Description

lambda-term 3.3.3 segfaults on Windows (GitHub Actions windows-latest runner, OCaml 4.14.3) when LTerm.stdout is force-evaluated. This affects utop and anything built on top of it (e.g. Reason's rtop).

Reproduction

On a Windows GitHub Actions runner (or any Windows environment where stdout may not be a real console handle):

echo "1 + 1;;" | utop 2>&1

Output:

OCaml version 4.14.3
Enter #help;; for help.

Segmentation fault

This also happens without piped input — just running utop segfaults.

Environment

• OS: Windows (GitHub Actions windows-latest runner)
• OCaml: 4.14.3
• lambda-term: 3.3.3
• utop: 2.16.0
• lwt: 6.1.1

Analysis

The crash appears to be in lt_term_get_size_from_fd in lTerm_term_stubs.c:

CAMLprim value lt_term_get_size_from_fd(value fd)
{
  CONSOLE_SCREEN_BUFFER_INFO info;
  if (!GetConsoleScreenBufferInfo(Handle_val(fd), &info)) {
    win32_maperr(GetLastError());
    uerror("GetConsoleScreenBufferInfo", Nothing);
  }
  ...
}