fix #954: also check if ghostscript is available before trying to cro…

…p the PDF plots

NEWS.md

@@ -18,6 +18,8 @@
 
 - `knitr::write_bib()` uses the `URL` in the package `DESCRIPTION` if it is provided, instead of the canonical CRAN URL for the package.
 
+- `hook_pdfcrop()` and `plot_crop()` will work only when both programs `pdfcrop` and `ghostscript` have been installed. Previously only `pdfcrop` was checked (thanks, @dalupus, #954).
+
 # CHANGES IN knitr VERSION 1.29
 
 ## NEW FEATURES

R/hooks-extra.R

@@ -5,15 +5,8 @@
 #' provides a few useful hooks, which can also serve as examples of how to
 #' define chunk hooks in \pkg{knitr}.
 #'
-#' The function \code{hook_pdfcrop()} can use the program \command{pdfcrop} to
-#' crop the extra white margin when the plot format is PDF to make better use of
-#' the space in the output document, otherwise we often have to struggle with
-#' \code{graphics::\link{par}()} to set appropriate margins. Note
-#' \command{pdfcrop} often comes with a LaTeX distribution such as MiKTeX or
-#' TeXLive, and you may not need to install it separately (use
-#' \code{Sys.which('pdfcrop')} to check it; if it not empty, you are able to use
-#' it). Similarly, when the plot format is not PDF (e.g. PNG), the \pkg{magick}
-#' package is used to crop the plot.
+#' The function \code{hook_pdfcrop()} calls \code{\link{pdf_crop}()} to crop the
+#' white margins of PDF plots.
 #'
 #' The function \code{hook_optipng()} calls the program \command{optipng} to
 #' optimize PNG images. Note the chunk option \code{optipng} can be used to

R/plot.R

@@ -300,10 +300,20 @@ fig_process = function(FUN, path, options) {
 
 #' Crop a plot (remove the edges) using PDFCrop or ImageMagick
 #'
-#' The command \command{pdfcrop} (often shipped with a LaTeX distribution) is
+#' The program \command{pdfcrop} (often shipped with a LaTeX distribution) is
 #' executed on a PDF plot file, and
 #' \code{magick::\link[magick:transform]{image_trim}()} is executed for other
 #' types of plot files.
+#'
+#' The program \command{pdfcrop} can crop the extra white margins when the plot
+#' format is PDF, to make better use of the space in the output document,
+#' otherwise we often have to struggle with \code{graphics::\link{par}()} to set
+#' appropriate margins. Note \command{pdfcrop} often comes with a LaTeX
+#' distribution such as TinyTeX, MiKTeX, or TeX Live, and you may not need to
+#' install it separately (use \code{Sys.which('pdfcrop')} to check it; if it not
+#' empty, you are able to use it). Note that \command{pdfcrop} depends on
+#' GhostScript. You can check if GhostScript is installed via
+#' \code{tools::find_gs_cmd()}.
 #' @param x Filename of the plot.
 #' @param quiet Whether to suppress standard output from the command.
 #' @export
@@ -315,7 +325,7 @@ plot_crop = function(x, quiet = TRUE) {
   is_pdf = grepl('[.]pdf$', x, ignore.case = TRUE)
   x2 = x
   x = path.expand(x)
-  if (is_pdf && !has_utility('pdfcrop')) return(x2)
+  if (is_pdf && !has_utility('pdfcrop') && !has_utility('ghostscript')) return(x2)
 
   if (!quiet) message('cropping ', x)
   if (is_pdf) {

R/utils.R

@@ -715,6 +715,8 @@ kpsewhich = function() {
 has_utility = function(name, package = name) {
   name2 = paste('util', name, sep = '_')  # e.g. util_pdfcrop
   if (is.logical(yes <- opts_knit$get(name2))) return(yes)
+  # a special case: use tools::find_gs_cmd() to find ghostscript
+  if (name == 'ghostscript') name = tools::find_gs_cmd()
   yes = nzchar(Sys.which(name))
   if (!yes) warning(package, ' not installed or not in PATH')
   opts_knit$set(setNames(list(yes), name2))