[RFC] [export] synctex support for ox-latex

[Aaron Ecay <aaronecay@gmail.com>]

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Hello,

Some months ago, I proposed a patch to implement synctex support for the
latex exporter.  Following feedback from Nicolas, I was working on
converting that code to use hooks and advice, without modifying core
org-mode functions.  It was a frustrating but very educational task, and
it is now complete.  I attach the patch (which consists only of a single
file addition to the contrib directory) to this message.

It is very simple to use: load the file, and then M-x
ox-synctex-activate.  Now every time you export latex to a pdf, the code
will patch the resultant synctex file so you can jump from a pdf viewer
to the (approximate) org source line that generated it.  The hooks and
advice can all be removed with M-x ox-synctex-deactivate.

Aaron

PS Note that you must do the latex compilation within org (C-c C-e l p);
you can’t export the .tex file and compile it from the command line.

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From 43d4bc0ee82874d4389dd7ead7fccd3c81c68418 Mon Sep 17 00:00:00 2001
From: Aaron Ecay <aaronecay@gmail.com>
Date: Wed, 23 Oct 2013 15:29:56 -0400
Subject: [PATCH] add synctex support

* contrib/lisp/ox-synctex.el: new file
---
 contrib/lisp/ox-synctex.el | 252 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 252 insertions(+)
 create mode 100644 contrib/lisp/ox-synctex.el

diff --git a/contrib/lisp/ox-synctex.el b/contrib/lisp/ox-synctex.el
new file mode 100644
index 0000000..6f04c14
--- /dev/null
+++ b/contrib/lisp/ox-synctex.el
@@ -0,0 +1,252 @@
+;;; ox-synctex.el --- Synctex functionality for org LaTeX export
+
+;; Copyright (C) 2013 Aaron Ecay
+
+;; Author: Aaron Ecay <aaronecay@gmail.com>
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This code provides synctex support for org mode export to latex.
+;; To activate, execute (ox-synctex-activate).  To deactivate,
+;; (ox-synctex-deactivate)
+
+;; TODOs:
+;; - support multi-file documents through #+include and friends
+;; - do something so that clicks on a minted source code block go to
+;;   the .org file and not the .pyg intermediate
+;; - ...
+
+;;; Code:
+
+;;;; Internal functions and variable
+
+(defvar ox-synctex--concordance nil
+  "The concordance resulting from the last export operation.")
+
+(defun ox-synctex--read-concordance (concordance src-line)
+  "Get the output line number from CONCORDANCE for input line SRC-LINE."
+  ;; TODO: not robust against malformed concordances
+  (while (and (caadr concordance)
+              (<= (caadr concordance) src-line))
+    (setq concordance (cdr concordance)))
+  (cdar concordance))
+
+(defun ox-synctex--propertize-buffer ()
+  "Put line-number text properties on a buffer.
+
+Each line gets a org-line-num-pre property, which is its line
+number in the buffer.  When export operations change the buffer,
+the text property will still reflect the original state of affairs."
+  (save-restriction
+    (widen)
+    (while (= 0 (forward-line 1))
+      (put-text-property (point) (point-at-eol)
+			 'ox-synctex-line-num
+			 (line-number-at-pos)))))
+
+(defun ox-synctex--line-number-at-pos (pos)
+  "Return the buffer line number at POS, widening if necessary.
+
+This function first looks for text properties set by
+`ox-synctex--propertize-buffer' which allow it to return an
+accurate line number in a buffer copy modified during export.  It
+falls back to the usual method of calculating line numbers if no
+text properties are found."
+  (or (get-text-property pos 'ox-synctex-line-num)
+      (save-excursion
+        (widen)
+        (line-number-at-pos pos))))
+
+(defun ox-synctex--add-line-to-element (element)
+  "Add begin and end line numbers to an element as returned by `org-element'."
+  (let* ((plist (cadr element))
+	 (beg (plist-get plist :begin))
+	 (end (plist-get plist :end)))
+    (and beg (plist-put plist :begin-line (ox-synctex--line-number-at-pos beg)))
+    (and end (plist-put plist :end-line (ox-synctex--line-number-at-pos end)))
+    element))
+
+
+(defun ox-synctex--propertize-string (data string)
+  "Add line number text properties to STRING, based on DATA.
+
+The function works by copying the properties added by
+`ox-synctex--add-line-to-element' to the string.  This will allow
+the construction of a concordance from the exported string."
+  (let ((len (length string)))
+    (when (> len 1)
+      (put-text-property 0 1 'org-line-num
+                         (org-element-property :begin-line data)
+                         string)
+      (put-text-property (1- len) len 'org-line-num
+                         (org-element-property :end-line data)
+                         string)))
+  string)
+
+(defun ox-synctex--build-concordance ()
+  "Build a concordance, based on text properties added by
+`ox-synctex--propertize-string' and accumulated in in an export
+result buffer.
+
+Has the form ((OUT-LINE . IN-LINE) ...)"
+  (save-excursion
+    (let ((res '())
+          next)
+      (goto-char (point-min))
+      (while (setq next (next-single-property-change (point) 'org-line-num))
+        (goto-char next)
+	(let ((ln (get-text-property (point) 'org-line-num)))
+	  ;; TODO: `ln' should never be nil, but sometimes it is.  For
+	  ;; now, we hack around that with this `when'.
+	  (when ln
+	    (setq res (cons (cons (line-number-at-pos) ln)
+			    res))))
+        (forward-char 1))
+      (setq res (nreverse res))
+      (setq next res)
+      (while (cdr next)
+        (if (equal (caar next) (caadr next))
+            (setcdr next (cddr next))
+          (setq next (cdr next))))
+      res)))
+
+(defun ox-synctex--patch-synctex (file)
+  "Patch the synctex file resulting from the last export
+operation, using the information stored in
+`ox-synctex--concordance'."
+  (let* ((file-base (file-name-nondirectory
+		     (replace-regexp-in-string "\\.tex\\'" "." file)))
+	 (synctex-file (concat file-base "synctex.gz")))
+    (cond
+     ((not ox-synctex--concordance)
+      (message "No concordance, not patching."))
+     ((not (file-exists-p synctex-file))
+      (message "No synctex file found, not patching."))
+     (t
+      (let* ((conc ox-synctex--concordance)
+	     (buf (find-file-noselect synctex-file)))
+	(with-current-buffer buf
+	  (let ((max-index 0)
+		the-index extra-path new-index)
+	    (goto-char (point-min))
+	    (while (re-search-forward "^Input:\\([0-9]+\\):" nil t)
+	      (setq max-index (max max-index (string-to-number (match-string 1)))))
+	    (setq new-index (number-to-string (1+ max-index)))
+	    (goto-char (point-min))
+	    (when (re-search-forward (concat "^Input:\\([0-9]+\\):\\(.*\\)"
+					     (regexp-quote file-base) "tex$")
+				     nil t)
+	      (setq the-index (string-to-number (match-string 1)))
+	      (setq extra-path (match-string 2))
+	      (goto-char (line-end-position))
+	      (insert (format "\nInput:%s:%s%sorg" new-index extra-path file-base)))
+	    (goto-char (point-min))
+	    (while (re-search-forward (format "^[vhxkgr$[()]\\(%s\\),\\([0-9]+\\):"
+					      the-index)
+				      nil t)
+	      (let ((new-line (ox-synctex--read-concordance
+			       ox-synctex--concordance
+			       (string-to-number (match-string 2)))))
+		(when new-line
+		  (replace-match new-index nil t nil 1)
+		  (replace-match (int-to-string new-line)
+				 nil t nil 2))))
+	    (save-buffer)))
+	(kill-buffer buf))))))
+
+;;;; Hooks and advice
+
+(defun ox-synctex--before-processing-hook (&rest ignore)
+  (ox-synctex--propertize-buffer))
+
+(defconst ox-synctex--parsers-to-patch
+  (append org-element-greater-elements org-element-all-elements))
+
+;;; Patch all `org-element' parsers to add line number info to their
+;;; return values.
+(dolist (parser ox-synctex--parsers-to-patch)
+  (let ((parser-fn (intern (format "org-element-%s-parser"
+				   (symbol-name parser)))))
+    (eval `(defadvice ,parser-fn (around ox-synctex)
+	     "Advice added by `ox-synctex'."
+	     ad-do-it
+	     (setq ad-return-value (ox-synctex--add-line-to-element
+				    ad-return-value))))))
+
+;;; Patch element->string conversion to carry through the line numbers
+;;; added above
+(defadvice org-export-transcoder (around ox-synctex)
+  ad-do-it
+  (when (and ad-return-value
+	     (org-export-derived-backend-p
+	      (plist-get (ad-get-arg 1) :back-end)
+	      'latex))
+    (setq ad-return-value
+	  `(lambda (data contents &optional info)
+	     (ox-synctex--propertize-string
+	      data
+	      (if info
+		  (,ad-return-value data contents info)
+		;; The plain text transcoder takes only 2 arguments;
+		;; here contents is really info.  I couldn't find a
+		;; better way to inspect the arity of elisp
+		;; functions...?
+		(,ad-return-value data contents)))))))
+
+;;; Patch to build the concordance once we have the export result.  We
+;;; need to hack around the fact that the original function strips
+;;; text properties from its return value which we need.
+(defadvice org-export-as (around ox-synctex)
+  (cl-letf (((symbol-function 'org-no-properties)
+	     (lambda (s &optional _restricted) s)))
+    ad-do-it)
+  (when (org-export-derived-backend-p (ad-get-arg 0) 'latex)
+    (with-temp-buffer
+      (insert ad-return-value)
+      (setq ox-synctex--concordance (ox-synctex--build-concordance))))
+  (setq ad-return-value (org-no-properties ad-return-value)))
+
+;;; Actually do the patching after compilation
+(defadvice org-latex-compile (around ox-synctex)
+  ad-do-it
+  (ox-synctex--patch-synctex (ad-get-arg 0))
+  ;; Some PDF viewers (eg evince) don't notice changes to the synctex
+  ;; file, so we need to poke them to reload the pdf after we've
+  ;; finished changing it.
+  (call-process dired-touch-program nil nil nil
+		(replace-regexp-in-string "\\.tex\\'" "." (ad-get-arg 0))))
+
+;;;; User-facing functions
+
+(defun ox-synctex-activate ()
+  (interactive)
+  (add-hook 'org-export-before-processing-hook
+            #'ox-synctex--before-processing-hook)
+  (ad-activate-regexp "ox-synctex"))
+
+(defun ox-synctex-deactivate ()
+  (interactive)
+  (remove-hook 'org-export-before-processing-hook
+	       #'ox-synctex--before-processing-hook)
+  (ad-deactivate-regexp "ox-synctex"))
+
+(provide 'ox-synctex)
+
+;; Local Variables:
+;; lexical-binding: t
+;; End:
+
+;;; ox-synctex.el ends here
-- 
1.8.4.1


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-- 
Aaron Ecay