Implement TypeSpecifierContext->getReturnType()

src/Analyser/TypeSpecifier.php

@@ -333,46 +333,6 @@ public function specifyTypesInCondition(
 				}
 			}
 
-			if (
-				!$context->null()
-				&& $expr->right instanceof FuncCall
-				&& count($expr->right->getArgs()) >= 3
-				&& $expr->right->name instanceof Name
-				&& in_array(strtolower((string) $expr->right->name), ['preg_match'], true)
-				&& IntegerRangeType::fromInterval(0, null)->isSuperTypeOf($leftType)->yes()
-			) {
-				return $this->specifyTypesInCondition(
-					$scope,
-					new Expr\BinaryOp\NotIdentical($expr->right, new ConstFetch(new Name('false'))),
-					$context,
-				)->setRootExpr($expr);
-			}
-
-			if (
-				!$context->null()
-				&& $expr->right instanceof FuncCall
-				&& count($expr->right->getArgs()) === 1
-				&& $expr->right->name instanceof Name
-				&& in_array(strtolower((string) $expr->right->name), ['strlen', 'mb_strlen'], true)
-				&& $leftType->isInteger()->yes()
-			) {
-				if (
-					$context->true() && (IntegerRangeType::createAllGreaterThanOrEqualTo(1 - $offset)->isSuperTypeOf($leftType)->yes())
-					|| ($context->false() && (new ConstantIntegerType(1 - $offset))->isSuperTypeOf($leftType)->yes())
-				) {
-					$argType = $scope->getType($expr->right->getArgs()[0]->value);
-					if ($argType->isString()->yes()) {
-						$accessory = new AccessoryNonEmptyStringType();
-
-						if (IntegerRangeType::createAllGreaterThanOrEqualTo(2 - $offset)->isSuperTypeOf($leftType)->yes()) {
-							$accessory = new AccessoryNonFalsyStringType();
-						}
-
-						$result = $result->unionWith($this->create($expr->right->getArgs()[0]->value, $accessory, $context, $scope)->setRootExpr($expr));
-					}
-				}
-			}
-
 			if ($leftType instanceof ConstantIntegerType) {
 				if ($expr->right instanceof Expr\PostInc) {
 					$result = $result->unionWith($this->createRangeTypes(
@@ -468,6 +428,26 @@ public function specifyTypesInCondition(
 				}
 			}
 
+			if (
+				!$context->null()
+				&& $expr->right instanceof Expr\FuncCall
+				&& $expr->right->name instanceof Name
+				&& in_array(strtolower((string) $expr->right->name), ['preg_match', 'strlen', 'mb_strlen'], true)
+			) {
+				if (!$scope instanceof MutatingScope) {
+					throw new ShouldNotHappenException();
+				}
+				$newScope = $scope->filterBySpecifiedTypes($result);
+				$callType = $newScope->getType($expr->right);
+				$newContext = $context->newWithReturnType($callType);
+
+				$result = $result->unionWith($this->specifyTypesInCondition(
+					$scope,
+					$expr->right,
+					$newContext,
+				)->setRootExpr($expr));
+			}
+
 			return $result;
 
 		} elseif ($expr instanceof Node\Expr\BinaryOp\Greater) {

src/Analyser/TypeSpecifierContext.php

@@ -3,6 +3,7 @@
 namespace PHPStan\Analyser;
 
 use PHPStan\ShouldNotHappenException;
+use PHPStan\Type\Type;
 
 /**
  * @api
@@ -18,17 +19,15 @@ final class TypeSpecifierContext
 	public const CONTEXT_FALSEY = self::CONTEXT_FALSE | self::CONTEXT_FALSEY_BUT_NOT_FALSE;
 	public const CONTEXT_BITMASK = 0b1111;
 
-	/** @var self[] */
-	private static array $registry;
+	private ?Type $returnType = null;
 
 	private function __construct(private ?int $value)
 	{
 	}
 
 	private static function create(?int $value): self
 	{
-		self::$registry[$value] ??= new self($value);
-		return self::$registry[$value];
+		return new self($value);
 	}
 
 	public static function createTrue(): self
@@ -89,4 +88,16 @@ public function null(): bool
 		return $this->value === null;
 	}
 
+	public function newWithReturnType(Type $type): self
+	{
+		$new = self::create($this->value);
+		$new->returnType = $type;
+		return $new;
+	}
+
+	public function getReturnType(): ?Type
+	{
+		return $this->returnType;
+	}
+
 }

src/Type/Php/StrlenTypeSpecifyingExtension.php

@@ -0,0 +1,74 @@
+<?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\DependencyInjection\AutowiredService;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
+use PHPStan\Type\Accessory\AccessoryNonFalsyStringType;
+use PHPStan\Type\Constant\ConstantIntegerType;
+use PHPStan\Type\FunctionTypeSpecifyingExtension;
+use PHPStan\Type\IntegerRangeType;
+use PHPStan\Type\NeverType;
+use function count;
+use function in_array;
+use function strtolower;
+
+#[AutowiredService]
+final class StrlenTypeSpecifyingExtension implements FunctionTypeSpecifyingExtension, TypeSpecifierAwareExtension
+{
+
+	private TypeSpecifier $typeSpecifier;
+
+	public function setTypeSpecifier(TypeSpecifier $typeSpecifier): void
+	{
+		$this->typeSpecifier = $typeSpecifier;
+	}
+
+	public function isFunctionSupported(FunctionReflection $functionReflection, FuncCall $node, TypeSpecifierContext $context): bool
+	{
+		return in_array(strtolower($functionReflection->getName()), ['strlen', 'mb_strlen'], true) && !$context->null();
+	}
+
+	public function specifyTypes(FunctionReflection $functionReflection, FuncCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
+	{
+		$args = $node->getArgs();
+		if (
+			count($args) < 1
+			|| $context->getReturnType() === null
+		) {
+			return new SpecifiedTypes();
+		}
+
+		$argType = $scope->getType($args[0]->value);
+		if (!$argType->isString()->yes()) {
+			return new SpecifiedTypes();
+		}
+
+		$returnType = $context->getReturnType();
+		if ($returnType instanceof NeverType) {
+			return $this->typeSpecifier->create($args[0]->value, $returnType, $context->negate(), $scope);
+		}
+
+		if (
+			$context->true() && IntegerRangeType::createAllGreaterThanOrEqualTo(1)->isSuperTypeOf($returnType)->yes()
+			|| ($context->false() && (new ConstantIntegerType(0))->isSuperTypeOf($returnType)->yes())
+		) {
+			$accessory = new AccessoryNonEmptyStringType();
+			if (IntegerRangeType::createAllGreaterThanOrEqualTo(2)->isSuperTypeOf($returnType)->yes()) {
+				$accessory = new AccessoryNonFalsyStringType();
+			}
+
+			return $this->typeSpecifier->create($args[0]->value, $accessory, $context, $scope)->setRootExpr($node);
+		}
+
+		return new SpecifiedTypes();
+	}
+
+}

tests/PHPStan/Analyser/nsrt/strlen-never.php

@@ -0,0 +1,50 @@
+<?php
+
+namespace StrlenNever;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param non-empty-string $nonES
+ * @param non-falsy-string $nonFalsy
+ * @param numeric-string $numericString
+ * @param lowercase-string $lower
+ * @param uppercase-string $upper
+ */
+function doFoo(string $s, $nonES, $nonFalsy, $numericString, $lower, $upper) {
+	if (strlen($s) <= 0) {
+		assertType("''", $s);
+	}
+	if (strlen($nonES) <= 0) {
+		assertType('*NEVER*', $nonES);
+	}
+	if (strlen($nonFalsy) <= 0) {
+		assertType('*NEVER*', $nonFalsy);
+	}
+	if (strlen($numericString) <= 0) {
+		assertType("*NEVER*", $numericString);
+	}
+	if (strlen($lower) <= 0) {
+		assertType("''", $lower);
+	}
+	if (strlen($upper) <= 0) {
+		assertType("''", $upper);
+	}
+
+	if (strlen($nonES) >= 0) {
+		assertType('non-empty-string', $nonES);
+	} else {
+		assertType('*NEVER*', $nonES);
+	}
+}
+
+
+function doBar(string $m): void
+{
+	if (strlen($m) >= 1) {
+		if (strlen($m) <= 0) {
+			assertType('*NEVER*', $m);
+		}
+	}
+}
+