Add null to array_map() callback parameters of shorter arrays

src/Analyser/ExprHandler/Helper/ContextualClosureParameterResolver.php

@@ -13,6 +13,7 @@
 use PHPStan\Parser\ArrowFunctionArgVisitor;
 use PHPStan\Parser\ClosureArgVisitor;
 use PHPStan\Parser\ImmediatelyInvokedClosureVisitor;
+use PHPStan\Reflection\ArrayMapCallbackParameterTypes;
 use PHPStan\Reflection\Native\NativeParameterReflection;
 use PHPStan\Reflection\ParameterReflection;
 use PHPStan\Reflection\PassedByReference;
@@ -90,17 +91,38 @@ public function resolve(
 			);
 		}
 
-		$parameters = [];
-		$nativeParameters = [];
+		$types = [];
+		$nativeTypes = [];
+		$arrayTypes = [];
+		$nativeArrayTypes = [];
+		$hasUnpackedArg = false;
 		foreach ($intrinsicArgs as $arg) {
+			$hasUnpackedArg = $hasUnpackedArg || $arg->unpack;
 			$result = $storage !== null ? $storage->findExpressionResult($arg->value) : null;
 			$type = $result !== null ? $result->getType() : $this->nodeScopeResolver->readScopeStateOrSyntheticType($arg->value, $scope);
 			$nativeType = $result !== null ? $result->getNativeType() : $this->nodeScopeResolver->readScopeStateOrSyntheticType($arg->value, $scope->doNotTreatPhpDocTypesAsCertain());
 			if ($arrayMapArgs !== null) {
+				$arrayTypes[] = $type;
+				$nativeArrayTypes[] = $nativeType;
 				$type = $type->getIterableValueType();
 				$nativeType = $nativeType->getIterableValueType();
 			}
+			$types[] = $type;
+			$nativeTypes[] = $nativeType;
+		}
+
+		// an unpacked arg is one parameter here, so its arrays cannot be told apart
+		if ($arrayMapArgs !== null && !$hasUnpackedArg) {
+			$types = ArrayMapCallbackParameterTypes::addPaddingNull($types, $arrayTypes);
+			$nativeTypes = ArrayMapCallbackParameterTypes::addPaddingNull($nativeTypes, $nativeArrayTypes);
+		}
+
+		$parameters = [];
+		foreach ($types as $type) {
 			$parameters[] = new DummyParameter('item', $type, optional: false, passedByReference: PassedByReference::createNo(), variadic: false, defaultValue: null);
+		}
+		$nativeParameters = [];
+		foreach ($nativeTypes as $nativeType) {
 			$nativeParameters[] = new DummyParameter('item', $nativeType, optional: false, passedByReference: PassedByReference::createNo(), variadic: false, defaultValue: null);
 		}
 

src/Reflection/ArrayMapCallbackParameterTypes.php

@@ -0,0 +1,70 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Reflection;
+
+use PHPStan\Turbo\ReferencedByTurboExtension;
+use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
+use function count;
+use function is_int;
+use function max;
+
+/**
+ * With more than one array, array_map() calls the callback once per index of
+ * the longest array, and passes null for each array that is shorter.
+ */
+#[ReferencedByTurboExtension(key: 'arrayMapCallbackParameterTypes')]
+final class ArrayMapCallbackParameterTypes
+{
+
+	/**
+	 * Adds null to the value type of each array that is shorter than another one
+	 * when both have their largest size. Only when the size of every array is known.
+	 *
+	 * The largest sizes are compared, not the smallest, because two arrays can be
+	 * one array: array_map($cb, $a, $a) never passes null, whatever sizes $a can have.
+	 *
+	 * @param list<Type> $valueTypes
+	 * @param list<Type> $arrayTypes the array each value type comes from
+	 * @return list<Type>
+	 */
+	public static function addPaddingNull(array $valueTypes, array $arrayTypes): array
+	{
+		if (count($arrayTypes) < 2) {
+			return $valueTypes;
+		}
+
+		$maxSizes = [];
+		foreach ($arrayTypes as $i => $arrayType) {
+			$sizes = [];
+			foreach ($arrayType->getArraySize()->getFiniteTypes() as $sizeType) {
+				foreach ($sizeType->getConstantScalarValues() as $size) {
+					if (!is_int($size)) {
+						continue;
+					}
+
+					$sizes[] = $size;
+				}
+			}
+
+			if ($sizes === []) {
+				// general arrays can have the same size, but the type system cannot say so
+				return $valueTypes;
+			}
+
+			$maxSizes[$i] = max($sizes);
+		}
+
+		$longestSize = max($maxSizes);
+		foreach ($valueTypes as $i => $valueType) {
+			if ($maxSizes[$i] === $longestSize) {
+				continue;
+			}
+
+			$valueTypes[$i] = TypeCombinator::addNull($valueType);
+		}
+
+		return $valueTypes;
+	}
+
+}

src/Reflection/ParametersAcceptorSelector.php

@@ -206,8 +206,10 @@ public static function applyIntrinsicArgOverrides(
 		) {
 			$arrayMapArgs = $args[0]->value->getAttribute(ArrayMapArgVisitor::ATTRIBUTE_NAME);
 			if ($arrayMapArgs !== null) {
-				$callbackParameters = [];
-				$nativeCallbackParameters = [];
+				$callbackValueTypes = [];
+				$callbackArrayTypes = [];
+				$nativeCallbackValueTypes = [];
+				$nativeCallbackArrayTypes = [];
 				foreach ($arrayMapArgs as $arg) {
 					$argType = ($typeGetter)($arg->value);
 					$nativeArgType = ($nativeTypeGetter)($arg->value);
@@ -217,7 +219,8 @@ public static function applyIntrinsicArgOverrides(
 							foreach ($constantArrays as $constantArray) {
 								$valueTypes = $constantArray->getValueTypes();
 								foreach ($valueTypes as $valueType) {
-									$callbackParameters[] = new DummyParameter('item', ($iterableValueTypeGetter)($valueType), optional: false, passedByReference: PassedByReference::createNo(), variadic: false, defaultValue: null);
+									$callbackValueTypes[] = ($iterableValueTypeGetter)($valueType);
+									$callbackArrayTypes[] = $valueType;
 								}
 							}
 						}
@@ -226,16 +229,28 @@ public static function applyIntrinsicArgOverrides(
 							foreach ($nativeConstantArrays as $constantArray) {
 								$valueTypes = $constantArray->getValueTypes();
 								foreach ($valueTypes as $valueType) {
-									$nativeCallbackParameters[] = new DummyParameter('item', ($iterableValueTypeGetter)($valueType), optional: false, passedByReference: PassedByReference::createNo(), variadic: false, defaultValue: null);
+									$nativeCallbackValueTypes[] = ($iterableValueTypeGetter)($valueType);
+									$nativeCallbackArrayTypes[] = $valueType;
 								}
 							}
 						}
 					} else {
-						$callbackParameters[] = new DummyParameter('item', ($iterableValueTypeGetter)($argType), optional: false, passedByReference: PassedByReference::createNo(), variadic: false, defaultValue: null);
-						$nativeCallbackParameters[] = new DummyParameter('item', ($iterableValueTypeGetter)($nativeArgType), optional: false, passedByReference: PassedByReference::createNo(), variadic: false, defaultValue: null);
+						$callbackValueTypes[] = ($iterableValueTypeGetter)($argType);
+						$callbackArrayTypes[] = $argType;
+						$nativeCallbackValueTypes[] = ($iterableValueTypeGetter)($nativeArgType);
+						$nativeCallbackArrayTypes[] = $nativeArgType;
 					}
 				}
 
+				$callbackParameters = [];
+				foreach (ArrayMapCallbackParameterTypes::addPaddingNull($callbackValueTypes, $callbackArrayTypes) as $valueType) {
+					$callbackParameters[] = new DummyParameter('item', $valueType, optional: false, passedByReference: PassedByReference::createNo(), variadic: false, defaultValue: null);
+				}
+				$nativeCallbackParameters = [];
+				foreach (ArrayMapCallbackParameterTypes::addPaddingNull($nativeCallbackValueTypes, $nativeCallbackArrayTypes) as $valueType) {
+					$nativeCallbackParameters[] = new DummyParameter('item', $valueType, optional: false, passedByReference: PassedByReference::createNo(), variadic: false, defaultValue: null);
+				}
+
 				$acceptor = $parametersAcceptors[0];
 				$parameters = $acceptor->getParameters();
 				if (isset($parameters[0])) {

src/Type/Php/ArrayMapFunctionReturnTypeExtension.php

@@ -8,6 +8,7 @@
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Node\Expr\TypeExpr;
 use PHPStan\Parser\ArrayMapArgVisitor;
+use PHPStan\Reflection\ArrayMapCallbackParameterTypes;
 use PHPStan\Reflection\FunctionReflection;
 use PHPStan\TrinaryLogic;
 use PHPStan\Type\Accessory\AccessoryArrayListType;
@@ -25,6 +26,7 @@
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
 use PHPStan\Type\TypeUtils;
+use function array_filter;
 use function array_map;
 use function array_reduce;
 use function array_slice;
@@ -53,11 +55,17 @@ public function getTypeFromFunctionCall(FunctionReflection $functionReflection,
 		$callableIsNull = $callableType->isNull()->yes();
 
 		if ($callableType->isCallable()->yes()) {
+			$arrayArgs = array_slice($args, 1);
+			$arrayTypes = array_map(static fn (Node\Arg $arg) => $scope->getType($arg->value), $arrayArgs);
+			$callbackValueTypes = array_map(static fn (Type $arrayType) => $arrayType->getIterableValueType(), $arrayTypes);
+			if (count(array_filter($arrayArgs, static fn (Node\Arg $arg) => $arg->unpack)) === 0) {
+				$callbackValueTypes = ArrayMapCallbackParameterTypes::addPaddingNull($callbackValueTypes, $arrayTypes);
+			}
 			$valueType = $scope->getType(new FuncCall(
 				$callback,
 				array_map(
-					static fn (Node\Arg $arg) => new Node\Arg(new TypeExpr($scope->getType($arg->value)->getIterableValueType())),
-					array_slice($args, 1),
+					static fn (Type $valueType) => new Node\Arg(new TypeExpr($valueType)),
+					$callbackValueTypes,
 				),
 			));
 		} elseif ($callableIsNull) {

src/Type/Php/ArrayMapParameterClosureTypeExtension.php

@@ -5,6 +5,7 @@
 use PhpParser\Node\Expr\FuncCall;
 use PHPStan\Analyser\Scope;
 use PHPStan\DependencyInjection\AutowiredService;
+use PHPStan\Reflection\ArrayMapCallbackParameterTypes;
 use PHPStan\Reflection\FunctionReflection;
 use PHPStan\Reflection\Native\NativeParameterReflection;
 use PHPStan\Reflection\ParameterReflection;
@@ -31,7 +32,8 @@ public function getTypeFromFunctionCall(FunctionReflection $functionReflection,
 			return null;
 		}
 
-		$callbackParameters = [];
+		$valueTypes = [];
+		$arrayTypes = [];
 		$argCount = count($args);
 		for ($i = 1; $i < $argCount; $i++) {
 			$arg = $args[$i];
@@ -43,14 +45,21 @@ public function getTypeFromFunctionCall(FunctionReflection $functionReflection,
 				}
 				foreach ($constantArrays as $constantArray) {
 					foreach ($constantArray->getValueTypes() as $valueType) {
-						$callbackParameters[] = $this->createParameter($scope->getIterableValueType($valueType));
+						$valueTypes[] = $scope->getIterableValueType($valueType);
+						$arrayTypes[] = $valueType;
 					}
 				}
 			} else {
-				$callbackParameters[] = $this->createParameter($scope->getIterableValueType($arrayType));
+				$valueTypes[] = $scope->getIterableValueType($arrayType);
+				$arrayTypes[] = $arrayType;
 			}
 		}
 
+		$callbackParameters = [];
+		foreach (ArrayMapCallbackParameterTypes::addPaddingNull($valueTypes, $arrayTypes) as $valueType) {
+			$callbackParameters[] = $this->createParameter($valueType);
+		}
+
 		return new ClosureType($callbackParameters, new MixedType());
 	}
 

tests/PHPStan/Analyser/nsrt/bug-13217.php

@@ -0,0 +1,110 @@
+<?php
+
+namespace Bug13217;
+
+use function PHPStan\Testing\assertNativeType;
+use function PHPStan\Testing\assertType;
+
+class Foo
+{
+
+	public function shorterSecondArray(): void
+	{
+		array_map(function ($a, $b) {
+			assertType('1|2', $a);
+			assertType('3|null', $b);
+			assertNativeType('1|2', $a);
+			assertNativeType('3|null', $b);
+		}, [1, 2], [3]);
+
+		array_map(fn ($a, $b) => assertType('3|null', $b), [1, 2], [3]);
+
+		assertType('non-empty-list<1|3>', array_map(fn ($a, $b) => $b ?? 1, [1, 2], [3]));
+	}
+
+	public function shorterFirstArray(): void
+	{
+		array_map(function ($a, $b) {
+			assertType('1|null', $a);
+			assertType('3|4', $b);
+			assertNativeType('1|null', $a);
+			assertNativeType('3|4', $b);
+		}, [1], [3, 4]);
+	}
+
+	public function sameSize(): void
+	{
+		array_map(function ($a, $b) {
+			assertType('1|2', $a);
+			assertType('3|4', $b);
+		}, [1, 2], [3, 4]);
+	}
+
+	/**
+	 * @param array{1, 2}|array{1} $maybe
+	 */
+	public function sizeRange(array $maybe): void
+	{
+		array_map(function ($a, $b) {
+			assertType('1|2|null', $a);
+			assertType('3|4|5', $b);
+			assertNativeType('mixed', $a);
+			assertNativeType('3|4|5', $b);
+		}, $maybe, [3, 4, 5]);
+
+		array_map(function ($a, $b) {
+			assertType('1|2', $a);
+			assertType('3|null', $b);
+		}, $maybe, [3]);
+
+		array_map(function ($a, $b) {
+			assertType('1|2', $a);
+			assertType('1|2', $b);
+		}, $maybe, $maybe);
+	}
+
+	public function singleArray(): void
+	{
+		array_map(function ($a) {
+			assertType('1|2', $a);
+		}, [1, 2]);
+	}
+
+	/**
+	 * @param list<int> $ints
+	 * @param list<string> $strings
+	 */
+	public function generalArrays(array $ints, array $strings): void
+	{
+		array_map(function ($a, $b) {
+			assertType('int', $a);
+			assertType('string', $b);
+		}, $ints, $strings);
+
+		array_map(function ($a) {
+			assertType('int', $a);
+		}, $ints);
+
+		array_map(function ($a, $b) {
+			assertType('int', $a);
+			assertType('3', $b);
+		}, $ints, [3]);
+	}
+
+	public function returnType(): void
+	{
+		assertType('non-empty-list<3|null>', array_map('Bug13217\\pick', [1, 2], [3]));
+	}
+
+}
+
+/**
+ * @template T
+ * @param mixed $a
+ * @param T $b
+ * @return T
+ */
+function pick($a, $b)
+{
+	return $b;
+}

tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php

@@ -706,6 +706,11 @@ public function testInTrait(): void
 		]);
 	}
 
+	public function testBug13217(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-13217.php'], []);
+	}
+
 	public function testBug12780(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-12780.php'], []);

tests/PHPStan/Rules/Variables/data/bug-13217.php

@@ -0,0 +1,3 @@
+<?php declare(strict_types = 1);
+
+array_map(fn($_, $bValue) => $bValue ?? 1, [1, 2], [3]);