PHP: detect undefined variables

PhpStorm has a nice built-in feature: detecting undefined variables.

I’m not a PhpStorm user. I use Sublime Text 2 and I’m not planing to switch to PhpStorm. So I need to detect undefined variables in my code in a different way.

PHPMD can detect undefined variables. Consider this PHP script, FooBar.php:

<?php
class FooBar{
	public function fooBar(){
		print 'foo'.$bar;
	}
}

You can test it with PHPMD like this:

$ phpmd FooBar.php text unusedcode
FooBar.php:4	Avoid unused local variables such as '$bar'.

But think about this:

<?php
class FooBar{
	public function fooBar(){
		print 'foo'.$bar;
		print 'foo'.$bar;
	}
}

PHPMD will not detect $bar as an undefined variable. I used $bar twice but it’s still undefined. PHPMD is not smart enough for this trick. PHP code can be smart. Even if a variable is not defined.

There is another better tool to test PHP code called PHP CodeSniffer.

Add the following lines to your composer.json file to use PHP CodeSniffer with Composer:

"require-dev": {
	"squizlabs/php_codesniffer": "~2.6"
}

You can even install custom plugins for PHP CodeSniffer. To detect undefined variables with PHP CodeSniffer I use the VariableAnalysis plugin.

Install VariableAnalysis:

1. First clone from GitHub to phpcs_variable_analysis:

    $ git clone git@github.com:illusori/PHP_Codesniffer-VariableAnalysis.git phpcs_variable_analysis
   

2. Change into phpcs_variable_analysis directory and run:

    $ ./install.sh -d /path/to/code_sniffer
   

   The path /path/to/code_sniffer can differ. Under OS X and PHP CodeSniffer 2.6.2 the directory is located under /usr/local/Cellar/php-code-sniffer/2.6.2/CodeSniffer. If you like to use it project-based use /path/to/project/vendor/squizlabs/php_codesniffer/CodeSniffer.

   For example:

    $ mkdir -p /usr/local/etc/php-code-sniffer/Standards/Generic/Sniffs/CodeAnalysis
    $ ./install.sh -d /usr/local/etc/php-code-sniffer
    Installing Sniffs to /usr/local/etc/php-code-sniffer/Standards/Generic/Sniffs/CodeAnalysis
   

3. Add VariableAnalysis to the ruleset, ruleset.xml file:

    <rule ref="Generic.CodeAnalysis.VariableAnalysis" />
   

   Unfortunately the whitelist property validUnusedVariableNames isn’t working for closure functions. This can be annoying if you use a lot $this variables. Using @codingStandardsIgnoreLine for the appropriate lines can fix this problem.

Testing the same script as above with PHP CodeSniffer warnings appear:

$ phpcs FooBar.php

FILE: FooBar.php
------------------------------------------------
FOUND 0 ERRORS AND 2 WARNINGS AFFECTING 2 LINES
------------------------------------------------
 4 | WARNING | [ ] Variable $bar is undefined.
 5 | WARNING | [ ] Variable $bar is undefined.
------------------------------------------------

That’s what I want, warnings.