Disallow empty()

Author: ondrejmirtes

Diff for: README.md

@@ -15,6 +15,7 @@
 * Variables assigned in `while` loop condition and `for` loop initial assignment cannot be used after the loop.
 * Types in `switch` condition and `case` value must match. PHP compares them loosely by default and that can lead to unexpected results.
 * Statically declared methods are called statically.
+* Disallow `empty()` - it's a very loose comparison (see [manual)(https://secure.php.net/manual/en/function.empty.php)), it's recommended to use more strict one.
 
 Additional rules are coming in subsequent releases!
 

Diff for: rules.neon

@@ -8,6 +8,7 @@ rules:
 	- PHPStan\Rules\BooleansInConditions\BooleanInElseIfConditionRule
 	- PHPStan\Rules\BooleansInConditions\BooleanInIfConditionRule
 	- PHPStan\Rules\BooleansInConditions\BooleanInTernaryOperatorRule
+	- PHPStan\Rules\DisallowedConstructs\DisallowedEmptyRule
 	- PHPStan\Rules\StrictCalls\DynamicCallOnStaticMethodsRule
 	- PHPStan\Rules\StrictCalls\StrictFunctionCallsRule
 	- PHPStan\Rules\SwitchConditions\MatchingTypeInSwitchCaseConditionRule

Diff for: src/Rules/DisallowedConstructs/DisallowedEmptyRule.php

@@ -0,0 +1,28 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\DisallowedConstructs;
+
+use PhpParser\Node;
+use PHPStan\Analyser\Scope;
+
+class DisallowedEmptyRule implements \PHPStan\Rules\Rule
+{
+
+	public function getNodeType(): string
+	{
+		return \PhpParser\Node\Expr\Empty_::class;
+	}
+
+	/**
+	 * @param \PhpParser\Node\Expr\Empty_ $node
+	 * @param \PHPStan\Analyser\Scope $scope
+	 * @return string[]
+	 */
+	public function processNode(Node $node, Scope $scope): array
+	{
+		return [
+			'Construct empty() is not allowed. Use more strict comparison.',
+		];
+	}
+
+}

Diff for: tests/Rules/DisallowedConstructs/DisallowedEmptyRuleTest.php

@@ -0,0 +1,25 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\DisallowedConstructs;
+
+use PHPStan\Rules\Rule;
+
+class DisallowedEmptyRuleTest extends \PHPStan\Testing\RuleTestCase
+{
+
+	protected function getRule(): Rule
+	{
+		return new DisallowedEmptyRule();
+	}
+
+	public function testRule(): void
+	{
+		$this->analyse([__DIR__ . '/data/empty.php'], [
+			[
+				'Construct empty() is not allowed. Use more strict comparison.',
+				3,
+			],
+		]);
+	}
+
+}

Diff for: tests/Rules/DisallowedConstructs/data/empty.php

@@ -0,0 +1,5 @@
+<?php
+
+if (empty($test)) {
+
+}