Don't use Pandoc inserted meta-data

Pandoc introduced its citations related meta-data like bibliography
and nocite which I did not prefer for few reasons:

1. It leaks full paths of the user's bibliography files in public.
2. Those meta-data fields are not needed by Hugo.
3. I like my style of YAML list fields better, it's more concise, and
   consistent with the YAML front-matter of non-Pandoc-Citation posts.

doc/ox-hugo-manual.org

@@ -2077,8 +2077,8 @@ Pandoc based citation parsing is enabled by setting the
 ~#+hugo_pandoc_citations:~ keyword or ~:EXPORT_HUGO_PANDOC_CITATIONS:~
 subtree property to ~t~. With this property set, the exported
 front-matter is *forced to YAML*, because Pandoc needs the
-front-matter to be in YAML format to parse fields like ~bibliography~
-~csl~ and ~nocite~.
+front-matter to be in YAML format to parse fields like ~csl~ and
+~nocite~.
 
 #+begin_note
 User needs to have the ~pandoc~ executable present in their ~PATH~.

ox-hugo-pandoc-cite.el

@@ -12,19 +12,22 @@
 ;;; Code:
 
 ;; TODO: Change the defconst to defvar
-(defconst ox-hugo-pandoc-cite-pandoc-args-list
+(defvar ox-hugo-pandoc-cite-pandoc-args-list
   '("--filter" "pandoc-citeproc"
     "-f" "markdown"
     "-t" "markdown-citations"
-    "--atx-headers"     ;Use "# foo" style heading for output markdown
-    "--standalone")     ;Include meta-data at the top
-  "Pandoc arguments used in `ox-hugo-pandoc-cite-run-pandoc'.
+    "--atx-headers")     ;Use "# foo" style heading for output markdown
+  "Pandoc arguments used in `ox-hugo-pandoc-cite--run-pandoc'.
 
 These arguments are added to the `pandoc' call in addition to the
 \"--bibliography\", output file and input file arguments in that
 function.")
 
-(defun ox-hugo-pandoc-cite-run-pandoc (outfile bib-list)
+(defvar ox-hugo-pandoc-cite-pandoc-meta-data
+  '("nocite" "csl")
+  "List of meta-data fields specific to Pandoc.")
+
+(defun ox-hugo-pandoc-cite--run-pandoc (outfile bib-list)
   "Run the `pandoc' process.
 
 OUTFILE is the Org exported file name.
@@ -55,22 +58,35 @@ BIB-LIST is a list of one or more bibliography files."
     ;;                outfile)                     ;Input file
     ))
 
-(defun ox-hugo-pandoc-cite--parse-citations-maybe (info outfile)
+(defun ox-hugo-pandoc-cite--remove-pandoc-meta-data (fm)
+  "Remove Pandoc meta-data from front-matter string FM and return it.
+
+The list of Pandoc specific meta-data is defined in
+`ox-hugo-pandoc-cite-pandoc-meta-data'."
+  (with-temp-buffer
+    (insert fm)
+    (goto-char (point-min))
+    (dolist (field ox-hugo-pandoc-cite-pandoc-meta-data)
+      (let ((regexp (format "^%s: " (regexp-quote field))))
+        (delete-matching-lines regexp)))
+    (buffer-substring-no-properties
+     (point-min) (point-max))))
+
+(defun ox-hugo-pandoc-cite--parse-citations-maybe (info)
   "Check if Pandoc needs to be run to parse citations.
 
-INFO is a plist used as a communication channel.
-
-OUTFILE is the Org exported file name."
+INFO is a plist used as a communication channel."
   ;; (message "pandoc citations keyword: %S"
   ;;          (org-hugo--plist-get-true-p info :hugo-pandoc-citations))
   ;; (message "pandoc citations prop: %S"
   ;;          (org-entry-get nil "EXPORT_HUGO_PANDOC_CITATIONS" :inherit))
-  (when (and outfile
-             (or (org-entry-get nil "EXPORT_HUGO_PANDOC_CITATIONS" :inherit)
-                 (org-hugo--plist-get-true-p info :hugo-pandoc-citations)))
-    (unless (executable-find "pandoc")
-      (user-error "[ox-hugo] pandoc executable not found in PATH"))
-    (ox-hugo-pandoc-cite--parse-citations info outfile)))
+  (let ((outfile (plist-get info :outfile)))
+    (when (and outfile
+               (or (org-entry-get nil "EXPORT_HUGO_PANDOC_CITATIONS" :inherit)
+                   (org-hugo--plist-get-true-p info :hugo-pandoc-citations)))
+      (unless (executable-find "pandoc")
+        (user-error "[ox-hugo] pandoc executable not found in PATH"))
+      (ox-hugo-pandoc-cite--parse-citations info outfile))))
 
 (defun ox-hugo-pandoc-cite--parse-citations (info outfile)
   "Parse Pandoc Citations in OUTFILE and update that file.
@@ -111,7 +127,18 @@ OUTFILE is the Org exported file name."
                                      fname))
                                  bib-list-1)))))))
     (if bib-list
-        (ox-hugo-pandoc-cite-run-pandoc outfile bib-list)
+        (let ((fm (plist-get info :front-matter)))
+          ;; (message "fm :: %S" fm)
+          (ox-hugo-pandoc-cite--run-pandoc outfile bib-list)
+          ;; Prepend the original ox-hugo generated front-matter to
+          ;; Pandoc output.
+          (let* ((fm (ox-hugo-pandoc-cite--remove-pandoc-meta-data fm))
+                 (post-pandoc-contents (with-temp-buffer
+                                         (insert-file-contents outfile)
+                                         (buffer-substring-no-properties
+                                          (point-min) (point-max))))
+                 (fm-plus-content (concat fm "\n" post-pandoc-contents)))
+            (write-region fm-plus-content nil outfile)))
       (message "[ox-hugo-pandoc-cite] No bibliography file was specified"))))
 
 

ox-hugo.el

@@ -125,6 +125,12 @@ helps set the bundle path correctly for such cases (where
 EXPORT_HUGO_BUNDLE and EXPORT_FILE_NAME are set in the same
 subtree).")
 
+(defvar org-hugo--fm nil
+  "Variable to store the current Hugo post's front-matter string.
+
+This variable is used to cache the original ox-hugo generated
+front-matter that's used after Pandoc Citation parsing.")
+
 (defvar org-hugo-allow-export-after-save t
   "Enable flag for `org-hugo-export-wim-to-md-after-save'.
 When nil, the above function will not export the Org file to
@@ -965,7 +971,10 @@ This is an internal function."
   (setq org-hugo--section nil)
   (setq org-hugo--bundle nil)
   (advice-remove 'org-babel-exp-code #'org-hugo--org-babel-exp-code)
-  (ox-hugo-pandoc-cite--parse-citations-maybe info outfile))
+  (plist-put info :outfile outfile)
+  (plist-put info :front-matter org-hugo--fm)
+  (ox-hugo-pandoc-cite--parse-citations-maybe info)
+  (setq org-hugo--fm nil))
 
 ;;;; HTMLized section number for headline
 (defun org-hugo--get-headline-number (headline info &optional toc)
@@ -2434,6 +2443,7 @@ INFO is a plist holding export options."
         (body (if (org-string-nw-p body) ;Insert extra newline if body is non-empty
                   (format "\n%s" body)
                 "")))
+    (setq org-hugo--fm fm)
     (format "%s%s%s" fm body org-hugo-footer)))
 
 ;;;;; Hugo Front Matter
@@ -2775,9 +2785,8 @@ the Hugo front-matter."
 INFO is a plist used as a communication channel."
   ;; (message "[hugo front matter DBG] info: %S" (pp info))
   (let* ((fm-format (if (org-hugo--plist-get-true-p info :hugo-pandoc-citations)
-                        ;; pandoc-citations parses fields like
-                        ;; bibliography, csl and nocite from YAML
-                        ;; front-matter.
+                        ;; pandoc parses fields like csl and nocite
+                        ;; from YAML front-matter.
                         "yaml"
                       (plist-get info :hugo-front-matter-format)))
          (author-list (and (plist-get info :with-author)

test/site/content/posts/citations-example.md

@@ -1,15 +1,7 @@
 ---
-bibliography:
-- '/home/kmodi/stow/pub\_dotfiles/emacs/dot-emacs.d/elisp/ox-hugo/test/site/content-org/bib/bib1.bib'
-- '/home/kmodi/stow/pub\_dotfiles/emacs/dot-emacs.d/elisp/ox-hugo/test/site/content-org/bib/bib2.bib'
-draft: False
-nocite:
-- '@giovanelli2016'
-- '@eilan2016'
-tags:
-- pandoc
-- citeproc
-title: Citations Example
+title: "Citations Example"
+tags: ["pandoc", "citeproc"]
+draft: false
 ---
 
 ## Section 1