gecko-dev/third_party/rust/textwrap

Textwrap

Textwrap is a library for wrapping and indenting text. It is most often used by command-line programs to format dynamic output nicely so it looks good in a terminal. You can also use Textwrap to wrap text set in a proportional font—such as text used to generate PDF files, or drawn on a HTML5 canvas using WebAssembly.

Usage

To use the textwrap crate, add this to your Cargo.toml file:

[dependencies]
textwrap = "0.16"

By default, this enables word wrapping with support for Unicode strings. Extra features can be enabled with Cargo features—and the Unicode support can be disabled if needed. This allows you slim down the library and so you will only pay for the features you actually use.

Please see the Cargo Features in the crate documentation for a full list of the available features as well as their impact on the size of your binary.

Documentation

API documentation

Getting Started

Word wrapping is easy using the wrap and fill functions:

#[cfg(feature = "smawk")] {
let text = "textwrap: an efficient and powerful library for wrapping text.";
assert_eq!(
    textwrap::wrap(text, 28),
    vec![
        "textwrap: an efficient",
        "and powerful library for",
        "wrapping text.",
    ]
);
}

Sharp-eyed readers will notice that the first line is 22 columns wide. So why is the word “and” put in the second line when there is space for it in the first line?

The explanation is that textwrap does not just wrap text one line at a time. Instead, it uses an optimal-fit algorithm which looks ahead and chooses line breaks which minimize the gaps left at ends of lines. This is controlled with the smawk Cargo feature, which is why the example is wrapped in the cfg-block.

Without look-ahead, the first line would be longer and the text would look like this:

#[cfg(not(feature = "smawk"))] {
let text = "textwrap: an efficient and powerful library for wrapping text.";
assert_eq!(
    textwrap::wrap(text, 28),
    vec![
        "textwrap: an efficient and",
        "powerful library for",
        "wrapping text.",
    ]
);
}

The second line is now shorter and the text is more ragged. The kind of wrapping can be configured via Options::wrap_algorithm.

If you enable the hyphenation Cargo feature, you get support for automatic hyphenation for about 70 languages via high-quality TeX hyphenation patterns.

Your program must load the hyphenation pattern and configure Options::word_splitter to use it:

#[cfg(feature = "hyphenation")] {
use hyphenation::{Language, Load, Standard};
use textwrap::{fill, Options, WordSplitter};

let dictionary = Standard::from_embedded(Language::EnglishUS).unwrap();
let options = textwrap::Options::new(28).word_splitter(WordSplitter::Hyphenation(dictionary));
let text = "textwrap: an efficient and powerful library for wrapping text.";

assert_eq!(
    textwrap::wrap(text, &options),
    vec![
        "textwrap: an efficient and",
        "powerful library for wrap-",
        "ping text."
    ]
);
}

The US-English hyphenation patterns are embedded when you enable the hyphenation feature. They are licensed under a permissive license and take up about 88 KB in your binary. If you need hyphenation for other languages, you need to download a precompiled .bincode file and load it yourself. Please see the hyphenation documentation for details.

Wrapping Strings at Compile Time

If your strings are known at compile time, please take a look at the procedural macros from the textwrap-macros crate.

Examples

The library comes with a collection of small example programs that shows various features.

If you want to see Textwrap in action right away, then take a look at examples/wasm/, which shows how to wrap sans-serif, serif, and monospace text. It uses WebAssembly and is automatically deployed to https://mgeisler.github.io/textwrap/.

For the command-line examples, you’re invited to clone the repository and try them out for yourself! Of special note is examples/interactive.rs. This is a demo program which demonstrates most of the available features: you can enter text and adjust the width at which it is wrapped interactively. You can also adjust the Options used to see the effect of different WordSplitters and wrap algorithms.

Run the demo with

$ cargo run --example interactive

The demo needs a Linux terminal to function.

Release History

Please see the CHANGELOG file for details on the changes made in each release.

License

Textwrap can be distributed according to the MIT license. Contributions will be accepted under the same license.