Report useless return values of function calls

Author: staabm

src/Rules/FunctionCallParametersCheck.php

@@ -4,6 +4,7 @@
 
 use PhpParser\Node;
 use PhpParser\Node\Expr;
+use PHPStan\Analyser\ArgumentsNormalizer;
 use PHPStan\Analyser\MutatingScope;
 use PHPStan\Analyser\Scope;
 use PHPStan\Php\PhpVersion;
@@ -29,6 +30,7 @@
 use function array_key_exists;
 use function count;
 use function implode;
+use function in_array;
 use function is_string;
 use function max;
 use function sprintf;
@@ -53,7 +55,7 @@ public function __construct(
 
 	/**
 	 * @param Node\Expr\FuncCall|Node\Expr\MethodCall|Node\Expr\StaticCall|Node\Expr\New_ $funcCall
-	 * @param array{0: string, 1: string, 2: string, 3: string, 4: string, 5: string, 6: string, 7: string, 8: string, 9: string, 10: string, 11: string, 12: string, 13?: string} $messages
+	 * @param array{0: string, 1: string, 2: string, 3: string, 4: string, 5: string, 6: string, 7: string, 8: string, 9: string, 10: string, 11: string, 12: string, 13?: string, 14?: string} $messages
 	 * @param 'attribute'|'callable'|'method'|'staticMethod'|'function'|'new' $nodeType
 	 * @return list<IdentifierRuleError>
 	 */
@@ -244,6 +246,30 @@ public function check(
 				->build();
 		}
 
+		if (
+			$funcCall instanceof Expr\FuncCall
+			&& isset($messages[14])
+			&& !$scope->isInFirstLevelStatement()
+			&& $funcCall->name instanceof Node\Name
+			&& in_array($funcCall->name->toString(), ['var_export', 'print_r', 'highlight_string', 'highlight_file'], true)
+		) {
+			$reorderedFuncCall = ArgumentsNormalizer::reorderFuncArguments(
+				$parametersAcceptor,
+				$funcCall,
+			);
+
+			if ($reorderedFuncCall !== null) {
+				$reorderedArgs = $reorderedFuncCall->getArgs();
+
+				if (count($reorderedArgs) === 1 || (count($reorderedArgs) >= 2 && $scope->getType($reorderedArgs[1]->value)->isFalse()->yes())) {
+					$errors[] = RuleErrorBuilder::message($messages[14])
+						->identifier(sprintf('%s.uselessReturn', $nodeType))
+						->line($funcCall->getStartLine())
+						->build();
+				}
+			}
+		}
+
 		[$addedErrors, $argumentsWithParameters] = $this->processArguments($parametersAcceptor, $funcCall->getStartLine(), $isBuiltin, $arguments, $hasNamedArguments, $messages[10], $messages[11]);
 		foreach ($addedErrors as $error) {
 			$errors[] = $error;

src/Rules/Functions/CallToFunctionParametersRule.php

@@ -64,6 +64,7 @@ public function processNode(Node $node, Scope $scope): array
 				'Unknown parameter $%s in call to function ' . $functionName . '.',
 				'Return type of call to function ' . $functionName . ' contains unresolvable type.',
 				'Parameter %s of function ' . $functionName . ' contains unresolvable type.',
+				'Return value of call to function ' . $functionName . ' is useless.',
 			],
 			'function',
 		);

tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php

@@ -1716,4 +1716,36 @@ public function testCountArrayShift(): void
 		$this->analyse([__DIR__ . '/data/count-array-shift.php'], $errors);
 	}
 
+	public function testUselessReturnValue(): void
+	{
+		$this->analyse([__DIR__ . '/data/useless-fn-return.php'], [
+			[
+				'Return value of call to function print_r is useless.',
+				47,
+			],
+			[
+				'Return value of call to function var_export is useless.',
+				56,
+			],
+			[
+				'Return value of call to function print_r is useless.',
+				64,
+			],
+		]);
+	}
+
+	public function testUselessReturnValuePhp8(): void
+	{
+		if (PHP_VERSION_ID < 80000) {
+			return;
+		}
+
+		$this->analyse([__DIR__ . '/data/useless-fn-return-php8.php'], [
+			[
+				'Return value of call to function print_r is useless.',
+				18,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Functions/data/useless-fn-return-php8.php

@@ -0,0 +1,24 @@
+<?php // lint >= 8.0
+
+namespace UselessFunctionReturnPhp8;
+
+class FooClass
+{
+	public function explicitReturnNamed(): void
+	{
+		error_log("Email-Template couldn't be found by parameters:" . print_r(return: true, value: [
+				'template' => 1,
+				'spracheid' => 2,
+			])
+		);
+	}
+
+	public function explicitNoReturnNamed(): void
+	{
+		error_log("Email-Template couldn't be found by parameters:" . print_r(return: false, value: [
+				'template' => 1,
+				'spracheid' => 2,
+			])
+		);
+	}
+}

tests/PHPStan/Rules/Functions/data/useless-fn-return.php

@@ -0,0 +1,71 @@
+<?php
+
+namespace UselessFunctionReturn;
+
+class FooClass
+{
+	public function fine(bool $bool): void
+	{
+		error_log(
+			"Email-Template couldn't be found by parameters:" . print_r([
+				'template' => 1,
+				'spracheid' => 2,
+			], true)
+		);
+
+		$x = print_r([
+			'template' => 1,
+			'spracheid' => 2,
+		], true);
+
+		print_r([
+			'template' => 1,
+			'spracheid' => 2,
+		]);
+
+		error_log(
+			"Email-Template couldn't be found by parameters:" . print_r([
+				'template' => 1,
+				'spracheid' => 2,
+			], $bool)
+		);
+
+		print_r([
+			'template' => 1,
+			'spracheid' => 2,
+		], $bool);
+
+		$x = print_r([
+			'template' => 1,
+			'spracheid' => 2,
+		], $bool);
+	}
+
+	public function missesReturn(): void
+	{
+		error_log(
+			"Email-Template couldn't be found by parameters:" . print_r([
+				'template' => 1,
+				'spracheid' => 2,
+			])
+		);
+	}
+
+	public function missesReturnVarDump(): string
+	{
+		return "Email-Template couldn't be found by parameters:" . var_export([
+				'template' => 1,
+				'spracheid' => 2,
+			]);
+	}
+
+	public function explicitNoReturn(): void
+	{
+		error_log("Email-Template couldn't be found by parameters:" . print_r([
+				'template' => 1,
+				'spracheid' => 2,
+			], false)
+		);
+	}
+
+}