bug#73530: [PATCH] Add imenu index function for Djvu files in doc-view

[Visuwesh <visuweshm@gmail.com>]

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[ஞாயிறு செப்டம்பர் 29, 2024] Tassilo Horn wrote:

> Am So, 29. Sep 2024, um 18:38, schrieb Visuwesh:
>> [ஞாயிறு செப்டம்பர் 29, 2024] Tassilo Horn wrote:
>>
>>>> Imenu calls the index function only when it finds that the index
>>>> hasn't been created yet so we can rely on that mechanism instead.
>>>> This would be simpler than using an idle timer.  WDYT?
>>>
>>> Then let's do it the simple way and then test how long the index
>>> building actually takes on reasonable large PDFs/DjVu files.
>>
>> OK, I will send an updated patch in a few days.
>
> Great, thank you! 

Please review the attached.


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From 8ccfe9440363569d6624153177d724bbcf2a122f Mon Sep 17 00:00:00 2001
From: Visuwesh <visuweshm@gmail.com>
Date: Sat, 28 Sep 2024 20:37:50 +0530
Subject: [PATCH] Add imenu index function for Djvu files in doc-view

* lisp/doc-view.el (doc-view-imenu-enabled): Tweak the default
value to check for 'djvused', and make it obsolete.
(doc-view--djvu-outline, doc-view--parse-djvu-outline): Add new
functions to return imenu index for a Djvu file.
(doc-view--outline): Add new function to create the imenu index
depending on the file type.
(doc-view--outline): Document new possible variable value.
(doc-view-imenu-index): Use the above function instead.
(doc-view-imenu-setup): Try to create the imenu index
unconditionally.
* doc/emacs/misc.texi (DocView Navigation): Mention index
creation using 'djvused' too.
* etc/NEWS: Announce the change.  (Bug#73530)
---
 doc/emacs/misc.texi | 15 +++----
 etc/NEWS            |  7 ++++
 lisp/doc-view.el    | 99 ++++++++++++++++++++++++++++++++++++++-------
 3 files changed, 98 insertions(+), 23 deletions(-)

diff --git a/doc/emacs/misc.texi b/doc/emacs/misc.texi
index e19e554fb26..332d5b1468f 100644
--- a/doc/emacs/misc.texi
+++ b/doc/emacs/misc.texi
@@ -581,17 +581,14 @@ DocView Navigation
 default size for DocView, customize the variable
 @code{doc-view-resolution}.
 
-@vindex doc-view-imenu-enabled
 @vindex doc-view-imenu-flatten
 @vindex doc-view-imenu-format
-  When the @command{mutool} program is available, DocView will use it
-to generate entries for an outline menu, making it accessible via the
-@code{imenu} facility (@pxref{Imenu}).  To disable this functionality
-even when @command{mutool} can be found on your system, customize the
-variable @code{doc-view-imenu-enabled} to the @code{nil} value.  You
-can further customize how @code{imenu} items are formatted and
-displayed using the variables @code{doc-view-imenu-format} and
-@code{doc-view-imenu-flatten}.
+  DocView can generate an outline menu for PDF and Djvu documents using
+the @command{mutool} and the @command{djvused} programs respectively
+when they are available.  This is made accessible via the @code{imenu}
+facility (@pxref{Imenu}).  You can customize how @code{imenu} items are
+formatted and displayed using the variables @code{doc-view-imenu-format}
+and @code{doc-view-imenu-flatten}.
 
 @findex doc-view-page-to-register
 @findex doc-view-jump-to-register
diff --git a/etc/NEWS b/etc/NEWS
index 607665a71bb..b6035e13639 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -268,6 +268,13 @@ Docview can store current page to buffer local registers with the new
 command 'doc-view-page-to-register' (bound to 'm'), and later can be
 restored with 'doc-view-jump-to-register' (bound to ''').
 
++++
+*** Docview can generate imenu index for Djvu files.
+When the 'djvused' program is available, Docview can now generate imenu
+index for Djvu files from its outline.
+The name of the 'djvused' program can be customized by changing the user
+option 'doc-view-djvused-program'.
+
 ** Tramp
 
 +++
diff --git a/lisp/doc-view.el b/lisp/doc-view.el
index 395993e6263..1c8bcaee2f1 100644
--- a/lisp/doc-view.el
+++ b/lisp/doc-view.el
@@ -29,6 +29,8 @@
 ;; and OXPS documents require `mutool' which comes with mupdf
 ;; (https://mupdf.com/index.html). Djvu documents require `ddjvu'
 ;; (from DjVuLibre).  ODF files require `soffice' (from LibreOffice).
+;; `djvused' (from DjVuLibre) can be optionally used to generate imenu
+;; outline for Djvu files when available.
 
 ;;; Commentary:
 
@@ -216,10 +218,23 @@ doc-view-mupdf-use-svg
   :type 'boolean
   :version "30.1")
 
-(defcustom doc-view-imenu-enabled (and (executable-find "mutool") t)
-  "Whether to generate an imenu outline when \"mutool\" is available."
+(defcustom doc-view-djvused-program (and (executable-find "djvused")
+                                         "djvused")
+  "Name of \"djvused\" program to generate imenu outline for Djvu files.
+This is part of DjVuLibre."
+  :type 'file
+  :version "31.1")
+
+(defcustom doc-view-imenu-enabled (and (or (executable-find "mutool")
+                                           (executable-find "djvused"))
+                                       t)
+  "Whether to generate imenu outline for PDF and Djvu files.
+This uses \"mutool\" for PDF files and \"djvused\" for Djvu files."
   :type 'boolean
-  :version "29.1")
+  :version "31.1")
+(make-obsolete-variable 'doc-view-imenu-enabled
+   "Imenu index is generated unconditionally, when available"
+   "31.1")
 
 (defcustom doc-view-imenu-title-format "%t (%p)"
   "Format spec for imenu's display of section titles from docview documents.
@@ -1953,7 +1968,9 @@ 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 PDF 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.")
 
 (defun doc-view--pdf-outline (&optional file-name)
   "Return a list describing the outline of FILE-NAME.
@@ -1968,6 +1985,7 @@ doc-view--pdf-outline
             (fn (expand-file-name fn)))
         (with-temp-buffer
           (unless (eql 0 (call-process "mutool" nil (current-buffer) nil "show" fn "outline"))
+            (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)
@@ -1978,6 +1996,42 @@ doc-view--pdf-outline
                   outline)))
         (nreverse outline)))))
 
+(defun doc-view--djvu-outline (&optional file-name)
+  "Return a list describing the outline of FILE-NAME.
+If FILE-NAME is nil or omitted, it defaults to the current buffer's file
+name.
+
+For the format, see `doc-view--pdf-outline'."
+  (unless file-name (setq file-name (buffer-file-name)))
+  (with-temp-buffer
+    (call-process doc-view-djvused-program nil (current-buffer) nil
+                  "-e" "print-outline" file-name)
+    (goto-char (point-min))
+    (when (eobp)
+      (setq doc-view--outline 'unavailable)
+      (imenu-unavailable-error "Unable to create imenu index using `djvused'"))
+    (nreverse (doc-view--parse-djvu-outline (read (current-buffer))))))
+
+(defun doc-view--parse-djvu-outline (bookmark &optional level)
+  "Return a list describing the djvu outline from BOOKMARK.
+Optional argument LEVEL is the current heading level, which defaults to 1."
+  (unless level (setq level 1))
+  (let ((res))
+    (unless (eq (car bookmark) 'bookmarks)
+      (user-error "Unknown outline type: %S" (car bookmark)))
+    (pcase-dolist (`(,title ,page . ,rest) (cdr bookmark))
+      (push `((level . ,level)
+              (title . ,title)
+              (page . ,(string-to-number (string-remove-prefix "#" page))))
+            res)
+      (when (and rest (listp (car rest)))
+        (setq res (append
+                   (doc-view--parse-djvu-outline
+                    (cons 'bookmarks rest)
+                    (+ level 1))
+                   res))))
+    res))
+
 (defun doc-view--imenu-subtree (outline act)
   "Construct a tree of imenu items for the given outline list and action.
 
@@ -2010,19 +2064,36 @@ doc-view-imenu-index
 For extensibility, callers can specify a FILE-NAME to indicate
 the buffer other than the current buffer, and a jumping function
 GOTO-PAGE-FN other than `doc-view-goto-page'."
-  (let* ((goto (or goto-page-fn 'doc-view-goto-page))
-         (act (lambda (_name _pos page) (funcall goto page)))
-         (outline (or doc-view--outline (doc-view--pdf-outline file-name))))
-    (car (doc-view--imenu-subtree outline act))))
+  (unless doc-view--outline
+    (setq doc-view--outline (doc-view--outline file-name)))
+  (unless (eq doc-view--outline 'unavailable)
+    (let* ((goto (or goto-page-fn #'doc-view-goto-page))
+           (act (lambda (_name _pos page) (funcall goto page)))
+           (outline doc-view--outline))
+      (car (doc-view--imenu-subtree outline act)))))
+
+(defun doc-view--outline (&optional file-name)
+  "Return the outline for the file FILE-NAME.
+If FILE-NAME is nil, use the current file instead."
+  (unless file-name (setq file-name (buffer-file-name)))
+  (let ((outline
+         (pcase doc-view-doc-type
+           ('djvu
+            (when doc-view-djvused-program
+              (doc-view--djvu-outline file-name)))
+           (_
+            (doc-view--pdf-outline file-name)))))
+    (when outline (imenu-add-to-menubar "Outline"))
+    ;; When the outline could not be made due to unavailability of the
+    ;; required program, or its absency from the document, return
+    ;; 'unavailable'.
+    (or outline 'unavailable)))
 
 (defun doc-view-imenu-setup ()
   "Set up local state in the current buffer for imenu, if needed."
-  (when doc-view-imenu-enabled
-    (setq-local imenu-create-index-function #'doc-view-imenu-index
-                imenu-submenus-on-top nil
-                imenu-sort-function nil
-                doc-view--outline (doc-view--pdf-outline))
-    (when doc-view--outline (imenu-add-to-menubar "Outline"))))
+  (setq-local imenu-create-index-function #'doc-view-imenu-index
+              imenu-submenus-on-top nil
+              imenu-sort-function nil))
 
 ;;;; User interface commands and the mode
 
-- 
2.45.2