Loosen up ArrayFilterStrictRule for unions with clearly truthy/falsey…

… types

src/Rules/Functions/ArrayFilterStrictRule.php

@@ -12,6 +12,7 @@
 use PHPStan\Rules\Rule;
 use PHPStan\Rules\RuleErrorBuilder;
 use PHPStan\Type\Type;
+use PHPStan\Type\UnionType;
 use PHPStan\Type\VerbosityLevel;
 use function count;
 use function sprintf;
@@ -82,6 +83,41 @@ public function processNode(Node $node, Scope $scope): array
 		}
 
 		if (count($args) === 1) {
+			if ($this->treatPhpDocTypesAsCertain) {
+				$arrayType = $scope->getType($args[0]->value);
+			} else {
+				$arrayType = $scope->getNativeType($args[0]->value);
+			}
+
+			$itemType = $arrayType->getIterableValueType();
+			if ($itemType instanceof UnionType) {
+				$hasTruthy = false;
+				$hasFalsey = false;
+				foreach ($itemType->getTypes() as $innerType) {
+					$booleanType = $innerType->toBoolean();
+					if ($booleanType->isTrue()->yes()) {
+						$hasTruthy = true;
+						continue;
+					}
+					if ($booleanType->isFalse()->yes()) {
+						$hasFalsey = true;
+						continue;
+					}
+
+					$hasTruthy = false;
+					$hasFalsey = false;
+					break;
+				}
+
+				if ($hasTruthy && $hasFalsey) {
+					return [];
+				}
+			} elseif ($itemType->isBoolean()->yes()) {
+				return [];
+			} elseif ($itemType->isArray()->yes()) {
+				return [];
+			}
+
 			return [RuleErrorBuilder::message('Call to function array_filter() requires parameter #2 to be passed to avoid loose comparison semantics.')->build()];
 		}
 

tests/Rules/Functions/ArrayFilterStrictRuleTest.php

@@ -55,4 +55,24 @@ public function testRule(): void
 		]);
 	}
 
+	public function testRuleAllowMissingCallbackInSomeCases(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->checkNullables = true;
+		$this->analyse([__DIR__ . '/data/array-filter-allow.php'], [
+			[
+				'Call to function array_filter() requires parameter #2 to be passed to avoid loose comparison semantics.',
+				27,
+			],
+			[
+				'Call to function array_filter() requires parameter #2 to be passed to avoid loose comparison semantics.',
+				37,
+			],
+			[
+				'Call to function array_filter() requires parameter #2 to be passed to avoid loose comparison semantics.',
+				49,
+			],
+		]);
+	}
+
 }

tests/Rules/Functions/data/array-filter-allow.php

@@ -0,0 +1,58 @@
+<?php
+
+namespace ArrayFilterAllow;
+
+use function array_filter;
+
+class Foo
+{
+
+	/**
+	 * @param array<self|null> $a
+	 */
+	public function doFoo(
+		array $a
+	): array
+	{
+		return array_filter($a);
+	}
+
+	/**
+	 * @param array<self> $a
+	 */
+	public function doFoo2(
+		array $a
+	): array
+	{
+		return array_filter($a);
+	}
+
+	/**
+	 * @param array<int|null> $a
+	 */
+	public function doFoo3(
+		array $a
+	): array
+	{
+		return array_filter($a);
+	}
+
+	/** @param array<bool> $a */
+	public function doFoo4(array $a): array
+	{
+		return array_filter($a);
+	}
+
+	/** @param array<int> $a */
+	public function doFoo5(array $a): array
+	{
+		return array_filter($a);
+	}
+
+	/** @param array<array<int>> $a */
+	public function doFoo6(array $a): array
+	{
+		return array_filter($a);
+	}
+
+}