typst/src/syntax/ident.rs

//! Unicode identifiers.

use std::ops::Deref;

use unicode_xid::UnicodeXID;

/// An identifier as defined by unicode with a few extra permissible characters.
///
/// This is defined as in the [Unicode Standard], but allows additionally
/// `-` and `_` as starting and continuing characters.
///
/// [Unicode Standard]: http://www.unicode.org/reports/tr31/
#[derive(Debug, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
pub struct Ident(pub String);

impl Ident {
    /// Create a new identifier from a string checking that it is a valid.
    pub fn new(ident: impl AsRef<str> + Into<String>) -> Option<Self> {
        if is_ident(ident.as_ref()) {
            Some(Self(ident.into()))
        } else {
            None
        }
    }

    /// Return a reference to the underlying string.
    pub fn as_str(&self) -> &str {
        self
    }
}

impl AsRef<str> for Ident {
    fn as_ref(&self) -> &str {
        self
    }
}

impl Deref for Ident {
    type Target = str;

    fn deref(&self) -> &Self::Target {
        self.0.as_str()
    }
}

/// Whether the string is a valid identifier.
pub fn is_ident(string: &str) -> bool {
    let mut chars = string.chars();
    if matches!(chars.next(), Some(c) if c.is_xid_start() || is_also_ok(c)) {
        chars.all(|c| c.is_xid_continue() || is_also_ok(c))
    } else {
        false
    }
}

fn is_also_ok(c: char) -> bool {
    c == '-' || c == '_'
}