gnu: Add r-prettydoc.

* gnu/packages/cran.scm (r-prettydoc): New variable.

gnu/packages/cran.scm

@@ -1025,6 +1025,71 @@ (define-public r-pma
 canonical correlation analysis.")
     (license license:gpl2+)))
 
+(define-public r-prettydoc
+  (package
+    (name "r-prettydoc")
+    (version "0.4.1")
+    (source (origin
+              (method url-fetch)
+              (uri (cran-uri "prettydoc" version))
+              (sha256
+               (base32
+                "0aa89jnqhz0l69inrgm1f1riq5bm3ksb8wjl8d4x2f320adsd50h"))
+              (snippet
+               '(for-each delete-file
+                          '("inst/resources/js/auto-render.min.js"
+                            "inst/resources/js/katex.min.js")))))
+    (properties `((upstream-name . "prettydoc")))
+    (build-system r-build-system)
+    (arguments
+     `(#:modules ((guix build utils)
+                  (guix build r-build-system)
+                  (srfi srfi-1))
+       #:phases
+       (modify-phases %standard-phases
+         (add-after 'unpack 'process-javascript
+           (lambda* (#:key inputs #:allow-other-keys)
+             (with-directory-excursion "inst/resources/js/"
+               (call-with-values
+                   (lambda ()
+                     (unzip2
+                      `((,(search-input-file inputs "dist/katex.js")
+                         "katex.min.js")
+                        (,(search-input-file inputs "dist/contrib/auto-render.js")
+                         "auto-render.min.js"))))
+                 (lambda (sources targets)
+                   (for-each (lambda (source target)
+                               (format #true "Processing ~a --> ~a~%"
+                                       source target)
+                               (invoke "esbuild" source "--minify"
+                                       (string-append "--outfile=" target)))
+                             sources targets)))))))))
+    (inputs (list pandoc))
+    (propagated-inputs (list r-rmarkdown))
+    (native-inputs
+     (list esbuild
+           r-knitr
+           r-rmarkdown
+           (let ((version "0.12.0"))
+             (origin
+               (method git-fetch)
+               (uri (git-reference
+                     (url "https://github.com/KaTeX/KaTeX")
+                     (commit (string-append "v" version))))
+               (file-name (git-file-name "js-katex" version))
+               (sha256
+                (base32
+                 "0pdfw28affnfpqpnf244acf5rkxdy2gk63669myy7ysg4z0i1n8j"))))))
+    (home-page "https://github.com/yixuan/prettydoc")
+    (synopsis "Create pretty documents from R markdown")
+    (description
+     "This is a package for creating tiny yet beautiful documents and
+vignettes from R Markdown.  The package provides the @code{html_pretty} output
+format as an alternative to the @code{html_document} and @code{html_vignette}
+engines that convert R Markdown into HTML pages.  Various themes and syntax
+highlight styles are supported.")
+    (license license:asl2.0)))
+
 (define-public r-proj4
   (package
     (name "r-proj4")