gecko-dev/third_party/rust/ansi_term/README.md

rust-ansi-term

This is a library for controlling colours and formatting, such as red bold text or blue underlined text, on ANSI terminals.

View the Rustdoc

Installation

This crate works with Cargo. Add the following to your Cargo.toml dependencies section:

[dependencies]
ansi_term = "0.8"

Basic usage

There are two main data structures in this crate that you need to be concerned with: ANSIString and Style. A Style holds stylistic information: colours, whether the text should be bold, or blinking, or whatever. There are also Colour variants that represent simple foreground colour styles. An ANSIString is a string paired with a Style.

(Yes, it’s British English, but you won’t have to write “colour” very often. Style is used the majority of the time.)

To format a string, call the paint method on a Style or a Colour, passing in the string you want to format as the argument. For example, here’s how to get some red text:

use ansi_term::Colour::Red;
println!("This is in red: {}", Red.paint("a red string"));

It’s important to note that the paint method does not actually return a string with the ANSI control characters surrounding it. Instead, it returns an ANSIString value that has a Display implementation that, when formatted, returns the characters. This allows strings to be printed with a minimum of String allocations being performed behind the scenes.

If you do want to get at the escape codes, then you can convert the ANSIString to a string as you would any other Display value:

use ansi_term::Colour::Red;
use std::string::ToString;
let red_string = Red.paint("a red string").to_string();

Bold, underline, background, and other styles

For anything more complex than plain foreground colour changes, you need to construct Style objects themselves, rather than beginning with a Colour. You can do this by chaining methods based on a new Style, created with Style::new(). Each method creates a new style that has that specific property set. For example:

use ansi_term::Style;
println!("How about some {} and {}?",
         Style::new().bold().paint("bold"),
         Style::new().underline().paint("underline"));

For brevity, these methods have also been implemented for Colour values, so you can give your styles a foreground colour without having to begin with an empty Style value:

use ansi_term::Colour::{Blue, Yellow};
println!("Demonstrating {} and {}!",
         Blue.bold().paint("blue bold"),
         Yellow.underline().paint("yellow underline"));
println!("Yellow on blue: {}", Yellow.on(Blue).paint("wow!"));

The complete list of styles you can use are: bold, dimmed, italic, underline, blink, reverse, hidden, and on for background colours.

In some cases, you may find it easier to change the foreground on an existing Style rather than starting from the appropriate Colour. You can do this using the fg method:

    use ansi_term::Style;
    use ansi_term::Colour::{Blue, Cyan, Yellow};
    println!("Yellow on blue: {}", Style::new().on(Blue).fg(Yellow).paint("yow!"));
    println!("Also yellow on blue: {}", Cyan.on(Blue).fg(Yellow).paint("zow!"));

Finally, you can turn a Colour into a Style with the normal method. This will produce the exact same ANSIString as if you just used the paint method on the Colour directly, but it’s useful in certain cases: for example, you may have a method that returns Styles, and need to represent both the “red bold” and “red, but not bold” styles with values of the same type. The Style struct also has a Default implementation if you want to have a style with nothing set.

use ansi_term::Style;
use ansi_term::Colour::Red;
Red.normal().paint("yet another red string");
Style::default().paint("a completely regular string");

Extended colours

You can access the extended range of 256 colours by using the Fixed colour variant, which takes an argument of the colour number to use. This can be included wherever you would use a Colour:

use ansi_term::Colour::Fixed;
Fixed(134).paint("A sort of light purple");
Fixed(221).on(Fixed(124)).paint("Mustard in the ketchup");

The first sixteen of these values are the same as the normal and bold standard colour variants. There’s nothing stopping you from using these as Fixed colours instead, but there’s nothing to be gained by doing so either.

You can also access full 24-bit color by using the RGB colour variant, which takes separate u8 arguments for red, green, and blue:

    use ansi_term::Colour::RGB;
    RGB(70, 130, 180).paint("Steel blue");

Combining successive coloured strings

The benefit of writing ANSI escape codes to the terminal is that they stack: you do not need to end every coloured string with a reset code if the text that follows it is of a similar style. For example, if you want to have some blue text followed by some blue bold text, it’s possible to send the ANSI code for blue, followed by the ANSI code for bold, and finishing with a reset code without having to have an extra one between the two strings.

This crate can optimise the ANSI codes that get printed in situations like this, making life easier for your terminal renderer. The ANSIStrings struct takes a slice of several ANSIString values, and will iterate over each of them, printing only the codes for the styles that need to be updated as part of its formatting routine.

The following code snippet uses this to enclose a binary number displayed in red bold text inside some red, but not bold, brackets:

use ansi_term::Colour::Red;
use ansi_term::{ANSIString, ANSIStrings};
let some_value = format!("{:b}", 42);
let strings: &[ANSIString<'static>] = &[
    Red.paint("["),
    Red.bold().paint(some_value),
    Red.paint("]"),
];
println!("Value: {}", ANSIStrings(strings));

There are several things to note here. Firstly, the paint method can take either an owned String or a borrowed &str. Internally, an ANSIString holds a copy-on-write (Cow) string value to deal with both owned and borrowed strings at the same time. This is used here to display a String, the result of the format! call, using the same mechanism as some statically-available &str slices. Secondly, that the ANSIStrings value works in the same way as its singular counterpart, with a Display implementation that only performs the formatting when required.

Byte strings

This library also supports formatting [u8] byte strings; this supports applications working with text in an unknown encoding. Style and Color support painting [u8] values, resulting in an ANSIByteString. This type does not implement Display, as it may not contain UTF-8, but it does provide a method write_to to write the result to any io::Write:

use ansi_term::Colour::Green;
Green.paint("user data".as_bytes()).write_to(&mut std::io::stdout()).unwrap();

Similarly, the type ANSIByteStrings supports writing a list of ANSIByteString values with minimal escape sequences:

use ansi_term::Colour::Green;
use ansi_term::ANSIByteStrings;
ANSIByteStrings(&[
    Green.paint("user data 1\n".as_bytes()),
    Green.bold().paint("user data 2\n".as_bytes()),
]).write_to(&mut std::io::stdout()).unwrap();