(perf): Deprecate link :outline properties

As it happens, turning sexps into strings is one of the
computationally expensive steps in EmacSQL.

With an enormous number of links in the database, that's a lot
of (:outline nil) to stringify into "(:outline nil)".

Its only use was in org-roam-node-insert-section,
where the information is very cheap to reconstruct.
It's already in one of the other arguments!

This has passed unnoticed because org-roam-db-sync has other
performance tarpits, but it will probably be noticed eventually after
those get fixed.

org-roam-db.el

@@ -108,7 +108,7 @@ ROAM_REFS."
   :type '(alist))
 
 ;;; Variables
-(defconst org-roam-db-version 18)
+(defconst org-roam-db-version 19)
 
 (defvar org-roam-db--connection (make-hash-table :test #'equal)
   "Database connection to Org-roam database.")
@@ -214,7 +214,7 @@ The query is expected to be able to fail, in this situation, run HANDLER."
        (source :not-null)
        (dest :not-null)
        (type :not-null)
-       (properties :not-null)]
+       properties]
       (:foreign-key [source] :references nodes [id] :on-delete :cascade)))))
 
 (defconst org-roam-db--table-indices
@@ -507,11 +507,8 @@ INFO is the org-element parsed buffer."
            (path (if (not option) path
                    (substring path 0 (match-beginning 0))))
            (source (org-roam-id-at-point))
-           (properties (list :outline (ignore-errors
-                                        ;; This can error if link is not under any headline
-                                        (org-get-outline-path 'with-self 'use-cache))))
-           (properties (if option (plist-put properties :search-option option)
-                         properties)))
+           (properties (when option
+                         (list :search-option option))))
       ;; For Org-ref links, we need to split the path into the cite keys
       (when (and source path)
         (if (and (boundp 'org-ref-cite-types)
@@ -533,9 +530,7 @@ INFO is the org-element parsed buffer."
     (goto-char (org-element-property :begin citation))
     (let ((key (org-element-property :key citation))
           (source (org-roam-id-at-point))
-          (properties (list :outline (ignore-errors
-                                       ;; This can error if link is not under any headline
-                                       (org-get-outline-path 'with-self 'use-cache)))))
+          (properties nil))
       (when (and source key)
         (org-roam-db-query
          [:insert :into citations

org-roam-mode.el

@@ -369,7 +369,7 @@ run at `post-command-hook'."
    (node :initform nil))
   "A `magit-section' used by `org-roam-mode' to outline NODE in its own heading.")
 
-(cl-defun org-roam-node-insert-section (&key source-node point properties)
+(cl-defun org-roam-node-insert-section (&key source-node point _properties)
   "Insert section for a link from SOURCE-NODE to some other node.
 The other node is normally `org-roam-buffer-current-node'.
 
@@ -393,7 +393,9 @@ the same time:
    other node) at POINT. Acts a child section of the previous
    one."
   (magit-insert-section section (org-roam-node-section)
-    (let ((outline (if-let ((outline (plist-get properties :outline)))
+    (let ((outline (if-let ((outline (append
+                                      (org-roam-node-olp source-node)
+                                      (list (org-roam-node-title source-node)))))
                        (mapconcat #'org-link-display-format outline " > ")
                      "Top")))
       (insert (concat (propertize (org-roam-node-title source-node)
@@ -534,8 +536,7 @@ SECTION-HEADING is the string used as a heading for the backlink section."
                        (funcall show-backlink-p backlink)))
           (org-roam-node-insert-section
            :source-node (org-roam-backlink-source-node backlink)
-           :point (org-roam-backlink-point backlink)
-           :properties (org-roam-backlink-properties backlink))))
+           :point (org-roam-backlink-point backlink))))
       (insert ?\n))))
 
 ;;;; Reflinks
@@ -590,8 +591,7 @@ Sorts by title."
       (dolist (reflink reflinks)
         (org-roam-node-insert-section
          :source-node (org-roam-reflink-source-node reflink)
-         :point (org-roam-reflink-point reflink)
-         :properties (org-roam-reflink-properties reflink)))
+         :point (org-roam-reflink-point reflink)))
       (insert ?\n))))
 
 ;;;; Grep