Keep colored output for --color=auto on Windows

[MichaelKim0407]

Since there is no termios module on Windows, there is no way to emulate a terminal, which means when using --color=auto option, we cannot trick subprocess to think that it is connected to a terminal instead of a pipe. Thus, with --color=auto option, there will be no colored output.

This trick is essential for --color=auto or -G for BSD.

One way to force colored output is to replace --color=auto with --color=always, however this will have undesired consequences when using a pipe or redirecting to a file. We can try to detect if os.stdout is a terminal or not. However the current solution also uses termios.

Any input is welcome.

[MichaelKim0407]

I figured that we can simple use isatty to detect is stdout is terminal or not. It is not *nix only.

However as I tested, isatty always returns False in git-bash, although it works correctly on Windows cmd...

[abhiramr]

Right now, it already works and the same effect can still be obtained using
ls-git -l --color
(Not sure if this is already a known consequence.)

[MichaelKim0407]

@abhiii5459 --color is --color=always, which means output is always colored, whether it's a terminal or a pipe/redirect. If you redirect the output to a file and edit it, you will actually see stuff like \033[01;31m which means bold red...

The tricky thing here is not --color=always, but --color=auto, in which case the program needs to detect whether the output is terminal or not, and then decide if output should be colored. But I haven't found a way to do it when running python in git-bash.