Add hook_farm_log_prepopulate_reference_fields() to allow modules to provide information about fields that can be prepopulated in log forms.

modules/farm/farm_log/farm_log.api.php

@@ -60,6 +60,22 @@ function hook_farm_log_categories_populate($log) {
   return $categories;
 }
 
+/**
+ * Allow modules to provide information about fields that should be
+ * prepopulated in log forms.
+ *
+ * @return array
+ *   Returns an array of field information.
+ */
+function hook_farm_log_prepopulate_reference_fields() {
+  return array(
+    'field_farm_asset' => array(
+      'entity_type' => 'farm_asset',
+      'url_param' => 'farm_asset',
+    ),
+  );
+}
+
 /**
  * @}
  */

modules/farm/farm_log/farm_log.module

@@ -325,15 +325,12 @@ function farm_log_prepopulate_log_form_name(&$form) {
 }
 
 /**
- * Helper function for populating entity reference fields in log forms.
- *
- * @param array $form
- *   The form array to modify, passed by reference.
+ * Implements hook_farm_log_prepopulate_reference_fields().
  */
-function farm_log_prepopulate_log_form_references(&$form) {
+function farm_log_farm_log_prepopulate_reference_fields() {
 
-  // Define the fields we will be populating.
-  $fields = array(
+  // Define the fields that will be prepopulated in log forms.
+  return array(
     'field_farm_asset' => array(
       'entity_type' => 'farm_asset',
       'url_param' => 'farm_asset',
@@ -352,6 +349,18 @@ function farm_log_prepopulate_log_form_references(&$form) {
       'entity_type' => 'user',
     ),
   );
+}
+
+/**
+ * Helper function for populating entity reference fields in log forms.
+ *
+ * @param array $form
+ *   The form array to modify, passed by reference.
+ */
+function farm_log_prepopulate_log_form_references(&$form) {
+
+  // Ask modules for information about fields that should be prepopulated.
+  $fields = module_invoke_all('farm_log_prepopulate_reference_fields');
 
   // Populate the fields.
   foreach ($fields as $field => $info) {