[PATCH] oc-natbib: Provide a fallback bibliography style

[Ihor Radchenko]

If we do not specify a bibliography style, LaTeX export will fail.
With the attached patch, the following simple-minded Org document will
export without errors:

 #+title: Testing org-cite \LaTeX export
 #+latex_header: \usepackage{natbib}
 #+bibliography: bibliography.bib
 #+options: toc:nil
 #+cite_export: natbib

 Hello World! This is a citation: [cite:@citationkey2023]

 #+print_bibliography:

Also, should we provide some commonly available natbib styles in the
defcustom?

>From f27e5b4f66b7e703f9b2fdaa5c1b5d756d38fd33 Mon Sep 17 00:00:00 2001
Message-Id: 
<f27e5b4f66b7e703f9b2fdaa5c1b5d756d38fd33.1674659339.git.yantar92@posteo.net>
From: Ihor Radchenko <yantar92@posteo.net>
Date: Wed, 25 Jan 2023 18:02:49 +0300
Subject: [PATCH] oc-natbib: Provide a fallback bibliography style

* lisp/oc-natbib.el (org-cite-natbib-bibliography-style): New custom
option for default bibliography style.
(org-cite-natbib-export-bibliography): Use the new custom option.
* etc/ORG-NEWS (New ~org-cite-natbib-export-bibliography~ option
defining fallback bibliography style): Document the new option.

If we do not specify a bibliography style, LaTeX export will fail.
After the patch, the following simple-minded Org document will export
without errors:

 #+title: Testing org-cite \LaTeX export
 #+latex_header: \usepackage{natbib}
 #+bibliography: bibliography.bib
 #+options: toc:nil
 #+cite_export: natbib

 Hello World! This is a citation: [cite:@citationkey2023]

 #+print_bibliography:
---
 etc/ORG-NEWS      | 10 ++++++++++
 lisp/oc-natbib.el | 21 ++++++++++++++++-----
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/etc/ORG-NEWS b/etc/ORG-NEWS
index 3ef76ec1a..04f6338a9 100644
--- a/etc/ORG-NEWS
+++ b/etc/ORG-NEWS
@@ -13,6 +13,16 @@ Please send Org bug reports to mailto:emacs-orgmode@gnu.org.
 
 * Version 9.7 (not released yet)
 ** New options
+*** New ~org-cite-natbib-export-bibliography~ option defining fallback 
bibliography style
+
+~natbib~ citation export processor now uses
+~org-cite-natbib-export-bibliography~ (defaults to ~unsrtnat~) as a
+fallback bibliography style if none is specified by user in
+=#+cite_export:= keyword.
+
+Previously, export would fail without explicitly selected bibliography
+style.
+
 *** New options for the "csl" citation export processor's LaTeX output
 
 The ~org-cite-csl-latex-label-separator~ and
diff --git a/lisp/oc-natbib.el b/lisp/oc-natbib.el
index 855be2a5c..9153afd86 100644
--- a/lisp/oc-natbib.el
+++ b/lisp/oc-natbib.el
@@ -77,6 +77,15 @@ (defcustom org-cite-natbib-options nil
     (const :tag "redefine \\thebibliography to issue \\section* instead of 
\\chapter*" sectionbib)
     (const :tag "keep all the authors' names in a citation on one line" 
nonamebreak)))
 
+(defcustom org-cite-natbib-bibliography-style 'unsrtnat
+  "Default bibliography style."
+  :group 'org-cite
+  :package-version '(Org . "9.7")
+  :type
+  '(choice
+    (const unsrtnat)
+    (symbol :tag "Other")))
+
 
 ;;; Internal functions
 (defun org-cite-natbib--style-to-command (style)
@@ -143,11 +152,13 @@ (defun org-cite-natbib-export-bibliography (_keys files 
style &rest _)
   "Print references from bibliography FILES.
 FILES is a list of absolute file names.  STYLE is the bibliography style, as
 a string or nil."
-  (concat (and style (format "\\bibliographystyle{%s}\n" style))
-          (format "\\bibliography{%s}"
-                  (mapconcat #'file-name-sans-extension
-                             files
-                             ","))))
+  (concat
+   (format "\\bibliographystyle{%s}\n"
+           (or style org-cite-natbib-bibliography-style))
+   (format "\\bibliography{%s}"
+           (mapconcat #'file-name-sans-extension
+                      files
+                      ","))))
 
 (defun org-cite-natbib-export-citation (citation style _ info)
   "Export CITATION object.
-- 
2.39.1

-- 
Ihor Radchenko // yantar92,
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/yantar92>