rust/src/lexer/mod.rs

use {Token, SyntaxKind};
use syntax_kinds::*;

mod ptr;
use self::ptr::Ptr;

mod classes;
use self::classes::*;

mod numbers;
use self::numbers::scan_number;

pub fn next_token(text: &str) -> Token {
    assert!(!text.is_empty());
    let mut ptr = Ptr::new(text);
    let c = ptr.bump().unwrap();
    let kind = next_token_inner(c, &mut ptr);
    let len = ptr.into_len();
    Token { kind, len }
}

fn next_token_inner(c: char, ptr: &mut Ptr) -> SyntaxKind {
    // Note: r as in r" or r#" is part of a raw string literal,
    // b as in b' is part of a byte literal.
    // They are not identifiers, and are handled further down.
    let ident_start = is_ident_start(c) && !string_literal_start(c, ptr.next(), ptr.nnext());
    if ident_start {
        return scan_ident(c, ptr);
    }

    if is_whitespace(c) {
        ptr.bump_while(is_whitespace);
        return WHITESPACE;
    }

    if is_dec_digit(c) {
        return scan_number(c, ptr);
    }

    // One-byte tokens.
    match c {
        ';' => return SEMI,
        ',' => return COMMA,
        '(' => return L_PAREN,
        ')' => return R_PAREN,
        '{' => return L_CURLY,
        '}' => return R_CURLY,
        '[' => return L_BRACK,
        ']' => return R_BRACK,
        '@' => return AT,
        '#' => return POUND,
        '~' => return TILDE,
        '?' => return QUESTION,
        '$' => return DOLLAR,

        // Multi-byte tokens.
        '.' => return match (ptr.next(), ptr.nnext()) {
            (Some('.'), Some('.')) => {
                ptr.bump();
                ptr.bump();
                DOTDOTDOT
            },
            (Some('.'), Some('=')) => {
                ptr.bump();
                ptr.bump();
                DOTDOTEQ
            },
            (Some('.'), _) => {
                ptr.bump();
                DOTDOT
            },
            _ => DOT
        },
        ':' => return match ptr.next() {
            Some(':') => {
                ptr.bump();
                COLONCOLON
            }
            _ => COLON
        },
        '=' => return match ptr.next() {
            Some('=') => {
                ptr.bump();
                EQEQ
            }
            Some('>') => {
                ptr.bump();
                FAT_ARROW
            }
            _ => EQ,
        },
        '!' => return match ptr.next() {
            Some('=') => {
                ptr.bump();
                NEQ
            }
            _ => NOT,
        },
        _ => (),
    }
    ERROR
}

fn scan_ident(c: char, ptr: &mut Ptr) -> SyntaxKind {
    let is_single_letter = match ptr.next() {
        None => true,
        Some(c) if !is_ident_continue(c) => true,
        _ => false,
    };
    if is_single_letter {
        return if c == '_' { UNDERSCORE } else { IDENT };
    }
    ptr.bump_while(is_ident_continue);
    IDENT
}

fn string_literal_start(c: char, c1: Option<char>, c2: Option<char>) -> bool {
    match (c, c1, c2) {
        ('r', Some('"'), _) |
        ('r', Some('#'), _) |
        ('b', Some('"'), _) |
        ('b', Some('\''), _) |
        ('b', Some('r'), Some('"')) |
        ('b', Some('r'), Some('#')) => true,
        _ => false
    }
}