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* Re: [POLL] Naming of "export features"
@ 2023-03-01  8:26 Pedro Andres Aranda Gutierrez
  2023-03-01  9:41 ` Ihor Radchenko
  0 siblings, 1 reply; 22+ messages in thread
From: Pedro Andres Aranda Gutierrez @ 2023-03-01  8:26 UTC (permalink / raw)
  To: Org Mode List

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Hi,

before I forget, I have been thinking about this a lot. It may look
tangetial but IMHO it is not...

One thing is having
```
(setq org-cite-export-processors '((beamer . biblatex)
                                (latex .  biblatex)))
```
in your emacs configuration (because you need it for most situations)
and another thing is that this options forces the export process to
check that you are using a bibliography in each and every document you
generate. I may want to write a quick document  with org-mode and
generate a PDF with the LaTEX backend and another thing is that I will
need to include a bibliography even if I don't need it.

Currently, with that config for ox-latex, this MWE chokes because
their is no reference to a bibliography:

------ mwe.org -------------
#+LATEX_CLASS: letter
#+DATE: 01-Mar-2023

Dear friends!

It sucks a bit to need a bibliography to export this letter!

Best, /PA
-----------------------------------
This is the minimal emacs config that chokes at PDF export (C-c C-e lo)
----- mwe.el -----------------
(require 'org)
(require 'ox-latex)
(setq org-cite-export-processors '((beamer . biblatex)
                               (latex .  biblatex)))
(setq org-latex-pdf-process
      '("latexmk -pdflatex='pdflatex --shell-escape
--interaction=nonstopmode' -pdf -f %f"))
(add-to-list 'org-latex-classes
             '("letter"
               "\\documentclass[a4paper]{letter}"))
-------------------------------

To try:

emacs -Q -l mwe.el mwe.org

and then C-c C-e l o in Emacs to get the attached error message and no PDF.

This is all on

GNU Emacs 30.0.50
Development version fad366506974 on master branch; build date 2023-02-23.

It would be nice to take this discussion as an opportunity to 'fix' this

Best, /PA

-- 
Fragen sind nicht da um beantwortet zu werden,
Fragen sind da um gestellt zu werden
Georg Kreisler

Headaches with a Juju log:
unit-basic-16: 09:17:36 WARNING juju.worker.uniter.operation we should
run a leader-deposed hook here, but we can't yet

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^ permalink raw reply	[flat|nested] 22+ messages in thread
[parent not found: <mailman.336.1676990100.5072.emacs-orgmode@gnu.org>]
* [PATCH] Introduce "export features"
@ 2023-02-10 17:20 Timothy
  2023-02-21 14:22 ` [POLL] Naming of " Timothy
  0 siblings, 1 reply; 22+ messages in thread
From: Timothy @ 2023-02-10 17:20 UTC (permalink / raw)
  To: emacs-orgmode

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Hello everyone,

I’m thrilled to finally be presenting a feature that I’ve been incubating for a
while now that I call “export features”. This work is based on the observation
that often we include content in export templates that is only relevant in
particular situations.

This leaves one having to choose between a “kitchen sink” approach where
everything that could be used is all included, or a “manual inclusion” approach
where the template is minimal and the relevant setup code must be manually
included each time.

I think it’s fair to say neither situation is ideal, and I’ve become
dissatisfied enough that I’ve sunk some time into working on a better way of
handling this. In this patch set it’s just being applied to LaTeX preambles, but
this is just a start — there are plans to apply this more broadly.

“export features” allow for the specification of qualities of the org buffer
being exported that imply certain “features”, and how those features may be
implemented in a particular export.

This is done by augmenting the backend struct with two new fields:
`feature-conditions' and `feature-implementations'.

The feature conditions are resolved during the annotation of `info', in the Org
buffer after `#+include' expansion and the removal of comments.

The feature implementations are expanded by the backend itself, in the case of
`ox-latex' this currently means during preamble construction.

With this change, `ox-latex' produces more minimal /and/ more capable exports out of
the box. The number of default packages has been ~halved, but OOTB capability
has been improved by dynamically adding them to the preamble when needed, and
now `\usepackage{svg}' is automatically added when exporting a buffer that
includes SVG images.

This also opens new frontiers for user customisation. For instance, adding
particular beamer customisations when using the `metropolis' beamer theme with the
following snippet:

┌────
│ (org-export-update-features 'beamer
│   (beamer-metropolis
│    :condition (string-match-p \"metropolis$\" (plist-get info :beamer-theme))
│    :snippet my-org-beamer-metropolis-tweaks
│    :order 3))
└────


Hopefully this gives you an idea of the feature. See the patches attached for
the implementation (and some hopefully informative code comments). Feel free to
toss any you may have question my way :)

All the best,
Timothy

-- 
Timothy (‘tecosaur’/‘TEC’), Org mode contributor.
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/tec>.

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From 5575a0f18277ef34f4003c1bccf650e4237e6048 Mon Sep 17 00:00:00 2001
From: TEC <git@tecosaur.net>
Date: Mon, 25 Jul 2022 23:37:13 +0800
Subject: [PATCH 1/6] ox: Introduce conditional/generated preamble

* lisp/ox.el (org-export-detect-features, org-export-expand-features,
org-export-generate-features-preamble): New functions for detecting
features and generating content based on them.
* lisp/ox.el (org-export-conditional-features): Customisation for
feature detection.
* lisp/ox.el (org-export-as): Add detected to features to info in the
slot :features.
---
 lisp/ox.el | 217 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 217 insertions(+)

diff --git a/lisp/ox.el b/lisp/ox.el
index 0a48e850a..1a75ed28d 100644
--- a/lisp/ox.el
+++ b/lisp/ox.el
@@ -2030,6 +2030,221 @@ (defun org-export-expand (blob contents &optional with-affiliated)
 	    (funcall (intern (format "org-element-%s-interpreter" type))
 		     blob contents))))
 
+\f
+;;; Conditional/Generated Preamble
+;;
+;; Many formats have some version of a preamble, whether it be HTML's
+;; <head>...</head> or the content before LaTeX's \begin{document}.
+;; Depending on the particular features in the Org document being
+;; exported, different setup snippets will be needed.  There's the
+;; "everything and the kitchen sink" approach of adding absolutely
+;; everything that might be needed, and the post-translation editing
+;; with filters approach, but neither really solve this problem nicely.
+;;
+;; The conditional/generated preamble defines mechanisms of detecting
+;; which "features" are used in a document, handles interactions
+;; between features, and provides/generates preamble content to
+;; support the features.
+
+(defcustom org-export-conditional-features
+  `(("^[ \t]*#\\+print_bibliography:" . bibliography)
+    (,(lambda (info)
+       (org-element-map (plist-get info :parse-tree)
+           'link
+         (lambda (link)
+           (and (member (org-element-property :type link)
+                        '("http" "https" "ftp" "file"))
+                (file-name-extension (org-element-property :path link))
+                (string= (downcase (file-name-extension
+                                    (org-element-property :path link)))
+                         "svg")))
+         info t))
+     . svg)
+    (,(lambda (info)
+       (org-element-map (plist-get info :parse-tree)
+           'link
+         (lambda (link)
+           (and (member (org-element-property :type link)
+                        '("http" "https" "ftp" "file"))
+                (file-name-extension (org-element-property :path link))
+                (member (downcase (file-name-extension
+                                   (org-element-property :path link)))
+                        image-file-name-extensions)))
+         info t))
+     . image)
+    (,(lambda (info)
+       (org-element-map (plist-get info :parse-tree)
+           'table #'identity info t))
+     . table)
+    (,(lambda (info)
+       (org-element-map (plist-get info :parse-tree)
+           '(src-block inline-src-block) #'identity info t))
+     . code))
+  "Org feature tests and associated feature flags.
+
+Alist where the car is a test for the presense of the feature,
+and the CDR is either a single feature symbol or a list of
+feature symbols.
+
+Feature tests can take any of the following forms:
+- Variable symbol, the value of which is fetched.
+- Function symbol, which is called with the export info
+  as the argument.
+- A string, which is used as a regexp search in the buffer.
+  The regexp matching is taken as confirmation of the existence
+  of the feature.
+
+When the test is a variable or function and produces a string
+value, that value is itself used as a test. Any other non-nil
+value will imply the existance of the feature."
+  :group 'org-export-general
+  :type '(alist :key-type
+                (choice (regexp :tag "Feature test regexp")
+                        (variable :tag "Feature variable")
+                        (function :tag "Feature test function"))
+                :value-type
+                (choice (symbol :tag "Feature symbol")
+                        (repeat symbol :tag "Feature symbols"))))
+
+(defun org-export-detect-features (info)
+  "Detect features from `org-export-conditional-features' in INFO."
+  (let (case-fold-search)
+    (delete-dups
+     (mapcan
+      (lambda (construct-feature)
+        (and (let ((out (pcase (car construct-feature)
+                          ((pred stringp) (car construct-feature))
+                          ((pred functionp)
+                           (funcall (car construct-feature) info))
+                          ((pred symbolp) (symbol-value (car construct-feature)))
+                          (_ (error "org-export-conditional-features key %s unable to be used" (car construct-feature))))))
+               (if (stringp out)
+                   (save-excursion
+                     (goto-char (point-min))
+                     (re-search-forward out nil t))
+                 out))
+             (if (listp (cdr construct-feature))
+                 (copy-sequence (cdr construct-feature))
+               (list (cdr construct-feature)))))
+      (append org-export-conditional-features
+              (plist-get info :conditional-features))))))
+
+(defun org-export-expand-features (info)
+  "Identify all implied implementations from features, in INFO.
+
+(plist-get info :feature-implementations) should be an alist of feature symbols
+and specification plists with the following keys:
+- :snippet, which is either,
+  - A string, which should be included in the preamble verbatim.
+  - A variable, the value of which should be included in the preamble.
+  - A function, which is called with two arguments — the export info,
+    and the list of feature flags.  The returned value is included in
+    the preamble.
+- :requires, a feature or list of features this feature will enable.
+- :when, a feature or list of features which are required for this
+  feature to be active.
+- :prevents, a feature or list of features that should be masked.
+- :order, for when inclusion order matters.  Feature implementations
+  with a lower order appear first.  The default is 0.
+
+This function processes :requires, :when, and :prevents in turn
+before finally sorting according to :order.
+
+After resolving the features, the :features key of INFO is
+updated to reflect the expanded set of features being used."
+  (let ((initial-features (plist-get info :features))
+        (implementations (plist-get info :feature-implementations))
+        required-features current-implementations)
+    ;; Process :requires.
+    (while initial-features
+      (push (car initial-features) required-features)
+      (setq initial-features
+            (if-let (requirements
+                     (plist-get (alist-get (car initial-features) implementations)
+                                :requires))
+                (if (consp requirements)
+                    (append requirements (cdr initial-features))
+                  (cons requirements (cdr initial-features)))
+              (cdr initial-features))))
+    ;; Get the implementations of required features.
+    (setq current-implementations
+          (mapcar (lambda (f) (assq f implementations))
+                  (delete-dups required-features)))
+    ;; Remove features with unfulfilled :when conditions.
+    (let ((processing t)
+          confirmed-features conditional-implementations
+          when)
+      ;; To correctly resolve all the various :when conditions,
+      ;; do not make any assumptions about which features are active.
+      ;; Initially only consider non-:when implementations to be
+      ;; active, then run through the list of unconfirmed :when
+      ;; implementations and check their conditions against the list
+      ;; of confirmed features.  Continue doing this until no more
+      ;; features are confirmed.
+      (dolist (impl current-implementations)
+        (if (plist-get (cdr impl) :when)
+            (push impl conditional-implementations)
+          (push (car impl) confirmed-features)))
+      (while processing
+        (setq processing nil)
+        (dolist (impl conditional-implementations)
+          (setq when (plist-get (cdr impl) :when))
+          (when (cond
+                 ((symbolp when)
+                  (memq when confirmed-features))
+                 ((consp when)
+                  (not (cl-set-difference when confirmed-features))))
+            (push (car impl) confirmed-features)
+            (setq conditional-implementations
+                  (delq impl conditional-implementations)
+                  processing t))))
+      ;; Now all that remains is implementations with unsatisfiable
+      ;; :when conditions.
+      (dolist (impl conditional-implementations)
+        (setq current-implementations
+              (delq impl current-implementations))))
+    ;; Get rid of prevented features.
+    (dolist (impl current-implementations)
+      (when-let ((prevented (pcase (plist-get (cdr impl) :prevents)
+                              ((and (pred consp) p) p)
+                              ((pred null) nil)
+                              ((and (pred atom) p) (list p)))))
+        (setq current-implementations
+              (cl-remove-if
+               (lambda (i) (memq (car i) prevented))
+               current-implementations))))
+    ;; Sort by :order.
+    (setq current-implementations
+          (sort current-implementations
+                (lambda (impl1 impl2)
+                  (< (or (plist-get (cdr impl1) :order) 0)
+                     (or (plist-get (cdr impl2) :order) 0)))))
+    ;; Update :features to reflect the features actually used.
+    (plist-put info :features (mapcar #'car current-implementations))
+    current-implementations))
+
+(defun org-export-generate-features-preamble (info)
+  "Generate preamble string according to features an implementations in INFO.
+More specifically, this function resolves feature implementations
+with `org-export-expand-features' and concatenates the snippets."
+  (let* ((feat-impl (org-export-expand-features info))
+         (feat-snippets
+          (mapcar
+           (lambda (impl)
+             (let ((snippet (plist-get (cdr impl) :snippet)))
+               (cond
+                ((null snippet) nil)
+                ((functionp snippet)
+                 (funcall snippet info))
+                ((symbolp snippet) (symbol-value snippet))
+                ((stringp snippet) snippet)
+                (t (error "org-export feature snippet %S is invalid." snippet)
+                   nil))))
+           feat-impl)))
+    (mapconcat
+     #'identity
+     (append (delq nil feat-snippets) (list ""))
+     "\n")))
 
 \f
 ;;; The Filter System
@@ -3186,6 +3401,8 @@ (defun org-export--annotate-info (backend info &optional subtreep visible-only e
     ;; the output of the selected citation export processor.
     (org-cite-process-citations info)
     (org-cite-process-bibliography info)
+    ;; With the complete tree, detect features.
+    (plist-put info :features (org-export-detect-features info))
     info))
 
 ;;;###autoload
-- 
2.39.0


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From 064e802169ce4ba99c019e908eb945f2a96274ba Mon Sep 17 00:00:00 2001
From: TEC <git@tecosaur.net>
Date: Mon, 6 Feb 2023 00:01:26 +0800
Subject: [PATCH 2/6] ox-latex: Apply new generated preamble to export

* lisp/ox-latex.el (org-latex-template, org-latex-make-preamble,
org-latex-guess-polyglossia-language, org-latex-guess-babel-language,
org-latex-guess-inputenc, org-latex-generate-engraved-preamble):
Refactor to make use of the generated export, and add a few new bells
and whistles.

* lisp/ox-beamer.el (org-beamer-template): Adjust to account for the
changes in ox-latex.el.
---
 lisp/org.el       |  15 --
 lisp/ox-beamer.el |  10 +-
 lisp/ox-latex.el  | 353 +++++++++++++++++++++++++++++-----------------
 3 files changed, 223 insertions(+), 155 deletions(-)

diff --git a/lisp/org.el b/lisp/org.el
index 4d12084d9..4fb16d079 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -3385,14 +3385,6 @@ (defun org-get-packages-alist (var)
 (defcustom org-latex-default-packages-alist
   '(("AUTO" "inputenc"  t ("pdflatex"))
     ("T1"   "fontenc"   t ("pdflatex"))
-    (""     "graphicx"  t)
-    (""     "longtable" nil)
-    (""     "wrapfig"   nil)
-    (""     "rotating"  nil)
-    ("normalem" "ulem"  t)
-    (""     "amsmath"   t)
-    (""     "amssymb"   t)
-    (""     "capt-of"   nil)
     (""     "hyperref"  nil))
   "Alist of default packages to be inserted in the header.
 
@@ -3403,15 +3395,8 @@ (defcustom org-latex-default-packages-alist
 Org mode to function properly:
 
 - inputenc, fontenc:  for basic font and character selection
-- graphicx: for including images
-- longtable: For multipage tables
 - wrapfig: for figure placement
 - rotating: for sideways figures and tables
-- ulem: for underline and strike-through
-- amsmath: for subscript and superscript and math environments
-- amssymb: for various symbols used for interpreting the entities
-  in `org-entities'.  You can skip some of this package if you don't
-  use any of the symbols.
 - capt-of: for captions outside of floats
 - hyperref: for cross references
 
diff --git a/lisp/ox-beamer.el b/lisp/ox-beamer.el
index 5df78d5a4..8924b412b 100644
--- a/lisp/ox-beamer.el
+++ b/lisp/ox-beamer.el
@@ -821,9 +821,7 @@ (defun org-beamer-template (contents info)
      ;; Time-stamp.
      (and (plist-get info :time-stamp-file)
 	  (format-time-string "%% Created %Y-%m-%d %a %H:%M\n"))
-     ;; LaTeX compiler
-     (org-latex--insert-compiler info)
-     ;; Document class and packages.
+     ;; Document class, packages, and some configuration.
      (org-latex-make-preamble info)
      ;; Insert themes.
      (let ((format-theme
@@ -872,12 +870,6 @@ (defun org-beamer-template (contents info)
      (let ((template (plist-get info :latex-hyperref-template)))
        (and (stringp template)
 	    (format-spec template (org-latex--format-spec info))))
-     ;; engrave-faces-latex preamble
-     (when (and (eq org-latex-src-block-backend 'engraved)
-                (org-element-map (plist-get info :parse-tree)
-                    '(src-block inline-src-block) #'identity
-                    info t))
-       (org-latex-generate-engraved-preamble info))
      ;; Document start.
      "\\begin{document}\n\n"
      ;; Title command.
diff --git a/lisp/ox-latex.el b/lisp/ox-latex.el
index dc2062df5..9794e6ecd 100644
--- a/lisp/ox-latex.el
+++ b/lisp/ox-latex.el
@@ -127,6 +127,8 @@ (org-export-define-backend 'latex
     (:description "DESCRIPTION" nil nil parse)
     (:keywords "KEYWORDS" nil nil parse)
     (:subtitle "SUBTITLE" nil nil parse)
+    (:conditional-features nil nil org-latex-conditional-features)
+    (:feature-implementations nil nil org-latex-feature-implementations)
     ;; Other variables.
     (:latex-active-timestamp-format nil nil org-latex-active-timestamp-format)
     (:latex-caption-above nil nil org-latex-caption-above)
@@ -1378,6 +1380,95 @@ (defun org-latex-generate-engraved-preamble (info)
        "% WARNING syntax highlighting unavailable as engrave-faces-latex was missing.\n")
      "\n")))
 
+;;;; Generated preamble
+
+(defcustom org-latex-conditional-features
+  `((t . !announce-start)
+    (t . !announce-end)
+    (t . !guess-pollyglossia)
+    (t . !guess-babel)
+    (t . !guess-inputenc)
+    (,(lambda (info)
+        (org-element-map (plist-get info :parse-tree)
+            '(latex-fragment latex-environment) #'identity info t))
+     . maths)
+    (,(lambda (info)
+        (org-element-map (plist-get info :parse-tree)
+            'underline #'identity info t))
+     . underline)
+    ("\\\\uu?line\\|\\\\uwave\\|\\\\sout\\|\\\\xout\\|\\\\dashuline\\|\\dotuline\\|\\markoverwith"
+     . underline)
+    (,(lambda (info)
+        (org-element-map (plist-get info :parse-tree)
+            'link
+          (lambda (link)
+            (and (member (org-element-property :type link)
+                         '("http" "https" "ftp" "file"))
+                 (file-name-extension (org-element-property :path link))
+                 (equal (downcase (file-name-extension
+                                   (org-element-property :path link)))
+                        "svg")))
+          info t))
+     . svg)
+    (org-latex-tables-booktabs . booktabs)
+    (,(lambda (info)
+        (eq (plist-get info :latex-src-block-backend) 'engraved))
+     . engraved-code)
+    ("^[ \t]*#\\+attr_latex: .*:float +wrap"
+     . float-wrap)
+    ("^[ \t]*#\\+attr_latex: .*:float +sideways"
+     . rotate)
+    ("^[ \t]*#\\+caption:\\|\\\\caption{" . caption))
+  "A LaTeX-specific extension to `org-export-conditional-features', which see.")
+
+(defcustom org-latex-feature-implementations
+  `((!announce-start
+     :snippet ,(lambda (info)
+                 (format "\n%%%% ox-latex features: %s"
+                         (plist-get info :features)))
+     :order -100)
+    (maths :snippet "\\usepackage{amsmath}\n\\usepackage{amssymb}" :order 0.2)
+    (underline :snippet "\\usepackage[normalem]{ulem}" :order 0.5)
+    (image :snippet "\\usepackage{graphicx}" :order 2)
+    (svg :snippet "\\usepackage[inkscapelatex=false]{svg}" :order 2 :when image)
+    (longtable :snippet "\\usepackage{longtable}" :when table :order 2)
+    (booktabs :snippet "\\usepackage{booktabs}" :when table :order 2)
+    (float-wrap :snippet "\\usepackage{wrapfig}" :order 2)
+    (rotate :snippet "\\usepackage{rotating}" :order 2)
+    (caption :snippet "\\usepackage{capt-of}")
+    (engraved-code :snippet org-latex-generate-engraved-preamble :when code)
+    (!guess-pollyglossia :snippet org-latex-guess-polyglossia-language)
+    (!guess-babel :snippet org-latex-guess-babel-language)
+    (!guess-inputenc :snippet org-latex-guess-inputenc)
+    (!announce-end :snippet "%% end ox-latex features\n" :order 100))
+  "Alist describing how export features should be supported in the preamble.
+
+Implementation alist has the feature symbol as the car, with the
+cdr forming a plist with the following keys:
+- :snippet, which is either,
+  - A string, which should be included in the preamble verbatim.
+  - A variable, the value of which should be included in the preamble.
+  - A function, which is called with two arguments — the export info,
+    and the list of feature flags. The returned value is included in
+    the preamble.
+- :requires, a feature or list of features which are needed.
+- :when, a feature or list of features which imply this feature.
+- :prevents, a feature or list of features that should be masked.
+- :order, for when inclusion order matters. Feature implementations
+  with a lower order appear first.  The default is 0."
+  :group 'org-export-general
+  :type '(plist :key-type
+          (choice (const :snippet)
+                  (const :requires)
+                  (const :when)
+                  (const :prevents)
+                  (const :order)
+                  (const :trigger))
+          :value-type
+          (choice (string :tag "Verbatim content")
+                  (variable :tag "Content variable")
+                  (function :tag "Generating function"))))
+
 ;;;; Compilation
 
 (defcustom org-latex-compiler-file-string "%% Intended LaTeX compiler: %s\n"
@@ -1620,29 +1711,29 @@ (defun org-latex--caption/label-string (element info)
 	      (org-trim label)
 	      (org-export-data main info))))))
 
-(defun org-latex-guess-inputenc (header)
+(defun org-latex-guess-inputenc (info)
   "Set the coding system in inputenc to what the buffer is.
 
-HEADER is the LaTeX header string.  This function only applies
-when specified inputenc option is \"AUTO\".
+INFO is the plist used as a communication channel.
+This function only applies when specified inputenc option is \"AUTO\".
 
 Return the new header, as a string."
-  (let* ((cs (or (ignore-errors
-		   (latexenc-coding-system-to-inputenc
-		    (or org-export-coding-system buffer-file-coding-system)))
-		 "utf8")))
-    (if (not cs) header
+  (let ((header (plist-get info :latex-full-header))
+        (cs (or (ignore-errors
+                  (latexenc-coding-system-to-inputenc
+                   (or org-export-coding-system buffer-file-coding-system)))
+                "utf8")))
+    (when (and cs (string-match "\\\\usepackage\\[\\(AUTO\\)\\]{inputenc}" header))
       ;; First translate if that is requested.
       (setq cs (or (cdr (assoc cs org-latex-inputenc-alist)) cs))
-      ;; Then find the \usepackage statement and replace the option.
-      (replace-regexp-in-string "\\\\usepackage\\[\\(AUTO\\)\\]{inputenc}"
-				cs header t nil 1))))
+      (plist-put info :latex-full-header
+                 (replace-match cs t t header 1))))
+  nil)
 
-(defun org-latex-guess-babel-language (header info)
+(defun org-latex-guess-babel-language (info)
   "Set Babel's language according to LANGUAGE keyword.
 
-HEADER is the LaTeX header string.  INFO is the plist used as
-a communication channel.
+INFO is the plist used as a communication channel.
 
 Insertion of guessed language only happens when Babel package has
 explicitly been loaded.  Then it is added to the rest of
@@ -1656,50 +1747,46 @@ (defun org-latex-guess-babel-language (header info)
 
 Return the new header."
   (let* ((language-code (plist-get info :language))
-	 (plist (cdr
-		 (assoc language-code org-latex-language-alist)))
-	 (language (plist-get plist :babel))
-	 (language-ini-only (plist-get plist :babel-ini-only))
-	 ;; If no language is set, or Babel package is not loaded, or
-	 ;; LANGUAGE keyword value is a language served by Babel
-	 ;; exclusively through ini files, return HEADER as-is.
-	 (header (if (or language-ini-only
-			 (not (stringp language-code))
-			 (not (string-match "\\\\usepackage\\[\\(.*\\)\\]{babel}" header)))
-		     header
-		   (let ((options (save-match-data
-				    (org-split-string (match-string 1 header) ",[ \t]*"))))
-		     ;; If LANGUAGE is already loaded, return header
-		     ;; without AUTO.  Otherwise, replace AUTO with language or
-		     ;; append language if AUTO is not present.  Languages that are
-		     ;; served in Babel exclusively through ini files are not added
-		     ;; to the babel argument, and must be loaded using
-		     ;; `\babelprovide'.
-		     (replace-match
-		      (mapconcat (lambda (option) (if (equal "AUTO" option) language option))
-				 (cond ((member language options) (delete "AUTO" options))
-				       ((member "AUTO" options) options)
-				       (t (append options (list language))))
-				 ", ")
-		      t nil header 1)))))
+         (plist (cdr (assoc language-code org-latex-language-alist)))
+         (language (plist-get plist :babel))
+         (header (plist-get info :latex-full-header))
+         (language-ini-only (plist-get plist :babel-ini-only))
+         (babel-header-options
+          ;; If no language is set, or Babel package is not loaded, or
+          ;; LANGUAGE keyword value is a language served by Babel
+          ;; exclusively through ini files, return HEADER as-is.
+          (and (not language-ini-only)
+               (stringp language-code)
+               (string-match "\\\\usepackage\\[\\(.*\\)\\]{babel}" header)
+               (let ((options (save-match-data
+                                (org-split-string (match-string 1 header) ",[ \t]*"))))
+                 (cond ((member language options) (delete "AUTO" options))
+                       ((member "AUTO" options) options)
+                       (t (append options (list language))))))))
+    (when babel-header-options
+      ;; If AUTO is present in the header options, replace it with `language'.
+      (setq header
+            (replace-match
+             (mapconcat (lambda (option) (if (equal "AUTO" option) language option))
+                        babel-header-options
+                        ", ")
+             t nil header 1)))
     ;; If `\babelprovide[args]{AUTO}' is present, AUTO is
     ;; replaced by LANGUAGE.
-    (if (not (string-match "\\\\babelprovide\\[.*\\]{\\(.+\\)}" header))
-	header
-      (let ((prov (match-string 1 header)))
-	(if (equal "AUTO" prov)
-	    (replace-regexp-in-string (format
-				       "\\(\\\\babelprovide\\[.*\\]\\)\\({\\)%s}" prov)
-				      (format "\\1\\2%s}"
-					      (or language language-ini-only))
-				      header t)
-	  header)))))
-
-(defun org-latex-guess-polyglossia-language (header info)
+    (when (string-match "\\\\babelprovide\\[.*\\]{AUTO}" header)
+      (setq header
+            (replace-regexp-in-string
+             (format
+              "\\(\\\\babelprovide\\[.*\\]\\)\\({\\)%s}" prov)
+             (format "\\1\\2%s}" (or language language-ini-only))
+             header t)))
+    (plist-put info :latex-full-header header))
+  nil)
+
+(defun org-latex-guess-polyglossia-language (info)
   "Set the Polyglossia language according to the LANGUAGE keyword.
 
-HEADER is the LaTeX header string.  INFO is the plist used as
-a communication channel.
+INFO is the plist used as a communication channel.
 
 Insertion of guessed language only happens when the Polyglossia
 package has been explicitly loaded.
@@ -1710,48 +1797,50 @@ (defun org-latex-guess-polyglossia-language (header info)
 using \setdefaultlanguage and not as an option to the package.
 
 Return the new header."
-  (let* ((language (plist-get info :language)))
+  (let ((header (plist-get info :latex-full-header))
+        (language (plist-get info :language)))
     ;; If no language is set or Polyglossia is not loaded, return
     ;; HEADER as-is.
-    (if (or (not (stringp language))
-	    (not (string-match
-		  "\\\\usepackage\\(?:\\[\\([^]]+?\\)\\]\\){polyglossia}\n"
-		  header)))
-	header
+    (when (and (stringp language)
+               (string-match
+                "\\\\usepackage\\(?:\\[\\([^]]+?\\)\\]\\){polyglossia}\n"
+                header))
       (let* ((options (org-string-nw-p (match-string 1 header)))
-	     (languages (and options
-			     ;; Reverse as the last loaded language is
-			     ;; the main language.
-			     (nreverse
-			      (delete-dups
-			       (save-match-data
-				 (org-split-string
-				  (replace-regexp-in-string
-				   "AUTO" language options t)
-				  ",[ \t]*"))))))
-	     (main-language-set
-	      (string-match-p "\\\\setmainlanguage{.*?}" header)))
-	(replace-match
-	 (concat "\\usepackage{polyglossia}\n"
-		 (mapconcat
-		  (lambda (l)
-		    (let* ((plist (cdr
-				   (assoc language org-latex-language-alist)))
-			   (polyglossia-variant (plist-get plist :polyglossia-variant))
-			   (polyglossia-lang (plist-get plist :polyglossia))
-			   (l (if (equal l language)
-				  polyglossia-lang
-				l)))
-		      (format (if main-language-set (format "\\setotherlanguage{%s}\n" l)
-				(setq main-language-set t)
-				"\\setmainlanguage%s{%s}\n")
-			      (if polyglossia-variant
-				  (format "[variant=%s]" polyglossia-variant)
-				"")
-			      l)))
-		  languages
-		  ""))
-	 t t header 0)))))
+             (languages (and options
+                             ;; Reverse as the last loaded language is
+                             ;; the main language.
+                             (nreverse
+                              (delete-dups
+                               (save-match-data
+                                 (org-split-string
+                                  (replace-regexp-in-string
+                                   "AUTO" language options t)
+                                  ",[ \t]*"))))))
+             (main-language-set
+              (string-match-p "\\\\setmainlanguage{.*?}" header))
+             (polyglossia-modified-header
+              (replace-match
+               (concat "\\usepackage{polyglossia}\n"
+                       (mapconcat
+                        (lambda (l)
+                          (let* ((plist (cdr (assoc language org-latex-language-alist)))
+                                 (polyglossia-variant (plist-get plist :polyglossia-variant))
+                                 (polyglossia-lang (plist-get plist :polyglossia))
+                                 (l (if (equal l language)
+                                        polyglossia-lang
+                                      l)))
+                            (format (if main-language-set (format "\\setotherlanguage{%s}\n" l)
+                                      (setq main-language-set t)
+                                      "\\setmainlanguage%s{%s}\n")
+                                    (if polyglossia-variant
+                                        (format "[variant=%s]" polyglossia-variant)
+                                      "")
+                                    l)))
+                        languages
+                        ""))
+               t t header 0)))
+        (plist-put info :latex-full-header polyglossia-modified-header))))
+  nil)
 
 (defun org-latex--remove-packages (pkg-alist info)
   "Remove packages based on the current LaTeX compiler.
@@ -1952,32 +2041,45 @@ (defun org-latex-make-preamble (info &optional template snippet?)
 specified in `org-latex-default-packages-alist' or
 `org-latex-packages-alist'."
   (let* ((class (plist-get info :latex-class))
-	 (class-template
-	  (or template
-	      (let* ((class-options (plist-get info :latex-class-options))
-		     (header (nth 1 (assoc class (plist-get info :latex-classes)))))
-		(and (stringp header)
-		     (if (not class-options) header
-		       (replace-regexp-in-string
-			"^[ \t]*\\\\documentclass\\(\\(\\[[^]]*\\]\\)?\\)"
-			class-options header t nil 1))))
-	      (user-error "Unknown LaTeX class `%s'" class))))
-    (org-latex-guess-polyglossia-language
-     (org-latex-guess-babel-language
-      (org-latex-guess-inputenc
-       (org-element-normalize-string
-	(org-splice-latex-header
-	 class-template
-	 (org-latex--remove-packages org-latex-default-packages-alist info)
-	 (org-latex--remove-packages org-latex-packages-alist info)
-	 snippet?
-	 (mapconcat #'org-element-normalize-string
-		    (list (plist-get info :latex-header)
-			  (and (not snippet?)
-			       (plist-get info :latex-header-extra)))
-		    ""))))
-      info)
-     info)))
+         (class-template
+          (or template
+              (let* ((class-options (plist-get info :latex-class-options))
+                     (header (nth 1 (assoc class (plist-get info :latex-classes)))))
+                (and (stringp header)
+                     (if (not class-options) header
+                       (replace-regexp-in-string
+                        "^[ \t]*\\\\documentclass\\(\\(\\[[^]]*\\]\\)?\\)"
+                        class-options header t nil 1))))
+              (user-error "Unknown LaTeX class `%s'" class)))
+         generated-preamble)
+    (plist-put info :latex-full-header
+               (org-element-normalize-string
+                (org-splice-latex-header
+                 class-template
+                 (org-latex--remove-packages org-latex-default-packages-alist info)
+                 (org-latex--remove-packages org-latex-packages-alist info)
+                 snippet?
+                 (mapconcat #'org-element-normalize-string
+                            (list (plist-get info :latex-header)
+                                  (and (not snippet?)
+                                       (plist-get info :latex-header-extra)))
+                            ""))))
+    (setq generated-preamble
+          (if snippet?
+              (progn
+                (org-latex-guess-inputenc info)
+                (org-latex-guess-babel-language info)
+                (org-latex-guess-polyglossia-language info)
+                "\n% Generated preamble omitted for snippets.")
+            (org-export-generate-features-preamble info)))
+    (concat
+     ;; Time-stamp.
+     (and (plist-get info :time-stamp-file)
+          (format-time-string "%% Created %Y-%m-%d %a %H:%M\n"))
+     ;; LaTeX compiler.
+     (org-latex--insert-compiler info)
+     (plist-get info :latex-full-header)
+     generated-preamble)))
 
 (defun org-latex-template (contents info)
   "Return complete document string after LaTeX conversion.
@@ -1986,12 +2088,7 @@ (defun org-latex-template (contents info)
   (let ((title (org-export-data (plist-get info :title) info))
 	(spec (org-latex--format-spec info)))
     (concat
-     ;; Time-stamp.
-     (and (plist-get info :time-stamp-file)
-	  (format-time-string "%% Created %Y-%m-%d %a %H:%M\n"))
-     ;; LaTeX compiler.
-     (org-latex--insert-compiler info)
-     ;; Document class and packages.
+     ;; Timestamp, compiler statement, document class and packages.
      (org-latex-make-preamble info)
      ;; Possibly limit depth for headline numbering.
      (let ((sec-num (plist-get info :section-numbers)))
@@ -2028,12 +2125,6 @@ (defun org-latex-template (contents info)
      (let ((template (plist-get info :latex-hyperref-template)))
        (and (stringp template)
             (format-spec template spec)))
-     ;; engrave-faces-latex preamble
-     (when (and (eq org-latex-src-block-backend 'engraved)
-                (org-element-map (plist-get info :parse-tree)
-                    '(src-block inline-src-block) #'identity
-                    info t))
-       (org-latex-generate-engraved-preamble info))
      ;; Document start.
      "\\begin{document}\n\n"
      ;; Title command.
-- 
2.39.0


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From ae319fccc64f35c52a247633c67f72c924396b03 Mon Sep 17 00:00:00 2001
From: TEC <git@tecosaur.net>
Date: Sun, 5 Feb 2023 12:34:55 +0800
Subject: [PATCH 3/6] ox: Feature condition/implementation convenience

* lisp/ox.el (org-export-update-features): Add a convenience function
for users to edit the feature condition/implementation lists.
---
 lisp/ox.el | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/lisp/ox.el b/lisp/ox.el
index 1a75ed28d..32f1c6016 100644
--- a/lisp/ox.el
+++ b/lisp/ox.el
@@ -2246,6 +2246,48 @@ (defun org-export-generate-features-preamble (info)
      (append (delq nil feat-snippets) (list ""))
      "\n")))
 
+(defun org-export-update-features (backend &rest feature-property-value-lists)
+  "For BACKEND's export spec, set all FEATURE-PROPERTY-VALUE-LISTS.
+
+Specifically, for each (FEATURE . PROPERTY-VALUE-LIST) entry of
+FEATURE-PROPERTY-VALUE-LISTS, each :PROPERTY VALUE pair of
+PROPERTY-VALUE-PAIRS is set to VALUE within the backend's feature
+implementation plist.  The sole exception to this is the
+:condition property, the value of which is set in the backend's
+feature condition plist instead.
+
+This can be used to both modify existing entries, and create new ones.
+
+\(fn BACKEND &rest (FEATURE PROPERTY-VALUE-PAIRS...)...)"
+  (declare (indent 1))
+  (let ((backend-var (intern (format "org-%s-feature-implementations" backend)))
+        (backend-cf (intern (format "org-%s-conditional-features" backend))))
+    (unless (boundp backend-var)
+      (error "Feature implementations for %s cannot be set as %s is undefined"
+             backend backend-var))
+    (dolist (feature-property-value-set feature-property-value-lists)
+      (let ((feature (car feature-property-value-set))
+            (property-value-pairs (copy-sequence (cdr feature-property-value-set))))
+        (while property-value-pairs
+          (if (eq (car property-value-pairs) :condition)
+              (let ((condition (progn (pop property-value-pairs)
+                                      (pop property-value-pairs))))
+                (unless (boundp backend-cf)
+                  (error "Feature condition for %s cannot be set as %s is undefined"
+                         backend backend-cf))
+                (cond
+                 ((rassoc feature (symbol-value backend-cf))
+                  (if condition
+                      (setcar (rassoc feature (symbol-value backend-cf))
+                              condition)
+                    (set backend-cf (delq (rassoc feature (symbol-value backend-cf))
+                                          (symbol-value backend-cf)))))
+                 (condition
+                  (add-to-list backend-cf (cons condition feature)))))
+            (setf (alist-get feature (symbol-value backend-var))
+                  (plist-put (alist-get feature (symbol-value backend-var))
+                             (pop property-value-pairs) (pop property-value-pairs)))))))))
+
 \f
 ;;; The Filter System
 ;;
-- 
2.39.0


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From 70bd6bcf11597d9865dba107a44030e1da17154b Mon Sep 17 00:00:00 2001
From: TEC <git@tecosaur.net>
Date: Mon, 6 Feb 2023 00:01:41 +0800
Subject: [PATCH 4/6] oc-*: Make use of conditional preamble for export

* lisp/oc-natbib.el (org-cite-natbib-use-package): Refactor to make use
of the conditional/generated preamble.

* lisp/oc-csl.el (org-cite-csl-finalizer): Refactor to make use of
the conditional/generated preamble.

* lisp/oc-biblatex.el (org-cite-biblatex-prepare-preamble): Refactor to
make use of the conditional/generated preamble.
---
 lisp/oc-biblatex.el | 82 ++++++++++++++++++---------------------------
 lisp/oc-csl.el      | 16 ---------
 lisp/oc-natbib.el   | 33 +++++++-----------
 lisp/ox-latex.el    | 15 +++++++++
 4 files changed, 61 insertions(+), 85 deletions(-)

diff --git a/lisp/oc-biblatex.el b/lisp/oc-biblatex.el
index b2d31f0f6..e8e420891 100644
--- a/lisp/oc-biblatex.el
+++ b/lisp/oc-biblatex.el
@@ -375,61 +375,45 @@ (defun org-cite-biblatex-export-citation (citation style _ info)
        (other
         (user-error "Invalid entry %S in `org-cite-biblatex-styles'" other))))))
 
-(defun org-cite-biblatex-prepare-preamble (output _keys files style &rest _)
-  "Prepare document preamble for \"biblatex\" usage.
-
-OUTPUT is the final output of the export process.  FILES is the list of file
-names used as the bibliography.
-
-This function ensures \"biblatex\" package is required.  It also adds resources
-to the document, and set styles."
-  (with-temp-buffer
-    (save-excursion (insert output))
-    (when (search-forward "\\begin{document}" nil t)
-      ;; Ensure there is a \usepackage{biblatex} somewhere or add one.
-      ;; Then set options.
-      (goto-char (match-beginning 0))
-      (let ((re (rx "\\usepackage"
-                    (opt (group "[" (*? anything) "]"))
-                    "{biblatex}")))
-        (cond
-         ;; No "biblatex" package loaded.  Insert "usepackage" command
-         ;; with appropriate options, including style.
-         ((not (re-search-backward re nil t))
-          (save-excursion
-            (insert
-             (format "\\usepackage%s{biblatex}\n"
-                     (org-cite-biblatex--package-options
-                      org-cite-biblatex-options style)))))
-         ;; "biblatex" package loaded, but without any option.
-         ;; Include style only.
-         ((not (match-beginning 1))
-          (search-forward "{" nil t)
-          (insert (org-cite-biblatex--package-options nil style)))
-         ;; "biblatex" package loaded with some options set.  Override
-         ;; style-related options with ours.
-         (t
-          (replace-match
-           (save-match-data
-             (org-cite-biblatex--package-options (match-string 1) style))
-           nil nil nil 1))))
-      ;; Insert resources below.
-      (forward-line)
-      (insert (mapconcat (lambda (f)
-                           (format "\\addbibresource%s{%s}"
-                                   (if (org-url-p f) "[location=remote]" "")
-                                   f))
-                         files
-                         "\n")
-              "\n"))
-    (buffer-string)))
+(defun org-cite-biblatex--generate-latex-preamble (info)
+  "Ensure that the biblatex package is loaded, and the necessary resources.
+This is performed by extracting relevant information from the
+INFO export plist, and modifying any existing
+\\usepackage{biblatex} statement in the LaTeX header."
+  (let ((style (org-cite-bibliography-style info))
+        (files (plist-get info :bibliography))
+        (usepackage-rx (rx "\\usepackage"
+                           (opt (group "[" (*? anything) "]"))
+                           "{biblatex}")))
+    (concat
+     (if (string-match usepackage-rx (plist-get info :latex-full-header))
+         ;; "biblatex" package loaded, but with none (or different) options.
+         ;; Replace with style-including command.
+         (plist-put info :latex-full-header
+                    (replace-match
+                     (format "\\usepackage%s{biblatex}"
+                             (save-match-data
+                               (org-cite-biblatex--package-options nil style)))
+                     t t
+                     (plist-get info :latex-full-header)))
+       ;; No "biblatex" package loaded.  Insert "usepackage" command
+       ;; with appropriate options, including style.
+       (format "\\usepackage%s{biblatex}\n"
+               (org-cite-biblatex--package-options
+                org-cite-biblatex-options style)))
+     ;; Load resources.
+     (mapconcat (lambda (f)
+                  (format "\\addbibresource%s{%s}"
+                          (if (org-url-p f) "[location=remote]" "")
+                          f))
+                files
+                "\n"))))
 
 \f
 ;;; Register `biblatex' processor
 (org-cite-register-processor 'biblatex
   :export-bibliography #'org-cite-biblatex-export-bibliography
   :export-citation #'org-cite-biblatex-export-citation
-  :export-finalizer #'org-cite-biblatex-prepare-preamble
   :cite-styles #'org-cite-biblatex-list-styles)
 
 (provide 'oc-biblatex)
diff --git a/lisp/oc-csl.el b/lisp/oc-csl.el
index 432738a97..f85646379 100644
--- a/lisp/oc-csl.el
+++ b/lisp/oc-csl.el
@@ -840,27 +840,11 @@ (defun org-cite-csl-render-bibliography (_keys _files _style props _backend info
        ;; process.
        (org-cite-parse-elements output)))))
 
-(defun org-cite-csl-finalizer (output _keys _files _style _backend info)
-  "Add \"hanging\" package if missing from LaTeX output.
-OUTPUT is the export document, as a string.  INFO is the export state, as a
-property list."
-  (org-cite-csl--barf-without-citeproc)
-  (if (not (eq 'org-latex (org-cite-csl--output-format info)))
-      output
-    (with-temp-buffer
-      (save-excursion (insert output))
-      (when (search-forward "\\begin{document}" nil t)
-	(goto-char (match-beginning 0))
-	;; Insert the CSL-specific parts of the LaTeX preamble.
-	(insert (org-cite-csl--generate-latex-preamble info)))
-      (buffer-string))))
-
 \f
 ;;; Register `csl' processor
 (org-cite-register-processor 'csl
   :export-citation #'org-cite-csl-render-citation
   :export-bibliography #'org-cite-csl-render-bibliography
-  :export-finalizer #'org-cite-csl-finalizer
   :cite-styles
   '((("author" "a") ("bare" "b") ("caps" "c") ("full" "f") ("bare-caps" "bc") ("caps-full" "cf") ("bare-caps-full" "bcf"))
     (("noauthor" "na") ("bare" "b") ("caps" "c") ("bare-caps" "bc"))
diff --git a/lisp/oc-natbib.el b/lisp/oc-natbib.el
index 855be2a5c..b5cb193e7 100644
--- a/lisp/oc-natbib.el
+++ b/lisp/oc-natbib.el
@@ -157,32 +157,25 @@ (defun org-cite-natbib-export-citation (citation style _ info)
           (org-cite-natbib--build-optional-arguments citation info)
           (org-cite-natbib--build-arguments citation)))
 
-(defun org-cite-natbib-use-package (output &rest _)
-  "Ensure output requires \"natbib\" package.
-OUTPUT is the final output of the export process."
-  (with-temp-buffer
-    (save-excursion (insert output))
-    (when (search-forward "\\begin{document}" nil t)
-      ;; Ensure there is a \usepackage{natbib} somewhere or add one.
-      (goto-char (match-beginning 0))
-      (let ((re (rx "\\usepackage" (opt "[" (*? nonl) "]") "{natbib}")))
-        (unless (re-search-backward re nil t)
-          (insert
-           (format "\\usepackage%s{natbib}\n"
-                   (if (null org-cite-natbib-options)
-                       ""
-                     (format "[%s]"
-                             (mapconcat #'symbol-name
-                                        org-cite-natbib-options
-                                        ","))))))))
-    (buffer-string)))
+(defun org-cite-natbib--generate-latex-preamble (info)
+  "Ensure that the \"natbib\" package is loaded.
+INFO is a plist used as a communication channel."
+  (and (not (string-match
+             (rx "\\usepackage" (opt "[" (*? nonl) "]") "{natbib}")
+             (plist-get info :latex-full-header)))
+       (format "\\usepackage%s{natbib}\n"
+               (if (null org-cite-natbib-options)
+                   ""
+                 (format "[%s]"
+                         (mapconcat #'symbol-name
+                                    org-cite-natbib-options
+                                    ","))))))
 
 \f
 ;;; Register `natbib' processor
 (org-cite-register-processor 'natbib
   :export-bibliography #'org-cite-natbib-export-bibliography
   :export-citation #'org-cite-natbib-export-citation
-  :export-finalizer #'org-cite-natbib-use-package
   :cite-styles
   '((("author" "a") ("caps" "a") ("full" "f"))
     (("noauthor" "na") ("bare" "b"))
diff --git a/lisp/ox-latex.el b/lisp/ox-latex.el
index 9794e6ecd..040824f45 100644
--- a/lisp/ox-latex.el
+++ b/lisp/ox-latex.el
@@ -1468,6 +1468,21 @@ (defcustom org-latex-feature-implementations
           (choice (string :tag "Verbatim content")
                   (variable :tag "Content variable")
                   (function :tag "Generating function"))))
+;; Citation features
+
+(org-export-update-features 'latex
+  (bibliography-csl
+   :condition (eq (org-cite-processor info) 'csl)
+   :when bibliography
+   :snippet org-cite-csl--generate-latex-preamble)
+  (bibliography-biblatex
+   :condition (eq (org-cite-processor info) 'biblatex)
+   :when bibliography
+   :snippet org-cite-biblatex--generate-latex-preamble)
+  (bibliography-natbib
+   :condition (eq (org-cite-processor info) 'natbib)
+   :when bibliography
+   :snippet org-cite-natbib--generate-latex-preamble))
 
 ;;;; Compilation
 
-- 
2.39.0


[-- Attachment #6: 0005-ox-Add-struct-feature-conditions-implementations.patch --]
[-- Type: text/x-patch, Size: 39169 bytes --]

From 32a2610cc301572bc14a6cb18d6138b653e91e80 Mon Sep 17 00:00:00 2001
From: TEC <git@tecosaur.net>
Date: Tue, 7 Feb 2023 01:57:06 +0800
Subject: [PATCH 5/6] ox: Add struct feature conditions/implementations

* lisp/ox.el (org-export--annotate-info, org-export-detect-features,
org-export-define-derived-backend, org-export-define-backend,
org-export-conditional-features): Refactor backend feature
conditions/implementations into a struct field.  This allows for parent
inheritance to be properly managed, and leads into future work making
features more widely used in the export process.
(org-export-expand-features, org-export-resolve-feature-implementations,
org-export-generate-features-preamble,
org-export-expand-feature-snippets): Rework `org-export-expand-features`
into `org-export-resolve-feature-implementations`, and
`org-export-generate-features-preamble` into
`org-export-expand-feature-snippets`.
(org-export-process-features, org-export-update-features): Introduce
`org-export-process-features' to simplify the application of features to
INFO.

* lisp/ox-latex.el (org-latex-make-preamble): Move the LaTeX feature
conditions/implementations into the backend definition, and use the
reworked function `org-export-expand-feature-snippets'.
---
 lisp/ox-latex.el | 156 +++++++--------
 lisp/ox.el       | 482 ++++++++++++++++++++++++++++++++++-------------
 2 files changed, 415 insertions(+), 223 deletions(-)

diff --git a/lisp/ox-latex.el b/lisp/ox-latex.el
index 040824f45..6221cc486 100644
--- a/lisp/ox-latex.el
+++ b/lisp/ox-latex.el
@@ -127,8 +127,6 @@ (org-export-define-backend 'latex
     (:description "DESCRIPTION" nil nil parse)
     (:keywords "KEYWORDS" nil nil parse)
     (:subtitle "SUBTITLE" nil nil parse)
-    (:conditional-features nil nil org-latex-conditional-features)
-    (:feature-implementations nil nil org-latex-feature-implementations)
     ;; Other variables.
     (:latex-active-timestamp-format nil nil org-latex-active-timestamp-format)
     (:latex-caption-above nil nil org-latex-caption-above)
@@ -172,7 +170,64 @@ (org-export-define-backend 'latex
     (:latex-toc-command nil nil org-latex-toc-command)
     (:latex-compiler "LATEX_COMPILER" nil org-latex-compiler)
     ;; Redefine regular options.
-    (:date "DATE" nil "\\today" parse)))
+    (:date "DATE" nil "\\today" parse))
+  :feature-conditions-alist
+  `((t !announce-start)
+    (t !announce-end)
+    (t !guess-pollyglossia)
+    (t !guess-babel)
+    (t !guess-inputenc)
+    (,(lambda (info)
+        (org-element-map (plist-get info :parse-tree)
+            '(latex-fragment latex-environment) #'identity info t))
+     maths)
+    (,(lambda (info)
+        (org-element-map (plist-get info :parse-tree)
+            'underline #'identity info t))
+     underline)
+    ("\\\\uu?line\\|\\\\uwave\\|\\\\sout\\|\\\\xout\\|\\\\dashuline\\|\\dotuline\\|\\markoverwith"
+     underline)
+    (,(lambda (info)
+        (org-element-map (plist-get info :parse-tree)
+            'link
+          (lambda (link)
+            (and (member (org-element-property :type link)
+                         '("http" "https" "ftp" "file"))
+                 (file-name-extension (org-element-property :path link))
+                 (equal (downcase (file-name-extension
+                                   (org-element-property :path link)))
+                        "svg")))
+          info t))
+     svg)
+    (org-latex-tables-booktabs booktabs)
+    (,(lambda (info)
+        (eq (plist-get info :latex-src-block-backend) 'engraved))
+     engraved-code)
+    ("^[ \t]*#\\+attr_latex: .*:float +wrap"
+     float-wrap)
+    ("^[ \t]*#\\+attr_latex: .*:float +sideways"
+     rotate)
+    ("^[ \t]*#\\+caption:\\|\\\\caption{" caption))
+  :feature-implementations-alist
+  `((!announce-start
+     :snippet ,(lambda (info)
+                 (format "\n%%%% ox-latex features: %s"
+                         (plist-get info :features)))
+     :order -100)
+    (maths :snippet "\\usepackage{amsmath}\n\\usepackage{amssymb}" :order 0.2)
+    (underline :snippet "\\usepackage[normalem]{ulem}" :order 0.5)
+    (image :snippet "\\usepackage{graphicx}" :order 2)
+    (svg :snippet "\\usepackage[inkscapelatex=false]{svg}" :order 2 :when image)
+    (longtable :snippet "\\usepackage{longtable}" :when table :order 2)
+    (booktabs :snippet "\\usepackage{booktabs}" :when table :order 2)
+    (float-wrap :snippet "\\usepackage{wrapfig}" :order 2)
+    (rotate :snippet "\\usepackage{rotating}" :order 2)
+    (caption :snippet "\\usepackage{capt-of}")
+    (engraved-code :snippet org-latex-generate-engraved-preamble :when code)
+    (!guess-pollyglossia :snippet org-latex-guess-polyglossia-language)
+    (!guess-babel :snippet org-latex-guess-babel-language)
+    (!guess-inputenc :snippet org-latex-guess-inputenc)
+    (!announce-end :snippet "%% end ox-latex features\n" :order 100)))
 
 
 \f
@@ -1380,94 +1435,6 @@ (defun org-latex-generate-engraved-preamble (info)
        "% WARNING syntax highlighting unavailable as engrave-faces-latex was missing.\n")
      "\n")))
 
-;;;; Generated preamble
-
-(defcustom org-latex-conditional-features
-  `((t . !announce-start)
-    (t . !announce-end)
-    (t . !guess-pollyglossia)
-    (t . !guess-babel)
-    (t . !guess-inputenc)
-    (,(lambda (info)
-        (org-element-map (plist-get info :parse-tree)
-            '(latex-fragment latex-environment) #'identity info t))
-     . maths)
-    (,(lambda (info)
-        (org-element-map (plist-get info :parse-tree)
-            'underline #'identity info t))
-     . underline)
-    ("\\\\uu?line\\|\\\\uwave\\|\\\\sout\\|\\\\xout\\|\\\\dashuline\\|\\dotuline\\|\\markoverwith"
-     . underline)
-    (,(lambda (info)
-        (org-element-map (plist-get info :parse-tree)
-            'link
-          (lambda (link)
-            (and (member (org-element-property :type link)
-                         '("http" "https" "ftp" "file"))
-                 (file-name-extension (org-element-property :path link))
-                 (equal (downcase (file-name-extension
-                                   (org-element-property :path link)))
-                        "svg")))
-          info t))
-     . svg)
-    (org-latex-tables-booktabs . booktabs)
-    (,(lambda (info)
-        (eq (plist-get info :latex-src-block-backend) 'engraved))
-     . engraved-code)
-    ("^[ \t]*#\\+attr_latex: .*:float +wrap"
-     . float-wrap)
-    ("^[ \t]*#\\+attr_latex: .*:float +sideways"
-     . rotate)
-    ("^[ \t]*#\\+caption:\\|\\\\caption{" . caption))
-  "A LaTeX-specific extension to `org-export-conditional-features', which see.")
-
-(defcustom org-latex-feature-implementations
-  `((!announce-start
-     :snippet ,(lambda (info)
-                 (format "\n%%%% ox-latex features: %s"
-                         (plist-get info :features)))
-     :order -100)
-    (maths :snippet "\\usepackage{amsmath}\n\\usepackage{amssymb}" :order 0.2)
-    (underline :snippet "\\usepackage[normalem]{ulem}" :order 0.5)
-    (image :snippet "\\usepackage{graphicx}" :order 2)
-    (svg :snippet "\\usepackage[inkscapelatex=false]{svg}" :order 2 :when image)
-    (longtable :snippet "\\usepackage{longtable}" :when table :order 2)
-    (booktabs :snippet "\\usepackage{booktabs}" :when table :order 2)
-    (float-wrap :snippet "\\usepackage{wrapfig}" :order 2)
-    (rotate :snippet "\\usepackage{rotating}" :order 2)
-    (caption :snippet "\\usepackage{capt-of}")
-    (engraved-code :snippet org-latex-generate-engraved-preamble :when code)
-    (!guess-pollyglossia :snippet org-latex-guess-polyglossia-language)
-    (!guess-babel :snippet org-latex-guess-babel-language)
-    (!guess-inputenc :snippet org-latex-guess-inputenc)
-    (!announce-end :snippet "%% end ox-latex features\n" :order 100))
-  "Alist describing how export features should be supported in the preamble.
-
-Implementation alist has the feature symbol as the car, with the
-cdr forming a plist with the following keys:
-- :snippet, which is either,
-  - A string, which should be included in the preamble verbatim.
-  - A variable, the value of which should be included in the preamble.
-  - A function, which is called with two arguments — the export info,
-    and the list of feature flags. The returned value is included in
-    the preamble.
-- :requires, a feature or list of features which are needed.
-- :when, a feature or list of features which imply this feature.
-- :prevents, a feature or list of features that should be masked.
-- :order, for when inclusion order matters. Feature implementations
-  with a lower order appear first.  The default is 0."
-  :group 'org-export-general
-  :type '(plist :key-type
-          (choice (const :snippet)
-                  (const :requires)
-                  (const :when)
-                  (const :prevents)
-                  (const :order)
-                  (const :trigger))
-          :value-type
-          (choice (string :tag "Verbatim content")
-                  (variable :tag "Content variable")
-                  (function :tag "Generating function"))))
 ;; Citation features
 
 (org-export-update-features 'latex
@@ -2086,7 +2053,12 @@ (defun org-latex-make-preamble (info &optional template snippet?)
                 (org-latex-guess-babel-language info)
                 (org-latex-guess-polyglossia-language info)
                 "\n% Generated preamble omitted for snippets.")
-            (org-export-generate-features-preamble info)))
+            (concat
+             "\n"
+             (string-join
+              (org-export-expand-feature-snippets info)
+              "\n\n")
+             "\n")))
     (concat
      ;; Time-stamp.
      (and (plist-get info :time-stamp-file)
diff --git a/lisp/ox.el b/lisp/ox.el
index 32f1c6016..6c7a11b66 100644
--- a/lisp/ox.el
+++ b/lisp/ox.el
@@ -1030,7 +1030,7 @@ ;;; Defining Back-ends
 
 (cl-defstruct (org-export-backend (:constructor org-export-create-backend)
 				  (:copier nil))
-  name parent transcoders options filters blocks menu)
+  name parent transcoders options filters blocks menu feature-conditions feature-implementations)
 
 ;;;###autoload
 (defun org-export-get-backend (name)
@@ -1136,6 +1136,62 @@ (defun org-export-get-all-filters (backend)
 	(setq filters (append filters (org-export-backend-filters backend))))
       filters)))
 
+(defvar org-export-conditional-features)
+
+(defun org-export-get-all-feature-conditions (backend)
+  "Return full feature condition alist for BACKEND.
+
+BACKEND is an export back-end, as return by, e.g,,
+`org-export-create-backend'.  Return value is an alist where keys
+are feature conditions, and values are feature symbols.
+
+Unlike `org-export-backend-feature-conditions', this function
+also returns conditions inherited from parent back-ends, if any."
+  (when (symbolp backend) (setq backend (org-export-get-backend backend)))
+  (and backend
+       (let ((conditions (org-export-backend-feature-conditions backend))
+             parent)
+         (while (setq parent (org-export-backend-parent backend))
+           (setq backend (org-export-get-backend parent))
+           (dolist (condition (org-export-backend-feature-conditions backend))
+             (push condition conditions)))
+         (dolist (condition org-export-conditional-features)
+           (unless (assq (car condition) conditions)
+             (push condition conditions)))
+         conditions)))
+
+(defun org-export-get-all-feature-implementations (backend)
+  "Return full feature implementation alist for BACKEND.
+
+BACKEND is an export back-end, as return by, e.g,,
+`org-export-create-backend'.  Return value is an alist where keys
+are feature symbols, and values are an implementation
+specification plist.
+
+Unlike `org-export-backend-feature-implementations', this function
+also returns implementations inherited from parent back-ends, if any."
+  (when (symbolp backend) (setq backend (org-export-get-backend backend)))
+  (and backend
+       (let ((implementations (org-export-backend-feature-implementations backend))
+             parent)
+         (while (setq parent (org-export-backend-parent backend))
+           (setq backend (org-export-get-backend parent))
+           (dolist (implementation (org-export-backend-feature-implementations backend))
+             (unless (assq (car implementation) implementations)
+               (push implementation implementations))))
+         implementations)))
+
+(defun org-export-install-features (info)
+  "Install feature conditions and implementations in the communication channel.
+INFO is a plist containing the current communication channel.
+Return the updated communication channel."
+  (plist-put info :feature-conditions
+             (org-export-get-all-feature-conditions
+              (plist-get info :back-end)))
+  (plist-put info :feature-implementations
+             (org-export-get-all-feature-implementations
+              (plist-get info :back-end))))
+
 (defun org-export-define-backend (backend transcoders &rest body)
   "Define a new back-end BACKEND.
 
@@ -1247,20 +1303,24 @@ (defun org-export-define-backend (backend transcoders &rest body)
     `org-export-options-alist' for more information about
     structure of the values."
   (declare (indent 1))
-  (let (filters menu-entry options)
+  (let (filters menu-entry options feature-conditions feature-implementations)
     (while (keywordp (car body))
       (let ((keyword (pop body)))
 	(pcase keyword
 	  (:filters-alist (setq filters (pop body)))
 	  (:menu-entry (setq menu-entry (pop body)))
 	  (:options-alist (setq options (pop body)))
+	  (:feature-conditions-alist (setq feature-conditions (pop body)))
+	  (:feature-implementations-alist (setq feature-implementations (pop body)))
 	  (_ (error "Unknown keyword: %s" keyword)))))
     (org-export-register-backend
      (org-export-create-backend :name backend
 				:transcoders transcoders
 				:options options
 				:filters filters
-				:menu menu-entry))))
+				:menu menu-entry
+                                :feature-conditions feature-conditions
+                                :feature-implementations feature-implementations))))
 
 (defun org-export-define-derived-backend (child parent &rest body)
   "Create a new back-end as a variant of an existing one.
@@ -1307,7 +1367,7 @@ (defun org-export-define-derived-backend (child parent &rest body)
 
   (org-export-to-buffer \\='my-latex \"*Test my-latex*\")"
   (declare (indent 2))
-  (let (filters menu-entry options transcoders)
+  (let (filters menu-entry options transcoders feature-conditions feature-implementations)
     (while (keywordp (car body))
       (let ((keyword (pop body)))
 	(pcase keyword
@@ -1315,6 +1375,8 @@ (defun org-export-define-derived-backend (child parent &rest body)
 	  (:menu-entry (setq menu-entry (pop body)))
 	  (:options-alist (setq options (pop body)))
 	  (:translate-alist (setq transcoders (pop body)))
+	  (:feature-conditions-alist (setq feature-conditions (pop body)))
+	  (:feature-implementations-alist (setq feature-implementations (pop body)))
 	  (_ (error "Unknown keyword: %s" keyword)))))
     (org-export-register-backend
      (org-export-create-backend :name child
@@ -1322,7 +1384,9 @@ (defun org-export-define-derived-backend (child parent &rest body)
 				:transcoders transcoders
 				:options options
 				:filters filters
-				:menu menu-entry))))
+				:menu menu-entry
+                                :feature-conditions feature-conditions
+                                :feature-implementations feature-implementations))))
 
 
 \f
@@ -2031,7 +2095,7 @@ (defun org-export-expand (blob contents &optional with-affiliated)
 		     blob contents))))
 
 \f
-;;; Conditional/Generated Preamble
+;;; Conditional/Generated Features
 ;;
 ;; Many formats have some version of a preamble, whether it be HTML's
 ;; <head>...</head> or the content before LaTeX's \begin{document}.
@@ -2042,12 +2106,35 @@ ;;; Conditional/Generated Preamble
 ;; with filters approach, but neither really solve this problem nicely.
 ;;
 ;; The conditional/generated preamble defines mechanisms of detecting
-;; which "features" are used in a document, handles interactions
-;; between features, and provides/generates preamble content to
+;; which "export features" are used in a document, handles
+;; interactions between features, and provides/generates content to
 ;; support the features.
+;;
+;; Each export feature condition takes the form of a
+;; (CONDITION . FEATURES) cons cell (see `org-export-detect-features'),
+;; and each implementation takes the form of a (FEATURE . (:KEY VALUE ...))
+;; associated plist (see `org-export-resolve-feature-implementations'
+;; and `org-export-expand-feature-snippets').
+;;
+;; This functionality is applied during export as follows:
+;; 1. The export feature conditions and implementations are installed
+;;    into the INFO plist with `org-export-install-features'.
+;;    This simply applies `org-export-get-all-feature-conditions' and
+;;    `org-export-get-all-feature-implementations', which merges the
+;;    backend's conditions/implementations with all of it's parents and
+;;    finally the global condition list
+;;    `org-export-conditional-features'.
+;; 2. The "export features" used in a document are detected with
+;;    `org-export-detect-features'.
+;; 3. The interaction between different feature implementations is
+;;    resolved with `org-export-resolve-feature-implementations',
+;;    producing an ordered list of implementations to be actually used
+;;    in an export.
+;; 4. The feature implementation's snippets are transformed into strings
+;;    to be inserted with `org-export-expand-feature-snippets'.
 
 (defcustom org-export-conditional-features
-  `(("^[ \t]*#\\+print_bibliography:" . bibliography)
+  `(("^[ \t]*#\\+print_bibliography:" bibliography)
     (,(lambda (info)
        (org-element-map (plist-get info :parse-tree)
            'link
@@ -2059,7 +2146,7 @@ (defcustom org-export-conditional-features
                                     (org-element-property :path link)))
                          "svg")))
          info t))
-     . svg)
+     svg)
     (,(lambda (info)
        (org-element-map (plist-get info :parse-tree)
            'link
@@ -2071,69 +2158,95 @@ (defcustom org-export-conditional-features
                                    (org-element-property :path link)))
                         image-file-name-extensions)))
          info t))
-     . image)
+     image)
     (,(lambda (info)
        (org-element-map (plist-get info :parse-tree)
            'table #'identity info t))
-     . table)
+     table)
     (,(lambda (info)
        (org-element-map (plist-get info :parse-tree)
            '(src-block inline-src-block) #'identity info t))
-     . code))
+     code))
   "Org feature tests and associated feature flags.
 
 Alist where the car is a test for the presense of the feature,
 and the CDR is either a single feature symbol or a list of
 feature symbols.
 
-Feature tests can take any of the following forms:
-- Variable symbol, the value of which is fetched.
-- Function symbol, which is called with the export info
-  as the argument.
-- A string, which is used as a regexp search in the buffer.
-  The regexp matching is taken as confirmation of the existence
-  of the feature.
-
-When the test is a variable or function and produces a string
-value, that value is itself used as a test. Any other non-nil
-value will imply the existance of the feature."
+See `org-export-detect-features' for how this is processed."
   :group 'org-export-general
   :type '(alist :key-type
                 (choice (regexp :tag "Feature test regexp")
                         (variable :tag "Feature variable")
                         (function :tag "Feature test function"))
                 :value-type
-                (choice (symbol :tag "Feature symbol")
-                        (repeat symbol :tag "Feature symbols"))))
+                (repeat symbol :tag "Feature symbols")))
 
 (defun org-export-detect-features (info)
-  "Detect features from `org-export-conditional-features' in INFO."
-  (let (case-fold-search)
-    (delete-dups
-     (mapcan
-      (lambda (construct-feature)
-        (and (let ((out (pcase (car construct-feature)
-                          ((pred stringp) (car construct-feature))
-                          ((pred functionp)
-                           (funcall (car construct-feature) info))
-                          ((pred symbolp) (symbol-value (car construct-feature)))
-                          (_ (error "org-export-conditional-features key %s unable to be used" (car construct-feature))))))
-               (if (stringp out)
-                   (save-excursion
-                     (goto-char (point-min))
-                     (re-search-forward out nil t))
-                 out))
-             (if (listp (cdr construct-feature))
-                 (copy-sequence (cdr construct-feature))
-               (list (cdr construct-feature)))))
-      (append org-export-conditional-features
-              (plist-get info :conditional-features))))))
-
-(defun org-export-expand-features (info)
-  "Identify all implied implementations from features, in INFO.
-
-(plist-get info :feature-implementations) should be an alist of feature symbols
-and specification plists with the following keys:
+  "Detect features from `org-export-conditional-features' in INFO.
+
+More specifically, for each (CONDITION . FEATURES) cons cell of
+the :feature-conditions list in INFO, the CONDITION is evaluated
+in two phases.
+
+In phase one, CONDITION is transformed like so:
+- If a variable symbol, the value is fetched
+- If a function symbol, the function is called with INFO as the
+  sole argument
+- If a string, passed on unmodified
+
+In phase two, if the CONDITION result is a string, it is used as
+a case-sensitive regexp search in the buffer.  The regexp
+matching is taken as confirmation of the existance of FEATURES.
+Any other non-nil value indicates the existance of FEATURES.
+
+A list of all detected feature symbols is returned.
+
+This function should be run in the processed export Org buffer,
+after includes have been expanded and commented trees removed."
+  (delete-dups
+   (mapcan
+    (org-export--single-feature-detector info)
+    (plist-get info :feature-conditions))))
+
+(defun org-export--single-feature-detector (info)
+  "Return a feature detection lambda that operates on INFO.
+
+The lambda has the signature ((CONDITION . FEATURES)), and
+return FEATURES if CONDITION is found to apply.
+
+CONDITION is evaluated in the context of INFO and the current buffer,
+in accordance with the docstring of `org-export-detect-features'.
+`copy-sequence' is applied to the FEATURES list so that `nconc' can
+safely be applied to it."
+  (lambda (condition-features)
+    (let ((condition (car condition-features))
+          (features (cdr condition-features))
+          (case-fold-search nil)
+          matcher)
+      (setq matcher
+            (cond
+             ((stringp condition) condition)
+             ((functionp condition) (funcall condition info))
+             ((symbolp condition) (symbol-value condition))
+             (t (error "org-export: Feature condition %s (for %s) unable to be used"
+                       condition features))))
+      (and (if (stringp matcher)
+               (save-excursion
+                 (goto-char (point-min))
+                 (re-search-forward matcher nil t))
+             matcher)
+           (copy-sequence features)))))
+
+(defun org-export-resolve-feature-implementations (info &optional features implementations)
+  "Resolve the IMPLEMENTATIONS of FEATURES, of INFO.
+
+FEATURES should be a list of all feature symbols to be resolved,
+and defaults to (plist-get info :features).  IMPLEMENTATIONS
+should be an alist of feature symbols and specification plists,
+and defaults to (plist-get info :feature-implementations).
+
+The following keys of the each implementation plist are recognised:
 - :snippet, which is either,
   - A string, which should be included in the preamble verbatim.
   - A variable, the value of which should be included in the preamble.
@@ -2148,12 +2261,10 @@ (plist-get info :feature-implementations) should be an alist of feature symbols
   with a lower order appear first.  The default is 0.
 
 This function processes :requires, :when, and :prevents in turn
-before finally sorting according to :order.
-
-After resolving the features, the :features key of INFO is
-updated to reflect the expanded set of features being used."
-  (let ((initial-features (plist-get info :features))
-        (implementations (plist-get info :feature-implementations))
+before finally sorting according to :order.  The final
+implementation list is returned."
+  (let ((initial-features (or features (plist-get info :features)))
+        (implementations (or implementations (plist-get info :feature-implementations)))
         required-features current-implementations)
     ;; Process :requires.
     (while initial-features
@@ -2214,79 +2325,188 @@ (plist-get info :feature-implementations) should be an alist of feature symbols
                (lambda (i) (memq (car i) prevented))
                current-implementations))))
     ;; Sort by :order.
-    (setq current-implementations
-          (sort current-implementations
-                (lambda (impl1 impl2)
-                  (< (or (plist-get (cdr impl1) :order) 0)
-                     (or (plist-get (cdr impl2) :order) 0)))))
-    ;; Update :features to reflect the features actually used.
-    (plist-put info :features (mapcar #'car current-implementations))
-    current-implementations))
-
-(defun org-export-generate-features-preamble (info)
-  "Generate preamble string according to features an implementations in INFO.
-More specifically, this function resolves feature implementations
-with `org-export-expand-features' and concatenates the snippets."
-  (let* ((feat-impl (org-export-expand-features info))
-         (feat-snippets
-          (mapcar
-           (lambda (impl)
-             (let ((snippet (plist-get (cdr impl) :snippet)))
+    (sort current-implementations
+          (lambda (impl1 impl2)
+            (< (or (plist-get (cdr impl1) :order) 0)
+               (or (plist-get (cdr impl2) :order) 0))))))
+
+(defun org-export-expand-feature-snippets (info &optional feature-implementations)
+  "Expand each of the feature :snippet keys in FEATURE-IMPLEMENTATIONS.
+FEATURE-IMPLEMENTATIONS is expected to be a list of implementation
+plists, if not provided explicitly it is extracted from the
+:feature-implementations key of INFO.
+
+Each implementation plist's :snippet value is expanded in order, in
+the following manner:
+- nil values are ignored
+- functions are called with INFO, and must produce a string or nil
+- variable symbols use the value, which must be a string or nil
+- strings are included verbatim
+- all other values throw an `error'."
+  (let (expanded-snippets snippet value)
+    (dolist (impl (or feature-implementations
+                      (plist-get info :feature-implementations)))
+      (setq snippet (plist-get (cdr impl) :snippet)
+            value (cond
+                   ((null snippet) nil)
+                   ((functionp snippet) (funcall snippet info))
+                   ((symbolp snippet) (symbol-value snippet))
+                   ((stringp snippet) snippet)
+                   (t (error "org-export: The %s feature snippet %S is invalid (must be either nil, a function/variable symbol, or a string)"
+                             (car impl) snippet))))
+      (cond
+       ((stringp value)
+        (push value expanded-snippets))
+       (value ; Non-string value, could come from function or variable.
+        (error "org-export: The %s feature snippet %s must give nil or a string, but instead gave %S"
+               (car impl)
                (cond
-                ((null snippet) nil)
-                ((functionp snippet)
-                 (funcall snippet info))
-                ((symbolp snippet) (symbol-value snippet))
-                ((stringp snippet) snippet)
-                (t (error "org-export feature snippet %S is invalid." snippet)
-                   nil))))
-           feat-impl)))
-    (mapconcat
-     #'identity
-     (append (delq nil feat-snippets) (list ""))
-     "\n")))
-
-(defun org-export-update-features (backend &rest feature-property-value-lists)
-  "For BACKEND's export spec, set all FEATURE-PROPERTY-VALUE-LISTS.
-
-Specifically, for each (FEATURE . PROPERTY-VALUE-LIST) entry of
-FEATURE-PROPERTY-VALUE-LISTS, each :PROPERTY VALUE pair of
-PROPERTY-VALUE-PAIRS is set to VALUE within the backend's feature
-implementation plist.  The sole exception to this is the
-:condition property, the value of which is set in the backend's
-feature condition plist instead.
+                ((and (functionp snippet) (symbolp snippet))
+                 (format "function (`%s')" snippet))
+                ((functionp snippet) "anonymous function")
+                (t (format "variable (`%s')" snippet)))
+               value))))
+    (nreverse expanded-snippets)))
+
+(defun org-export-process-features (info)
+  "Install feature conditions/implementations in INFO, and resolve them.
+See `org-export-detect-features' and `org-export-resolve-feature-implementations' for
+more information on what this entails."
+  (org-export-install-features info)
+  (let* ((features (org-export-detect-features info))
+         (resolved-implementations
+          (org-export-resolve-feature-implementations info features)))
+    (plist-put info :feature-implementations resolved-implementations)
+    (plist-put info :features (mapcar #'car resolved-implementations))))
 
-This can be used to both modify existing entries, and create new ones.
-
-\(fn BACKEND &rest (FEATURE PROPERTY-VALUE-PAIRS...)...)"
+;;;###autoload
+(defmacro org-export-update-features (backend &rest feature-property-value-lists)
+  "For BACKEND's export spec, set each FEATURE's :PROPERTY to VALUE.
+
+The behaviour of this macro is best behaved with an example.
+For instance, to add some preamble content from the variable
+\"my-org-beamer-metropolis-tweaks\" when using the metropolis theme
+with beamer export:
+
+  (org-export-update-features \\='beamer
+    (beamer-metropolis
+     :condition (string-match-p \"metropolis$\" (plist-get info :beamer-theme))
+     :snippet my-org-beamer-metropolis-tweaks
+     :order 3))
+
+The modifies the beamer backend, either creating or updating the
+\"beamer-metropolis\" feature.  The :condition property adds a
+condition which detects the feature, and all other properties are
+applied to the feature's implementation plist.  Setting
+:condition to t means the feature will always be enabled, and
+conversely setting :condition to nil means the feature will never
+be enabled.
+
+When setting the :condition and :snippet properties, any sexp is
+is implicitly converted to,
+  (lambda (info) SEXPR)
+
+Each (FEATURE . (:PROPERTY VALUE)) form that is processed is
+taken from the single &rest argument
+FEATURE-PROPERTY-VALUE-LISTS.
+
+\(fn BACKEND &rest (FEATURE . (:PROPERTY VALUE)...)...)"
   (declare (indent 1))
-  (let ((backend-var (intern (format "org-%s-feature-implementations" backend)))
-        (backend-cf (intern (format "org-%s-conditional-features" backend))))
-    (unless (boundp backend-var)
-      (error "Feature implementations for %s cannot be set as %s is undefined"
-             backend backend-var))
-    (dolist (feature-property-value-set feature-property-value-lists)
-      (let ((feature (car feature-property-value-set))
-            (property-value-pairs (copy-sequence (cdr feature-property-value-set))))
-        (while property-value-pairs
-          (if (eq (car property-value-pairs) :condition)
-              (let ((condition (progn (pop property-value-pairs)
-                                      (pop property-value-pairs))))
-                (unless (boundp backend-cf)
-                  (error "Feature condition for %s cannot be set as %s is undefined"
-                         backend backend-cf))
-                (cond
-                 ((rassoc feature (symbol-value backend-cf))
-                  (if condition
-                      (setcar (rassoc feature (symbol-value backend-cf))
-                              condition)
-                    (set backend-cf (delq (rassoc feature (symbol-value backend-cf))
-                                          (symbol-value backend-cf)))))
-                 (condition
-                  (add-to-list backend-cf (cons condition feature)))))
-            (setf (alist-get feature (symbol-value backend-var))
-                  (plist-put (alist-get feature (symbol-value backend-var))
-                             (pop property-value-pairs) (pop property-value-pairs)))))))))
+  (org-with-gensyms (backend-struct the-entry the-features the-condition the-feat-impl cond-feat)
+    (let ((backend-expr
+           (if (and (eq (car-safe backend) 'quote)
+                    (symbolp (cadr backend))
+                    (not (cddr backend)))
+               (or (org-export-get-backend (cadr backend))
+                   `(org-export-get-backend ',(cadr backend)))
+             `(if (symbolp ,backend)
+                  (org-export-get-backend ,backend)
+                backend)))
+          (backend-impls
+           (list 'aref backend-struct
+                 (cl-struct-slot-offset 'org-export-backend 'feature-implementations)))
+          (backend-conds
+           (list 'aref backend-struct
+                 (cl-struct-slot-offset 'org-export-backend 'feature-conditions)))
+          body condition-set-p implementation-set-p)
+      (dolist (feature-property-value-set feature-property-value-lists)
+        (when (eq (car feature-property-value-set) 'quote)
+          (pop feature-property-value-set))
+        (let ((features (car feature-property-value-set))
+              (property-value-pairs (cdr feature-property-value-set))
+              let-body property value)
+          (while property-value-pairs
+            (setq property (pop property-value-pairs)
+                  value (pop property-value-pairs))
+            (cond
+             ((consp value)
+              (unless (memq (car value) '(function quote))
+                (if (and (memq property '(:condition :snippet))
+                         (not (functionp value)))
+                    (setq value `(lambda (info) ,value))
+                  (setq value (list 'quote value)))))
+             ((memq value '(nil t))) ; Leave unmodified.
+             ((symbolp value)
+              (setq value (list 'quote value))))
+            (if (eq property :condition)
+                (progn
+                  (unless condition-set-p
+                    (setq condition-set-p t))
+                  (push
+                   (if value
+                       (let ((the-features
+                              (if (consp features) features (list features))))
+                         `(let* ((,the-condition ,value)
+                                 (,the-entry (assoc ,the-condition ,backend-conds)))
+                            (if ,the-entry
+                                (setcdr ,the-entry
+                                        (append ',the-features (cdr ,the-entry)))
+                              (push (cons ,the-condition ',the-features)
+                                    ,backend-conds))))
+                     (let ((single-feature
+                            (if (consp features)
+                                (intern (string-join (mapcar #'symbol-name features)
+                                                     "-and-"))
+                              features)))
+                       `(dolist (,cond-feat ,backend-conds)
+                          (cond
+                           ((equal (cdr ,cond-feat) (list ,single-feature))
+                            (setf ,backend-conds (delq ,cond-feat ,backend-conds)))
+                           ((memq ,single-feature (cdr ,cond-feat))
+                            (setcdr ,cond-feat
+                                    (delq ,single-feature (cdr ,cond-feat))))))))
+                   body))
+              (unless implementation-set-p
+                (setq implementation-set-p t))
+              (push
+               (if let-body
+                   `(plist-put (cdr ,the-feat-impl) ,property ,value)
+                 `(setcdr ,the-feat-impl
+                   (plist-put (cdr ,the-feat-impl) ,property ,value)))
+               let-body)))
+          (when let-body
+            (let ((the-feature
+                   (if (consp features)
+                       (intern (string-join (mapcar #'symbol-name features)
+                                            "-and-"))
+                     features)))
+              (when (consp features)
+                (push
+                 `(plist-put (cdr ,the-feat-impl) :when ',features)
+                 let-body))
+              (push
+               `(let ((,the-feat-impl
+                       (or (assoc ',the-feature ,backend-impls)
+                           (car (push (list ',the-feature ,property nil)
+                                      ,backend-impls)))))
+                  ,@(nreverse let-body))
+               body)))))
+      `(let ((,backend-struct ,backend-expr))
+         ,@(and (not (org-export-backend-p backend-expr))
+                `((unless (org-export-backend-p ,backend-struct)
+                    (error "`%s' is not a loaded export backend" ,backend))))
+         ,@(nreverse body)
+         nil))))
 
 \f
 ;;; The Filter System
@@ -3443,8 +3663,8 @@ (defun org-export--annotate-info (backend info &optional subtreep visible-only e
     ;; the output of the selected citation export processor.
     (org-cite-process-citations info)
     (org-cite-process-bibliography info)
-    ;; With the complete tree, detect features.
-    (plist-put info :features (org-export-detect-features info))
+    ;; Install all the feature conditions and implementations.
+    (org-export-process-features info)
     info))
 
 ;;;###autoload
-- 
2.39.0


[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #7: 0006-ox-latex-Reformat-feature-announcement-comment.patch --]
[-- Type: text/x-patch, Size: 1561 bytes --]

From 41a5c7bf4a668c3ae296da6cf46ecf654f393465 Mon Sep 17 00:00:00 2001
From: TEC <git@tecosaur.net>
Date: Thu, 9 Feb 2023 01:17:49 +0800
Subject: [PATCH 6/6] ox-latex: Reformat feature announcement comment

* lisp/ox-latex.el: Reformat the feature announcement comment to make it
easier to read.
---
 lisp/ox-latex.el | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/lisp/ox-latex.el b/lisp/ox-latex.el
index 6221cc486..4e7f30f8b 100644
--- a/lisp/ox-latex.el
+++ b/lisp/ox-latex.el
@@ -211,8 +211,19 @@ (org-export-define-backend 'latex
   :feature-implementations-alist
   `((!announce-start
      :snippet ,(lambda (info)
-                 (format "\n%%%% ox-latex features: %s"
-                         (plist-get info :features)))
+                 (with-temp-buffer
+                   (setq-local left-margin 2)
+                   (insert (string-join
+                            (mapcar #'symbol-name
+                                    (plist-get info :features))
+                            ", ")
+                           ".")
+                   (fill-region-as-paragraph (point-min) (point-max))
+                   (goto-char (point-min))
+                   (insert "%% ox-latex features:\n% ")
+                   (while (search-forward "\n" nil t)
+                     (insert "%"))
+                   (buffer-string)))
      :order -100)
     (maths :snippet "\\usepackage{amsmath}\n\\usepackage{amssymb}" :order 0.2)
     (underline :snippet "\\usepackage[normalem]{ulem}" :order 0.5)
-- 
2.39.0


^ permalink raw reply related	[flat|nested] 22+ messages in thread

end of thread, other threads:[~2023-03-02 11:30 UTC | newest]

Thread overview: 22+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2023-03-01  8:26 [POLL] Naming of "export features" Pedro Andres Aranda Gutierrez
2023-03-01  9:41 ` Ihor Radchenko
2023-03-01 11:38   ` Pedro Andres Aranda Gutierrez
2023-03-02 11:30     ` Ihor Radchenko
     [not found] <mailman.336.1676990100.5072.emacs-orgmode@gnu.org>
2023-02-23 15:06 ` No Wayman
  -- strict thread matches above, loose matches on Subject: below --
2023-02-10 17:20 [PATCH] Introduce " Timothy
2023-02-21 14:22 ` [POLL] Naming of " Timothy
2023-02-22  1:46   ` Dr. Arne Babenhauserheide
2023-02-22  2:40     ` Timothy
2023-02-23 15:55       ` No Wayman
2023-02-23 16:17         ` No Wayman
2023-02-22 12:23   ` Ihor Radchenko
2023-02-23 15:31     ` No Wayman
2023-02-23 16:04     ` Bruce D'Arcus
2023-02-23 19:04       ` Ihor Radchenko
2023-02-23 19:55     ` Sébastien Miquel
2023-02-24 10:27       ` Ihor Radchenko
2023-02-24 12:46         ` Sébastien Miquel
2023-02-24 13:03           ` Ihor Radchenko
2023-02-24 21:38             ` Sébastien Miquel
2023-02-26 12:28               ` Ihor Radchenko
2023-02-26 14:06                 ` Sébastien Miquel
2023-02-27 19:32                   ` Ihor Radchenko

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