Add stream test that loses buffer after cast

Co-authored-by: Arnaud Le Blanc <[email protected]>

Author: Girgias

ext/standard/tests/streams/stream_cast_loses_data.phpt

@@ -0,0 +1,33 @@
+--TEST--
+Casting a stream can lose data and needs to emit a warning
+--FILE--
+<?php
+
+$tempnam = tempnam(sys_get_temp_dir(), 'test');
+
+$stream = popen('echo 1; echo 2; rm ' . escapeshellarg($tempnam), 'r');
+
+do {
+    usleep(10);
+    clearstatcache();
+} while (file_exists($tempnam));
+
+// fills the read buffer with up to 8192 bytes
+fgets($stream);
+
+// cast $stream and read fd until eof. Print each line that was read, prefixed with "proc open stdin:"
+$process = proc_open(
+    'sed "s/^/proc open stdin:/"',
+    [
+        0 => $stream,
+        1 => ['pipe', 'w'],
+    ],
+    $pipes,
+);
+
+var_dump(stream_get_contents($pipes[1]));
+
+?>
+--EXPECTF--
+Warning: proc_open(): 2 bytes of buffered data lost during stream conversion! in %s on line %d
+string(0) ""