Make Solr backend factories more extensible.

module/VuFind/src/VuFind/Search/Factory/AbstractSolrBackendFactory.php

@@ -266,11 +266,13 @@ abstract class AbstractSolrBackendFactory implements FactoryInterface
     /**
      * Get the Solr URL.
      *
+     * @param string $config name of configuration file (null for default)
+     *
      * @return string|array
      */
-    protected function getSolrUrl()
+    protected function getSolrUrl($config = null)
     {
-        $url = $this->config->get('config')->Index->url;
+        $url = $this->config->get($config ?? 'config')->Index->url;
         $core = $this->getSolrCore();
         if (is_object($url)) {
             return array_map(

module/VuFind/src/VuFind/Search/Factory/SolrWebBackendFactory.php

@@ -68,15 +68,17 @@ class SolrWebBackendFactory extends AbstractSolrBackendFactory
     /**
      * Get the Solr URL.
      *
+     * @param string $config name of configuration file (null for default)
+     *
      * @return string
      */
-    protected function getSolrUrl()
+    protected function getSolrUrl($config = null)
     {
-        // Allow the searchConfig to override the default config if set.
-        $webconfig = $this->config->get($this->searchConfig);
-        return isset($webconfig->Index->url)
-            ? $webconfig->Index->url . '/' . $this->getSolrCore()
-            : parent::getSolrUrl();
+        // Only override parent default if valid value present in config:
+        $configToCheck = $config ?? $this->searchConfig;
+        $webConfig = $this->config->get($configToCheck);
+        $finalConfig = isset($webConfig->Index->url) ? $configToCheck : null;
+        return parent::getSolrUrl($finalConfig);
     }
 
     /**