Support for is_countable()

conf/config.neon

@@ -455,6 +455,11 @@ services:
 		tags:
 			- phpstan.typeSpecifier.functionTypeSpecifyingExtension
 
+	-
+		class: PHPStan\Type\Php\IsCountableFunctionTypeSpecifyingExtension
+		tags:
+			- phpstan.typeSpecifier.functionTypeSpecifyingExtension
+
 	-
 		class: PHPStan\Type\Php\IsResourceFunctionTypeSpecifyingExtension
 		tags:

src/Reflection/SignatureMap/functionMap.php

@@ -5620,6 +5620,7 @@
 'is_array' => ['bool', 'var'=>'mixed'],
 'is_bool' => ['bool', 'var'=>'mixed'],
 'is_callable' => ['bool', 'var'=>'mixed', 'syntax_only='=>'bool', '&w_callable_name='=>'string'],
+'is_countable' => ['bool', 'var'=>'mixed'],
 'is_dir' => ['bool', 'filename'=>'string'],
 'is_double' => ['bool', 'var'=>''],
 'is_executable' => ['bool', 'filename'=>'string'],

src/Type/Php/IsCountableFunctionTypeSpecifyingExtension.php

@@ -0,0 +1,52 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use PhpParser\Node\Expr\FuncCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Analyser\SpecifiedTypes;
+use PHPStan\Analyser\TypeSpecifier;
+use PHPStan\Analyser\TypeSpecifierAwareExtension;
+use PHPStan\Analyser\TypeSpecifierContext;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\ArrayType;
+use PHPStan\Type\FunctionTypeSpecifyingExtension;
+use PHPStan\Type\MixedType;
+use PHPStan\Type\ObjectType;
+use PHPStan\Type\UnionType;
+
+class IsCountableFunctionTypeSpecifyingExtension implements FunctionTypeSpecifyingExtension, TypeSpecifierAwareExtension
+{
+
+	/** @var \PHPStan\Analyser\TypeSpecifier */
+	private $typeSpecifier;
+
+	public function isFunctionSupported(FunctionReflection $functionReflection, FuncCall $node, TypeSpecifierContext $context): bool
+	{
+		return strtolower($functionReflection->getName()) === 'is_countable'
+			&& isset($node->args[0])
+			&& !$context->null();
+	}
+
+	public function specifyTypes(FunctionReflection $functionReflection, FuncCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
+	{
+		if ($context->null()) {
+			throw new \PHPStan\ShouldNotHappenException();
+		}
+
+		return $this->typeSpecifier->create(
+			$node->args[0]->value,
+			new UnionType([
+				new ArrayType(new MixedType(), new MixedType()),
+				new ObjectType(\Countable::class),
+			]),
+			$context
+		);
+	}
+
+	public function setTypeSpecifier(TypeSpecifier $typeSpecifier): void
+	{
+		$this->typeSpecifier = $typeSpecifier;
+	}
+
+}

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -7608,6 +7608,49 @@ public function testGetParentClass(
 		);
 	}
 
+	public function dataIsCountable(): array
+	{
+		return [
+			[
+				'array|Countable',
+				'$union',
+				"'is'",
+			],
+			[
+				'string',
+				'$union',
+				"'is_not'",
+			],
+		];
+	}
+
+	/**
+	 * @dataProvider dataIsCountable
+	 * @param string $description
+	 * @param string $expression
+	 * @param string $evaluatedPointExpression
+	 */
+	public function testIsCountable(
+		string $description,
+		string $expression,
+		string $evaluatedPointExpression
+	): void
+	{
+		if (PHP_VERSION_ID < 70300) {
+			$this->markTestSkipped('Test requires PHP 7.3');
+		}
+		$this->assertTypes(
+			__DIR__ . '/data/is_countable.php',
+			$description,
+			$expression,
+			[],
+			[],
+			[],
+			[],
+			$evaluatedPointExpression
+		);
+	}
+
 	private function assertTypes(
 		string $file,
 		string $description,

tests/PHPStan/Analyser/data/is_countable.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace IsCountable;
+
+class Foo
+{
+
+	/**
+	 * @param array|\Countable|string $union
+	 */
+	public function doFoo(
+		$union
+	)
+	{
+		if (is_countable($union)) {
+			'is';
+		} else {
+			'is_not';
+		}
+	}
+
+}