Re: [PATCH] Cygwin: pty: keep interactive console input for native programs via Cygwin

Hi Johannes,

On Mon, 20 Jul 2026 09:43:18 +0000
"Johannes Schindelin  wrote:
> From: Johannes Schindelin <[email protected]>
> 
> Currently, when a native Windows program starts a Cygwin program while a
> pseudo console is active, and the Cygwin program then starts another
> native Windows program, the final program can lose access to console
> input. It then behaves as though its standard input were redirected
> instead of remaining interactive.
> 
> For example, a native `git.exe` may invoke shell aliases (i.e. execute a
> shell command) that would in turn call interactive Git commands who
> would no longer work because their standard input appeared to be
> redirected. This can be demonstrated as follows:
> 
>   git -c 'alias.console-probe=!powershell.exe -NoLogo -NoProfile -Command "
>     Write-Output ([Console]::IsInputRedirected)
>     try {
>       [void][Console]::KeyAvailable
>       exit 0
>     } catch {
>       exit 1
>     }
>   "' console-probe
> 
> Running this command with a Win32 version of `git.exe` currently prints
> `True` and exits with exit code 1. In the latest official release, where
> this bug is not present, it prints `False` and results in exit code 0.
> 
> The reason is to be fonud in the archetype code. Reminder: For each
> pseudo terminal (pty), the archetype is the shared pty fhandler that
> owns the underlying native handles and supplies them to every
> per-file-descriptor fhandler for that pty.
> 
> `open_with_arch()` calls `open()`, copies the first pty fhandler's state
> into the archetype, and then calls `open_setup()`. At that stage, pcon
> handle adoption already took place in `open_setup()`. This was not
> anticipated by 60a88896dc (Cygwin: pty: do not leak nat handles when
> adopting the pcon's in open_setup(), 2026-06-25), which tried to fix a
> leak by closing the superseded native handles as they were replaced in
> `open_setup()`.  Because `open_with_arch()` had already copied those
> handle values into the archetype, closing them invalidated the
> archetype's copies.
> 
> The archetype therefore retained stale values for those closed handles,
> which later pty fd fhandlers would inherit. If Windows reuses one of
> those values for a newly duplicated pcon handle, closing the stale value
> closes the new handle instead. The nested native program then receives
> unusable console input.
> 
> Preserve usable console input by moving the unchanged transactional pcon
> handle adoption to `open()`, before the archetype snapshot. The archetype
> then receives valid pcon handles, all pty fd fhandlers inherit live
> handles, and the superseded raw pipe handles are closed exactly once.
> 
> This commit is best viewed with `--color-moved`.
> 
> Fixes: 60a88896dce0 ("Cygwin: pty: do not leak nat handles when
>  adopting the pcon's in open_setup()")
> Assisted-by: GPT-5.6 Sol
> Signed-off-by: Johannes Schindelin <[email protected]>

How can I reproduce the issue in cygwin?
I tried:
$ git -c 'alias.console-probe=!powershell.exe -NoLogo -NoProfile -Command "
    Write-Output ([Console]::IsInputRedirected)
    try {
      [void][Console]::KeyAvailable
      exit 0
    } catch {
      exit 1
    }
  "' console-probe
False
$ '/cygdrive/c/Program Files/Git/mingw64/bin/git.exe' -c 'alias.console-probe=!powershell.exe -NoLogo -NoProfile -Command "
    Write-Output ([Console]::IsInputRedirected)
    try {
      [void][Console]::KeyAvailable
      exit 0
    } catch {
      exit 1
    }
  "' console-probe
False
$ '/cygdrive/c/Program Files/Git/bin/git.exe'  -c 'alias.console-probe=!powershell.exe -NoLogo -NoProfile -Command "
    Write-Output ([Console]::IsInputRedirected)
    try {
      [void][Console]::KeyAvailable
      exit 0
    } catch {
      exit 1
    }
  "' console-probe
False
$

All look successfull on master branch...

-- 
Takashi Yano <[email protected]>