Add function qa_get_canonical to auto-generate canonical URL

Also add canonical tag to question lists and tag pages.

qa-include/app/page.php

@@ -828,3 +828,26 @@ function qa_get_state()
 	global $qa_state;
 	return $qa_state;
 }
+
+
+/**
+ * Generate a canonical URL for the current request. Preserves certain GET parameters.
+ * @return string The full canonical URL.
+ */
+function qa_get_canonical()
+{
+	$params = array();
+
+	// variable assignment intentional here
+	if (($start = qa_get_start()) > 0) {
+		$params['start'] = $start;
+	}
+	if ($sort = qa_get('sort')) {
+		$params['sort'] = $sort;
+	}
+	if ($by = qa_get('by')) {
+		$params['by'] = $by;
+	}
+
+	return qa_path_html(qa_request(), $params, qa_opt('site_url'));
+}

qa-include/app/q-list.php

@@ -124,6 +124,8 @@ function qa_q_list_page_content($questions, $pagesize, $start, $count, $sometitl
 		$qa_content['page_links'] = qa_html_page_links(qa_request(), $start, $pagesize, $count, qa_opt('pages_prev_next'), $pagelinkparams);
 	}
 
+	$qa_content['canonical'] = qa_get_canonical();
+
 	if (empty($qa_content['page_links'])) {
 		$qa_content['suggest_next'] = $suggest;
 	}

qa-include/pages/tag.php

@@ -79,6 +79,8 @@ foreach ($questions as $postid => $question) {
 		qa_post_html_fields($question, $userid, qa_cookie_get(), $usershtml, null, qa_post_html_options($question));
 }
 
+$qa_content['canonical'] = qa_get_canonical();
+
 $qa_content['page_links'] = qa_html_page_links(qa_request(), $start, $pagesize, $tagword['tagcount'], qa_opt('pages_prev_next'));
 
 if (empty($qa_content['page_links']))

qa-include/pages/tags.php

@@ -70,6 +70,8 @@ if (count($populartags)) {
 } else
 	$qa_content['title'] = qa_lang_html('main/no_tags_found');
 
+$qa_content['canonical'] = qa_get_canonical();
+
 $qa_content['page_links'] = qa_html_page_links(qa_request(), $start, $pagesize, $tagcount, qa_opt('pages_prev_next'));
 
 if (empty($qa_content['page_links']))

qa-include/pages/users-newest.php

@@ -83,8 +83,7 @@ if (!empty($users)) {
 	$qa_content['title'] = qa_lang_html('main/no_active_users');
 }
 
-// set the canonical url based on possible pagination
-$qa_content['canonical'] = qa_path_html(qa_request(), ($start > 0 ? array('start' => $start) : null), qa_opt('site_url'));
+$qa_content['canonical'] = qa_get_canonical();
 
 $qa_content['page_links'] = qa_html_page_links(qa_request(), $start, $pageSize, $userCount, qa_opt('pages_prev_next'));
 

qa-include/pages/users.php

@@ -74,9 +74,7 @@ if (count($users)) {
 	$qa_content['title'] = qa_lang_html('main/no_active_users');
 }
 
-
-// set the canonical url based on possible pagination
-$qa_content['canonical'] = qa_path_html(qa_request(), ($start > 0 ? array('start' => $start) : null), qa_opt('site_url'));
+$qa_content['canonical'] = qa_get_canonical();
 
 $qa_content['page_links'] = qa_html_page_links(qa_request(), $start, $pagesize, $usercount, qa_opt('pages_prev_next'));