While loop - condition always false

Author: ondrejmirtes

conf/config.level4.neon

@@ -137,6 +137,13 @@ services:
 		tags:
 			- phpstan.rules.rule
 
+	-
+		class: PHPStan\Rules\Comparison\WhileLoopAlwaysFalseConditionRule
+		arguments:
+			treatPhpDocTypesAsCertain: %treatPhpDocTypesAsCertain%
+		tags:
+			- phpstan.rules.rule
+
 	-
 		class: PHPStan\Rules\TooWideTypehints\TooWideMethodReturnTypehintRule
 		arguments:

src/Rules/Comparison/WhileLoopAlwaysFalseConditionRule.php

@@ -0,0 +1,62 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Comparison;
+
+use PhpParser\Node\Stmt\While_;
+use PHPStan\Rules\RuleErrorBuilder;
+use PHPStan\Type\Constant\ConstantBooleanType;
+
+/**
+ * @implements \PHPStan\Rules\Rule<While_>
+ */
+class WhileLoopAlwaysFalseConditionRule implements \PHPStan\Rules\Rule
+{
+
+	private ConstantConditionRuleHelper $helper;
+
+	private bool $treatPhpDocTypesAsCertain;
+
+	public function __construct(
+		ConstantConditionRuleHelper $helper,
+		bool $treatPhpDocTypesAsCertain
+	)
+	{
+		$this->helper = $helper;
+		$this->treatPhpDocTypesAsCertain = $treatPhpDocTypesAsCertain;
+	}
+
+	public function getNodeType(): string
+	{
+		return While_::class;
+	}
+
+	public function processNode(
+		\PhpParser\Node $node,
+		\PHPStan\Analyser\Scope $scope
+	): array
+	{
+		$exprType = $this->helper->getBooleanType($scope, $node->cond);
+		if ($exprType instanceof ConstantBooleanType && !$exprType->getValue()) {
+			$addTip = function (RuleErrorBuilder $ruleErrorBuilder) use ($scope, $node): RuleErrorBuilder {
+				if (!$this->treatPhpDocTypesAsCertain) {
+					return $ruleErrorBuilder;
+				}
+
+				$booleanNativeType = $this->helper->getNativeBooleanType($scope, $node->cond);
+				if ($booleanNativeType instanceof ConstantBooleanType) {
+					return $ruleErrorBuilder;
+				}
+
+				return $ruleErrorBuilder->tip('Because the type is coming from a PHPDoc, you can turn off this check by setting <fg=cyan>treatPhpDocTypesAsCertain: false</> in your <fg=cyan>%configurationFile%</>.');
+			};
+
+			return [
+				$addTip(RuleErrorBuilder::message('While loop condition is always false.'))->line($node->cond->getLine())
+					->build(),
+			];
+		}
+
+		return [];
+	}
+
+}

tests/PHPStan/Rules/Comparison/WhileLoopAlwaysFalseConditionRuleTest.php

@@ -0,0 +1,50 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Comparison;
+
+/**
+ * @extends \PHPStan\Testing\RuleTestCase<WhileLoopAlwaysFalseConditionRule>
+ */
+class WhileLoopAlwaysFalseConditionRuleTest extends \PHPStan\Testing\RuleTestCase
+{
+
+	/** @var bool */
+	private $treatPhpDocTypesAsCertain = true;
+
+	protected function getRule(): \PHPStan\Rules\Rule
+	{
+		return new WhileLoopAlwaysFalseConditionRule(
+			new ConstantConditionRuleHelper(
+				new ImpossibleCheckTypeHelper(
+					$this->createReflectionProvider(),
+					$this->getTypeSpecifier(),
+					[],
+					$this->treatPhpDocTypesAsCertain
+				),
+				$this->treatPhpDocTypesAsCertain
+			),
+			$this->treatPhpDocTypesAsCertain
+		);
+	}
+
+	protected function shouldTreatPhpDocTypesAsCertain(): bool
+	{
+		return $this->treatPhpDocTypesAsCertain;
+	}
+
+	public function testRule(): void
+	{
+		$this->analyse([__DIR__ . '/data/while-loop-false.php'], [
+			[
+				'While loop condition is always false.',
+				10,
+			],
+			[
+				'While loop condition is always false.',
+				20,
+				'Because the type is coming from a PHPDoc, you can turn off this check by setting <fg=cyan>treatPhpDocTypesAsCertain: false</> in your <fg=cyan>%configurationFile%</>.',
+			],
+		]);
+	}
+
+}

tests/PHPStan/Rules/Comparison/data/while-loop-false.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace WhileLoopFalse;
+
+class Foo
+{
+
+	public function doFoo(): void
+	{
+		while (false) {
+
+		}
+	}
+
+	/**
+	 * @param 0 $s
+	 */
+	public function doBar($s): void
+	{
+		while ($s) {
+
+		}
+	}
+
+	/**
+	 * @param string $s
+	 */
+	public function doBar2($s): void
+	{
+		while ($s === null) { // reported by StrictComparisonOfDifferentTypesRule
+
+		}
+	}
+
+}