[TypeDeclaration] Add AddFunctionReturnTypeRector

config/level/type-declaration/type-declaration.yaml

@@ -1,3 +1,4 @@
 services:
     Rector\Php\Rector\FunctionLike\ParamTypeDeclarationRector: ~
     Rector\Php\Rector\FunctionLike\ReturnTypeDeclarationRector: ~
+    Rector\TypeDeclaration\Rector\Function_\AddFunctionReturnTypeRector: ~

packages/BetterPhpDocParser/src/Attributes/Ast/AttributeAwareNodeFactory.php

@@ -73,7 +73,7 @@ final class AttributeAwareNodeFactory
         }
 
         if ($node instanceof PhpDocNode) {
-            $this->nodeTraverser->traverseWithCallable($node, function (Node $node) {
+            $this->nodeTraverser->traverseWithCallable($node, function (Node $node): AttributeAwareNodeInterface {
                 if ($node instanceof AttributeAwareNodeInterface) {
                     return $node;
                 }

packages/BetterPhpDocParser/src/NodeDecorator/StringsTypePhpDocNodeDecorator.php

@@ -32,7 +32,7 @@ final class StringsTypePhpDocNodeDecorator implements PhpDocNodeDecoratorInterfa
     ): AttributeAwarePhpDocNode {
         $this->nodeTraverser->traverseWithCallable(
             $attributeAwarePhpDocNode,
-            function (AttributeAwareNodeInterface $phpParserNode) {
+            function (AttributeAwareNodeInterface $phpParserNode): AttributeAwareNodeInterface {
                 $typeNode = $this->resolveTypeNode($phpParserNode);
                 if ($typeNode === null) {
                     return $phpParserNode;

packages/CakePHP/src/Rector/Name/ChangeSnakedFixtureNameToCamelRector.php

@@ -84,7 +84,7 @@ CODE_SAMPLE
     {
         [$prefix, $table] = explode('.', $name->value);
         $table = array_map(
-            function ($token) {
+            function ($token): string {
                 $tokens = explode('_', $token);
 
                 return implode('', array_map('ucfirst', $tokens));

packages/CodeQuality/src/Rector/BooleanAnd/SimplifyEmptyArrayCheckRector.php

@@ -53,7 +53,7 @@ final class SimplifyEmptyArrayCheckRector extends AbstractRector
         $matchedNodes = $this->binaryOpManipulator->matchFirstAndSecondConditionNode(
             $node,
             // is_array(...)
-            function (Node $node) {
+            function (Node $node): bool {
                 return $node instanceof FuncCall && $this->isName($node, 'is_array');
             },
             Empty_::class

packages/CodeQuality/src/Rector/Foreach_/ForeachToInArrayRector.php

@@ -181,7 +181,7 @@ CODE_SAMPLE
         return $this->binaryOpManipulator->matchFirstAndSecondConditionNode(
             $binaryOp,
             Variable::class,
-            function (Node $node, Node $otherNode) use ($expr) {
+            function (Node $node, Node $otherNode) use ($expr): bool {
                 return $this->areNodesEqual($otherNode, $expr);
             }
         );

packages/CodeQuality/src/Rector/Identical/GetClassToInstanceOfRector.php

@@ -56,10 +56,10 @@ final class GetClassToInstanceOfRector extends AbstractRector
     {
         $matchedNodes = $this->binaryOpManipulator->matchFirstAndSecondConditionNode(
             $node,
-            function (Node $node) {
+            function (Node $node): bool {
                 return $this->isClassReference($node);
             },
-            function (Node $node) {
+            function (Node $node): bool {
                 return $this->isGetClassFuncCallNode($node);
             }
         );

packages/CodeQuality/src/Rector/Identical/SimplifyArraySearchRector.php

@@ -58,10 +58,10 @@ final class SimplifyArraySearchRector extends AbstractRector
     {
         $matchedNodes = $this->binaryOpManipulator->matchFirstAndSecondConditionNode(
             $node,
-            function (Node $node) {
+            function (Node $node): bool {
                 return $node instanceof FuncCall && $this->isName($node, 'array_search');
             },
-            function (Node $node) {
+            function (Node $node): bool {
                 return $this->isBool($node);
             }
         );

packages/CodeQuality/src/Rector/Identical/SimplifyConditionsRector.php

@@ -77,10 +77,10 @@ final class SimplifyConditionsRector extends AbstractRector
     {
         $matchedNodes = $this->binaryOpManipulator->matchFirstAndSecondConditionNode(
             $binaryOp,
-            function (Node $binaryOp) {
+            function (Node $binaryOp): bool {
                 return $binaryOp instanceof Identical || $binaryOp instanceof NotIdentical;
             },
-            function (Node $binaryOp) {
+            function (Node $binaryOp): bool {
                 return $this->isBool($binaryOp);
             }
         );

packages/CodeQuality/src/Rector/Ternary/SimplifyTautologyTernaryRector.php

@@ -52,10 +52,10 @@ final class SimplifyTautologyTernaryRector extends AbstractRector
 
         $isMatch = $this->binaryOpManipulator->matchFirstAndSecondConditionNode(
             $node->cond,
-            function (Node $leftNode) use ($node) {
+            function (Node $leftNode) use ($node): bool {
                 return $this->areNodesEqual($leftNode, $node->if);
             },
-            function (Node $leftNode) use ($node) {
+            function (Node $leftNode) use ($node): bool {
                 return $this->areNodesEqual($leftNode, $node->else);
             }
         );

packages/CodingStyle/src/Rector/Identical/IdenticalFalseToBooleanNotRector.php

@@ -50,10 +50,10 @@ final class IdenticalFalseToBooleanNotRector extends AbstractRector
     {
         $matchedNodes = $this->binaryOpManipulator->matchFirstAndSecondConditionNode(
             $node,
-            function (Node $node) {
+            function (Node $node): bool {
                 return ! $node instanceof BinaryOp;
             },
-            function (Node $node) {
+            function (Node $node): bool {
                 return $this->isFalse($node);
             }
         );

packages/CodingStyle/src/Rector/Namespace_/ImportFullyQualifiedNamesRector.php

@@ -220,7 +220,7 @@ CODE_SAMPLE
         $this->newUseStatements = [];
         $this->newFunctionUseStatements = [];
 
-        $this->callableNodeTraverser->traverseNodesWithCallable($node->stmts, function (Node $node) {
+        $this->callableNodeTraverser->traverseNodesWithCallable($node->stmts, function (Node $node): ?Name {
             if (! $node instanceof Name) {
                 return null;
             }
@@ -277,6 +277,8 @@ CODE_SAMPLE
 
                 return new Name($shortName);
             }
+
+            return null;
         });
 
         // for doc blocks

packages/ConsoleDiffer/src/Console/Formatter/DiffConsoleFormatter.php

@@ -34,7 +34,7 @@ final class DiffConsoleFormatter
 
     private function formatWithTemplate(string $diff, string $template): string
     {
-        return sprintf($template, implode(PHP_EOL, array_map(function ($string) {
+        return sprintf($template, implode(PHP_EOL, array_map(function ($string): string {
             // make "+" lines green
             $string = Strings::replace($string, '#^(\+.*)#', '<fg=green>$1</fg=green>');
             // make "-" lines red

packages/ContributorTools/src/Command/CreateRectorCommand.php

@@ -254,7 +254,7 @@ final class CreateRectorCommand extends Command implements ContributorCommandInt
     {
         foreach ($sections as $section) {
             $pattern = '#("' . preg_quote($section, '#') . '": )\[(.*?)\](,)#ms';
-            $jsonContent = Strings::replace($jsonContent, $pattern, function (array $match) {
+            $jsonContent = Strings::replace($jsonContent, $pattern, function (array $match): string {
                 $inlined = Strings::replace($match[2], '#\s+#', ' ');
                 $inlined = trim($inlined);
                 $inlined = '[' . $inlined . ']';

packages/ContributorTools/src/Finder/RectorsFinder.php

@@ -17,7 +17,7 @@ final class RectorsFinder
     {
         $allRectors = $this->findInDirectories([__DIR__ . '/../../../../packages', __DIR__ . '/../../../../src']);
 
-        return array_map(function (RectorInterface $rector) {
+        return array_map(function (RectorInterface $rector): string {
             return get_class($rector);
         }, $allRectors);
     }

packages/ContributorTools/src/Node/NodeInfoResult.php

@@ -34,7 +34,7 @@ final class NodeInfoResult
      */
     private function sortNodeInfosByClass(array $nodeInfos): array
     {
-        usort($nodeInfos, function (NodeInfo $firstNodeInfo, NodeInfo $secondNodeInfo) {
+        usort($nodeInfos, function (NodeInfo $firstNodeInfo, NodeInfo $secondNodeInfo): int {
             return $firstNodeInfo->getClass() <=> $secondNodeInfo->getClass();
         });
 

packages/DeadCode/src/Rector/ClassMethod/RemoveOverriddenValuesRector.php

@@ -99,7 +99,7 @@ CODE_SAMPLE
      */
     private function resolveAssignedVariables(FunctionLike $functionLike): array
     {
-        return $this->betterNodeFinder->find($functionLike, function (Node $node) {
+        return $this->betterNodeFinder->find($functionLike, function (Node $node): bool {
             if (! $node->getAttribute(AttributeKey::PARENT_NODE) instanceof Assign) {
                 return false;
             }
@@ -130,7 +130,7 @@ CODE_SAMPLE
      */
     private function resolveUsedVariables(Node $node, array $assignedVariables): array
     {
-        return $this->betterNodeFinder->find($node, function (Node $node) use ($assignedVariables) {
+        return $this->betterNodeFinder->find($node, function (Node $node) use ($assignedVariables): bool {
             if (! $node instanceof Variable) {
                 return false;
             }
@@ -216,7 +216,10 @@ CODE_SAMPLE
         // sort
         usort(
             $nodesByTypeAndPosition,
-            function (VariableNodeUseInfo $firstVariableNodeUseInfo, VariableNodeUseInfo $secondVariableNodeUseInfo) {
+            function (
+                VariableNodeUseInfo $firstVariableNodeUseInfo,
+                VariableNodeUseInfo $secondVariableNodeUseInfo
+            ): int {
                 return $firstVariableNodeUseInfo->getStartTokenPosition() <=> $secondVariableNodeUseInfo->getStartTokenPosition();
             }
         );
@@ -285,7 +288,7 @@ CODE_SAMPLE
 
         $isVariableAssigned = (bool) $this->betterNodeFinder->findFirst($assignNode->expr, function (Node $node) use (
             $nodeByTypeAndPosition
-        ) {
+        ): bool {
             return $this->areNodesEqual($node, $nodeByTypeAndPosition->getVariableNode());
         });
 

packages/NetteToSymfony/src/Rector/ClassMethod/RouterListToControllerAnnotationsRector.php

@@ -209,7 +209,7 @@ CODE_SAMPLE
     private function resolveAssignRouteNodes(ClassMethod $classMethod): array
     {
         // look for <...>[] = IRoute<Type>
-        return $this->betterNodeFinder->find($classMethod->stmts, function (Node $classMethod) {
+        return $this->betterNodeFinder->find($classMethod->stmts, function (Node $classMethod): bool {
             if (! $classMethod instanceof Assign) {
                 return false;
             }

packages/NodeTypeResolver/src/Php/AbstractTypeInfo.php

@@ -7,6 +7,7 @@ use PhpParser\Node\Identifier;
 use PhpParser\Node\Name;
 use PhpParser\Node\Name\FullyQualified;
 use PhpParser\Node\NullableType;
+use Rector\Exception\ShouldNotHappenException;
 use Rector\Php\TypeAnalyzer;
 use Traversable;
 
@@ -91,12 +92,14 @@ abstract class AbstractTypeInfo
      */
     public function getTypeNode(bool $forceFqn = false)
     {
-        $types = $forceFqn ? $this->fqnTypes : $this->types;
         if (! $this->isTypehintAble()) {
             return null;
         }
 
-        $type = $types[0];
+        $type = $this->resolveTypeForTypehint($forceFqn);
+        if ($type === null) {
+            throw new ShouldNotHappenException();
+        }
 
         if ($this->typeAnalyzer->isPhpReservedType($type)) {
             if ($this->isNullable) {
@@ -124,8 +127,12 @@ abstract class AbstractTypeInfo
             return false;
         }
 
-        $typeCount = count($this->types);
+        // are object subtypes
+        if ($this->areMutualObjectSubtypes($this->types)) {
+            return true;
+        }
 
+        $typeCount = count($this->types);
         if ($typeCount >= 2 && $this->isArraySubtype($this->types)) {
             return true;
         }
@@ -293,4 +300,50 @@ abstract class AbstractTypeInfo
 
         return $types === $arraySubtypeGroup;
     }
+
+    /**
+     * @param string[] $types
+     */
+    private function areMutualObjectSubtypes(array $types): bool
+    {
+        return $this->resolveMutualObjectSubtype($types) !== null;
+    }
+
+    /**
+     * @param string[] $types
+     */
+    private function resolveMutualObjectSubtype(array $types): ?string
+    {
+        foreach ($types as $type) {
+            if ($this->classLikeExists($type)) {
+                return null;
+            }
+
+            foreach ($types as $subloopType) {
+                if (! is_a($subloopType, $type, true)) {
+                    continue 2;
+                }
+            }
+
+            return $type;
+        }
+
+        return null;
+    }
+
+    private function resolveTypeForTypehint(bool $forceFqn): ?string
+    {
+        if ($this->areMutualObjectSubtypes($this->types)) {
+            return $this->resolveMutualObjectSubtype($this->types);
+        }
+
+        $types = $forceFqn ? $this->fqnTypes : $this->types;
+
+        return $types[0];
+    }
+
+    private function classLikeExists(string $type): bool
+    {
+        return ! class_exists($type) && ! interface_exists($type) && ! trait_exists($type);
+    }
 }

packages/NodeTypeResolver/src/PhpDoc/NodeAnalyzer/DocBlockManipulator.php

@@ -410,7 +410,9 @@ final class DocBlockManipulator
         $phpDocInfo = $this->createPhpDocInfoFromNode($node);
         $phpDocNode = $phpDocInfo->getPhpDocNode();
 
-        $this->nodeTraverser->traverseWithCallable($phpDocNode, function (AttributeAwareNodeInterface $node) {
+        $this->nodeTraverser->traverseWithCallable($phpDocNode, function (
+            AttributeAwareNodeInterface $node
+        ): AttributeAwareNodeInterface {
             if (! $node instanceof IdentifierTypeNode) {
                 return $node;
             }
@@ -447,7 +449,7 @@ final class DocBlockManipulator
         $this->nodeTraverser->traverseWithCallable($phpDocNode, function (AttributeAwareNodeInterface $node) use (
             $namespacePrefix,
             $excludedClasses
-        ) {
+        ): AttributeAwareNodeInterface {
             if (! $node instanceof IdentifierTypeNode) {
                 return $node;
             }

packages/NodeTypeResolver/src/PhpDoc/NodeAnalyzer/FqnNamePhpDocNodeDecorator.php

@@ -54,7 +54,7 @@ final class FqnNamePhpDocNodeDecorator implements PhpDocNodeDecoratorInterface
     {
         $this->nodeTraverser->traverseWithCallable(
             $attributeAwarePhpDocNode,
-            function (AttributeAwareNodeInterface $attributeAwarePhpDocNode) use ($node) {
+            function (AttributeAwareNodeInterface $attributeAwarePhpDocNode) use ($node): AttributeAwareNodeInterface {
                 if (! $attributeAwarePhpDocNode instanceof IdentifierTypeNode) {
                     return $attributeAwarePhpDocNode;
                 }
@@ -77,7 +77,7 @@ final class FqnNamePhpDocNodeDecorator implements PhpDocNodeDecoratorInterface
         // collect to particular node types
         $this->nodeTraverser->traverseWithCallable(
             $attributeAwarePhpDocNode,
-            function (AttributeAwareNodeInterface $attributeAwarePhpDocNode) {
+            function (AttributeAwareNodeInterface $attributeAwarePhpDocNode): AttributeAwareNodeInterface {
                 if (! $this->isTypeAwareNode($attributeAwarePhpDocNode)) {
                     return $attributeAwarePhpDocNode;
                 }

packages/Php/src/Rector/Assign/AssignArrayToStringRector.php

@@ -152,7 +152,7 @@ CODE_SAMPLE
             return true;
         }
 
-        $variableAssign = $this->betterNodeFinder->findFirstPrevious($assign, function (Node $node) use ($expr) {
+        $variableAssign = $this->betterNodeFinder->findFirstPrevious($assign, function (Node $node) use ($expr): bool {
             if (! $node instanceof Assign) {
                 return false;
             }

packages/Php/src/Rector/FuncCall/ArrayKeyFirstLastRector.php

@@ -88,7 +88,7 @@ CODE_SAMPLE
         /** @var FuncCall|null $keyFuncCall */
         $keyFuncCall = $this->betterNodeFinder->findFirst($nextExpression, function (Node $node) use (
             $resetOrEndFuncCall
-        ) {
+        ): bool {
             if (! $node instanceof FuncCall) {
                 return false;
             }

packages/Php/src/Rector/FuncCall/ParseStrWithResultArgumentRector.php

@@ -79,7 +79,7 @@ CODE_SAMPLE
 
         $this->callableNodeTraverser->traverseNodesWithCallable([$nextExpression], function (Node $node) use (
             $resultVariable
-        ) {
+        ): ?Variable {
             if ($node instanceof FuncCall) {
                 if ($this->isName($node, 'get_defined_vars')) {
                     return $resultVariable;

packages/Php/src/Rector/FuncCall/PregReplaceEModifierRector.php

@@ -129,7 +129,7 @@ CODE_SAMPLE
 
         $stmt = $contentNodes[0]->expr;
 
-        $this->callableNodeTraverser->traverseNodesWithCallable([$stmt], function (Node $node) {
+        $this->callableNodeTraverser->traverseNodesWithCallable([$stmt], function (Node $node): Node {
             if (! $node instanceof String_) {
                 return $node;
             }

packages/PhpSpecToPHPUnit/src/LetManipulator.php

@@ -36,7 +36,7 @@ final class LetManipulator
 
             $hasBeConstructedThrough = (bool) $this->betterNodeFinder->find(
                 (array) $method->stmts,
-                function (Node $node) {
+                function (Node $node): ?bool {
                     if (! $node instanceof MethodCall) {
                         return null;
                     }

packages/RemovingStatic/src/Rector/Class_/NewUniqueObjectToEntityFactoryRector.php

@@ -146,7 +146,7 @@ CODE_SAMPLE
 
         $this->callableNodeTraverser->traverseNodesWithCallable($node->stmts, function (Node $node) use (
             $classesUsingTypes
-        ) {
+        ): ?MethodCall {
             if (! $node instanceof New_) {
                 return null;
             }

packages/RemovingStatic/src/Rector/Class_/StaticTypeToSetterInjectionRector.php

@@ -137,7 +137,7 @@ CODE_SAMPLE
         foreach ($this->staticTypes as $implements => $staticType) {
             $containsEntityFactoryStaticCall = (bool) $this->betterNodeFinder->findFirst(
                 $class->stmts,
-                function (Node $node) use ($staticType) {
+                function (Node $node) use ($staticType): bool {
                     return $this->isEntityFactoryStaticCall($node, $staticType);
                 }
             );

packages/Symfony/src/Rector/HttpKernel/GetRequestRector.php

@@ -148,7 +148,7 @@ CODE_SAMPLE
         }
 
         // "$this->getRequest()"
-        $isGetRequestMethod = (bool) $this->betterNodeFinder->find($node, function (Node $node) {
+        $isGetRequestMethod = (bool) $this->betterNodeFinder->find($node, function (Node $node): bool {
             return $this->isName($node, 'getRequest');
         });
 
@@ -158,7 +158,7 @@ CODE_SAMPLE
 
         // "$this->get('request')"
         /** @var MethodCall[] $getMethodCalls */
-        $getMethodCalls = $this->betterNodeFinder->find($node, function (Node $node) {
+        $getMethodCalls = $this->betterNodeFinder->find($node, function (Node $node): bool {
             if (! $node instanceof MethodCall) {
                 return false;
             }

packages/Symfony/src/Rector/New_/RootNodeTreeBuilderRector.php

@@ -103,7 +103,7 @@ CODE_SAMPLE
             return null;
         }
 
-        return $this->betterNodeFinder->findFirst([$nextExpression], function (Node $node) {
+        return $this->betterNodeFinder->findFirst([$nextExpression], function (Node $node): bool {
             if (! $node instanceof MethodCall) {
                 return false;
             }

packages/Symfony/src/Rector/New_/StringToArrayArgumentProcessRector.php

@@ -155,7 +155,9 @@ CODE_SAMPLE
 
     private function findPreviousNodeAssign(Node $node, Node $firstArgument): ?Assign
     {
-        return $this->betterNodeFinder->findFirstPrevious($node, function (Node $checkedNode) use ($firstArgument) {
+        return $this->betterNodeFinder->findFirstPrevious($node, function (Node $checkedNode) use (
+            $firstArgument
+        ): ?Assign {
             if (! $checkedNode instanceof Assign) {
                 return null;
             }

packages/Twig/src/Rector/SimpleFunctionAndFilterRector.php

@@ -132,7 +132,7 @@ CODE_SAMPLE
             return null;
         }
 
-        $this->callableNodeTraverser->traverseNodesWithCallable([$node->expr], function (Node $node) {
+        $this->callableNodeTraverser->traverseNodesWithCallable([$node->expr], function (Node $node): ?Node {
             if (! $node instanceof ArrayItem) {
                 return null;
             }

packages/TypeDeclaration/src/Rector/Closure/AddClosureReturnTypeRector.php

@@ -0,0 +1,97 @@
+<?php declare(strict_types=1);
+
+namespace Rector\TypeDeclaration\Rector\Closure;
+
+use PhpParser\Node;
+use PHPStan\Analyser\Scope;
+use Rector\NodeTypeResolver\Node\AttributeKey;
+use Rector\PhpParser\Node\Manipulator\FunctionLikeManipulator;
+use Rector\Rector\AbstractRector;
+use Rector\RectorDefinition\CodeSample;
+use Rector\RectorDefinition\RectorDefinition;
+
+final class AddClosureReturnTypeRector extends AbstractRector
+{
+    /**
+     * @var FunctionLikeManipulator
+     */
+    private $functionLikeManipulator;
+
+    public function __construct(FunctionLikeManipulator $functionLikeManipulator)
+    {
+        $this->functionLikeManipulator = $functionLikeManipulator;
+    }
+
+    public function getDefinition(): RectorDefinition
+    {
+        return new RectorDefinition('Add known return type to functions', [
+            new CodeSample(
+                <<<'CODE_SAMPLE'
+class SomeClass
+{
+    public function run($meetups)
+    {
+        return array_filter($meetups, function (Meetup $meetup) {
+            return is_object($meetup);
+        });
+    }
+}
+CODE_SAMPLE
+                ,
+                <<<'CODE_SAMPLE'
+class SomeClass
+{
+    public function run($meetups)
+    {
+        return array_filter($meetups, function (Meetup $meetup): bool {
+            return is_object($meetup);
+        });
+    }
+}
+CODE_SAMPLE
+            ),
+        ]);
+    }
+
+    /**
+     * @return string[]
+     */
+    public function getNodeTypes(): array
+    {
+        return [Node\Expr\Closure::class];
+    }
+
+    /**
+     * @param Node\Expr\Closure $node
+     */
+    public function refactor(Node $node): ?Node
+    {
+        if (! $this->isAtLeastPhpVersion('7.0')) {
+            return null;
+        }
+
+        if ($node->returnType) {
+            return null;
+        }
+
+        /** @var Scope|null $scope */
+        $scope = $node->getAttribute(AttributeKey::SCOPE);
+        if ($scope === null) {
+            return null;
+        }
+
+        $staticReturnType = $this->functionLikeManipulator->resolveStaticReturnTypeInfo($node);
+        if ($staticReturnType === null) {
+            return null;
+        }
+
+        $returnTypeNode = $staticReturnType->getTypeNode();
+        if ($returnTypeNode === null) {
+            return null;
+        }
+
+        $node->returnType = $returnTypeNode;
+
+        return $node;
+    }
+}

packages/TypeDeclaration/tests/Rector/Closure/AddClosureReturnTypeRector/AddClosureReturnTypeRectorTest.php

@@ -0,0 +1,24 @@
+<?php declare(strict_types=1);
+
+namespace Rector\TypeDeclaration\Tests\Rector\Closure\AddClosureReturnTypeRector;
+
+use Rector\Testing\PHPUnit\AbstractRectorTestCase;
+use Rector\TypeDeclaration\Rector\Closure\AddClosureReturnTypeRector;
+
+final class AddClosureReturnTypeRectorTest extends AbstractRectorTestCase
+{
+    public function test(): void
+    {
+        $this->doTestFiles([
+            __DIR__ . '/Fixture/fixture.php.inc',
+            __DIR__ . '/Fixture/return_type_object.php.inc',
+            __DIR__ . '/Fixture/callable_false_positive.php.inc',
+            __DIR__ . '/Fixture/subtype_of_object.php.inc',
+        ]);
+    }
+
+    protected function getRectorClass(): string
+    {
+        return AddClosureReturnTypeRector::class;
+    }
+}

packages/TypeDeclaration/tests/Rector/Closure/AddClosureReturnTypeRector/Fixture/callable_false_positive.php.inc

@@ -0,0 +1,59 @@
+<?php
+
+namespace Rector\TypeDeclaration\Tests\Rector\Function_\AddClosureReturnTypeRector\Fixture;
+
+class CallableFalsePositive
+{
+    /**
+     * @param callable[]|string[] $callables
+     * @return callable[]
+     */
+    public function populate(array $callables): array
+    {
+        $populatedCallables = [];
+
+        foreach ($callables as $key => $callable) {
+            // 1. convert instant assign to callable
+            if (!is_callable($callable)) {
+                $populatedCallables[$key] = function () use ($callable) {
+                    return $callable;
+                };
+                continue;
+            }
+        }
+
+        return $populatedCallables;
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\TypeDeclaration\Tests\Rector\Function_\AddClosureReturnTypeRector\Fixture;
+
+class CallableFalsePositive
+{
+    /**
+     * @param callable[]|string[] $callables
+     * @return callable[]
+     */
+    public function populate(array $callables): array
+    {
+        $populatedCallables = [];
+
+        foreach ($callables as $key => $callable) {
+            // 1. convert instant assign to callable
+            if (!is_callable($callable)) {
+                $populatedCallables[$key] = function () use ($callable) : string {
+                    return $callable;
+                };
+                continue;
+            }
+        }
+
+        return $populatedCallables;
+    }
+}
+
+?>

packages/TypeDeclaration/tests/Rector/Closure/AddClosureReturnTypeRector/Fixture/fixture.php.inc

@@ -0,0 +1,31 @@
+<?php
+
+namespace Rector\TypeDeclaration\Tests\Rector\Function_\AddClosureReturnTypeRector\Fixture;
+
+class SomeClass
+{
+    public function run($meetups)
+    {
+        return array_filter($meetups, function ($meetup) {
+            return is_object($meetup);
+        });
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\TypeDeclaration\Tests\Rector\Function_\AddClosureReturnTypeRector\Fixture;
+
+class SomeClass
+{
+    public function run($meetups)
+    {
+        return array_filter($meetups, function ($meetup) : bool {
+            return is_object($meetup);
+        });
+    }
+}
+
+?>

packages/TypeDeclaration/tests/Rector/Closure/AddClosureReturnTypeRector/Fixture/return_type_object.php.inc

@@ -0,0 +1,35 @@
+<?php
+
+namespace Rector\TypeDeclaration\Tests\Rector\Function_\AddClosureReturnTypeRector\Fixture;
+
+use PhpParser\Node\Stmt\Class_;
+
+class ReturnTypeObject
+{
+    public function shouldSkip()
+    {
+        $nonAnonymousClassNodes = array_filter([], function (Class_ $classNode) {
+            return $classNode->name;
+        });
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\TypeDeclaration\Tests\Rector\Function_\AddClosureReturnTypeRector\Fixture;
+
+use PhpParser\Node\Stmt\Class_;
+
+class ReturnTypeObject
+{
+    public function shouldSkip()
+    {
+        $nonAnonymousClassNodes = array_filter([], function (Class_ $classNode) : ?\PhpParser\Node\Identifier {
+            return $classNode->name;
+        });
+    }
+}
+
+?>

packages/TypeDeclaration/tests/Rector/Closure/AddClosureReturnTypeRector/Fixture/subtype_of_object.php.inc

@@ -0,0 +1,69 @@
+<?php
+
+namespace Rector\TypeDeclaration\Tests\Rector\Function_\AddClosureReturnTypeRector\Fixture;
+
+use Nette\Utils\Strings;
+use PhpParser\Node;
+use PhpParser\Node\Expr\ArrayDimFetch;
+use PhpParser\Node\Expr\Variable;
+use PhpParser\Node\Scalar\LNumber;
+use PhpParser\Node\Scalar\String_;
+
+class SubtypeOfObject
+{
+    public function run($stmt)
+    {
+        $this->callableNodeTraverser->traverseNodesWithCallable([$stmt], function (Node $node)
+        {
+            if (!$node instanceof String_) {
+                return $node;
+            }
+
+            $match = Strings::match($node->value, '#(\\$|\\\\)(?<number>\d+)#');
+            if (!$match) {
+                return $node;
+            }
+
+            $matchesVariable = new Variable('matches');
+
+            return new ArrayDimFetch($matchesVariable, new LNumber((int)$match['number']));
+        });
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\TypeDeclaration\Tests\Rector\Function_\AddClosureReturnTypeRector\Fixture;
+
+use Nette\Utils\Strings;
+use PhpParser\Node;
+use PhpParser\Node\Expr\ArrayDimFetch;
+use PhpParser\Node\Expr\Variable;
+use PhpParser\Node\Scalar\LNumber;
+use PhpParser\Node\Scalar\String_;
+
+class SubtypeOfObject
+{
+    public function run($stmt)
+    {
+        $this->callableNodeTraverser->traverseNodesWithCallable([$stmt], function (Node $node) : \PhpParser\Node
+        {
+            if (!$node instanceof String_) {
+                return $node;
+            }
+
+            $match = Strings::match($node->value, '#(\\$|\\\\)(?<number>\d+)#');
+            if (!$match) {
+                return $node;
+            }
+
+            $matchesVariable = new Variable('matches');
+
+            return new ArrayDimFetch($matchesVariable, new LNumber((int)$match['number']));
+        });
+    }
+}
+
+?>

phpstan.neon

@@ -155,3 +155,6 @@ parameters:
         - '#Empty array passed to foreach#'
         - '#Method Rector\\RemovingStatic\\UniqueObjectFactoryFactory\:\:resolveClassShortName\(\) should return string but returns string\|false#'
         - '#Strict comparison using \=\=\= between PhpParser\\Node\\Expr\\ArrayItem and null will always evaluate to false#'
+        - '#Anonymous function should have native typehint "string"#'
+        - '#Parameter \#2 \.\.\.\$args of function array_merge expects array, array<int, string\>\|false given#'
+        - '#Method Rector\\Collector\\CallableCollectorPopulator\:\:populate\(\) should return array<Closure\> but returns array<int\|string, callable\>#'

rector.yaml

@@ -15,4 +15,5 @@ parameters:
     php_version_features: '7.1'
 
 services:
-    Rector\CodingStyle\Rector\Namespace_\ImportFullyQualifiedNamesRector: ~
+#    Rector\CodingStyle\Rector\Namespace_\ImportFullyQualifiedNamesRector: ~
+    Rector\TypeDeclaration\Rector\Closure\AddClosureReturnTypeRector: ~

src/Collector/CallableCollectorPopulator.php

@@ -9,8 +9,8 @@ use ReflectionFunction;
 final class CallableCollectorPopulator
 {
     /**
-     * @param string[]|callable[]|Closure[] $callables
+     * @param string[]|Closure[]|mixed[] $callables
-     * @return callable[]
+     * @return Closure[]
      */
     public function populate(array $callables): array
     {

src/FileSystem/FilesFinder.php

@@ -124,7 +124,7 @@ final class FilesFinder
             return;
         }
 
-        $finder->filter(function (SplFileInfo $splFileInfo) {
+        $finder->filter(function (SplFileInfo $splFileInfo): bool {
             // return false to remove file
             foreach ($this->excludePaths as $excludePath) {
                 if (Strings::match($splFileInfo->getRealPath(), '#' . preg_quote($excludePath, '#') . '#')) {

src/Php/Regex/RegexPatternArgumentManipulator.php

@@ -185,7 +185,7 @@ final class RegexPatternArgumentManipulator
         }
 
         /** @var Assign[] $assignNode */
-        return $this->betterNodeFinder->find([$methodNode], function (Node $node) use ($variable) {
+        return $this->betterNodeFinder->find([$methodNode], function (Node $node) use ($variable): ?Assign {
             if (! $node instanceof Assign) {
                 return null;
             }

src/PhpParser/Node/BetterNodeFinder.php

@@ -149,7 +149,7 @@ final class BetterNodeFinder
     {
         $assignNodes = $this->findInstanceOf($node, Assign::class);
 
-        return array_filter($assignNodes, function (Assign $assign) use ($variable) {
+        return array_filter($assignNodes, function (Assign $assign) use ($variable): bool {
             if ($this->betterStandardPrinter->areNodesEqual($assign->var, $variable)) {
                 return true;
             }

src/PhpParser/Node/Manipulator/BinaryOpManipulator.php

@@ -63,7 +63,7 @@ final class BinaryOpManipulator
             return $condition;
         }
 
-        return function (Node $node) use ($condition) {
+        return function (Node $node) use ($condition): bool {
             return is_a($node, $condition, true);
         };
     }

src/PhpParser/Node/Manipulator/CallManipulator.php

@@ -100,7 +100,7 @@ final class CallManipulator
 
     private function containsFuncGetArgsFuncCall(Node $node): bool
     {
-        return (bool) $this->betterNodeFinder->findFirst($node, function (Node $node) {
+        return (bool) $this->betterNodeFinder->findFirst($node, function (Node $node): ?bool {
             if (! $node instanceof FuncCall) {
                 return null;
             }
@@ -134,7 +134,7 @@ final class CallManipulator
         $externalFunctionNode = $this->betterNodeFinder->findFirst($externalFileContent, function (Node $node) use (
             $requiredExternalType,
             $functionName
-        ) {
+        ): ?bool {
             if (! is_a($node, $requiredExternalType, true)) {
                 return null;
             }

src/PhpParser/Node/Manipulator/ClassConstManipulator.php

@@ -47,7 +47,7 @@ final class ClassConstManipulator
             return [];
         }
 
-        return $this->betterNodeFinder->find($classNode, function (Node $node) use ($classConst) {
+        return $this->betterNodeFinder->find($classNode, function (Node $node) use ($classConst): bool {
             // itself
             if ($this->betterStandardPrinter->areNodesEqual($node, $classConst)) {
                 return false;

src/PhpParser/Node/Manipulator/ClassManipulator.php

@@ -236,7 +236,7 @@ final class ClassManipulator
      */
     public function getMethods(Class_ $class): array
     {
-        return array_filter($class->stmts, function (Node $node) {
+        return array_filter($class->stmts, function (Node $node): bool {
             return $node instanceof ClassMethod;
         });
     }

src/PhpParser/Node/Manipulator/ClassMethodManipulator.php

@@ -68,7 +68,7 @@ final class ClassMethodManipulator
     {
         $isUsedDirectly = (bool) $this->betterNodeFinder->findFirst((array) $classMethod->stmts, function (Node $node) use (
             $param
-        ) {
+        ): bool {
             return $this->betterStandardPrinter->areNodesEqual($node, $param->var);
         });
 
@@ -77,7 +77,7 @@ final class ClassMethodManipulator
         }
 
         /** @var FuncCall[] $compactFuncCalls */
-        $compactFuncCalls = $this->betterNodeFinder->find((array) $classMethod->stmts, function (Node $node) {
+        $compactFuncCalls = $this->betterNodeFinder->find((array) $classMethod->stmts, function (Node $node): bool {
             if (! $node instanceof FuncCall) {
                 return false;
             }
@@ -152,7 +152,7 @@ final class ClassMethodManipulator
      */
     public function isStaticClassMethod(ClassMethod $classMethod): bool
     {
-        return (bool) $this->betterNodeFinder->findFirst((array) $classMethod->stmts, function (Node $node) {
+        return (bool) $this->betterNodeFinder->findFirst((array) $classMethod->stmts, function (Node $node): bool {
             if (! $node instanceof Variable) {
                 return false;
             }

src/PhpParser/Node/Manipulator/FunctionLikeManipulator.php

@@ -2,6 +2,7 @@
 
 namespace Rector\PhpParser\Node\Manipulator;
 
+use PhpParser\Node\Expr\Closure;
 use PhpParser\Node\FunctionLike;
 use PhpParser\Node\Stmt\ClassMethod;
 use PhpParser\Node\Stmt\Function_;
@@ -42,7 +43,7 @@ final class FunctionLikeManipulator
 
     /**
      * Based on static analysis of code, looking for return types
-     * @param ClassMethod|Function_ $functionLike
+     * @param ClassMethod|Function_|Closure $functionLike
      */
     public function resolveStaticReturnTypeInfo(FunctionLike $functionLike): ?ReturnTypeInfo
     {

src/PhpParser/Node/Value/ValueResolver.php

@@ -82,7 +82,7 @@ final class ValueResolver
             return $this->constExprEvaluator;
         }
 
-        $this->constExprEvaluator = new ConstExprEvaluator(function (Expr $expr) {
+        $this->constExprEvaluator = new ConstExprEvaluator(function (Expr $expr): ?string {
             if ($expr instanceof Dir) {
                 // __DIR__
                 return $this->resolveDirConstant($expr);

src/Rector/BetterStandardPrinterTrait.php

@@ -77,7 +77,7 @@ trait BetterStandardPrinterTrait
      */
     protected function isNodeUsedIn(Node $seekedNode, $nodes): bool
     {
-        return (bool) $this->betterNodeFinder->findFirst($nodes, function (Node $node) use ($seekedNode) {
+        return (bool) $this->betterNodeFinder->findFirst($nodes, function (Node $node) use ($seekedNode): bool {
             return $this->areNodesEqual($node, $seekedNode);
         });
     }

src/Rector/Class_/RenameClassRector.php

@@ -38,6 +38,7 @@ final class RenameClassRector extends AbstractRector
      * @var string[]
      */
     private $alreadyProcessedClasses = [];
+
     /**
      * @var ClassNaming
      */
@@ -50,8 +51,7 @@ final class RenameClassRector extends AbstractRector
         DocBlockManipulator $docBlockManipulator,
         ClassNaming $classNaming,
         array $oldToNewClasses = []
-    )
+    ) {
-    {
         $this->docBlockManipulator = $docBlockManipulator;
         $this->classNaming = $classNaming;
         $this->oldToNewClasses = $oldToNewClasses;
@@ -120,21 +120,7 @@ CODE_SAMPLE
         }
 
         if ($node instanceof Name) {
-            $name = $this->getName($node);
+            return $this->refactorName($node);
-            if ($name === null) {
-                return null;
-            }
-
-            $newName = $this->oldToNewClasses[$name] ?? null;
-            if (! $newName) {
-                return null;
-            }
-
-            if (! $this->isClassToInterfaceValidChange($node, $newName)) {
-                return null;
-            }
-
-            return new FullyQualified($newName);
         }
 
         if ($node instanceof Namespace_) {
@@ -145,7 +131,7 @@ CODE_SAMPLE
             $node = $this->refactorClassLikeNode($node);
         }
 
-        if (! $node) {
+        if ($node === null) {
             return null;
         }
 
@@ -222,7 +208,7 @@ CODE_SAMPLE
         }
 
         $classNode = $this->getClassOfNamespaceToRefactor($node);
-        if (! $classNode) {
+        if ($classNode === null) {
             return null;
         }
 
@@ -243,7 +229,7 @@ CODE_SAMPLE
 
     private function getClassOfNamespaceToRefactor(Namespace_ $namespace): ?ClassLike
     {
-        $foundClass = $this->betterNodeFinder->findFirst($namespace, function (Node $node) {
+        $foundClass = $this->betterNodeFinder->findFirst($namespace, function (Node $node): bool {
             if (! $node instanceof ClassLike) {
                 return false;
             }
@@ -286,4 +272,23 @@ CODE_SAMPLE
 
         return $classLike;
     }
+
+    private function refactorName(Node $node): ?FullyQualified
+    {
+        $name = $this->getName($node);
+        if ($name === null) {
+            return null;
+        }
+
+        $newName = $this->oldToNewClasses[$name] ?? null;
+        if (! $newName) {
+            return null;
+        }
+
+        if (! $this->isClassToInterfaceValidChange($node, $newName)) {
+            return null;
+        }
+
+        return new FullyQualified($newName);
+    }
 }

src/Rector/Psr4/MultipleClassFileToPsr4ClassesRector.php

@@ -4,6 +4,7 @@ namespace Rector\Rector\Psr4;
 
 use Nette\Utils\FileSystem;
 use PhpParser\Node;
+use PhpParser\Node\Identifier;
 use PhpParser\Node\Stmt\Class_;
 use PhpParser\Node\Stmt\Namespace_;
 use Rector\FileSystemRector\Rector\AbstractFileSystemRector;
@@ -123,7 +124,7 @@ CODE_SAMPLE
         /** @var Class_[] $classNodes */
         $classNodes = $this->betterNodeFinder->findInstanceOf($nodes, Class_::class);
 
-        $nonAnonymousClassNodes = array_filter($classNodes, function (Class_ $classNode) {
+        $nonAnonymousClassNodes = array_filter($classNodes, function (Class_ $classNode): ?Identifier {
             return $classNode->name;
         });
 

src/Reflection/FunctionReflectionResolver.php

@@ -41,7 +41,7 @@ final class FunctionReflectionResolver
         $nodes = $this->parser->parseFile($stubFileLocation);
 
         /** @var Function_|null $function */
-        $function = $this->betterNodeFinder->findFirst($nodes, function (Node $node) use ($nodeName) {
+        $function = $this->betterNodeFinder->findFirst($nodes, function (Node $node) use ($nodeName): bool {
             if (! $node instanceof Function_) {
                 return false;
             }