Added a Model.buildRules event

This will help listeners such as behaviors to inject rules only in a
table lifetime.

src/ORM/Table.php

@@ -83,6 +83,9 @@
  *   $primary parameter indicates whether or not this is the root query,
  *   or an associated query.
  *
+ *   - `buildRules(Event $event, RulesChecker $rules)`
+ *   Allows listeners to modify the rules checker by adding more rules.
+ *
  * - `beforeRules(Event $event, Entity $entity, RulesChecker $rules)`
  *   Fired before an entity is validated using the rules checker. By stopping this event,
  *   you can return the final value of the rules checking operation.
@@ -1876,7 +1879,9 @@ public function rulesChecker() {
 		if ($this->_rulesChecker !== null) {
 			return $this->_rulesChecker;
 		}
-		return $this->_rulesChecker = $this->buildRules(new RulesChecker(['repository' => $this]));
+		$this->_rulesChecker = $this->buildRules(new RulesChecker(['repository' => $this]));
+		$this->dispatchEvent('Model.buildRules', ['rules' => $this->_rulesChecker]);
+		return $this->_rulesChecker;
 	}
 
 /**

tests/TestCase/ORM/RulesCheckerIntegrationTest.php

@@ -429,4 +429,25 @@ public function testUseAfterRules() {
 
 		$this->assertSame($entity, $table->save($entity));
 	}
+
+/**
+ * Tests that rules can be changed using the buildRules event
+ *
+ * @group save
+ * @return void
+ */
+	public function testUseBuildRulesEvent() {
+		$entity = new Entity([
+			'title' => 'An Article',
+			'author_id' => 500
+		]);
+
+		$table = TableRegistry::get('Articles');
+		$table->eventManager()->attach(function ($event, $rules) {
+			$rules->add($rules->existsIn('author_id', TableRegistry::get('Authors'), 'Nope'));
+		}, 'Model.buildRules');
+
+		$this->assertFalse($table->save($entity));
+	}
+
 }