That would require writing a static analyzer which is outside our scope at this 
point. Right now it simply runs the compile-phase and none of the things you are 
asking for can be done by the compiler. The executor can do some of this, but not 
without actually executing the script, which you don't want. The closest thing to 
a full static analyzer is Facebook's HipHop project if you run it in analyze-only 
mode.

That's a shame.  One of the annoying things about not keeping up with every 
single PHP release is that you don't know things are deprecated until you've 
spent time developing and then check the error logs during the testing phase.  
Then you have to either spend time rewriting the code or live with using 
deprecated functions for a while.

You could read the UPGRADING doc we provide with every new release.

I could, but then there's the problem of reading a backlog of upgrading documents 
when I don't religiously update PHP, and also the issue of remembering which 
functions are deprecated and which aren't at the time of programming without 
checking the docs :-)

However, I do understand that this is beyond the scope of the compiler and, 
therefore, the -l command line option.

It's not like there are a lot of them to read:

Mar 2012 PHP 5.4
Jun 2009 PHP 5.3
Nov 2006 PHP 5.2
Nov 2005 PHP 5.1
Jul 2004 PHP 5.0

So 5 of them in the past 9 years or so. We don't deprecate anything in the point 
releases between these.