Dynamic return type extension for understanding compact function

conf/config.neon

@@ -896,6 +896,11 @@ services:
 		tags:
 			- phpstan.broker.dynamicStaticMethodReturnTypeExtension
 
+	-
+		class: PHPStan\Type\Php\CompactFunctionReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicFunctionReturnTypeExtension
+
 	-
 		class: PHPStan\Type\Php\CountFunctionReturnTypeExtension
 		tags:

resources/functionMap.php

@@ -1048,7 +1048,7 @@
 'com_message_pump' => ['bool', 'timeoutms='=>'int'],
 'com_print_typeinfo' => ['bool', 'comobject_or_typelib'=>'object', 'dispinterface='=>'string', 'wantsink='=>'bool'],
 'com_release' => [''],
-'compact' => ['array', '...var_names='=>'string|array'],
+'compact' => ['array<string, mixed>', '...var_names='=>'string|array'],
 'COMPersistHelper::__construct' => ['void', 'com_object'=>'object'],
 'COMPersistHelper::GetCurFile' => ['string'],
 'COMPersistHelper::GetMaxStreamSize' => ['int'],

src/Type/Php/CompactFunctionReturnTypeExtension.php

@@ -0,0 +1,85 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use PhpParser\Node\Expr\FuncCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Reflection\ParametersAcceptorSelector;
+use PHPStan\Type\Constant\ConstantArrayType;
+use PHPStan\Type\Constant\ConstantArrayTypeBuilder;
+use PHPStan\Type\Constant\ConstantStringType;
+use PHPStan\Type\DynamicFunctionReturnTypeExtension;
+use PHPStan\Type\Type;
+
+class CompactFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
+{
+
+	public function isFunctionSupported(FunctionReflection $functionReflection): bool
+	{
+		return $functionReflection->getName() === 'compact';
+	}
+
+	public function getTypeFromFunctionCall(
+		FunctionReflection $functionReflection,
+		FuncCall $functionCall,
+		Scope $scope
+	): Type
+	{
+		$defaultReturnType = ParametersAcceptorSelector::selectSingle($functionReflection->getVariants())->getReturnType();
+		if (count($functionCall->args) === 0) {
+			return $defaultReturnType;
+		}
+
+		if ($scope->canAnyVariableExist()) {
+			return $defaultReturnType;
+		}
+
+		$array = ConstantArrayTypeBuilder::createEmpty();
+		foreach ($functionCall->args as $arg) {
+			$type = $scope->getType($arg->value);
+			$constantStrings = $this->findConstantStrings($type);
+			if ($constantStrings === null) {
+				return $defaultReturnType;
+			}
+			foreach ($constantStrings as $constantString) {
+				$has = $scope->hasVariableType($constantString->getValue());
+				if ($has->no()) {
+					continue;
+				}
+
+				$array->setOffsetValueType($constantString, $scope->getVariableType($constantString->getValue()), $has->maybe());
+			}
+		}
+
+		return $array->getArray();
+	}
+
+	/**
+	 * @param Type $type
+	 * @return array<int, ConstantStringType>|null
+	 */
+	private function findConstantStrings(Type $type): ?array
+	{
+		if ($type instanceof ConstantStringType) {
+			return [$type];
+		}
+
+		if ($type instanceof ConstantArrayType) {
+			$result = [];
+			foreach ($type->getValueTypes() as $valueType) {
+				$constantStrings = $this->findConstantStrings($valueType);
+				if ($constantStrings === null) {
+					return null;
+				}
+
+				$result = array_merge($result, $constantStrings);
+			}
+
+			return $result;
+		}
+
+		return null;
+	}
+
+}

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -10743,6 +10743,11 @@ public function dataBug4415(): array
 		return $this->gatherAssertTypes(__DIR__ . '/data/bug-4415.php');
 	}
 
+	public function dataCompact(): array
+	{
+		return $this->gatherAssertTypes(__DIR__ . '/data/compact.php');
+	}
+
 	/**
 	 * @param string $file
 	 * @return array<string, mixed[]>
@@ -10955,6 +10960,7 @@ private function gatherAssertTypes(string $file): array
 	 * @dataProvider dataClosureReturnType
 	 * @dataProvider dataBug4398
 	 * @dataProvider dataBug4415
+	 * @dataProvider dataCompact
 	 * @param string $assertType
 	 * @param string $file
 	 * @param mixed ...$args

tests/PHPStan/Analyser/data/compact.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace CompactExtension;
+
+use function PHPStan\Analyser\assertType;
+
+assertType('array<string, mixed>', compact(['foo' => 'bar']));
+
+function (string $dolor): void {
+	$foo = 'bar';
+	$bar = 'baz';
+	if (rand(0, 1)) {
+		$lorem = 'ipsum';
+	}
+	assertType('array(\'foo\' => \'bar\', \'bar\' => \'baz\')', compact('foo', ['bar']));
+	assertType('array(\'foo\' => \'bar\', \'bar\' => \'baz\', ?\'lorem\' => \'ipsum\')', compact([['foo']], 'bar', 'lorem'));
+
+	assertType('array<string, mixed>', compact($dolor));
+	assertType('array<string, mixed>', compact([$dolor]));
+
+	assertType('array()', compact([]));
+};