#6840 Report useless array filter

conf/bleedingEdge.neon

@@ -3,5 +3,6 @@ parameters:
 		bleedingEdge: true
 		skipCheckGenericClasses: []
 		explicitMixedInUnknownGenericNew: true
+		arrayFilter: true
 	stubFiles:
 		- ../stubs/bleedingEdge/Countable.stub

conf/config.level5.neon

@@ -5,6 +5,10 @@ parameters:
 	checkFunctionArgumentTypes: true
 	checkArgumentsPassedByReference: true
 
+conditionalTags:
+	PHPStan\Rules\Functions\ArrayFilterRule:
+		phpstan.rules.rule: %featureToggles.arrayFilter%
+
 rules:
 	- PHPStan\Rules\DateTimeInstantiationRule
 	- PHPStan\Rules\Functions\ImplodeFunctionRule
@@ -16,3 +20,6 @@ services:
 			reportMaybes: %reportMaybes%
 		tags:
 			- phpstan.rules.rule
+
+	-
+		class: PHPStan\Rules\Functions\ArrayFilterRule

conf/config.neon

@@ -28,6 +28,7 @@ parameters:
 			- FilterIterator
 			- RecursiveCallbackFilterIterator
 		explicitMixedInUnknownGenericNew: false
+		arrayFilter: false
 	fileExtensions:
 		- php
 	checkAdvancedIsset: false
@@ -205,6 +206,7 @@ parametersSchema:
 		disableRuntimeReflectionProvider: bool(),
 		skipCheckGenericClasses: listOf(string()),
 		explicitMixedInUnknownGenericNew: bool(),
+		arrayFilter: bool(),
 	])
 	fileExtensions: listOf(string())
 	checkAdvancedIsset: bool()

src/Rules/Functions/ArrayFilterRule.php

@@ -0,0 +1,87 @@
+<?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 ArrayFilterRule 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 [];
+		}
+
+		$functionName = $this->reflectionProvider->resolveFunctionName($node->name, $scope);
+
+		if ($functionName === null || strtolower($functionName) !== 'array_filter') {
+			return [];
+		}
+
+		$args = $node->getArgs();
+		if (count($args) !== 1) {
+			return [];
+		}
+
+		$arrayType = $scope->getType($args[0]->value);
+
+		if ($arrayType->isIterableAtLeastOnce()->no()) {
+			$message = 'Parameter #1 $array (%s) to function array_filter is empty, call has no effect.';
+			return [
+				RuleErrorBuilder::message(sprintf(
+					$message,
+					$arrayType->describe(VerbosityLevel::value()),
+				))->build(),
+			];
+		}
+
+		$falsyType = StaticTypeFactory::falsey();
+		$isSuperType = $falsyType->isSuperTypeOf($arrayType->getIterableValueType());
+
+		if ($isSuperType->no()) {
+			$message = 'Parameter #1 $array (%s) to function array_filter does not contain falsy values, the array will always stay the same.';
+			return [
+				RuleErrorBuilder::message(sprintf(
+					$message,
+					$arrayType->describe(VerbosityLevel::value()),
+				))->build(),
+			];
+		}
+
+		if ($isSuperType->yes()) {
+			$message = 'Parameter #1 $array (%s) to function array_filter contains falsy values only, the result will always be an empty array.';
+			return [
+				RuleErrorBuilder::message(sprintf(
+					$message,
+					$arrayType->describe(VerbosityLevel::value()),
+				))->build(),
+			];
+		}
+
+		return [];
+	}
+
+}

tests/PHPStan/Command/data/file-without-errors.php

@@ -1,3 +1,3 @@
 <?php
 
-array_filter([]);
+array_filter([0, 1, 2]);

tests/PHPStan/Rules/Functions/ArrayFilterRuleTest.php

@@ -0,0 +1,71 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Functions;
+
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+
+/**
+ * @extends RuleTestCase<ArrayFilterRule>
+ */
+class ArrayFilterRuleTest extends RuleTestCase
+{
+
+	protected function getRule(): Rule
+	{
+		return new ArrayFilterRule($this->createReflectionProvider());
+	}
+
+	public function testFile(): void
+	{
+		$expectedErrors = [
+			[
+				'Parameter #1 $array (array{1, 3}) to function array_filter does not contain falsy values, the array will always stay the same.',
+				11,
+			],
+			[
+				'Parameter #1 $array (array{\'test\'}) to function array_filter does not contain falsy values, the array will always stay the same.',
+				12,
+			],
+			[
+				'Parameter #1 $array (array{true, true}) to function array_filter does not contain falsy values, the array will always stay the same.',
+				17,
+			],
+			[
+				'Parameter #1 $array (array{stdClass}) to function array_filter does not contain falsy values, the array will always stay the same.',
+				18,
+			],
+			[
+				'Parameter #1 $array (array<stdClass>) to function array_filter does not contain falsy values, the array will always stay the same.',
+				20,
+			],
+			[
+				'Parameter #1 $array (array{0}) to function array_filter contains falsy values only, the result will always be an empty array.',
+				23,
+			],
+			[
+				'Parameter #1 $array (array{null}) to function array_filter contains falsy values only, the result will always be an empty array.',
+				24,
+			],
+			[
+				'Parameter #1 $array (array{null, null}) to function array_filter contains falsy values only, the result will always be an empty array.',
+				25,
+			],
+			[
+				'Parameter #1 $array (array{null, 0}) to function array_filter contains falsy values only, the result will always be an empty array.',
+				26,
+			],
+			[
+				'Parameter #1 $array (array<false|null>) to function array_filter contains falsy values only, the result will always be an empty array.',
+				27,
+			],
+			[
+				'Parameter #1 $array (array{}) to function array_filter is empty, call has no effect.',
+				28,
+			],
+		];
+
+		$this->analyse([__DIR__ . '/data/array_filter_empty.php'], $expectedErrors);
+	}
+
+}

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

@@ -0,0 +1,28 @@
+<?php
+
+/** @var \stdClass[] $objects */
+$objects = [];
+/** @var array<\stdClass|null> $objectsOrNull */
+$objectsOrNull = [];
+/** @var array<false|null> $falsey */
+$falsey = [];
+
+array_filter([0,1,3]);
+array_filter([1,3]);
+array_filter(['test']);
+array_filter(['', 'test']);
+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);
+
+array_filter([0]);
+array_filter([null]);
+array_filter([null, null]);
+array_filter([null, 0]);
+array_filter($falsey);
+array_filter([]);