Feature request: Add support for "reverse" color effect

[bwpge]

Just wanted to prefix this with a sincere thank you for all your hard work and great libraries/tools you given to us 😄

I tried searching the closed issues for anything related to "reverse", "invert", or "negative" keywords but did not find anything.

Issue

termcolor does not expose any way to use the "reverse" color effect (see n = 7: https://en.wikipedia.org/wiki/ANSI_escape_code#SGR_(Select_Graphic_Rendition)_parameters).

Using the reverse effect instead of hardcoding "black/white on green background" or something similar provides more consistent styled output, since many terminal themes use different primary/intense colors than the background color.

It also properly handles light and dark backgrounds, which cannot be determined using 16 theme colors. Hardcoding RGB colors can guarantee legible output, but will not be consistent with the user's theme.

Proposed Feature

ColorSpec could offer reverse and set_reverse methods, similar to effects such as bold and underline.

Usage might look something like:

let mut stdout = StandardStream::stdout(ColorChoice::Always);
stdout.set_color(ColorSpec::new().set_reverse(true))?;

Naive Implementation

Adding a field to ColorSpec:

/// A color specification.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct ColorSpec {
    fg_color: Option<Color>,
    bg_color: Option<Color>,
    bold: bool,
    reverse: bool, // added
    intense: bool,
    underline: bool,
    dimmed: bool,
    italic: bool,
    reset: bool,
    strikethrough: bool,
}

For the WriteColor implementation for Ansi<W>, a small adjustment might work fine for non-Windows terminals;

fn set_color(&mut self, spec: &ColorSpec) -> io::Result<()> {
    if spec.reset {
        self.reset()?;
    }
    // begin: added
    if spec.reverse {
        self.write_str("\x1B[7m")?;
    }
    // end: added
    if spec.bold {
        self.write_str("\x1B[1m")?;
    }
    // ...
    Ok(())
}

Windows Considerations

I have no clue how windows handles this, nor am I familiar with GetConsoleMode or SetConsoleMode. It seems some of that is handled by the winapi-utils crate, so I haven't really dug in too much on it.

References

• https://en.wikipedia.org/wiki/ANSI_escape_code
• https://en.wikipedia.org/wiki/Reverse_video
• Value = 7, called "Negative": https://learn.microsoft.com/en-us/windows/console/console-virtual-terminal-sequences#text-formatting

[bwpge]

Adding additional reference for Windows implementation.

Since wincolor uses set_text_attribute from winapi_util (through the Console::set method), it seems this could be done using COMMON_LVB_REVERSE_VIDEO.

References:

• https://docs.rs/winapi-util/latest/winapi_util/console/fn.set_text_attributes.html
• https://learn.microsoft.com/en-us/windows/console/setconsoletextattribute
• https://learn.microsoft.com/en-us/windows/console/console-screen-buffers#character-attributes