I have to find out the earliest PHP4 version my code will run under (I already know it runs on PHP5 and on PHP 4.4.9 (the last PHP4 version -- included in MAMP).
Are there code inspection tools that will do this? Do I need to install each PHP version and see what happens :-)
I don't think there is a tool for that. I guess you don't have to install all PHP version, try major releases, like 4.1, 4.2, 4.3, etc To my mind minor releases don't have language syntax changes or anything major, usually it's bug fixes
Before you manually download and install various versions of PHP, try to download the XAMPP versions, that have the old php binaries packaged:
There is a PEAR package for this: PHP_CompatInfo
Find out the minimum version and the extensions required for a piece of code to run
Example: http://pear.php.net/manual/en/package.php.php-compatinfo.basic.php
I use (unit) tests for this purpose.
for v in $versions; do
php$v -f tests.php
done