Narrow to non-empty-string via Strings::length

extension.neon

@@ -137,3 +137,13 @@ services:
 		class: PHPStan\Type\Nette\StringsReplaceCallbackClosureTypeExtension
 		tags:
 			- phpstan.staticMethodParameterClosureTypeExtension
+
+	-
+		class: PHPStan\Type\Nette\StringsLengthTypeSpecifiyingExtension
+		tags:
+			- phpstan.typeSpecifier.staticMethodTypeSpecifyingExtension
+
+	-
+		class: PHPStan\Type\Nette\StringsLengthDynamicReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicStaticMethodReturnTypeExtension

src/Type/Nette/StringsLengthDynamicReturnTypeExtension.php

@@ -0,0 +1,43 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Nette;
+
+use Nette\Utils\Strings;
+use PhpParser\Node\Expr\StaticCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\MethodReflection;
+use PHPStan\Type\DynamicStaticMethodReturnTypeExtension;
+use PHPStan\Type\IntegerRangeType;
+use PHPStan\Type\Type;
+
+class StringsLengthDynamicReturnTypeExtension implements DynamicStaticMethodReturnTypeExtension
+{
+
+	public function getClass(): string
+	{
+		return Strings::class;
+	}
+
+	public function isStaticMethodSupported(MethodReflection $methodReflection): bool
+	{
+		return $methodReflection->getName() === 'length';
+	}
+
+	public function getTypeFromStaticMethodCall(MethodReflection $methodReflection, StaticCall $methodCall, Scope $scope): ?Type
+	{
+		$args = $methodCall->getArgs();
+		$stringArg = $args[0] ?? null;
+
+		if ($stringArg === null) {
+			return null;
+		}
+
+		$type = $scope->getType($stringArg->value);
+		if ($type->isNonEmptyString()->yes()) {
+			return IntegerRangeType::fromInterval(1, null);
+		}
+
+		return null;
+	}
+
+}

src/Type/Nette/StringsLengthTypeSpecifiyingExtension.php

@@ -0,0 +1,60 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Nette;
+
+use Nette\Utils\Strings;
+use PhpParser\Node\Expr\StaticCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Analyser\SpecifiedTypes;
+use PHPStan\Analyser\TypeSpecifier;
+use PHPStan\Analyser\TypeSpecifierAwareExtension;
+use PHPStan\Analyser\TypeSpecifierContext;
+use PHPStan\Reflection\MethodReflection;
+use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
+use PHPStan\Type\IntersectionType;
+use PHPStan\Type\StaticMethodTypeSpecifyingExtension;
+use PHPStan\Type\StringType;
+
+class StringsLengthTypeSpecifiyingExtension implements StaticMethodTypeSpecifyingExtension, TypeSpecifierAwareExtension
+{
+
+	private TypeSpecifier $typeSpecifier;
+
+	public function setTypeSpecifier(TypeSpecifier $typeSpecifier): void
+	{
+		$this->typeSpecifier = $typeSpecifier;
+	}
+
+	public function getClass(): string
+	{
+		return Strings::class;
+	}
+
+	public function isStaticMethodSupported(MethodReflection $staticMethodReflection, StaticCall $node, TypeSpecifierContext $context): bool
+	{
+		return $context->true() && $staticMethodReflection->getName() === 'length';
+	}
+
+	public function specifyTypes(MethodReflection $staticMethodReflection, StaticCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
+	{
+		$args = $node->getArgs();
+		$stringArg = $args[0] ?? null;
+
+		if ($stringArg === null) {
+			return new SpecifiedTypes();
+		}
+
+		$type = $scope->getType($stringArg->value);
+		if (!$type->isString()->yes()) {
+			return new SpecifiedTypes();
+		}
+
+		return $this->typeSpecifier->create(
+			$stringArg->value,
+			new IntersectionType([new StringType(), new AccessoryNonEmptyStringType()]),
+			$context,
+			$scope,
+		);
+	}
+
+}

strings.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace StringsTypesNarrowing;
+
+use Nette\Utils\Strings;
+use function PHPStan\Testing\assertType;
+
+function doFoo(string $string) {
+	assertType('string', $string);
+	if (Strings::length($string)) {
+		assertType('non-empty-string', $string);
+	} else {
+		assertType('string', $string);
+	}
+	assertType('string', $string);
+
+	if (Strings::length($string) === 0) {
+		assertType('string', $string);
+	}
+	assertType('string', $string);
+}

tests/Type/Nette/MultiplierTest.php → tests/Type/Nette/TypeInferenceTest.php

@@ -8,7 +8,7 @@
 use function class_exists;
 use function version_compare;
 
-class MultiplierTest extends TypeInferenceTestCase
+class TypeInferenceTest extends TypeInferenceTestCase
 {
 
 	public function dataFileAsserts(): iterable
@@ -26,6 +26,8 @@ public function dataFileAsserts(): iterable
 		} else {
 			yield from self::gatherAssertTypes(__DIR__ . '/data/multiplier.php');
 		}
+
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/strings-length.php');
 	}
 
 	/**

tests/Type/Nette/data/strings-length.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace StringsTypesNarrowing;
+
+use Nette\Utils\Strings;
+use function PHPStan\Testing\assertType;
+
+function doFoo(string $string) {
+	assertType('string', $string);
+	if (Strings::length($string)) {
+		assertType('non-empty-string', $string);
+		assertType('int<1, max>', Strings::length($string));
+	} else {
+		assertType('string', $string);
+		assertType('0', Strings::length($string));
+	}
+	assertType('string', $string);
+	assertType('int', Strings::length($string));
+
+	if (Strings::length($string) === 0) {
+		assertType('string', $string);
+	}
+	assertType('string', $string);
+}
+
+/**
+ * @param non-empty-string $nonES
+ */
+function doBar(string $nonES) {
+	assertType('int<1, max>', Strings::length($nonES));
+}