PrettyPrinter:Unnecessary escape in single quoted.

[algo13]

>php-parse --pretty-print "<?php echo 'path\to';
====> Code <?php echo 'path\to';
==> Pretty print:
<?php

echo 'path\\to';

[nikic]

Escaping \ is not unnecessary if you consider something like '\\\''. This parses to string contents \', and printing it as '\\'' would not be correct. This is the cause of the build failure @ https://travis-ci.org/nikic/PHP-Parser/jobs/122780318.

[algo13]

sorry.
It was my mistake.

print \0 ?

>php-parse --pretty-print "<?php echo trim('str', \"\n\");
#!/usr/bin/env php
====> Code <?php echo trim('str', "\n");
==> Pretty print:
<?php

echo trim('str', "\n");

>php-parse --pretty-print "<?php echo trim('str', \"\0\");
====> Code <?php echo trim('str', "\0");
==> Pretty print:
<?php

echo trim('str', " "); //< real \0

[nikic]

Escaping \0 sounds like a good idea. However we should probably escape the entire \0-\37 control character range (excluding the existing \n\r\t\f\v) and not just \0.

[nikic]

Merged as 371c783, extended to the whole control character range.