winpty: auto-detect redirects of stdin/stdout

[rimrul]

Running commands through winpty with a redirected stdin or
stdout only leads to error messages, that are at best not very
helpful to users and at worst outright confusing users.
We can do better by adding a thin wrapper script that detects
when it is and isn't appropriate to run a command through winpty
and acts accordingly.

This is an alternative to #414 that doesn't use undocumented options and shouldn't cause commands to think they're outputting to a console when they aren't.

[dscho]

That's an interesting idea!

However, I would like to see this in winpty.exe directly, rather than requiring a shell script wrapper (these things really bring a performance hit with them, on Windows).

I'd be totally willing to carry a patch in MSYS2-packages/winpty/ and build our own versions of the winpty package, but I could also imagine that the MSYS2 project would be quite keen on that.

What I have in mind is a new option that opts out of this new handling, so that by default we're checking isatty(0) && isatty(1) and if either one is redirected, simply spawn the child process with inherited handles (so that we do not have to pipe stdin/stdout/stderr back and forth) and skip the rest of winpty.

What do you think @rimrul?

[rimrul]

these things really bring a performance hit with them, on Windows

I've assumed the performance impact to be negligible when executing a shell script in bash, but you're probably right, this is probably a whole new bash proccess, just for this.

I could also imagine that the MSYS2 project would be quite keen on that.

That definitely sounds plausible.

What do you think @rimrul?

I'll see what I can do.

[dscho]

What do you think @rimrul?

I'll see what I can do.

Thank you!