Fix CacheInterface::get() return type

extension.neon

@@ -336,3 +336,8 @@ services:
 		tags:
 			- phpstan.properties.readWriteExtension
 			- phpstan.additionalConstructorsExtension
+
+	# CacheInterface::get() return type
+	-
+		factory: PHPStan\Type\Symfony\CacheInterfaceGetDynamicReturnTypeExtension
+		tags: [phpstan.broker.dynamicMethodReturnTypeExtension]

src/Type/Symfony/CacheInterfaceGetDynamicReturnTypeExtension.php

@@ -0,0 +1,48 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Symfony;
+
+use PhpParser\Node\Expr\MethodCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\MethodReflection;
+use PHPStan\Reflection\ParametersAcceptorSelector;
+use PHPStan\Type\DynamicMethodReturnTypeExtension;
+use PHPStan\Type\GeneralizePrecision;
+use PHPStan\Type\Type;
+
+final class CacheInterfaceGetDynamicReturnTypeExtension implements DynamicMethodReturnTypeExtension
+{
+
+	public function getClass(): string
+	{
+		return 'Symfony\Contracts\Cache\CacheInterface';
+	}
+
+	public function isMethodSupported(MethodReflection $methodReflection): bool
+	{
+		return $methodReflection->getName() === 'get';
+	}
+
+	public function getTypeFromMethodCall(MethodReflection $methodReflection, MethodCall $methodCall, Scope $scope): ?Type
+	{
+		if (!isset($methodCall->getArgs()[1])) {
+			return null;
+		}
+
+		$callbackReturnType = $scope->getType($methodCall->getArgs()[1]->value);
+		if ($callbackReturnType->isCallable()->yes()) {
+			$parametersAcceptor = ParametersAcceptorSelector::selectFromArgs(
+				$scope,
+				$methodCall->getArgs(),
+				$callbackReturnType->getCallableParametersAcceptors($scope)
+			);
+			$returnType = $parametersAcceptor->getReturnType();
+
+			// generalize template parameters
+			return $returnType->generalize(GeneralizePrecision::templateArgument());
+		}
+
+		return null;
+	}
+
+}

tests/Type/Symfony/data/cache.php

@@ -12,6 +12,26 @@ function testCacheCallable(\Symfony\Contracts\Cache\CacheInterface  $cache): voi
 	assertType('string', $result);
 };
 
+/**
+ * @param callable():string $fn
+ */
+function testNonScalarCacheCallable(\Symfony\Contracts\Cache\CacheInterface $cache, callable $fn): void {
+	$result = $cache->get('foo', $fn);
+
+	assertType('string', $result);
+};
+
+
+/**
+ * @param callable():non-empty-string $fn
+ */
+function testCacheCallableReturnTypeGeneralization(\Symfony\Contracts\Cache\CacheInterface $cache, callable $fn): void {
+	$result = $cache->get('foo', $fn);
+
+	assertType('string', $result);
+};
+
+
 /**
  * @param \Symfony\Contracts\Cache\CallbackInterface<\stdClass> $cb
  */