save/restore TTY attributes in test suite

[rolandwalker]

defending against a tig crash

[jonas]

What's the motivation for this? Tests are not supposed to touch the TTY.

[rolandwalker]

I believe the motivation is fairly covered in #725 (comment), but even without #725, there were some cases where a tig crash during tests left the TTY in a wrong state.

Ncurses may do some unexpected things to resolve conflicts: eg tig gives ncurses /dev/null for the third argument to newterm(), but then tig calls raw() and so on. And raw() must call ioctl(), which is only possible on an fd which refers to a device or special file (tty). raw() might be returning ENOTTY and we fail to check the return value.

But in at least some cases it seems that ncurses decides to muddle through with some undefined behavior. For example it switches to STDIN for wgetch() after being told that infd referred to /dev/null.

That is from memory, and I don't have the code in front of me, so some details may be wrong.

Feel free to decline the PR — it is just a bit of defensive driving. The explanation is for your interest.

[jonas]

Ah, OK. Thanks for the explanation. Makes sense.