Fix error message for non-existent bootstrap file

[johnmaguire]

PHP_CodeSniffer::realpath() either returns false, or a file path. We don't need to check file_exists() because PHP_CodeSniffer::realpath() does it for us. However, we do want to show a proper filename in the event that the referenced file does not exist.

[johnmaguire]

Additionally, I ran into another bug, but I'm less sure how to solve it properly.

One of the ways I was planning to utilize this functionality was by adding the a <arg> directive to our ruleset.xml. Unfortunately there are a couple issues with this:

1. I can't come up with a good way to resolve the path in relation to the ruleset.xml. i.e. I'm imaginging a bootstrap.php shipped in the same directory as ruleset.xml. PHP_CodeSniffer::realpath() currently has no concept of this. I'm not sure if there's an easy way to add it? It would require knowing which ruleset.xml is currently being parsed at the time we parse the bootstrap argument. This is a bit of a misnomer though because PHP_CodeSniffer can process multiple ruleset.xml's, and for all we know --bootstrap was passed via a command-line argument.
2. Sort of on the same vein, <arg name="bootstrap" value="~/path/to/standard/bootstrap.php"/> currently does not work. I did a little bit of tracing, and I think it has to do with the fact that although command-line arguments are evaluated prior to process() being called, the arg from ruleset.xml does not appear to be.

For point 2, I had added a log of $this->values just after the $this->setCommandLineValues($args) call in getCommandLineValues() on line 377, and saw that it had parsed the standard and other values I had passed in via CLI, but had (I suppose obviously) not interpreted the args out of the ruleset.xml yet.

I added a log in process() prior to the bootstrap inclusion loop and found the same thing.

However, it does eventually get parsed. I know because I get an error for a non-existent file, for example. Any direction on where I might look to fix this issue would be appreciated. :)

And thank you for this project.

[gsherwood]

Thanks for the fix. I also moved the bootstrap file inclusion down to just before the run starts so you can specify it in a ruleset, although you're not going to be able to include it using a relative path just yet. I think that would require a specific bootstrap tag in the ruleset so special processing can take place inside the ruleset processing code. If you need that feature, open a new issue and we can track it there.