Apply out-of-stock-last ordering on search result pages

src/Adapter/MySQL.php

@@ -404,8 +404,13 @@ protected function computeOrderByField(array $filterToTableMapping)
          * to order products by their position in the search results we got from the core, with inverted order
          */
         if ($orderField == 'p.position' && !empty($this->getInitialPopulation()->getFilters()['id_product']['='][0])) {
-            return 'FIELD(p.id_product,' . implode(',', $this->getInitialPopulation()->getFilters()['id_product']['='][0]) . ') ' .
+            $orderField = 'FIELD(p.id_product,' . implode(',', $this->getInitialPopulation()->getFilters()['id_product']['='][0]) . ') ' .
             ($this->getOrderDirection() === 'asc' ? 'DESC' : 'ASC');
+
+            // Push out-of-stock products to the end on search pages too. Without this, the relevance
+            // ordering was returned as is and bypassed the "out of stock last" behaviour that the
+            // category, manufacturer and other listings get below through computeShowLast().
+            return $this->computeShowLast($orderField, $filterToTableMapping);
         }
 
         // Alter order by field and add some products to the end of the list, if required

tests/php/FacetedSearch/Adapter/MySQLTest.php

@@ -78,6 +78,41 @@ public function testGetEmptyQuery()
         );
     }
 
+    /**
+     * On search pages the products are ordered by their relevance (their position in the pool
+     * returned by the core search). The "out of stock last" behaviour must still be applied on
+     * top of that relevance ordering, exactly like on category/manufacturer listings.
+     *
+     * @see https://github.com/PrestaShop/ps_facetedsearch/issues/1236
+     */
+    public function testGetQueryAppliesOutOfStockLastOnSearchRelevanceOrdering()
+    {
+        $configurationMock = Mockery::mock(Configuration::class);
+        $configurationMock->shouldReceive('get')
+            ->with('PS_LAYERED_FILTER_SHOW_OUT_OF_STOCK_LAST')
+            ->andReturn(true);
+        Configuration::setStaticExpectations($configurationMock);
+
+        $productMock = Mockery::namedMock(Product::class);
+        $productMock->shouldReceive('isAvailableWhenOutOfStock')
+            ->with(2)
+            ->andReturn(false);
+
+        // A search query: the pool of product ids becomes the initial population and the order
+        // field is the relevance "position".
+        $this->adapter->addFilter('id_product', [1, 2, 3], '=');
+        $this->adapter->useFiltersAsInitialPopulation();
+        $this->adapter->setOrderField('position');
+        $this->adapter->setOrderDirection('asc');
+
+        $query = $this->adapter->getQuery();
+
+        // Out-of-stock products are pushed to the end...
+        $this->assertContains('IFNULL(p.quantity, 0) <= 0', $query);
+        // ...while the relevance ordering is preserved within each group.
+        $this->assertContains('FIELD(p.id_product,1,2,3) DESC', $query);
+    }
+
     /**
      * @dataProvider oneSelectFieldDataProvider
      */