Replace highlight_string() stub with a return type extension

conf/config.neon

@@ -1497,6 +1497,11 @@ services:
 		tags:
 			- phpstan.broker.dynamicFunctionReturnTypeExtension
 
+	-
+		class: PHPStan\Type\Php\HighlightStringDynamicReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicFunctionReturnTypeExtension
+
 	-
 		class: PHPStan\Type\Php\IntdivThrowTypeExtension
 		tags:

src/Php/PhpVersion.php

@@ -343,4 +343,9 @@ public function hasExitAsFunction(): bool
 		return $this->versionId >= 80400;
 	}
 
+	public function highlightStringDoesNotReturnFalse(): bool
+	{
+		return $this->versionId >= 80400;
+	}
+
 }

src/Type/Php/HighlightStringDynamicReturnTypeExtension.php

@@ -0,0 +1,51 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use PhpParser\Node\Expr\FuncCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Php\PhpVersion;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\BooleanType;
+use PHPStan\Type\Constant\ConstantBooleanType;
+use PHPStan\Type\DynamicFunctionReturnTypeExtension;
+use PHPStan\Type\StringType;
+use PHPStan\Type\Type;
+use function count;
+
+final class HighlightStringDynamicReturnTypeExtension implements DynamicFunctionReturnTypeExtension
+{
+
+	public function __construct(private PhpVersion $phpVersion)
+	{
+	}
+
+	public function isFunctionSupported(FunctionReflection $functionReflection): bool
+	{
+		return $functionReflection->getName() === 'highlight_string';
+	}
+
+	public function getTypeFromFunctionCall(FunctionReflection $functionReflection, FuncCall $functionCall, Scope $scope): Type
+	{
+		$args = $functionCall->getArgs();
+		if (count($args) < 2) {
+			if ($this->phpVersion->highlightStringDoesNotReturnFalse()) {
+				return new ConstantBooleanType(true);
+			}
+
+			return new BooleanType();
+		}
+
+		$returnType = $scope->getType($args[1]->value);
+		if ($returnType->isTrue()->yes()) {
+			return new StringType();
+		}
+
+		if ($this->phpVersion->highlightStringDoesNotReturnFalse()) {
+			return new ConstantBooleanType(true);
+		}
+
+		return new BooleanType();
+	}
+
+}

stubs/core.stub

@@ -35,12 +35,6 @@ function highlight_file($var, bool $return = false) {}
  */
 function show_source($var, bool $return = false) {}
 
-/**
- * @param mixed $var
- * @return ($return is true ? string : bool)
- */
-function highlight_string($var, bool $return = false) {}
-
 /**
  * @param mixed $var
  * @param bool $return

tests/PHPStan/Analyser/nsrt/pr-1244-php-84.php

@@ -0,0 +1,35 @@
+<?php // lint >= 8.4
+
+namespace Pr1244Php84;
+
+use function PHPStan\Testing\assertType;
+
+function foo() {
+	/** @var string $string */
+	$string = doFoo();
+
+	assertType('null', var_export());
+	assertType('null', var_export($string));
+	assertType('null', var_export($string, false));
+	assertType('string', var_export($string, true));
+
+	assertType('true', highlight_string());
+	assertType('true', highlight_string($string));
+	assertType('true', highlight_string($string, false));
+	assertType('string', highlight_string($string, true));
+
+	assertType('bool', highlight_file());
+	assertType('bool', highlight_file($string));
+	assertType('bool', highlight_file($string, false));
+	assertType('string', highlight_file($string, true));
+
+	assertType('bool', show_source());
+	assertType('bool', show_source($string));
+	assertType('bool', show_source($string, false));
+	assertType('string', show_source($string, true));
+
+	assertType('true', print_r());
+	assertType('true', print_r($string));
+	assertType('true', print_r($string, false));
+	assertType('string', print_r($string, true));
+}

tests/PHPStan/Analyser/nsrt/pr-1244.php

@@ -1,4 +1,4 @@
-<?php
+<?php // lint < 8.4
 
 namespace Pr1244;