(feat): tag completion via capf (#1017)

org-roam-db.el

@@ -314,6 +314,16 @@ Insertions can fail if the key is already in the database."
                             :limit 1]
                            file)))
 
+(defun org-roam-db--get-tags ()
+  "Return all distinct tags from the cache."
+  (let ((rows (org-roam-db-query [:select :distinct [tags] :from tags]))
+        acc)
+    (dolist (row rows)
+      (dolist (tag (car row))
+        (unless (member tag acc)
+          (push tag acc))))
+    acc))
+
 (defun org-roam-db--connected-component (file)
   "Return all files reachable from/connected to FILE, including the file itself.
 If the file does not have any connections, nil is returned."

org-roam.el

@@ -1098,16 +1098,28 @@ This function hooks into `org-open-at-point' via
 (defun org-roam-complete-at-point ()
   "Do appropriate completion for the thing at point."
   (let ((end (point))
-        start
+        (start (point))
+        (exit-fn (lambda (&rest _) nil))
         collection)
-    (cond (;; In an open bracket
+    (cond
+     (;; completing roam_tags
+      (looking-back "^#\\+roam_tags:.*" (line-beginning-position))
+      (when (looking-at "\\>")
+        (setq start (save-excursion (skip-syntax-backward "w")
+                                    (point))
+              end (point)))
+      (setq collection #'org-roam-db--get-tags
+            exit-fn (lambda (str _status)
+                      (delete-char (- (length str)))
+                      (insert "\"" str "\""))))
+     (;; In an open bracket
       (looking-back (concat "^.*" org-roam-open-bracket-regexp) (line-beginning-position))
       (setq start (match-beginning 1)
             end (match-end 1))
       (save-match-data
         (save-excursion
           (goto-char start)
-               (when (looking-at org-roam-title-headline-split-regexp)
+          (when (looking-at (concat org-roam-title-headline-split-regexp "\]\]"))
             (let ((title (match-string-no-properties 1))
                   (has-headline-p (not (string-empty-p (match-string-no-properties 2))))
                   (headline-start (match-beginning 3)))
@@ -1133,6 +1145,7 @@ This function hooks into `org-open-at-point' via
                    (lambda (_)
                      (cl-remove-if (apply-partially 'string= prefix) (funcall collection))))
                 collection)
+              :exit-function exit-fn
               'ignore)))))
 
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