API: resource getter functions now return hash tables.

The `citar-get-files`, `citar-get-links`, and `citar-get-notes` functions now
return hash tables mapping each key to a list of associated resources. They
used to just return lists of resources for all the given keys, but that
interface doesn't allow callers to determine which key corresponds to each
resource.

The `:items` function in the notes source API has also been modified, and must
now return a hash table instead of a list of notes.

citar-file.el

@@ -26,10 +26,10 @@
 (make-obsolete-variable 'citar-file-extensions
                         'citar-library-file-extensions "1.0")
 
-(declare-function citar-get-value "citar")
-(declare-function citar--bibliography-files "citar")
-(declare-function citar--check-configuration "citar")
-(declare-function citar--get-notes-config "citar")
+(declare-function citar-get-value "citar" (field key-or-entry))
+(declare-function citar--bibliography-files "citar" (&rest buffers))
+(declare-function citar--check-configuration "citar" (&rest variables))
+(declare-function citar--get-resources-using-function "citar" (func &optional keys))
 
 ;;;; File related variables
 
@@ -163,13 +163,15 @@ Note: this function is intended to be used in
 `citar-has-files-functions'. Use `citar-has-files' to test
 whether entries have associated files."
   (when citar-file-variable
-    (apply-partially #'citar-get-value citar-file-variable)))
+    (lambda (citekey) (and (citar-get-value citar-file-variable citekey) t))))
 
-(defun citar-file--get-from-file-field (keys)
-  "Return list of files for KEYS.
+(defun citar-file--get-from-file-field (&optional keys)
+  "Return files for KEYS by parsing the `citar-file-variable' field.
 
-Parse and return files given in the bibliography field named by
-`citar-file-variable'.
+Return a hash table mapping each element of KEYS to a list of
+files given in the bibliography entry named by
+`citar-file-variable'. If KEYS is nil, return files for all
+entries.
 
 Note: this function is intended to be used in
 `citar-get-files-functions'. Use `citar-get-files' to get all
@@ -179,30 +181,27 @@ files associated with KEYS."
                                 'citar-file-parser-functions)
     (let ((dirs (append citar-library-paths
                         (mapcar #'file-name-directory (citar--bibliography-files)))))
-      (mapcan
-       (lambda (citekey)
-         (when-let ((fieldvalue (citar-get-value filefield citekey)))
+      (citar--get-resources-using-function
+       (lambda (citekey entry)
+         (when-let ((fieldvalue (citar-get-value filefield entry)))
            (citar-file--parse-file-field fieldvalue dirs citekey)))
        keys))))
 
 ;;;; Scanning library directories
 
 (defun citar-file--has-library-files ()
   "Return predicate testing whether cite key has library files."
-  (citar--check-configuration 'citar-library-paths 'citar-library-file-extensions)
-  (let ((files (citar-file--directory-files
-                citar-library-paths nil citar-library-file-extensions
-                citar-file-additional-files-separator)))
-    (lambda (key)
-      (gethash key files))))
+  (let ((files (citar-file--get-library-files)))
+    (unless (hash-table-empty-p files)
+      (lambda (citekey)
+        (and (gethash citekey files) t)))))
 
-(defun citar-file--get-library-files (keys)
+(defun citar-file--get-library-files (&optional keys)
   "Return list of files for KEYS in ENTRIES."
-  (citar--check-configuration 'citar-library-paths)
-  (let ((files (citar-file--directory-files citar-library-paths keys
-                                            citar-library-file-extensions
-                                            citar-file-additional-files-separator)))
-    (mapcan (lambda (key) (gethash key files)) keys)))
+  (citar--check-configuration 'citar-library-paths 'citar-library-file-extensions)
+  (citar-file--directory-files
+   citar-library-paths keys citar-library-file-extensions
+   citar-file-additional-files-separator))
 
 (defun citar-file--make-filename-regexp (keys extensions &optional additional-sep)
   "Regexp matching file names starting with KEYS and ending with EXTENSIONS.
@@ -307,7 +306,7 @@ need to scan the contents of DIRS in this case."
 
 ;;;; Note files
 
-(defun citar-file--note-directory-files (&optional keys)
+(defun citar-file--get-notes (&optional keys)
   "Return note files associated with KEYS.
 Return hash table whose keys are elements of KEYS and values are
 lists of note file names found in `citar-notes-paths' having
@@ -319,8 +318,9 @@ extensions in `citar-file-note-extensions'."
 
 (defun citar-file--has-notes ()
   "Return predicate testing whether cite key has associated notes."
-  (let ((files (citar-file--note-directory-files)))
-    (lambda (key) (gethash key files))))
+  (let ((notes (citar-file--get-notes)))
+    (unless (hash-table-empty-p notes)
+      (lambda (citekey) (and (gethash citekey notes) t)))))
 
 (defun citar-file--create-note (key entry)
   "Create a note file from KEY and ENTRY."
@@ -331,11 +331,6 @@ extensions in `citar-file-note-extensions'."
           (funcall citar-note-format-function key entry)))
     (user-error "Make sure `citar-notes-paths' and `citar-file-note-extensions' are non-nil")))
 
-(defun citar-file--get-notes (keys)
-  "Return list of notes associated with KEYS."
-  (let ((notes (citar-file--note-directory-files keys)))
-    (apply #'append (map-values notes))))
-
 (defun citar-file--get-note-filename (key)
   "Return existing or new note filename for KEY.