support deprecated magic __toString() in echo statement

src/Rules/Deprecations/EchoDeprecatedToStringRule.php

@@ -0,0 +1,107 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Deprecations;
+
+use PhpParser\Node;
+use PhpParser\Node\Stmt\Echo_;
+use PHPStan\Analyser\Scope;
+use PHPStan\Rules\RuleLevelHelper;
+use PHPStan\Type\ErrorType;
+use PHPStan\Type\ObjectType;
+use PHPStan\Type\Type;
+
+/**
+ * @implements \PHPStan\Rules\Rule<Echo_>
+ */
+class EchoDeprecatedToStringRule implements \PHPStan\Rules\Rule
+{
+
+	/** @var RuleLevelHelper */
+	private $ruleLevelHelper;
+
+	public function __construct(RuleLevelHelper $ruleLevelHelper)
+	{
+		$this->ruleLevelHelper = $ruleLevelHelper;
+	}
+
+	public function getNodeType(): string
+	{
+		return Echo_::class;
+	}
+
+	public function processNode(Node $node, Scope $scope): array
+	{
+		if (DeprecatedScopeHelper::isScopeDeprecated($scope)) {
+			return [];
+		}
+
+		$messages = [];
+
+		foreach ($node->exprs as $key => $expr) {
+			if ($expr instanceof Node\Expr\Variable) {
+				$message = $this->checkExpr($expr, $scope);
+
+				if ($message) {
+					$messages[] = $message;
+				}
+			} elseif ($expr instanceof Node\Expr\BinaryOp\Concat) {
+				$message = $this->checkExpr($expr->left, $scope);
+				if ($message) {
+					$messages[] = $message;
+				}
+
+				$message = $this->checkExpr($expr->right, $scope);
+				if ($message) {
+					$messages[] = $message;
+				}
+			}
+		}
+
+		return $messages;
+	}
+
+	private function checkExpr(Node\Expr $expr, Scope $scope): ?string
+	{
+		$type = $this->ruleLevelHelper->findTypeToCheck(
+			$scope,
+			$expr,
+			'',
+			static function (Type $type): bool {
+				return !$type->toString() instanceof ErrorType;
+			}
+		)->getType();
+
+		if (!$type instanceof ObjectType) {
+			return null;
+		}
+
+		$classReflection = $type->getClassReflection();
+
+		if ($classReflection === null) {
+			return null;
+		}
+
+		$methodReflection = $classReflection->getNativeMethod('__toString');
+
+		if (!$methodReflection->isDeprecated()->yes()) {
+			return null;
+		}
+
+		$description = $methodReflection->getDeprecatedDescription();
+		if ($description === null) {
+			return sprintf(
+				'Call to deprecated method %s() of class %s.',
+				$methodReflection->getName(),
+				$methodReflection->getDeclaringClass()->getName()
+			);
+		}
+
+		return sprintf(
+			"Call to deprecated method %s() of class %s:\n%s",
+			$methodReflection->getName(),
+			$methodReflection->getDeclaringClass()->getName(),
+			$description
+		);
+	}
+
+}

tests/Rules/Deprecations/EchoDeprecatedToStringRuleTest.php

@@ -0,0 +1,38 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Deprecations;
+
+use PHPStan\Rules\RuleLevelHelper;
+
+/**
+ * @extends \PHPStan\Testing\RuleTestCase<EchoDeprecatedToStringRule>
+ */
+class EchoDeprecatedToStringRuleTest extends \PHPStan\Testing\RuleTestCase
+{
+
+	protected function getRule(): \PHPStan\Rules\Rule
+	{
+		$ruleLevelHelper = new RuleLevelHelper($this->createBroker(), true, false, true);
+
+		return new EchoDeprecatedToStringRule($ruleLevelHelper);
+	}
+
+	public function testDeprecatedMagicMethodToStringCall(): void
+	{
+		require_once __DIR__ . '/data/echo-deprecated-magic-method-tostring.php';
+		$this->analyse(
+			[__DIR__ . '/data/echo-deprecated-magic-method-tostring.php'],
+			[
+				[
+					'Call to deprecated method __toString() of class CheckDeprecatedStaticMethodCall\MagicBar.',
+					8,
+				],
+				[
+					'Call to deprecated method __toString() of class CheckDeprecatedStaticMethodCall\MagicBar.',
+					9,
+				],
+			]
+		);
+	}
+
+}

tests/Rules/Deprecations/data/echo-deprecated-magic-method-tostring.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace CheckDeprecatedStaticMethodCall;
+
+function ()
+{
+	$bar = new MagicBar();
+	echo $bar;
+	echo $bar . "hallo";
+};
+
+class MagicBar
+{
+	/**
+	 * @deprecated
+	 */
+	public function __toString()
+	{
+		return 'a string';
+	}
+}