Keep the openssl cipher probe's warnings inside the probe

openssl_get_cipher_methods() reports algorithms openssl_cipher_iv_length()
rejects on PHP 8.0-8.4 (php/php-src#19994) - 40 of 248 on PHP 8.4.23 - so
the provider filters them out by probing each one, and each rejection warns.

The @ operator is not enough on its own: a user error handler that does not
consult error_reporting() is still called for a suppressed diagnostic, and
whatever installs one is out of our hands. A handler of our own on top of the
stack for the duration of the probe swallows the warning whoever else is
listening, and leaves theirs in place afterwards.

The reported cipher list, and so the result cache key, is unchanged.

Author: SanderMuller

src/Type/Php/OpenSslCipherMethodsProvider.php

@@ -12,6 +12,8 @@
 use function implode;
 use function in_array;
 use function openssl_cipher_iv_length;
+use function restore_error_handler;
+use function set_error_handler;
 use function openssl_get_cipher_methods;
 use function sort;
 use function strtolower;
@@ -50,10 +52,22 @@ private function getSupportedCipherMethods(): array
 			// openssl_get_cipher_methods() reports algorithms that are not actually
 			// supported on PHP 8.0-8.4 due to https://github.com/php/php-src/issues/19994
 			// Filter by actually testing each algorithm with openssl_cipher_iv_length().
-			$methods = array_values(array_filter(
-				openssl_get_cipher_methods(true),
-				static fn (string $algorithm): bool => @openssl_cipher_iv_length($algorithm) !== false,
-			));
+			//
+			// Probing an unsupported algorithm warns, and @ is not enough on its own: a user error
+			// handler that does not consult error_reporting() is still called for a suppressed
+			// diagnostic, and whatever installs one is out of our hands. A handler of our own on top
+			// of the stack for the duration of the probe swallows the warning whoever else is
+			// listening, and leaves theirs in place afterwards.
+			set_error_handler(static fn (): bool => true);
+
+			try {
+				$methods = array_values(array_filter(
+					openssl_get_cipher_methods(true),
+					static fn (string $algorithm): bool => openssl_cipher_iv_length($algorithm) !== false,
+				));
+			} finally {
+				restore_error_handler();
+			}
 		}
 
 		$this->supportedCipherMethods = array_map('strtolower', $methods);

tests/PHPStan/Type/Php/OpenSslCipherMethodsProviderTest.php

@@ -3,6 +3,8 @@
 namespace PHPStan\Type\Php;
 
 use PHPStan\Testing\PHPStanTestCase;
+use function restore_error_handler;
+use function set_error_handler;
 
 class OpenSslCipherMethodsProviderTest extends PHPStanTestCase
 {
@@ -28,6 +30,36 @@ public function testHashIgnoresTheOrderTheCiphersAreReportedIn(): void
 		);
 	}
 
+	/**
+	 * Reading the ciphers out of the runtime means probing each one, and on PHP 8.0-8.4
+	 * openssl_get_cipher_methods() reports algorithms openssl_cipher_iv_length() rejects with a
+	 * warning (php/php-src#19994) - 40 of 248 on PHP 8.4.23. `@` does not settle that: a user error
+	 * handler that does not consult error_reporting() is still called for a suppressed diagnostic.
+	 * See phpstan/phpstan#15176.
+	 *
+	 * Vacuous on a PHP where nothing is rejected, which is why the count is not asserted - only that
+	 * whatever the probe does stays inside it.
+	 */
+	public function testProbingTheRuntimeLeaksNoWarningThroughAnUnsuppressedHandler(): void
+	{
+		$leaked = [];
+		set_error_handler(static function (int $errno, string $errstr) use (&$leaked): bool {
+			// deliberately does not check error_reporting(), so the @ operator does not hide anything
+			$leaked[] = $errstr;
+
+			return true;
+		});
+
+		try {
+			$hash = (new OpenSslCipherMethodsProvider())->getHash();
+		} finally {
+			restore_error_handler();
+		}
+
+		$this->assertSame([], $leaked, 'Probing the runtime for supported ciphers must not emit warnings.');
+		$this->assertNotSame('', $hash);
+	}
+
 	/**
 	 * @param list<string> $supportedCipherMethods
 	 */