tidy: Make errors be printed in red and underlined

[scialex]

This is what it looks like with this patch

[alexcrichton]

Sadly I think that this is a unix-only-ism and may not work on windows, do you know if python translates this under the hood for windows?

[scialex]

@alexcrichton No. I bet there is some package on PyPI that does it but I don't know of one off the top of my head. OTOH this is just a Lint tool, even if it does not work all that will change is that something like "?[4;31m" will be printed before the error and "[0m" will be printed after it, which doesn't seem like all that bad an outcome considering it will help most people...

[ghost]

@scialex I think https://pypi.python.org/pypi/colorama is what you have in mind.

But for now we should be able to detect if we can print colours with https://docs.python.org/3/library/curses.html#curses.has_colors. r=me with that change.

[scialex]

@jakub- that won't work. Starting up curses clears the screen, which would somewhat defeat the purpose. It would also totally kill things like the travis, which rely on pipes working intelligently.

[bstrie]

We print colors elsewhere, so surely this shouldn't be blocked on that. If the problem is underlining, then I'd be fine removing the underlining and keeping the color. Even without the underline it stands out quite nicely.

Or am I misunderstanding how we handle color?

[alexcrichton]

I believe that all of our color printing from the compiler at least will perform detection of support at runtime. Not all shells work by printing these escapes (notably windows ones don't), and the compiler detects the best way to do so. If there was an easy way to guard this for only shells that support this form of colorization, then that would be great!

[nodakai]

Using the curses module should be preferred over hard-coding ANSI escape sequences. Cf. http://en.wikipedia.org/wiki/Tput#Usage

I'm not sure if Windows console is supported, but we can probably check with the curses.has_colors() method.

[scialex]

@nodakai No what we really need is something like https://pypi.python.org/pypi/colorama as @jakub- suggested. The problem with using curses is that is screws up piping if we aren't very careful, which would kill travis.

[nodakai]

Ah, I overlooked @jakub- already mentioned curses.has_colors()...

So we have two issues:

1. Windows(NT) doesn't support ANSI escape sequence at all. colorama addresses this issue by wrapping stdout and translating them to corresponding Win32 API. That's a nice addition. But...
2. Some tools like Travis which parses redirected stdout might get confused by ANSI escape sequences. colorama doesn't help here, so something like os.isatty() would be necessary after all.

(foo)$ cat a.py    
import colorama
print(colorama.Fore.RED + "Hello")
(foo)$ python a.py | xxd
0000000: 1b5b 3331 6d48 656c 6c6f 0a              .[31mHello.

Because of 2, we need to programatically switch on/off terminal coloring depending on the result of os.isatty(). Then hard-coding ANSI escape sequence is no good and we need a clever use of either curses.tigetstr() etc. or colorama.Fore.*.

In my previous comment, I almost suggested to disable terminal coloring on Windows by simply checking curses.has_colors() (because I don't use Windows at all 😁)

[alexcrichton]

Closing due to inactivity, but feel free to reopen with the windows issues addressed!