#6840 Report useless array filter

Author: leongersen

conf/config.level5.neon

@@ -8,6 +8,7 @@ parameters:
 rules:
 	- PHPStan\Rules\DateTimeInstantiationRule
 	- PHPStan\Rules\Functions\ImplodeFunctionRule
+	- PHPStan\Rules\Functions\ArrayFilterEmptyRule
 
 services:
 	-

src/Rules/Functions/ArrayFilterEmptyRule.php

@@ -0,0 +1,63 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Functions;
+
+use PhpParser\Node;
+use PhpParser\Node\Expr\FuncCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\ReflectionProvider;
+use PHPStan\Rules\Rule;
+use PHPStan\Rules\RuleErrorBuilder;
+use PHPStan\Type\StaticTypeFactory;
+use PHPStan\Type\VerbosityLevel;
+use function count;
+use function sprintf;
+use function strtolower;
+
+/**
+ * @implements Rule<Node\Expr\FuncCall>
+ */
+class ArrayFilterEmptyRule implements Rule
+{
+
+	public function __construct(private ReflectionProvider $reflectionProvider)
+	{
+	}
+
+	public function getNodeType(): string
+	{
+		return FuncCall::class;
+	}
+
+	public function processNode(Node $node, Scope $scope): array
+	{
+		if (!($node->name instanceof Node\Name)) {
+			return [];
+		}
+
+		if (strtolower($this->reflectionProvider->resolveFunctionName($node->name, $scope)) !== 'array_filter') {
+			return [];
+		}
+
+		$args = $node->getArgs();
+		if (count($args) !== 1) {
+			return [];
+		}
+
+		$arrayType = $scope->getType($args[0]->value);
+		$falsyType = StaticTypeFactory::falsey();
+
+		if ($falsyType->isSuperTypeOf($arrayType->getIterableValueType())->no()) {
+			$message = 'Parameter #1 $array (%s) to function array_filter cannot contain empty values, call has no effect.';
+			return [
+				RuleErrorBuilder::message(sprintf(
+					$message,
+					$arrayType->describe(VerbosityLevel::value()),
+				))->build(),
+			];
+		}
+
+		return [];
+	}
+
+}

tests/PHPStan/Rules/Functions/ArrayFilterEmptyRuleTest.php

@@ -0,0 +1,47 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Functions;
+
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+
+/**
+ * @extends RuleTestCase<ArrayFilterEmptyRule>
+ */
+class ArrayFilterEmptyRuleTest extends RuleTestCase
+{
+
+	protected function getRule(): Rule
+	{
+		return new ArrayFilterEmptyRule($this->createReflectionProvider());
+	}
+
+	public function testFile(): void
+	{
+		$expectedErrors = [
+			[
+				'Parameter #1 $array (array{1, 3}) to function array_filter cannot contain empty values, call has no effect.',
+				10,
+			],
+			[
+				'Parameter #1 $array (array{\'test\'}) to function array_filter cannot contain empty values, call has no effect.',
+				11,
+			],
+			[
+				'Parameter #1 $array (array{true, true}) to function array_filter cannot contain empty values, call has no effect.',
+				17,
+			],
+			[
+				'Parameter #1 $array (array{stdClass}) to function array_filter cannot contain empty values, call has no effect.',
+				18,
+			],
+			[
+				'Parameter #1 $array (array<stdClass>) to function array_filter cannot contain empty values, call has no effect.',
+				20,
+			],
+		];
+
+		$this->analyse([__DIR__ . '/data/array_filter_empty.php'], $expectedErrors);
+	}
+
+}

tests/PHPStan/Rules/Functions/data/array_filter_empty.php

@@ -0,0 +1,21 @@
+<?php
+
+/** @var \stdClass[] $objects */
+$objects = [];
+/** @var array<\stdClass|null> $objectsOrNull */
+$objectsOrNull = [];
+
+array_filter([0]);
+array_filter([0,1,3]);
+array_filter([1,3]);
+array_filter(['test']);
+array_filter(['', 'test']);
+array_filter([null]);
+array_filter([null, 'test']);
+array_filter([false, 'test']);
+array_filter([true, false]);
+array_filter([true, true]);
+array_filter([new \stdClass()]);
+array_filter([new \stdClass(), null]);
+array_filter($objects);
+array_filter($objectsOrNull);