Fix counting *scanf() format string placeholders

Update PrintfHelper.php to make

    public function getScanfPlaceholdersCount(string $format): ?int`

return the sscanf() vetted number of placeholders that return/assign
conversions.

Addresses long-standing regressions reported originally in
[phpstan-10260].

References:

- [phpstan-10260]
- phpstan/phpstan#10260 (comment)
- [phpstan-src-5591]
- [phpstan-14567]
- https://3v4l.org/WR85Q

[phpstan-10260]: phpstan/phpstan#10260
[phpstan-src-5591]: #5591
[phpstan-14567]: phpstan/phpstan#14567

Author: hakre

src/Rules/Functions/PrintfHelper.php

@@ -5,12 +5,14 @@
 use Nette\Utils\Strings;
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Php\PhpVersion;
+use ValueError;
 use function array_filter;
 use function array_keys;
 use function count;
 use function in_array;
 use function max;
 use function sprintf;
+use function sscanf;
 use function strlen;
 use const PREG_SET_ORDER;
 
@@ -26,24 +28,36 @@ public function __construct(private PhpVersion $phpVersion)
 
 	public function getPrintfPlaceholdersCount(string $format): ?int
 	{
-		return $this->getPlaceholdersCount(self::PRINTF_SPECIFIER_PATTERN, $format, false);
+		return $this->getPlaceholdersCount(self::PRINTF_SPECIFIER_PATTERN, $format);
 	}
 
 	/** @phpstan-return array<int, non-empty-list<PrintfPlaceholder>> parameter index => placeholders */
 	public function getPrintfPlaceholders(string $format): ?array
 	{
-		return $this->parsePlaceholders(self::PRINTF_SPECIFIER_PATTERN, $format, false);
+		return $this->parsePlaceholders(self::PRINTF_SPECIFIER_PATTERN, $format);
 	}
 
 	public function getScanfPlaceholdersCount(string $format): ?int
 	{
-		return $this->getPlaceholdersCount('(?<specifier>[cdDeEfinosuxX%s]|\[[^\]]+\])', $format, true);
+		if ($this->phpVersion->throwsValueErrorForInternalFunctions()) {
+			try {
+				$result = sscanf('', '%*n' . $format);
+			} catch (ValueError) {
+				return null;
+			}
+		} else {
+			$result = @sscanf('', '%*n' . $format);
+		}
+		if ($result === null) {
+			return null;
+		}
+		return count($result);
 	}
 
 	/**
 	 * @phpstan-return array<int, non-empty-list<PrintfPlaceholder>>|null parameter index => placeholders
 	 */
-	private function parsePlaceholders(string $specifiersPattern, string $format, bool $isScanf): ?array
+	private function parsePlaceholders(string $specifiersPattern, string $format): ?array
 	{
 		$addSpecifier = '';
 		if ($this->phpVersion->supportsHhPrintfSpecifier()) {
@@ -72,10 +86,6 @@ private function parsePlaceholders(string $specifiersPattern, string $format, bo
 			$showValueSuffix = false;
 
 			if (isset($placeholder['width']) && $placeholder['width'] !== '') {
-				if ($isScanf) {
-					// In scanf, * means assignment suppression - skip this placeholder entirely
-					continue;
-				}
 				$parsedPlaceholders[] = new PrintfPlaceholder(
 					sprintf('"%s" (width)', $placeholder[0]),
 					$parameterIdx++,
@@ -136,9 +146,9 @@ private function getAcceptingTypeBySpecifier(string $specifier): string
 		return 'mixed';
 	}
 
-	private function getPlaceholdersCount(string $specifiersPattern, string $format, bool $isScanf): ?int
+	private function getPlaceholdersCount(string $specifiersPattern, string $format): ?int
 	{
-		$placeholdersMap = $this->parsePlaceholders($specifiersPattern, $format, $isScanf);
+		$placeholdersMap = $this->parsePlaceholders($specifiersPattern, $format);
 		if ($placeholdersMap === null) {
 			return null;
 		}

tests/PHPStan/Rules/Functions/PrintfHelperTest.php

@@ -0,0 +1,72 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Functions;
+
+use Override;
+use PHPStan\Php\PhpVersion;
+use PHPStan\Testing\PHPStanTestCase;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\RequiresPhp;
+use ValueError;
+use const PHP_VERSION_ID;
+
+class PrintfHelperTest extends PHPStanTestCase
+{
+
+	private PrintfHelper $printf;
+
+	#[Override]
+	protected function setUp(): void
+	{
+		$this->printf = $this->getPhpVersionIdAwareHelper(PHP_VERSION_ID);
+	}
+
+	#[RequiresPhp('< 8.0.0')]
+	public function testReturnsNullForInvalidPatternOnLegacyPhpVersion(): void
+	{
+		$this->assertNull($this->printf->getScanfPlaceholdersCount('%a'));
+	}
+
+	#[RequiresPhp('>= 8.0.0')]
+	public function testReturnsNullForInvalidPatternOnPhp8(): void
+	{
+		$this->assertNull($this->printf->getScanfPlaceholdersCount('%a'));
+	}
+
+	#[RequiresPhp('>= 8.0.0')]
+	#[DataProvider('dataLegacyVersionIds')]
+	public function testLegacyVersionStillThrowsValueErrorOnPhp8(int $versionId): void
+	{
+		$helper = $this->getPhpVersionIdAwareHelper($versionId);
+		$this->expectException(ValueError::class);
+		$this->expectExceptionMessage('Bad scan conversion character "a"');
+		$helper->getScanfPlaceholdersCount('%a');
+		$this->fail('check your phpunit');
+	}
+
+	private function getPhpVersionIdAwareHelper(int $versionId): PrintfHelper
+	{
+		return new PrintfHelper($this->getPhpVersion($versionId));
+	}
+
+	private function getPhpVersion(int $versionId): PhpVersion
+	{
+		return new PhpVersion($versionId);
+	}
+
+	public static function dataLegacyVersionIds(): array
+	{
+		return [
+			'PHP 4.3.14' => [40314],
+			'PHP 5.0.20' => [50020],
+			'PHP 5.3.23' => [50323],
+			'PHP 5.5.36' => [50536],
+			'PHP 7.0.16' => [70016],
+			'PHP 7.1.0' => [70100],
+			'PHP 7.2.22' => [70222],
+			'PHP 7.3.0' => [70300],
+			'PHP 7.4.33' => [70433],
+		];
+	}
+
+}