Description:
------------
Very important to know (from log) and to log in which variable (name of the variable) error like "NOTICE (Undefined offset: 1)" occurred! Still it is NOT POSSIBLE!

This is important when one of these situations occur (the more situations occurred the more difficult to detect the exact variable (name)):
1. code changes rapidly (so error line can even mislead without variable name); 
2. variables data is from database (and database changes rapidly in big database so it is impossible to detect in which variable name);
3. there are multiple variables in the same line.

Test script:
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<?php
$A = [1 => ''];
$B = [1 => ''];
$X_variable_name = [];

set_error_handler('log_handler');
function log_handler ( $errno, $errstr,  $errfile, $errline, $errcontext ) {
	$bt = debug_backtrace();
	//print_r($bt);
	$bt0 = (isset($bt[0]) && isset($bt[0]['file']) ? basename(dirname($bt[0]['file'])).'/'.basename($bt[0]['file']).':'.$bt[0]['line'] : '');
	$bt1 = (isset($bt[1]) ? basename(dirname($bt[1]['file'])).'/'.basename($bt[1]['file']).':'.$bt[1]['line'] : '');
	$bt2 = (isset($bt[2]) ? basename(dirname($bt[2]['file'])).'/'.basename($bt[2]['file']).':'.$bt[2]['line'] : '');
	$errorType = [E_ERROR => 'ERROR',E_WARNING  => 'WARNING',E_PARSE  => 'PARSING ERROR',E_NOTICE => 'NOTICE',E_CORE_ERROR => 'CORE ERROR',E_CORE_WARNING   => 'CORE WARNING',E_COMPILE_ERROR  => 'COMPILE ERROR',E_COMPILE_WARNING => 'COMPILE WARNING',E_USER_ERROR  => 'USER ERROR',E_USER_WARNING => 'USER WARNING',E_USER_NOTICE  => 'USER NOTICE',E_STRICT   => 'STRICT NOTICE',E_RECOVERABLE_ERROR  => 'RECOVERABLE ERROR'];
	echo date("y-m-d H:i:s").' '.$errorType[$errno]." ($errstr) ".$errfile.":$errline "./*print_r($errcontext, true).*/' '.$bt0.' 1:'.$bt1.' 2:'.$bt2."\n";
	//debug_print_backtrace();
}
echo $A[1].$B[1].$X_variable_name[1];

Expected result:
----------------
19-05-07 14:07:06 NOTICE (Undefined offset: 1 in variable: X_variable_name) /home/tests/php/error_log.php:65  php/error_log.php:65 1: 2:


Actual result:
--------------
19-05-07 14:07:06 NOTICE (Undefined offset: 1) /home/tests/php/error_log.php:65  php/error_log.php:65 1: 2: