Implemented Summon query expansion.

- Resolves VUFIND-929.

config/vufind/Summon.ini

@@ -77,6 +77,7 @@ IsScholarly:true = scholarly_limit
 IsFullText:true = fulltext_limit
 excludeNewspapers:true = exclude_newspapers
 holdingsOnly:false = add_other_libraries
+queryExpansion:true = include_synonyms
 
 ; The order of display is as shown below
 ; The name of the index field is on the left

languages/en-gb.ini

@@ -371,6 +371,7 @@ Import Record = "Import Record"
 Import to = "Import to "
 in = in
 In This Collection = "In This Collection"
+include_synonyms = "Expand results using synonyms"
 information = "Information"
 Institution = Institution
 Institutional Login = "Institutional Login"

languages/en.ini

@@ -371,6 +371,7 @@ Import Record = "Import Record"
 Import to = "Import to "
 in = in
 In This Collection = "In This Collection"
+include_synonyms = "Expand results using synonyms"
 information = "Information"
 Institution = Institution
 Institutional Login = "Institutional Login"

module/VuFind/src/VuFind/Search/Summon/Params.php

@@ -129,12 +129,15 @@ class Params extends \VuFind\Search\Base\Params
         // Grab checkbox facet details using the standard method:
         $facets = parent::getCheckboxFacets();
 
-        // Special case -- if we have a "holdings only" facet, we want this to
-        // always appear, even on the "no results" screen, since setting this
-        // facet actually EXPANDS the result set, rather than reducing it:
+        // Special case -- if we have a "holdings only" or "expand query" facet,
+        // we want this to always appear, even on the "no results" screen, since
+        // setting this facet actually EXPANDS rather than reduces the result set.
         if (isset($facets['holdingsOnly'])) {
             $facets['holdingsOnly']['alwaysVisible'] = true;
         }
+        if (isset($facets['queryExpansion'])) {
+            $facets['queryExpansion']['alwaysVisible'] = true;
+        }
 
         // Return modified list:
         return $facets;
@@ -225,6 +228,12 @@ class Params extends \VuFind\Search\Base\Params
                         $params->set(
                             'holdings', strtolower(trim($safeValue)) == 'true'
                         );
+                    } else if ($filt['field'] == 'queryExpansion') {
+                        // Special case -- "query expansion" is a separate parameter
+                        // from other facets.
+                        $params->set(
+                            'expand', strtolower(trim($safeValue)) == 'true'
+                        );
                     } else if ($filt['field'] == 'excludeNewspapers') {
                         // Special case -- support a checkbox for excluding
                         // newspapers: