Fix for handling non-stringable types in dynamic variable access

Author: zonuexe

src/Rules/Variables/DefinedVariableRule.php

@@ -5,8 +5,13 @@
 use PhpParser\Node;
 use PhpParser\Node\Expr\Variable;
 use PHPStan\Analyser\Scope;
+use PHPStan\Rules\IdentifierRuleError;
 use PHPStan\Rules\Rule;
 use PHPStan\Rules\RuleErrorBuilder;
+use PHPStan\Type\Constant\ConstantStringType;
+use PHPStan\Type\VerbosityLevel;
+use function array_map;
+use function array_merge;
 use function in_array;
 use function is_string;
 use function sprintf;
@@ -31,11 +36,33 @@ public function getNodeType(): string
 
 	public function processNode(Node $node, Scope $scope): array
 	{
-		if (!is_string($node->name)) {
-			return [];
+		$errors = [];
+		if (is_string($node->name)) {
+			$variableNames = [$node->name];
+		} else {
+			$fetchType = $scope->getType($node->name);
+			$variableNames = array_map(static fn (ConstantStringType $type): string => $type->getValue(), $fetchType->getConstantStrings());
+			$fetchStringType = $fetchType->toString();
+			if (! $fetchStringType->isString()->yes()) {
+				$errors[] = RuleErrorBuilder::message(sprintf('Cannot access variable with a non-stringable type %s.', $fetchType->describe(VerbosityLevel::typeOnly())))
+					->identifier('variable.fetchInvalidExpression')
+					->build();
+			}
+		}
+
+		foreach ($variableNames as $name) {
+			$errors = array_merge($errors, $this->processSingleVariable($scope, $node, $name));
 		}
 
-		if ($this->cliArgumentsVariablesRegistered && in_array($node->name, [
+		return $errors;
+	}
+
+	/**
+	 * @return list<IdentifierRuleError>
+	 */
+	private function processSingleVariable(Scope $scope, Variable $node, string $variableName): array
+	{
+		if ($this->cliArgumentsVariablesRegistered && in_array($variableName, [
 			'argc',
 			'argv',
 		], true)) {
@@ -49,18 +76,18 @@ public function processNode(Node $node, Scope $scope): array
 			return [];
 		}
 
-		if ($scope->hasVariableType($node->name)->no()) {
+		if ($scope->hasVariableType($variableName)->no()) {
 			return [
-				RuleErrorBuilder::message(sprintf('Undefined variable: $%s', $node->name))
+				RuleErrorBuilder::message(sprintf('Undefined variable: $%s', $variableName))
 					->identifier('variable.undefined')
 					->build(),
 			];
 		} elseif (
 			$this->checkMaybeUndefinedVariables
-			&& !$scope->hasVariableType($node->name)->yes()
+			&& !$scope->hasVariableType($variableName)->yes()
 		) {
 			return [
-				RuleErrorBuilder::message(sprintf('Variable $%s might not be defined.', $node->name))
+				RuleErrorBuilder::message(sprintf('Variable $%s might not be defined.', $variableName))
 					->identifier('variable.undefined')
 					->build(),
 			];

tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php

@@ -971,6 +971,32 @@ public function testBug9474(): void
 		$this->analyse([__DIR__ . '/data/bug-9474.php'], []);
 	}
 
+	public function testBug9475(): void
+	{
+		$this->cliArgumentsVariablesRegistered = true;
+		$this->polluteScopeWithLoopInitialAssignments = true;
+		$this->checkMaybeUndefinedVariables = true;
+		$this->polluteScopeWithAlwaysIterableForeach = true;
+		$this->analyse([__DIR__ . '/data/bug-9475.php'], [
+			[
+				'Cannot access variable with a non-stringable type $this(Bug9475\Variables).',
+				12,
+			],
+			[
+				'Cannot access variable with a non-stringable type $this(Bug9475\Variables).',
+				13,
+			],
+			[
+				'Cannot access variable with a non-stringable type object.',
+				14,
+			],
+			[
+				'Cannot access variable with a non-stringable type array.',
+				15,
+			],
+		]);
+	}
+
 	public function testEnum(): void
 	{
 		if (PHP_VERSION_ID < 80100) {

tests/PHPStan/Rules/Variables/data/bug-9475.php

@@ -0,0 +1,21 @@
+<?php declare(strict_types = 1);
+
+namespace Bug9475;
+
+use Stringable;
+
+final class Variables
+{
+
+	public function test(string $name, Stringable $stringable, object $object, array $array): void
+	{
+		echo 'Hello, ' . $$this;
+		echo 'Hello, ' . ${$this};
+		echo 'Hello, ' . ${$object};
+		echo 'Hello, ' . ${$array};
+
+		echo 'Hello, ' . ${$name}; // valid
+		echo 'Hello, ' . ${$stringable}; // valid
+	}
+
+}