Subject: bug#73638: 31.0.50; doc-view: imenu index cannot be made for LaTeX PDFs

From: Visuwesh <[email-masked]>
Date: Mon, 07 Oct 2024 18:23:39 +0530

[திங்கள் அக்டோபர் 07, 2024] Tassilo Horn wrote:

> Visuwesh <[email-masked]> writes:
>
>>>> Maybe it would also a good idea to use a :stderr buffer with
>>>> make-process and put its contents into the imenu-unavailable-error.
>>>> That way, chances are better we get the reason for failure delivered
>>>> in bug reports.
>>>
>>> I do not think it is worth the trouble since only syntax errors are
>>> likely to surface up in stderr which would be very unlikely.  If the
>>> PDF file does not have an outline, there would be nothing printed by
>>> our script so end-of-file error should catch that case.
>>
>> Actually, this wasn't quite correct I think.  We would have stray > in
>> the buffer and read would return the symbol >.  I corrected that in
>> the attached.
>
> The patch looks good.  But during testing, it seems that the index is
> always off by one page, i.e., the index for some section brings me to
> page 117 but the section heading is actually on page 118.
>
> I have that both with the Peter Atkins et al. book you suggested as well
> as with own papers which didn't work at all previously due to #nameddest
> references.

Ugghhh, looks like the page number returned by the JS function is
zero-indexed.  Thanks for the catch (and sorry for the many mistakes and
hence the back-and-forth).  Should be corrected in the attached patch.

>From 84563a74cc2fba7279153f08d442b69c2977f2b4 Mon Sep 17 00:00:00 2001
From: Visuwesh <[email-masked]>
Date: Sun, 6 Oct 2024 18:02:06 +0530
Subject: [PATCH] Make imenu index generation for PDFs more reliable

Do away with parsing the output of "mutool show FILE outline"
since the URI reported in its output may not include the page
number of the heading, and instead may contained "nameddest"
elements which cannot be resolved using "mutool".  Instead, use
a MuPDF JS script to generate the PDF outline allowing to
resolve such URIs.

* lisp/doc-view.el (doc-view--outline-rx): Remove as no longer
needed.
(doc-view--outline): Reflect that outline can be generated for
non-PDF files too.
(doc-view--mutool-pdf-outline-script): Add new variable to hold
the JS script used to generate the outline.
(doc-view--pdf-outline): Use the script.  (bug#73638)
---
 lisp/doc-view.el | 48 ++++++++++++++++++++++++++++++++----------------
 1 file changed, 32 insertions(+), 16 deletions(-)

diff --git a/lisp/doc-view.el b/lisp/doc-view.el
index 446beeafd9f..a49cbc69717 100644
--- a/lisp/doc-view.el
+++ b/lisp/doc-view.el
@@ -1969,14 +1969,26 @@ doc-view-search-previous-match
 	(doc-view-goto-page (caar (last doc-view--current-search-matches)))))))
 
 ;;;; Imenu support
-(defconst doc-view--outline-rx
-  "[^\t]+\\(\t+\\)\"\\(.+\\)\"\t#\\(?:page=\\)?\\([0-9]+\\)")
-
 (defvar-local doc-view--outline nil
-  "Cached PDF outline, so that it is only computed once per document.
+  "Cached document outline, so that it is only computed once per document.
 It can be the symbol `unavailable' to indicate that outline is
 unavailable for the document.")
 
+(defvar doc-view--mutool-pdf-outline-script
+  "var document = new Document.openDocument(\"%s\", \"application/pdf\");
+var outline = document.loadOutline();
+if(!outline) quit();
+function pp(outl, level){print(\"((level . \" + level + \")\");\
+print(\"(title . \" + repr(outl.title) + \")\");\
+print(\"(page . \" + document.resolveLink(outl.uri)+1 + \"))\");\
+if(outl.down){for(var i=0; i<outl.down.length; i++){pp(outl.down[i], level+1);}}};
+function run(){print(\"BEGIN(\");\
+for(var i=0; i<outline.length; i++){pp(outline[i], 1);}print(\")\");};
+run()"
+  "JS script to extract the PDF's outline using mutool.
+The script has to be minified to pass it to the REPL.  The \"BEGIN\"
+marker is here to skip past the prompt characters.")
+
 (defun doc-view--pdf-outline (&optional file-name)
   "Return a list describing the outline of FILE-NAME.
 Return a list describing the current file if FILE-NAME is nil.
@@ -1986,21 +1998,25 @@ doc-view--pdf-outline
 structure is extracted by `doc-view--imenu-subtree'."
   (let ((fn (or file-name (buffer-file-name))))
     (when fn
-      (let ((outline nil)
-            (fn (expand-file-name fn)))
-        (with-temp-buffer
-          (unless (eql 0 (call-process doc-view-pdfdraw-program nil
-                                       (current-buffer) nil "show" fn "outline"))
+      (with-temp-buffer
+        (let ((proc (make-process
+                     :name "doc-view-pdf-outline"
+                     :command (list "mutool" "run")
+                     :buffer (current-buffer))))
+          (process-send-string proc (format doc-view--mutool-pdf-outline-script
+                                            (expand-file-name fn)))
+          ;; Need to send this twice for some reason...
+          (process-send-eof)
+          (process-send-eof)
+          (while (accept-process-output proc))
+          (unless (eq (process-status proc) 'exit)
             (setq doc-view--outline 'unavailable)
             (imenu-unavailable-error "Unable to create imenu index using `mutool'"))
           (goto-char (point-min))
-          (while (re-search-forward doc-view--outline-rx nil t)
-            (push `((level . ,(length (match-string 1)))
-                    (title . ,(replace-regexp-in-string "\\\\[rt]" " "
-                                                        (match-string 2)))
-                    (page . ,(string-to-number (match-string 3))))
-                  outline)))
-        (nreverse outline)))))
+          (when (search-forward "BEGIN" nil t)
+            (condition-case nil
+                (read (current-buffer))
+              (end-of-file nil))))))))
 
 (defun doc-view--djvu-outline (&optional file-name)
   "Return a list describing the outline of FILE-NAME.
-- 
2.45.2