Re: winpty injection

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Thomas,

On Thu, 16 Aug 2018, Thomas Wolff wrote:

> Am 09.04.2018 um 11:57 schrieb Corinna Vinschen:
> > On Apr  6 21:22, Johannes Schindelin wrote:
> > >
> > > On Fri, 6 Apr 2018, Thomas Wolff wrote:
> > >
> > > > Am 06.04.2018 um 12:31 schrieb Johannes Schindelin:
> > > > > On Fri, 6 Apr 2018, Thomas Wolff wrote:
> > > > >
> > > > > > These symptoms suggest to me: winpty is not the culprit, but its
> > > > > > presence in the invocation chain seems to trigger the effect in a
> > > > > > yet unclear way.
> > > > > Sure, `winpty` is not the culprit.
> > > > >
> > > > Actually, as it turns out, winpty *is* the culprit. I've raised winpty
> > > > issue https://github.com/rprichard/winpty/issues/140 about it.
> > > I am not sure you understand the issue here. The `winpty` helper opens a
> > > Win32 console for the native Windows application to use. Then it polls
> > > this (hidden) console for changes and tries to reflect them in the Cygwin
> > > pty.
> > >
> > > If that Windows application writes something to that console containing
> > > Escape sequences, then those Escape sequences occupy certain cells in that
> > > matrix of rows and columns making up that console.
> > >
> > > However, if the Windows application uses random-access functions to put
> > > individual characters into cells specified by given absolute positions,
> > > winpty cannot tell the difference. So what winpty would be asked to
> > > consider an ANSI sequence may never have been an ANSI sequence.
> > >
> > > Sure, this is a construed example, but it shows that you should not be so
> > > sure that winpty *can* detect ANSI sequences and handle them in a way that
> > > *you* want.
> > > [...]
> > > In the least, therefore, it should be configurable. And I would even argue
> > > that the default behavior should remain the same as current in Cygwin: do
> > > not use winpty by default.
> > >
> > > Of course, this is just my opinion, and I am but a user and infrequent
> > > contributor to Cygwin. But I would hope that the Cygwin maintainers use a
> > > lot of care and reluctant deliberation when considering a potentially
> > > disruptive change such as this, a change that may very well occupy a lot
> > > of time in dealing with the unwanted fallout.
> > Point taken.  Nicely explained.
> >
> > However, that makes calling winpty from Cygwin a somewhat questionable
> > endeavor.  Adding optional code paths which are in all likelyhood not
> > used very often, thus not tested very often, thus bound to rot, are not
> > really something I'm looking forward to.
> It seems that the new Windows ConPTY API will be a more reliable solution to
> these issues:
> https://blogs.msdn.microsoft.com/commandline/2018/08/02/windows-command-line-introducing-the-windows-pseudo-console-conpty/

And of course this will not apply to any Windows 7 or Windows 8 users. Or
to users who are for some reason stuck with a Windows 10 that is not
updated to the latest and greatest update.

Don't get me wrong, I am delighted what my colleagues do there, they are
doing great work, and Windows 10 will offer very nice features that Cygwin
can use to make things more reliable and/or faster.

Cygwin wants to support more Windows versions, though, so winpty will
still be needed, methinks.

Ciao,
Johannes