ENH: Provide more control over elemental block indexing.

Provides a new configuration variable to exclude specific elemental block classes from being indexed in search.
Provides a new extension point for modifying exactly what gets indexed for each block.
Provides a new configuration variable to define the delimiter used
between blocks in the search index.

A single space delimiter is non-intrusive and will not require any changes within existing projects to avoid changes to the way content is indexed - but providing an option for configuring the delimiter can help avoid false-positive results in phrase queries.

docs/en/searching-blocks.md

@@ -29,4 +29,27 @@ You can disable it via YAML config in favour of your own index definition:
 SilverStripe\FullTextSearch\Search\FullTextSearch:
   indexes:
     - MyCustomIndex
+```
+
+You can define whether each block is included in your search index using the
+`search_indexable` configuration variable, which is `true` by default:
+
+```yml
+App\Models\MyCustomElementalBlock:
+  search_indexable: false
+```
+
+You can also customise the content that is indexed for your blocks. By default
+the block is rendered in full using the templating engine, and the resultant
+markup is included in the index. You can override the `getContentForSearchIndex`
+method on your elemental blocks to change that. This is useful, for example, if
+your templates include hardcoded text or references to other content you don't
+want to be indexed.
+
+If you want to use a specific delimiter between each block, that can be configured
+as well. The default is a space, but you might for example want to use an ellipses
+to make it clear in search results where one piece of content ends and another begins.
+```yml
+DNADesign\Elemental\Extensions\ElementalPageExtension:
+  search_index_element_delimiter: ' ... '
 ```

src/Extensions/ElementalPageExtension.php

@@ -25,6 +25,17 @@ class ElementalPageExtension extends ElementalAreasExtension
         'ElementalArea',
     ];
 
+    /**
+     * The delimiter to separate distinct elements in indexed content.
+     *
+     * When using the getElementsForSearch() method to index all elements in a single field,
+     * a custom delimiter can be used help to avoid false positive results for phrase queries.
+     *
+     * @config
+     * @var string
+     */
+    private static $search_index_element_delimiter = ' ';
+
     /**
      * Returns the contents of each ElementalArea has_one's markup for use in Solr or Elastic search indexing
      *
@@ -43,8 +54,14 @@ public function getElementsForSearch()
                 /** @var ElementalArea $area */
                 $area = $this->owner->$key();
                 if ($area) {
-                    // Replace HTML tags with spaces
-                    $output[] = strip_tags(str_replace('<', ' <', $area->forTemplate()));
+                    foreach ($area->Elements() as $element) {
+                        if ($element->getSearchIndexable()) {
+                            $content = $element->getContentForSearchIndex();
+                            if ($content) {
+                                $output[] = $content;
+                            }
+                        }
+                    }
                 }
             }
         } finally {
@@ -53,7 +70,7 @@ public function getElementsForSearch()
             // CMS layout can break on the response. (SilverStripe 4.1.1)
             SSViewer::set_themes($oldThemes);
         }
-        return implode($output);
+        return implode($this->config()->get('search_index_element_delimiter'), $output);
     }
 
     public function MetaTags(&$tags)

src/Models/BaseElement.php

@@ -32,6 +32,7 @@
 use SilverStripe\View\Parsers\URLSegmentFilter;
 use SilverStripe\View\Requirements;
 use SilverStripe\ORM\CMSPreviewable;
+use SilverStripe\Core\Config\Config;
 
 /**
  * Class BaseElement
@@ -174,6 +175,15 @@ class BaseElement extends DataObject implements CMSPreviewable
      */
     private static $displays_title_in_template = true;
 
+    /**
+     * Determines whether a block should be indexable in search.
+     *
+     * @config
+     * @var boolean
+     * @see ElementalPageExtension::getElementsForSearch()
+     */
+    private static $search_indexable = true;
+
     /**
      * Store used anchor names, this is to avoid title clashes
      * when calling 'getAnchor'
@@ -476,6 +486,33 @@ public function Top()
         return (Controller::has_curr()) ? Controller::curr() : null;
     }
 
+    /**
+     * Determines whether this elemental block is indexable in search.
+     *
+     * By default, this uses the configurable variable search_indexable, but
+     * this method can be overridden to provide more complex logic if required.
+     *
+     * @return boolean
+     */
+    public function getSearchIndexable(): bool
+    {
+        return (bool)$this->config()->get('search_indexable', Config::UNINHERITED);
+    }
+
+    /**
+     * Provides content to be indexed in search.
+     *
+     * @return string|null
+     */
+    public function getContentForSearchIndex(): ?string
+    {
+        // Strips tags but be sure there's a space between words.
+        $content = trim(strip_tags(str_replace('<', ' <', $this->forTemplate())));
+        // Allow projects to update indexable content of third-party elements.
+        $this->extend('updateContentForSearchIndex', $content);
+        return $content;
+    }
+
     /**
      * Default way to render element in templates. Note that all blocks should
      * be rendered through their {@link ElementController} class as this