This script will pre populate all fields with their field ID

prepopulate-id.php

<?php
/**
 * This function will prefill every field with its Field ID number
 * Email, address and phone fields are also supported
 * Radio buttons will select its first option by default.
 *
 * Change the number 8 below to the number of your form. eg: gform_pre_render_FORMID
 *
 *@author Johan De Reiziger
 *@link https://geekontheroad.com
 *
 **/



add_filter( 'gform_pre_render_8', 'auto_fill_form' );

function auto_fill_form($form) {

    $fields = $form["fields"];

    foreach($form["fields"] as $key => $field) {
        if($field["type"] == "text") {
            $field["defaultValue"] = $field["id"];
        } else if($field["type"] == "textarea") {
            $field["defaultValue"] = $field["id"] . " textarea";
        } else if($field["type"] == "email") {
            $field["defaultValue"] = $field["id"]."@example.com";
        } else if($field["type"] == "radio") {
            
            $first = true;
            $choices = array();
            foreach ($field["choices"] as $key => $choice) {
                if ($first == true) {
                    $choices[] = array("text"=>$choice["text"], "value"=>$choice["value"], "isSelected"=>true);
                    $first = false;
                } else {
                    $choices[] = array("text"=>$choice["text"], "value"=>$choice["value"], "isSelected"=>false);
                }               
                
            }
            $field["choices"] = $choices;

        }  else if ($field["type"] == "phone") {
            $field["defaultValue"] = "(513) 122-1132";
            
        } else if ($field["type"] == "address") {
            $inputs = array();
            foreach ($field["inputs"] as $key => $details) {
                //error_log( print_r($details, TRUE) );
                if($details["label"] == "State / Province") {
                    $details["defaultValue"] = "Alabama";
                    $inputs[] = $details;
                    continue;
                }
                $details["defaultValue"] = $field["id"] . $details["label"];
                $inputs[] = $details;
            }
            $field["inputs"] = $inputs;
        }
    }

    return $form;

}

?>