If there's already a link[rel=profile], don't create another

For example, Twenty Twenty has a link[rel=profile], though it doesn't have a head[profile].
ampproject · Jan 29, 2020 · 7f60c5c · 7f60c5c
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Showing 2 changed files with 24 additions and 7 deletions.
diff --git a/src/Dom/Document.php b/src/Dom/Document.php
@@ -541,17 +541,29 @@ private function move_invalid_head_nodes_to_body() {
 	 * Converts a possible head[profile] attribute to link[rel=profile].
 	 *
 	 * The head[profile] attribute is only valid in HTML4, not HTML5.
-	 * So if it exists, add it to the <head> as a link[rel=profile] and strip the attribute.
+	 * So if it exists and there's no link[rel=profile], add it to the <head> as a link[rel=profile].
 	 */
 	private function convert_head_profile_to_link() {
 		$profile = $this->head->getAttribute( 'profile' );
-		if ( $profile ) {
-			$link = $this->createElement( 'link' );
-			$link->setAttribute( 'rel', 'profile' );
-			$link->setAttribute( 'href', $profile );
-			$this->head->appendChild( $link );
-			$this->head->removeAttribute( 'profile' );
+		if ( ! $profile ) {
+			return;
 		}
+
+		// If there's already a head > link[rel=profile], don't create another.
+		$links = $this->head->getElementsByTagName( 'link' );
+		foreach( $links as $link ) {
+			if ( 'profile' === $link->getAttribute( 'rel' ) ) {
+				$this->head->removeAttribute( 'profile' );
+				return;
+			}
+		}
+
+		// Create a <link> and append it to <head>.
+		$new_link = $this->createElement( 'link' );
+		$new_link->setAttribute( 'rel', 'profile' );
+		$new_link->setAttribute( 'href', $profile );
+		$this->head->appendChild( $new_link );
+		$this->head->removeAttribute( 'profile' );
 	}
 
 	/**

diff --git a/tests/php/test-class-amp-dom-document.php b/tests/php/test-class-amp-dom-document.php
@@ -169,6 +169,11 @@ public function data_dom_document() {
 				'<!DOCTYPE html><html><head profile="https://example.com"></head><body></body></html>',
 				'<!DOCTYPE html><html><head><meta charset="utf-8"><link rel="profile" href="https://example.com"></head><body></body></html>',
 			],
+			'link_rel_profile_already_exists'          => [
+				'utf-8',
+				'<!DOCTYPE html><html><head profile="https://example.com"><link rel="profile" href="https://foo.com"></head><body></body></html>',
+				'<!DOCTYPE html><html><head><meta charset="utf-8"><link rel="profile" href="https://foo.com"></head><body></body></html>',
+			],
 		];
 	}