Output colors support?

[sebasmagri]

As per log's review. Check out pretty_env_logger.
Issue in log

[budziq]

I'd love such feature.

Unfortunately I see is no way to support color output in cross platform way without changing the architecture somewhat (Builder::format having to return a String).
https://github.com/seanmonstar/pretty-env-logger shows colored output only on ANSI compliant terminals (as there you just need to add ansi control codes to the console). I've encountered this issue when working on https://github.com/azerupi/mdBook/pull/369

[KodrAus]

We should be able to support basic colour support now that the output isn't a plain string.

I'll have a play with it using term-painter and see where it gets us. Are there any other recommendations for terminal colouring libs?

[lnicola]

I've also seen https://github.com/BurntSushi/ripgrep/tree/master/termcolor and https://github.com/SergioBenitez/yansi.

[KodrAus]

Hmm, termcolor looks interesting, thanks I'll dig into it! In classic @BurntSushi style it looks like it solves all of life's problems.

[KodrAus]

Hmm, so the whole termcolor API is pretty interesting. Looks like Buffers + WriteColor could neatly solve this and #31 too, but means a new public dependency.

I'll spend some time spiking it out.

[lnicola]

It seems pretty lightweight, with no extra dependencies except on Windows.

[KodrAus]

Ah sorry I think half that comment stayed in my head.

If we want to support colours using termcolor then we'd need to change our format function from accepting a Box<Write> to accepting a Box<WriteColor> or something. In that case we're publicly exposing termcolor's API and need to be careful about upgrading it. That might not actually be a problem though. Just something I want to keep in mind.

It does look like a pretty self-contained crate though, so if this works out I don't think I'd have a problem depending on it in env_logger.

[BurntSushi]

I'm happy to see you're considering termcolor, but I would be careful of making it a public dep. I've never been particularly happy with its API. In particular, I think it is somewhat cumbersome to use. I think the idea of a WriteColor trait and the buffering strategy for multithreaded support is probably here to stay, but I'm particularly open to changing how colors are set and such.

Unfortunately, I don't have any specific plans as of yet to improve the API, but at this stage in the game I'm somewhat pretty relaxed about doing a semver bump on it.

[KodrAus]

Thanks for your thoughts @BurntSushi! If the API is still a bit unstable then we probably should avoid exposing it publicly, since I hope we can keep the next major release of env_logger around as long as the next major release of log.

I'm pretty sold on the Buffer API, which we can use privately for #31. For colours I'll play with introducing a concrete structure for the format writer rather than a trait object so we've got some more control and can at least provide some private methods for the default format to use colours.

[BurntSushi]

@KodrAus Sounds good!