str_pad() function return type extension

conf/config.neon

@@ -1265,6 +1265,11 @@ services:
 		tags:
 			- phpstan.broker.dynamicFunctionReturnTypeExtension
 
+	-
+		class: PHPStan\Type\Php\StrPadFunctionReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicFunctionReturnTypeExtension
+
 	-
 		class: PHPStan\Type\Php\ParseUrlFunctionDynamicReturnTypeExtension
 		tags:

src/Type/Php/StrPadFunctionReturnTypeExtension.php

@@ -0,0 +1,53 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use PhpParser\Node\Expr\FuncCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
+use PHPStan\Type\DynamicFunctionReturnTypeExtension;
+use PHPStan\Type\IntegerRangeType;
+use PHPStan\Type\IntersectionType;
+use PHPStan\Type\StringType;
+
+class StrPadFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
+{
+
+	public function isFunctionSupported(FunctionReflection $functionReflection): bool
+	{
+		return $functionReflection->getName() === 'str_pad';
+	}
+
+	public function getTypeFromFunctionCall(
+		FunctionReflection $functionReflection,
+		FuncCall $functionCall,
+		Scope $scope
+	): \PHPStan\Type\Type
+	{
+		$args = $functionCall->args;
+		if (count($args) < 2) {
+			return new StringType();
+		}
+
+		$inputType = $scope->getType($args[0]->value);
+		$lengthType = $scope->getType($args[1]->value);
+
+		if ($inputType->isNonEmptyString()->yes()) {
+			return new IntersectionType([
+				new StringType(),
+				new AccessoryNonEmptyStringType(),
+			]);
+		}
+
+		if (IntegerRangeType::fromInterval(1, null)->isSuperTypeOf($lengthType)->yes()) {
+			return new IntersectionType([
+				new StringType(),
+				new AccessoryNonEmptyStringType(),
+			]);
+		}
+
+		return new StringType();
+	}
+
+}

tests/PHPStan/Analyser/data/non-empty-string.php

@@ -304,6 +304,11 @@ public function doFoo(string $s, string $nonEmpty)
 		assertType('0', strlen(''));
 		assertType('int<0, max>', strlen($s));
 		assertType('int<1, max>', strlen($nonEmpty));
+
+		assertType('non-empty-string', str_pad($nonEmpty, 0));
+		assertType('non-empty-string', str_pad($nonEmpty, 1));
+		assertType('string', str_pad($s, 0));
+		assertType('non-empty-string', str_pad($s, 1));
 	}
 
 }