Don’t break NetNewsWire’s footnote detection1.29.1-customcustom

If NetNewsWire detects that a link points to a footnote within the same
post, then tapping on that link will produce a popover displaying the
text of said footnote. Otherwise, it is treated as a regular link and
opened in the default web browser.

Detecting a footnote requires two things:

1. The link URL must consist only of a fragment (i.e. it begins with
   `#`).

2. There must exist another element (typically `<li>`) in the post’s
   HTML with an `id` attribute matching the fragment (that is, the text
   after `#`).

Because FreshRSS’s web frontend can display multiple articles at once,
all relative URLs (including bare fragments) are automatically converted
to absolute URLs at ingestion time, and `id` attributes are replaced
with `data-sanitized-id` attributes. These changes avoid conflicts in
the web UI, but they break NNW’s footnote detection.

Since I use FreshRSS solely as a backend service for NNW (and other
clients), it is reasonable for me to disable those two sanitization
steps in order to take full advantage of NNW’s features.

Remove `id` from the list of attributes to rename, and add it to the
list of allowed attributes (as otherwise, it would be stripped
entirely). Convert the `absolutize_url()` function into a no-op if the
relative URL provided appears to be a local fragment.

2 files changed, 6 insertions, 1 deletions

diff --git a/app/Models/SimplePieCustom.php b/app/Models/SimplePieCustom.php
index 89b98c701..a1ef33abd 100644
--- a/app/Models/SimplePieCustom.php
+++ b/app/Models/SimplePieCustom.php
@@ -61,7 +61,7 @@ final class FreshRSS_SimplePieCustom extends \SimplePie\SimplePie
 		$this->set_curl_options($curl_options);
 
 		$this->strip_comments(true);
-		$this->rename_attributes(['id', 'class']);
+		$this->rename_attributes(['class']);
 		$this->allow_aria_attr(true);
 		$this->allow_data_attr(true);
 		$this->allowed_html_attributes([
@@ -69,6 +69,7 @@ final class FreshRSS_SimplePieCustom extends \SimplePie\SimplePie
 			'dir',
 			'draggable',
 			'hidden',
+			'id',
 			'lang',
 			'role',
 			'title',
diff --git a/lib/simplepie/simplepie/src/Misc.php b/lib/simplepie/simplepie/src/Misc.php
index a31c22bb2..d72a69a88 100644
--- a/lib/simplepie/simplepie/src/Misc.php
+++ b/lib/simplepie/simplepie/src/Misc.php
@@ -50,6 +50,10 @@ class Misc
      */
     public static function absolutize_url(string $relative, string $base)
     {
+        if (str_starts_with($relative, "#")) {
+            return $relative;
+        }
+
         $iri = \SimplePie\IRI::absolutize(new \SimplePie\IRI($base), $relative);
         if ($iri === false) {
             return false;