Add backend defvar to define --read function

bibtex-completion.el

@@ -364,6 +364,9 @@ Only entries of these types are checked in order to resolve
 cross-references.  The default list is usually sufficient; adding
 more types can slow down resolution for large biblioraphies.")
 
+(defvar bibtex-completion-read-backend 'bibtex-completion--completing-read
+  "The function called by bibtex-completion--read to return a set of keys.")
+
 (defvar bibtex-completion-display-formats-internal nil
   "Stores `bibtex-completion-display-formats' together with the \"used width\" of each format string.
 This is set internally.")
@@ -380,7 +383,6 @@ bibliography file is reparsed.")
 (defvar bibtex-completion-string-hash-table nil
   "A hash table used for string replacements.")
 
-
 (defun bibtex-completion-normalize-bibliography (&optional type)
   "Return a list of bibliography file(s) in `bibtex-completion-bibliography'.
 If there are org mode bibliography-files, their corresponding
@@ -497,7 +499,8 @@ for string replacement."
 (defun bibtex-completion--read ()
   "Select BibTeX entries in completion system."
   ;; define a completion function that defaults to completing-read, but can be overridden
-  (list (bibtex-completion--completing-read)))
+  (list (funcall bibtex-completion-read-backend)))
+  ;; (list (bibtex-completion--completing-read)))
 
 (defun bibtex-completion--completing-read ()
   "Read bibtex-completion entries for completion using completing-read."