {
   }
 }
 
+has_crop_tools <- function() {
+  tools <- c(
+    pdfcrop = find_program("pdfcrop"),
+    ghostcript = tools::find_gs_cmd()
+  )
+  missing <- tools[tools == ""]
+  if (length(missing) == 0) return(TRUE)
+  x <- paste0(names(missing), collapse = ", ")
+  warning(
+    sprintf("\nTool(s) not installed or not in PATH: %s", x),
+    "\n-> As a result, figure cropping will be disabled."
+  )
+  FALSE
+}
+
 # given a string, escape the regex metacharacters it contains:
 # regex metas are these,
 #   . \ | ( ) [ { ^ $ * + ?