unicode_normalization/
stream_safe.rs

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1use core::iter::FusedIterator;
2
3use crate::lookups::{
4    canonical_combining_class, canonical_fully_decomposed, compatibility_fully_decomposed,
5    stream_safe_trailing_nonstarters,
6};
7use crate::normalize::{hangul_decomposition_length, is_hangul_syllable};
8use crate::tables::stream_safe_leading_nonstarters;
9
10pub(crate) const MAX_NONSTARTERS: usize = 30;
11const COMBINING_GRAPHEME_JOINER: char = '\u{034F}';
12
13/// UAX15-D4: This iterator keeps track of how many non-starters there have been
14/// since the last starter in *NFKD* and will emit a Combining Grapheme Joiner
15/// (U+034F) if the count exceeds 30.
16pub struct StreamSafe<I> {
17    iter: I,
18    nonstarter_count: usize,
19    buffer: Option<char>,
20}
21
22impl<I> StreamSafe<I> {
23    pub(crate) fn new(iter: I) -> Self {
24        Self {
25            iter,
26            nonstarter_count: 0,
27            buffer: None,
28        }
29    }
30}
31
32impl<I: Iterator<Item = char>> Iterator for StreamSafe<I> {
33    type Item = char;
34
35    #[inline]
36    fn next(&mut self) -> Option<char> {
37        let next_ch = match self.buffer.take().or_else(|| self.iter.next()) {
38            None => return None,
39            Some(c) => c,
40        };
41        let d = classify_nonstarters(next_ch);
42        if self.nonstarter_count + d.leading_nonstarters > MAX_NONSTARTERS {
43            // Since we're emitting a CGJ, the suffix of the emitted string in NFKD has no trailing
44            // nonstarters, so we can reset the counter to zero. Put `next_ch` back into the
45            // iterator (via `self.buffer`), and we'll reclassify it next iteration.
46            self.nonstarter_count = 0;
47            self.buffer = Some(next_ch);
48            return Some(COMBINING_GRAPHEME_JOINER);
49        }
50
51        // Is the character all nonstarters in NFKD? If so, increment our counter of contiguous
52        // nonstarters in NKFD.
53        if d.leading_nonstarters == d.decomposition_len {
54            self.nonstarter_count += d.decomposition_len;
55        }
56        // Otherwise, reset the counter to the decomposition's number of trailing nonstarters.
57        else {
58            self.nonstarter_count = d.trailing_nonstarters;
59        }
60        Some(next_ch)
61    }
62}
63
64impl<I: Iterator<Item = char> + FusedIterator> FusedIterator for StreamSafe<I> {}
65
66#[derive(Debug)]
67pub(crate) struct Decomposition {
68    pub(crate) leading_nonstarters: usize,
69    pub(crate) trailing_nonstarters: usize,
70    pub(crate) decomposition_len: usize,
71}
72
73#[inline]
74pub(crate) fn classify_nonstarters(c: char) -> Decomposition {
75    // As usual, fast path for ASCII (which is always a starter)
76    if c <= '\x7f' {
77        return Decomposition {
78            leading_nonstarters: 0,
79            trailing_nonstarters: 0,
80            decomposition_len: 1,
81        };
82    }
83    // Next, special case Hangul, since it's not handled by our tables.
84    if is_hangul_syllable(c) {
85        return Decomposition {
86            leading_nonstarters: 0,
87            trailing_nonstarters: 0,
88            decomposition_len: hangul_decomposition_length(c),
89        };
90    }
91    let decomp = compatibility_fully_decomposed(c).or_else(|| canonical_fully_decomposed(c));
92    match decomp {
93        Some(decomp) => Decomposition {
94            leading_nonstarters: stream_safe_leading_nonstarters(c),
95            trailing_nonstarters: stream_safe_trailing_nonstarters(c),
96            decomposition_len: decomp.len(),
97        },
98        None => {
99            let is_nonstarter = canonical_combining_class(c) != 0;
100            let nonstarter = if is_nonstarter { 1 } else { 0 };
101            Decomposition {
102                leading_nonstarters: nonstarter,
103                trailing_nonstarters: nonstarter,
104                decomposition_len: 1,
105            }
106        }
107    }
108}
109
110#[cfg(test)]
111mod tests {
112    use super::{classify_nonstarters, StreamSafe};
113    use crate::lookups::canonical_combining_class;
114    use crate::normalize::decompose_compatible;
115
116    #[cfg(not(feature = "std"))]
117    use alloc::{string::String, vec::Vec};
118
119    use core::char;
120
121    fn stream_safe(s: &str) -> String {
122        StreamSafe::new(s.chars()).collect()
123    }
124
125    #[test]
126    fn test_simple() {
127        let technically_okay = "Da\u{0300}\u{0301}\u{0302}\u{0303}\u{0304}\u{0305}\u{0306}\u{0307}\u{0308}\u{0309}\u{030a}\u{030b}\u{030c}\u{030d}\u{030e}\u{030f}\u{0310}\u{0311}\u{0312}\u{0313}\u{0314}\u{0315}\u{0316}\u{0317}\u{0318}\u{0319}\u{031a}\u{031b}\u{031c}\u{031d}ngerzone";
128        assert_eq!(stream_safe(technically_okay), technically_okay);
129
130        let too_much = "Da\u{0300}\u{0301}\u{0302}\u{0303}\u{0304}\u{0305}\u{0306}\u{0307}\u{0308}\u{0309}\u{030a}\u{030b}\u{030c}\u{030d}\u{030e}\u{030f}\u{0310}\u{0311}\u{0312}\u{0313}\u{0314}\u{0315}\u{0316}\u{0317}\u{0318}\u{0319}\u{031a}\u{031b}\u{031c}\u{031d}\u{032e}ngerzone";
131        let fixed_it = "Da\u{0300}\u{0301}\u{0302}\u{0303}\u{0304}\u{0305}\u{0306}\u{0307}\u{0308}\u{0309}\u{030a}\u{030b}\u{030c}\u{030d}\u{030e}\u{030f}\u{0310}\u{0311}\u{0312}\u{0313}\u{0314}\u{0315}\u{0316}\u{0317}\u{0318}\u{0319}\u{031a}\u{031b}\u{031c}\u{031d}\u{034f}\u{032e}ngerzone";
132        assert_eq!(stream_safe(too_much), fixed_it);
133
134        let woah_nelly = "Da\u{0300}\u{0301}\u{0302}\u{0303}\u{0304}\u{0305}\u{0306}\u{0307}\u{0308}\u{0309}\u{030a}\u{030b}\u{030c}\u{030d}\u{030e}\u{030f}\u{0310}\u{0311}\u{0312}\u{0313}\u{0314}\u{0315}\u{0316}\u{0317}\u{0318}\u{0319}\u{031a}\u{031b}\u{031c}\u{031d}\u{032e}\u{0300}\u{0301}\u{0302}\u{0303}\u{0304}\u{0305}\u{0306}\u{0307}\u{0308}\u{0309}\u{030a}\u{030b}\u{030c}\u{030d}\u{030e}\u{030f}\u{0310}\u{0311}\u{0312}\u{0313}\u{0314}\u{0315}\u{0316}\u{0317}\u{0318}\u{0319}\u{031a}\u{031b}\u{031c}\u{031d}\u{032e}ngerzone";
135        let its_cool = "Da\u{0300}\u{0301}\u{0302}\u{0303}\u{0304}\u{0305}\u{0306}\u{0307}\u{0308}\u{0309}\u{030a}\u{030b}\u{030c}\u{030d}\u{030e}\u{030f}\u{0310}\u{0311}\u{0312}\u{0313}\u{0314}\u{0315}\u{0316}\u{0317}\u{0318}\u{0319}\u{031a}\u{031b}\u{031c}\u{031d}\u{034f}\u{032e}\u{0300}\u{0301}\u{0302}\u{0303}\u{0304}\u{0305}\u{0306}\u{0307}\u{0308}\u{0309}\u{030a}\u{030b}\u{030c}\u{030d}\u{030e}\u{030f}\u{0310}\u{0311}\u{0312}\u{0313}\u{0314}\u{0315}\u{0316}\u{0317}\u{0318}\u{0319}\u{031a}\u{031b}\u{031c}\u{034f}\u{031d}\u{032e}ngerzone";
136        assert_eq!(stream_safe(woah_nelly), its_cool);
137    }
138
139    #[test]
140    fn test_all_nonstarters() {
141        let s = "\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}\u{0300}";
142        let expected = "\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{034F}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}\u{300}";
143        assert_eq!(stream_safe(s), expected);
144    }
145
146    #[test]
147    fn test_classify_nonstarters() {
148        // Highest character in the `compat_fully_decomp` table is 2FA1D
149        for ch in 0..0x2FA1E {
150            let ch = match char::from_u32(ch) {
151                Some(c) => c,
152                None => continue,
153            };
154            let c = classify_nonstarters(ch);
155            let mut s = Vec::new();
156            decompose_compatible(ch, |c| s.push(c));
157
158            assert_eq!(s.len(), c.decomposition_len);
159
160            let num_leading = s
161                .iter()
162                .take_while(|&c| canonical_combining_class(*c) != 0)
163                .count();
164            let num_trailing = s
165                .iter()
166                .rev()
167                .take_while(|&c| canonical_combining_class(*c) != 0)
168                .count();
169
170            assert_eq!(num_leading, c.leading_nonstarters);
171            assert_eq!(num_trailing, c.trailing_nonstarters);
172        }
173    }
174}
unicode_normalization/stream_safe.rs

unicode_normalization/
stream_safe.rs
