session_write_close() returns true when the session data could not be written #24561

Description

session_write_close() returns true even when the session data could not be written. The manual says it "Returns true on success or false on failure", but php_session_flush() returns true whenever the session was active, and php_session_save_current_state() does not report the write result.

The following code:

<?php
ini_set('session.use_cookies', 0);
ini_set('session.cache_limiter', '');
class H implements SessionHandlerInterface {
    function open($p, $n): bool { return true; }
    function close(): bool { return true; }
    function read($id): string|false { return ''; }
    function write($id, $data): bool { echo "write() called, returning false\n"; return false; }
    function destroy($id): bool { return true; }
    function gc($m): int|false { return 0; }
}
session_set_save_handler(new H, false);
session_id('abc');
session_start();
$_SESSION['x'] = 1;
var_dump(session_write_close());

Resulted in this output:

write() called, returning false

Warning: session_write_close(): Failed to write session data using user defined save handler. (session.save_path: , handler: H::write) in ... on line 17
bool(true)

But I expected this output instead:

write() called, returning false

Warning: session_write_close(): Failed to write session data using user defined save handler. (session.save_path: , handler: H::write) in ... on line 17
bool(false)

The same happens when encoding fails (e.g. a key containing |): the recently added ext/session/tests/session_write_close_encode_failure.phpt expects bool(true) after the "Failed to write session data" warning, so I'm not sure whether returning true here is intended (meaning "the session was closed") or whether session_write_close() should report the failed write. If it should, I'm happy to send a PR for master (php_session_save_current_state() returning its result and php_session_flush() passing it on), since it changes the return value.

PHP Version

PHP 8.4.28-dev (PHP-8.4 at b4ca62e); same code on master

Operating System

Linux x86-64

This issue was found by an LLM-Enhanced Static Analysis Engine and verified manually.