Fixes #15

README.md

@@ -54,4 +54,7 @@ Does not allow for any `else` or `elseif` statements.
 Functions/methods must be 20 lines of code or fewer.
 
 ### Codor.Files.FunctionParameter ###
-Functions/methods must have no more than 3 parameters.
+Functions/methods must have no more than 3 parameters.
+
+### Codor.Files.ReturnNull ###
+Functions/methods must not returl `null`.

src/Codor/Sniffs/Files/ReturnNullSniff.php

@@ -0,0 +1,50 @@
+<?php
+
+namespace Codor\Sniffs\Files;
+
+use PHP_CodeSniffer_Sniff;
+use PHP_CodeSniffer_File;
+
+class ReturnNullSniff implements PHP_CodeSniffer_Sniff
+{
+
+    /**
+     * Returns the token types that this sniff is interested in.
+     * @return array
+     */
+    public function register()
+    {
+        return [T_RETURN];
+    }
+
+    /**
+     * Processes the tokens that this sniff is interested in.
+     *
+     * @param PHP_CodeSniffer_File $phpcsFile The file where the token was found.
+     * @param integer              $stackPtr  The position in the stack where
+     *                                    the token was found.
+     * @return void
+     */
+    public function process(PHP_CodeSniffer_File $phpcsFile, $stackPtr)
+    {
+        $tokens = $phpcsFile->getTokens();
+        $returnTokenIndex = $stackPtr;
+
+        $returnValueToken = '';
+        for ($index = $returnTokenIndex; $index < count($tokens); $index++) {
+            if ($tokens[$index]['type'] === 'T_SEMICOLON') {
+                $returnValueToken = $tokens[$index - 1];
+                break;
+            }
+        }
+
+        if ($returnValueToken == '') {
+            return;
+        }
+
+        if ($returnValueToken['type'] === 'T_NULL') {
+            $error = "Return null value found.";
+            $phpcsFile->addError($error, $stackPtr);
+        }
+    }
+}

tests/Sniffs/Files/Assets/ReturnNullSniff/FunctionThatReturnsNull.inc

@@ -0,0 +1,19 @@
+<?php
+
+function foobar()
+{
+	return null;
+}
+
+function barbaz()
+{
+	return true;
+}
+
+class someClass
+{
+	public function bazbar()
+	{
+		return null;
+	}
+}

tests/Sniffs/Files/ReturnNullSniffTest.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Codor\Tests\Sniffs\ControlStructures;
+
+use Codor\Tests\BaseTestCase;
+
+/** @group Files */
+class ReturnNullSniffTest extends BaseTestCase
+{
+
+    /**
+     * Sets up the test class.
+     * @return void
+     */
+    public function setup()
+    {
+        parent::setup();
+
+        $this->runner->setSniff('Codor.Files.ReturnNull')->setFolder(__DIR__.'/Assets/ReturnNullSniff/');
+    }
+
+    /** @test */
+    public function it_detects_functions_that_return_null()
+    {
+        $results = $this->runner->sniff('FunctionThatReturnsNull.inc');
+        $this->assertEquals(2, $results->getErrorCount());
+        $this->assertEquals(0, $results->getWarningCount());
+    }
+}