Log plugin activation errors to a file

wp-config.php

<?php
// Add this to the bottom of wp-config.php to log plugin activation errors:

add_action( 'activated_plugin','fpt_save_error' );
function fpt_save_error( $tmp_plugin ) {
	$out_txt  = PHP_EOL . date( "Y/m/d H:i" ) . ' Plugin activation: ' . $tmp_plugin . ' ---messages--->' . PHP_EOL;
	$out_txt .= ob_get_contents();
	$out_txt .= PHP_EOL . '<---- end plugin activation ---' . PHP_EOL;
	file_put_contents( ABSPATH. 'wp-content/uploads/plugin_activation.log', $out_txt, FILE_APPEND );
}