string_width

gleam add string_width@2

import string_width

pub fn main() {
  string_width.dimensions("hello,\n안녕하세요", [])
  // --> #(2, 10)

  string_width.line("👩‍👩‍👦‍👦", [string_width.HandleGraphemeClusters])
  // --> 2
}

A small package estimating the required number of cells when printing a string on the terminal. It supports all Gleam targets and passes the tests of the NPM string-width package.

Limitations

• Many terminals don’t support grapheme clusters properly, so by default, the values returned by this library try to match the behaviour of libc instead of modern text rendering pipelines.

• The width of many characters is context-dependent and may vary based on the current locale, selected font, operating system, or surrounding context; The numbers reported by the functions in this library may not be fully accurate.

  If you encounter a mismatch that is consistent across multiple environments, feel free to open an issue or ping me on Discord!

• The behaviour when encountering stray variant selectors does not match other similar libraries.

Sources

The table lookup technique used by this library is heavily based on the musl libc wcwidth implementation. I built updated tables using the Unicode 16.0 data, and added support for ambiguous characters. It also uses the regex of the ansi-regex npm package, and the test cases of the string-width npm package.

• UAX #11 East Asian Width: https://www.unicode.org/reports/tr11/
• Grapheme Clusters in Terminals: https://mitchellh.com/writing/grapheme-clusters-in-terminals
• get-east-asian-width: https://github.com/sindresorhus/get-east-asian-width
• string-width: https://github.com/sindresorhus/string-width
• ansi-regex: https://github.com/chalk/ansi-regex
• musl-libc wcwidth: https://git.musl-libc.org/cgit/musl/tree/src/ctype/wcwidth.c
• glibc wcwidth: https://sourceware.org/git/?p=glibc.git;a=blob;f=wcsmbs/wcwidth.h;hb=HEAD