Fix accepted types for fputcsv fields parameter

src/Reflection/SignatureMap/NativeFunctionReflectionProvider.php

@@ -6,12 +6,14 @@
 use PHPStan\Reflection\Native\NativeFunctionReflection;
 use PHPStan\Reflection\Native\NativeParameterReflection;
 use PHPStan\TrinaryLogic;
+use PHPStan\Type\ArrayType;
 use PHPStan\Type\BooleanType;
 use PHPStan\Type\FloatType;
 use PHPStan\Type\Generic\TemplateTypeMap;
 use PHPStan\Type\IntegerType;
 use PHPStan\Type\NullType;
 use PHPStan\Type\StringAlwaysAcceptingObjectWithToStringType;
+use PHPStan\Type\StringType;
 use PHPStan\Type\UnionType;
 
 class NativeFunctionReflectionProvider
@@ -63,6 +65,26 @@ public function findFunctionReflection(string $functionName): ?NativeFunctionRef
 							new BooleanType(),
 						]);
 					}
+
+					if (
+						$parameterSignature->getName() === 'fields'
+						&& $lowerCasedFunctionName === 'fputcsv'
+					) {
+						$type = new ArrayType(
+							new UnionType([
+								new StringType(),
+								new IntegerType(),
+							]),
+							new UnionType([
+								new StringAlwaysAcceptingObjectWithToStringType(),
+								new IntegerType(),
+								new FloatType(),
+								new NullType(),
+								new BooleanType(),
+							])
+						);
+					}
+
 					return new NativeParameterReflection(
 						$parameterSignature->getName(),
 						$parameterSignature->isOptional(),

tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php

@@ -411,6 +411,28 @@ public function testUnpackOperator(): void
 		]);
 	}
 
+	public function testFputCsv(): void
+	{
+		$this->analyse([__DIR__ . '/data/fputcsv-fields-parameter.php'], [
+			[
+				'Parameter #2 $fields of function fputcsv expects array<int|string, bool|float|int|string|null>, array<int, Fputcsv\Person> given.',
+				35,
+			],
+		]);
+	}
+
+
+	public function testPutCsvWithStringable(): void
+	{
+		if (PHP_VERSION_ID < 80000) {
+			$this->markTestSkipped('Test skipped on lower version than 8.0 (needs Stringable interface, added in PHP8)');
+		}
+
+		$this->analyse([__DIR__ . '/data/fputcsv-fields-parameter-php8.php'], [
+			// No issues expected
+		]);
+	}
+
 	public function testFunctionWithNumericParameterThatCreatedByAddition(): void
 	{
 		$this->analyse([__DIR__ . '/data/function-with-int-parameter-that-created-by-addition.php'], [

tests/PHPStan/Rules/Functions/data/fputcsv-fields-parameter-php8.php

@@ -0,0 +1,19 @@
+<?php declare(strict_types = 1);
+
+namespace FputcsvPhp8;
+
+class StringablePerson implements \Stringable {
+	public function __toString(): string {
+		return "stringable name";
+	}
+}
+
+class CsvWriterPhp8
+{
+	/** @param resource $handle */
+	public function write($handle): void
+	{
+		// This is valid. StringablePerson should be treated as a string
+		fputcsv($handle, [new StringablePerson()]);
+	}
+}

tests/PHPStan/Rules/Functions/data/fputcsv-fields-parameter.php

@@ -0,0 +1,40 @@
+<?php declare(strict_types=1);
+
+namespace Fputcsv;
+
+class Person
+{
+}
+
+class PersonWithToString
+{
+	public function __toString(): string
+	{
+		return "to string name";
+	}
+}
+
+class CsvWriter
+{
+	/** @param resource $handle */
+	public function writeCsv($handle): void
+	{
+		// These are all valid scalers
+		fputcsv($handle, [
+			"string",
+			1,
+			3.5,
+			true,
+			false,
+			null, // Yes this is accepted by fputcsv,
+		]);
+
+		// Arrays can have string for keys (which are ignored)
+		fputcsv($handle, ["foo" => "bar",]);
+
+		fputcsv($handle, [new Person,]); // Problem on this line
+
+		// This is valid. PersonWithToString should be cast to string by fputcsv
+		fputcsv($handle, [new PersonWithToString()]);
+	}
+}