Provide a uniform way to inform users about missing third-party packages

* lisp/org-macs.el (org-require-package): New macro trying to load a
library and displaying custom error message or warning on failure.
The actual package (not library) name can be provided as optional
argument.

* lisp/ob-R.el (org-babel-R-initiate-session):
* lisp/ob-clojure.el (ob-clojure-eval-with-inf-clojure):
(ob-clojure-eval-with-cider):
(ob-clojure-eval-with-slime):
* lisp/ob-forth.el (org-babel-forth-session-execute):
* lisp/ob-gnuplot.el (org-babel-execute:gnuplot):
(org-babel-gnuplot-initiate-session):
* lisp/ob-haskell.el (org-babel-interpret-haskell):
(org-babel-haskell-initiate-session):
* lisp/ob-js.el (org-babel-execute:js):
(org-babel-js-initiate-session):
* lisp/ob-julia.el (org-babel-julia-initiate-session):
* lisp/ob-lisp.el (org-babel-execute:lisp):
* lisp/ob-ocaml.el (org-babel-prep-session:ocaml):
* lisp/ob-octave.el (org-babel-octave-initiate-session):
* lisp/ob-processing.el (org-babel-processing-view-sketch):
* lisp/ob-ruby.el (org-babel-execute:ruby):
(org-babel-ruby-initiate-session):
* lisp/ol-bbdb.el (org-bbdb-open):
(org-bbdb-complete-link):
(org-bbdb-anniv-export-ical):
* lisp/org-agenda.el:
* lisp/org-plot.el (org-plot/gnuplot):
* lisp/org.el:
* lisp/ox-ascii.el (org-ascii-table):
* lisp/ox-html.el (org-html-htmlize-generate-css):
* lisp/ox-org.el: Use the new macro.

* lisp/oc-csl.el: Add FIXME. oc-csl uses a custom function doing
similar job.

* lisp/ob-js.el (org-babel-js-initiate-session): Add FIXME noting that
the third-party package is outdated.

lisp/ob-R.el

@@ -276,7 +276,7 @@ This function is called by `org-babel-execute-src-block'."
 	  (when (get-buffer session)
 	    ;; Session buffer exists, but with dead process
 	    (set-buffer session))
-	  (require 'ess) (R)
+          (org-require-package 'ess "ESS") (R)
 	  (let ((R-proc (get-process (or ess-local-process-name
 					 ess-current-process-name))))
 	    (while (process-get R-proc 'callbacks)

lisp/ob-clojure.el

@@ -186,8 +186,7 @@ or set the `:backend' header argument"))))
 (defvar inf-clojure-comint-prompt-regexp)
 (defun ob-clojure-eval-with-inf-clojure (expanded params)
   "Evaluate EXPANDED code block with PARAMS using inf-clojure."
-  (condition-case nil (require 'inf-clojure)
-    (user-error "inf-clojure not available"))
+  (org-require-package 'inf-clojure)
   ;; Maybe initiate the inf-clojure session
   (unless (and inf-clojure-buffer
 	       (buffer-live-p (get-buffer inf-clojure-buffer)))
@@ -228,8 +227,7 @@ or set the `:backend' header argument"))))
 
 (defun ob-clojure-eval-with-cider (expanded params)
   "Evaluate EXPANDED code block with PARAMS using cider."
-  (condition-case nil (require 'cider)
-    (user-error "cider not available"))
+  (org-require-package 'cider "Cider")
   (let ((connection (cider-current-connection (cdr (assq :target params))))
 	(result-params (cdr (assq :result-params params)))
 	result0)
@@ -256,8 +254,7 @@ or set the `:backend' header argument"))))
 
 (defun ob-clojure-eval-with-slime (expanded params)
   "Evaluate EXPANDED code block with PARAMS using slime."
-  (condition-case nil (require 'slime)
-    (user-error "slime not available"))
+  (org-require-package 'slime "SLIME")
   (with-temp-buffer
     (insert expanded)
     (slime-eval

lisp/ob-forth.el

@@ -55,7 +55,7 @@ This function is called by `org-babel-execute-src-block'."
 	(car (last all-results))))))
 
 (defun org-babel-forth-session-execute (body params)
-  (require 'forth-mode)
+  (org-require-package 'forth-mode)
   (let ((proc (forth-proc))
 	(rx " \\(\n:\\|compiled\n\\|ok\n\\)")
 	(result-start))

lisp/ob-gnuplot.el

@@ -198,7 +198,7 @@ code."
 (defun org-babel-execute:gnuplot (body params)
   "Execute a block of Gnuplot code.
 This function is called by `org-babel-execute-src-block'."
-  (require 'gnuplot)
+  (org-require-package 'gnuplot)
   (let ((session (cdr (assq :session params)))
         (result-type (cdr (assq :results params)))
         (body (org-babel-expand-body:gnuplot body params))
@@ -262,7 +262,7 @@ This function is called by `org-babel-execute-src-block'."
 If there is not a current inferior-process-buffer in SESSION
 then create one.  Return the initialized session.  The current
 `gnuplot-mode' doesn't provide support for multiple sessions."
-  (require 'gnuplot)
+  (org-require-package 'gnuplot)
   (unless (string= session "none")
     (save-window-excursion
       (gnuplot-send-string-to-gnuplot "" "line")

lisp/ob-haskell.el

@@ -122,7 +122,7 @@ a parameter, such as \"ghc -v\"."
 	  (cdr (assq :rowname-names params)) (cdr (assq :rownames params))))))))
 
 (defun org-babel-interpret-haskell (body params)
-  (require 'inf-haskell)
+  (org-require-package 'inf-haskell "haskell-mode")
   (add-hook 'inferior-haskell-hook
             (lambda ()
               (setq-local comint-prompt-regexp
@@ -167,7 +167,7 @@ a parameter, such as \"ghc -v\"."
   "Initiate a haskell session.
 If there is not a current inferior-process-buffer in SESSION
 then create one.  Return the initialized session."
-  (require 'inf-haskell)
+  (org-require-package 'inf-haskell "haskell-mode")
   (or (get-buffer "*haskell*")
       (save-window-excursion (run-haskell) (sleep-for 0.25) (current-buffer))))
 

lisp/ob-js.el

@@ -96,7 +96,7 @@ This function is called by `org-babel-execute-src-block'."
 		  ;; Indium Node REPL.  Separate case because Indium
 		  ;; REPL is not inherited from Comint mode.
 		  ((string= session "*JS REPL*")
-		   (require 'indium-repl)
+                   (org-require-package 'indium-repl "indium")
 		   (unless (get-buffer session)
 		     (indium-run-node org-babel-js-cmd))
 		   (indium-eval full-body))
@@ -168,7 +168,7 @@ Return the initialized session."
    ((string= session "none")
     (warn "Session evaluation of ob-js is not supported"))
    ((string= "*skewer-repl*" session)
-    (require 'skewer-repl)
+    (org-require-package 'skewer-repl "skewer-mode")
     (let ((session-buffer (get-buffer "*skewer-repl*")))
       (if (and session-buffer
 	       (org-babel-comint-buffer-livep (get-buffer session-buffer))
@@ -180,7 +180,7 @@ Return the initialized session."
 	(skewer-repl)
 	session-buffer)))
    ((string= "*Javascript REPL*" session)
-    (require 'js-comint)
+    (org-require-package 'js-comint)
     (let ((session-buffer "*Javascript REPL*"))
       (if (and (org-babel-comint-buffer-livep (get-buffer session-buffer))
 	       (comint-check-proc session-buffer))
@@ -189,7 +189,9 @@ Return the initialized session."
 	(sit-for .5)
 	session-buffer)))
    ((string= "mozrepl" org-babel-js-cmd)
-    (require 'moz)
+    ;; FIXME: According to https://github.com/bard/mozrepl, this REPL
+    ;; is outdated and does not work for Firefox >54.
+    (org-require-package 'moz "mozrepl")
     (let ((session-buffer (save-window-excursion
 			    (run-mozilla nil)
 			    (rename-buffer session)

lisp/ob-julia.el

@@ -196,7 +196,8 @@ end"
 	  (when (get-buffer session)
 	    ;; Session buffer exists, but with dead process
 	    (set-buffer session))
-          (require 'ess) (set-buffer (julia))
+          (org-require-package 'ess "ESS")
+          (set-buffer (julia))
 	  (rename-buffer
 	   (if (bufferp session)
 	       (buffer-name session)

lisp/ob-lisp.el

@@ -90,9 +90,9 @@ current directory string."
   "Execute a block of Common Lisp code with Babel.
 BODY is the contents of the block, as a string.  PARAMS is
 a property list containing the parameters of the block."
-  (require (pcase org-babel-lisp-eval-fn
-	     (`slime-eval 'slime)
-	     (`sly-eval 'sly)))
+  (pcase org-babel-lisp-eval-fn
+    (`slime-eval (org-require-package 'slime "SLIME"))
+    (`sly-eval (org-require-package 'sly "SLY")))
   (org-babel-reassemble-table
    (let ((result
           (funcall (if (member "output" (cdr (assq :result-params params)))

lisp/ob-ocaml.el

@@ -109,7 +109,7 @@
 (defvar tuareg-interactive-buffer-name)
 (defun org-babel-prep-session:ocaml (session _params)
   "Prepare SESSION according to the header arguments in PARAMS."
-  (require 'tuareg)
+  (org-require-package 'tuareg)
   (let ((tuareg-interactive-buffer-name (if (and (not (string= session "none"))
                                                  (not (string= session "default"))
                                                  (stringp session))

lisp/ob-octave.el

@@ -154,8 +154,10 @@ create.  Return the initialized session."
   "Create an octave inferior process buffer.
 If there is not a current inferior-process-buffer in SESSION then
 create.  Return the initialized session."
-  (if matlabp (require 'matlab) (or (require 'octave-inf nil 'noerror)
-				    (require 'octave)))
+  (if matlabp
+      (org-require-package 'matlab "matlab-mode")
+    (or (require 'octave-inf nil 'noerror)
+	(require 'octave)))
   (unless (string= session "none")
     (let ((session (or session
 		       (if matlabp "*Inferior Matlab*" "*Inferior Octave*"))))

lisp/ob-processing.el

@@ -78,7 +78,7 @@
 (defun org-babel-processing-view-sketch ()
   "Show the sketch of the Processing block under point in an external viewer."
   (interactive)
-  (require 'processing-mode)
+  (org-require-package 'processing-mode)
   (let ((info (org-babel-get-src-block-info)))
     (if (string= (nth 0 info) "processing")
 	(let* ((body (nth 1 info))

lisp/ob-ruby.el

@@ -86,7 +86,7 @@ This function is called by `org-babel-execute-src-block'."
 		     body params (org-babel-variable-assignments:ruby params)))
          (result (if (member "xmp" result-params)
 		     (with-temp-buffer
-		       (require 'rcodetools)
+		       (org-require-package 'rcodetools "rcodetools (gem package)")
 		       (insert full-body)
 		       (xmp (cdr (assq :xmp-option params)))
 		       (buffer-string))
@@ -161,7 +161,7 @@ Emacs-lisp table, otherwise return the results as a string."
 If there is not a current inferior-process-buffer in SESSION
 then create one.  Return the initialized session."
   (unless (string= session "none")
-    (require 'inf-ruby)
+    (org-require-package 'inf-ruby)
     (let* ((command (cdr (or (assq :ruby params)
 			     (assoc inf-ruby-default-implementation
 				    inf-ruby-implementations))))

lisp/oc-csl.el

@@ -417,6 +417,7 @@ Label is in match group 1.")
 
 
 ;;; Internal functions
+;; FIXME: We use `org-require-package' in other places.
 (defun org-cite-csl--barf-without-citeproc ()
   "Raise an error if Citeproc library is not loaded."
   (unless (featurep 'citeproc)

lisp/ol-bbdb.el

@@ -255,7 +255,7 @@ italicized, in all other cases it is left unchanged."
 
 (defun org-bbdb-open (name _)
   "Follow a BBDB link to NAME."
-  (require 'bbdb-com)
+  (org-require-package 'bbdb-com "bbdb")
   (let ((inhibit-redisplay (not debug-on-error)))
     (if (fboundp 'bbdb-name)
 	(org-bbdb-open-old name)
@@ -369,7 +369,7 @@ This is used by Org to re-create the anniversary hash table."
   "Extract anniversaries from BBDB for display in the agenda.
 When called programmatically, this function expects the `date'
 variable to be globally bound."
-  (require 'bbdb)
+  (org-require-package 'bbdb)
   (require 'diary-lib)
   (unless (hash-table-p org-bbdb-anniv-hash)
     (setq org-bbdb-anniv-hash
@@ -500,7 +500,7 @@ must be positive"))
 
 (defun org-bbdb-complete-link ()
   "Read a bbdb link with name completion."
-  (require 'bbdb-com)
+  (org-require-package 'bbdb-com "bbdb")
   (let ((rec (bbdb-completing-read-record "Name: ")))
     (concat "bbdb:"
 	    (bbdb-record-name (if (listp rec)
@@ -509,7 +509,7 @@ must be positive"))
 
 (defun org-bbdb-anniv-export-ical ()
   "Extract anniversaries from BBDB and convert them to icalendar format."
-  (require 'bbdb)
+  (org-require-package 'bbdb)
   (require 'diary-lib)
   (unless (hash-table-p org-bbdb-anniv-hash)
     (setq org-bbdb-anniv-hash

lisp/org-agenda.el

@@ -3635,8 +3635,7 @@ the agenda to write."
 		(kill-buffer (current-buffer))
 		(message "Org file written to %s" file)))
 	     ((member extension '("html" "htm"))
-	      (or (require 'htmlize nil t)
-		  (error "Please install htmlize from https://github.com/hniksic/emacs-htmlize"))
+              (org-require-package 'htmlize)
 	      (declare-function htmlize-buffer "htmlize" (&optional buffer))
 	      (set-buffer (htmlize-buffer (current-buffer)))
 	      (when org-agenda-export-html-style

lisp/org-macs.el

@@ -107,6 +107,15 @@ Version mismatch is commonly encountered in the following situations:
 
 ;;; Macros
 
+(defmacro org-require-package (symbol &optional name noerror)
+  "Try to load library SYMBOL and display error otherwise.
+With optional parameter NAME, use NAME as package name instead of
+SYMBOL.  Show warning instead of error when NOERROR is non-nil."
+  `(unless (require ,symbol nil t)
+     (,(if noerror 'warn 'user-error)
+      "`%s' failed to load required package \"%s\""
+      this-command ,(or name symbol))))
+
 (defmacro org-with-gensyms (symbols &rest body)
   (declare (debug (sexp body)) (indent 1))
   `(let ,(mapcar (lambda (s)

lisp/org-plot.el

@@ -641,7 +641,7 @@ manner suitable for prepending to a user-specified script."
 If not given options will be taken from the +PLOT
 line directly before or after the table."
   (interactive)
-  (require 'gnuplot)
+  (org-require-package 'gnuplot)
   (save-window-excursion
     (delete-other-windows)
     (when (get-buffer "*gnuplot*") ; reset *gnuplot* if it already running

lisp/org.el

@@ -15449,7 +15449,7 @@ in Org mode.
 \\{org-cdlatex-mode-map}"
   :lighter " OCDL"
   (when org-cdlatex-mode
-    (require 'cdlatex)
+    (org-require-package 'cdlatex)
     (run-hooks 'cdlatex-mode-hook)
     (cdlatex-compute-tables))
   (unless org-cdlatex-texmathp-advice-is-done

lisp/ox-ascii.el

@@ -1856,7 +1856,7 @@ contextual information."
       (cond ((eq (org-element-property :type table) 'org) contents)
 	    ((and (plist-get info :ascii-table-use-ascii-art)
 		  (eq (plist-get info :ascii-charset) 'utf-8)
-		  (require 'ascii-art-to-unicode nil t))
+		  (org-require-package 'ascii-art-to-unicode nil 'noerror))
 	     (with-temp-buffer
 	       (insert (org-remove-indentation
 			(org-element-property :value table)))

lisp/ox-html.el

@@ -1823,8 +1823,7 @@ If you then set `org-html-htmlize-output-type' to `css', calls
 to the function `org-html-htmlize-region-for-paste' will
 produce code that uses these same face definitions."
   (interactive)
-  (unless (require 'htmlize nil t)
-    (error "htmlize library missing.  Aborting"))
+  (org-require-package 'htmlize)
   (and (get-buffer "*html*") (kill-buffer "*html*"))
   (with-temp-buffer
     (let ((fl (face-list))

lisp/ox-org.el

@@ -320,8 +320,7 @@ publishing directory.
 Return output file name."
   (org-publish-org-to 'org filename ".org" plist pub-dir)
   (when (plist-get plist :htmlized-source)
-    (or (require 'htmlize nil t)
-	(error "Please install htmlize from https://github.com/hniksic/emacs-htmlize"))
+    (org-require-package 'htmlize)
     (require 'ox-html)
     (let* ((org-inhibit-startup t)
 	   (htmlize-output-type 'css)