Bleeding edge - closure uses $this rule (level 0)

Based on slevomat/coding-standard#734

Author: ondrejmirtes

conf/bleedingEdge.neon

@@ -1,3 +1,4 @@
 parameters:
 	featureToggles:
+		closureUsesThis: true
 		randomIntParameters: true

conf/config.level0.neon

@@ -1,8 +1,12 @@
 parameters:
 	customRulesetUsed: false
 	missingClosureNativeReturnCheckObjectTypehint: false
+	featureToggles:
+		closureUsesThis: false
 
 conditionalTags:
+	PHPStan\Rules\Functions\ClosureUsesThisRule:
+		phpstan.rules.rule: %featureToggles.closureUsesThis%
 	PHPStan\Rules\Missing\MissingClosureNativeReturnTypehintRule:
 		phpstan.rules.rule: %checkMissingClosureNativeReturnTypehintRule%
 
@@ -55,6 +59,9 @@ services:
 		arguments:
 			checkFunctionNameCase: %checkFunctionNameCase%
 
+	-
+		class: PHPStan\Rules\Functions\ClosureUsesThisRule
+
 	-
 		class: PHPStan\Rules\Methods\CallMethodsRule
 		tags:

src/Rules/Functions/ClosureUsesThisRule.php

@@ -0,0 +1,45 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Functions;
+
+use PhpParser\Node;
+use PHPStan\Analyser\Scope;
+use PHPStan\Rules\Rule;
+use PHPStan\Rules\RuleErrorBuilder;
+use PHPStan\Type\ThisType;
+
+/**
+ * @implements Rule<Node\Expr\Closure>
+ */
+class ClosureUsesThisRule implements Rule
+{
+
+	public function getNodeType(): string
+	{
+		return Node\Expr\Closure::class;
+	}
+
+	public function processNode(Node $node, Scope $scope): array
+	{
+		if ($node->static) {
+			return [];
+		}
+
+		$messages = [];
+		foreach ($node->uses as $closureUse) {
+			$varType = $scope->getType($closureUse->var);
+			if (!is_string($closureUse->var->name)) {
+				continue;
+			}
+			if (!$varType instanceof ThisType) {
+				continue;
+			}
+
+			$messages[] = RuleErrorBuilder::message(sprintf('Anonymous function uses $this assigned to variable $%s. Use $this directly in the function body.', $closureUse->var->name))
+				->line($closureUse->getLine())
+				->build();
+		}
+		return $messages;
+	}
+
+}

tests/PHPStan/Rules/Functions/ClosureUsesThisRuleTest.php

@@ -0,0 +1,29 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Functions;
+
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+
+/**
+ * @extends RuleTestCase<ClosureUsesThisRule>
+ */
+class ClosureUsesThisRuleTest extends RuleTestCase
+{
+
+	protected function getRule(): Rule
+	{
+		return new ClosureUsesThisRule();
+	}
+
+	public function testRule(): void
+	{
+		$this->analyse([__DIR__ . '/data/closure-uses-this.php'], [
+			[
+				'Anonymous function uses $this assigned to variable $that. Use $this directly in the function body.',
+				16,
+			],
+		]);
+	}
+
+}

tests/PHPStan/Rules/Functions/data/closure-uses-this.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace ClosureUsesThis;
+
+class Foo
+{
+
+	public function doFoo()
+	{
+		$f = function () { // ok
+
+		};
+
+		$that = $this;
+		$f = function () use (
+			$that
+		) { // report
+
+		};
+
+		$f = static function () use ($that) { // ok
+
+		};
+	}
+
+}