/rust/registry/src/index.crates.io-1949cf8c6b5b557f/regex-syntax-0.8.6/src/utf8.rs

Source
/*!
Converts ranges of Unicode scalar values to equivalent ranges of UTF-8 bytes.

This is sub-module is useful for constructing byte based automatons that need
to embed UTF-8 decoding. The most common use of this module is in conjunction
with the [`hir::ClassUnicodeRange`](crate::hir::ClassUnicodeRange) type.

See the documentation on the `Utf8Sequences` iterator for more details and
an example.

# Wait, what is this?

This is simplest to explain with an example. Let's say you wanted to test
whether a particular byte sequence was a Cyrillic character. One possible
scalar value range is `[0400-04FF]`. The set of allowed bytes for this
range can be expressed as a sequence of byte ranges:

```text
[D0-D3][80-BF]
```

This is simple enough: simply encode the boundaries, `0400` encodes to
`D0 80` and `04FF` encodes to `D3 BF`, and create ranges from each
corresponding pair of bytes: `D0` to `D3` and `80` to `BF`.

However, what if you wanted to add the Cyrillic Supplementary characters to
your range? Your range might then become `[0400-052F]`. The same procedure
as above doesn't quite work because `052F` encodes to `D4 AF`. The byte ranges
you'd get from the previous transformation would be `[D0-D4][80-AF]`. However,
this isn't quite correct because this range doesn't capture many characters,
for example, `04FF` (because its last byte, `BF` isn't in the range `80-AF`).

Instead, you need multiple sequences of byte ranges:

```text
[D0-D3][80-BF]  # matches codepoints 0400-04FF
[D4][80-AF]     # matches codepoints 0500-052F
```

This gets even more complicated if you want bigger ranges, particularly if
they naively contain surrogate codepoints. For example, the sequence of byte
ranges for the basic multilingual plane (`[0000-FFFF]`) look like this:

```text
[0-7F]
[C2-DF][80-BF]
[E0][A0-BF][80-BF]
[E1-EC][80-BF][80-BF]
[ED][80-9F][80-BF]
[EE-EF][80-BF][80-BF]
```

Note that the byte ranges above will *not* match any erroneous encoding of
UTF-8, including encodings of surrogate codepoints.

And, of course, for all of Unicode (`[000000-10FFFF]`):

```text
[0-7F]
[C2-DF][80-BF]
[E0][A0-BF][80-BF]
[E1-EC][80-BF][80-BF]
[ED][80-9F][80-BF]
[EE-EF][80-BF][80-BF]
[F0][90-BF][80-BF][80-BF]
[F1-F3][80-BF][80-BF][80-BF]
[F4][80-8F][80-BF][80-BF]
```

This module automates the process of creating these byte ranges from ranges of
Unicode scalar values.

# Lineage

I got the idea and general implementation strategy from Russ Cox in his
[article on regexps](https://web.archive.org/web/20160404141123/https://swtch.com/~rsc/regexp/regexp3.html) and RE2.
Russ Cox got it from Ken Thompson's `grep` (no source, folk lore?).
I also got the idea from
[Lucene](https://github.com/apache/lucene-solr/blob/ae93f4e7ac6a3908046391de35d4f50a0d3c59ca/lucene/core/src/java/org/apache/lucene/util/automaton/UTF32ToUTF8.java),
which uses it for executing automata on their term index.
*/

use core::{char, fmt, iter::FusedIterator, slice};

use alloc::{vec, vec::Vec};

const MAX_UTF8_BYTES: usize = 4;

/// Utf8Sequence represents a sequence of byte ranges.
///
/// To match a Utf8Sequence, a candidate byte sequence must match each
/// successive range.
///
/// For example, if there are two ranges, `[C2-DF][80-BF]`, then the byte
/// sequence `\xDD\x61` would not match because `0x61 < 0x80`.
#[derive(Copy, Clone, Eq, PartialEq, PartialOrd, Ord)]
pub enum Utf8Sequence {
    /// One byte range.
    One(Utf8Range),
    /// Two successive byte ranges.
    Two([Utf8Range; 2]),
    /// Three successive byte ranges.
    Three([Utf8Range; 3]),
    /// Four successive byte ranges.
    Four([Utf8Range; 4]),
}

impl Utf8Sequence {
    /// Creates a new UTF-8 sequence from the encoded bytes of a scalar value
    /// range.
    ///
    /// This assumes that `start` and `end` have the same length.
    fn from_encoded_range(start: &[u8], end: &[u8]) -> Self {
        assert_eq!(start.len(), end.len());
        match start.len() {
            2 => Utf8Sequence::Two([
                Utf8Range::new(start[0], end[0]),
                Utf8Range::new(start[1], end[1]),
            ]),
            3 => Utf8Sequence::Three([
                Utf8Range::new(start[0], end[0]),
                Utf8Range::new(start[1], end[1]),
                Utf8Range::new(start[2], end[2]),
            ]),
            4 => Utf8Sequence::Four([
                Utf8Range::new(start[0], end[0]),
                Utf8Range::new(start[1], end[1]),
                Utf8Range::new(start[2], end[2]),
                Utf8Range::new(start[3], end[3]),
            ]),
            n => unreachable!("invalid encoded length: {}", n),
        }
    }

    /// Returns the underlying sequence of byte ranges as a slice.
    pub fn as_slice(&self) -> &[Utf8Range] {
        use self::Utf8Sequence::*;
        match *self {
            One(ref r) => slice::from_ref(r),
            Two(ref r) => &r[..],
            Three(ref r) => &r[..],
            Four(ref r) => &r[..],
        }
    }

    /// Returns the number of byte ranges in this sequence.
    ///
    /// The length is guaranteed to be in the closed interval `[1, 4]`.
    pub fn len(&self) -> usize {
        self.as_slice().len()
    }

    /// Reverses the ranges in this sequence.
    ///
    /// For example, if this corresponds to the following sequence:
    ///
    /// ```text
    /// [D0-D3][80-BF]
    /// ```
    ///
    /// Then after reversal, it will be
    ///
    /// ```text
    /// [80-BF][D0-D3]
    /// ```
    ///
    /// This is useful when one is constructing a UTF-8 automaton to match
    /// character classes in reverse.
    pub fn reverse(&mut self) {
        match *self {
            Utf8Sequence::One(_) => {}
            Utf8Sequence::Two(ref mut x) => x.reverse(),
            Utf8Sequence::Three(ref mut x) => x.reverse(),
            Utf8Sequence::Four(ref mut x) => x.reverse(),
        }
    }

    /// Returns true if and only if a prefix of `bytes` matches this sequence
    /// of byte ranges.
    pub fn matches(&self, bytes: &[u8]) -> bool {
        if bytes.len() < self.len() {
            return false;
        }
        for (&b, r) in bytes.iter().zip(self) {
            if !r.matches(b) {
                return false;
            }
        }
        true
    }
}

impl<'a> IntoIterator for &'a Utf8Sequence {
    type IntoIter = slice::Iter<'a, Utf8Range>;
    type Item = &'a Utf8Range;

    fn into_iter(self) -> Self::IntoIter {
        self.as_slice().iter()
    }
}

impl fmt::Debug for Utf8Sequence {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        use self::Utf8Sequence::*;
        match *self {
            One(ref r) => write!(f, "{:?}", r),
            Two(ref r) => write!(f, "{:?}{:?}", r[0], r[1]),
            Three(ref r) => write!(f, "{:?}{:?}{:?}", r[0], r[1], r[2]),
            Four(ref r) => {
                write!(f, "{:?}{:?}{:?}{:?}", r[0], r[1], r[2], r[3])
            }
        }
    }
}

/// A single inclusive range of UTF-8 bytes.
#[derive(Clone, Copy, Eq, PartialEq, PartialOrd, Ord)]
pub struct Utf8Range {
    /// Start of byte range (inclusive).
    pub start: u8,
    /// End of byte range (inclusive).
    pub end: u8,
}

impl Utf8Range {
    fn new(start: u8, end: u8) -> Self {
        Utf8Range { start, end }
    }

    /// Returns true if and only if the given byte is in this range.
    pub fn matches(&self, b: u8) -> bool {
        self.start <= b && b <= self.end
    }
}

impl fmt::Debug for Utf8Range {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if self.start == self.end {
            write!(f, "[{:X}]", self.start)
        } else {
            write!(f, "[{:X}-{:X}]", self.start, self.end)
        }
    }
}

/// An iterator over ranges of matching UTF-8 byte sequences.
///
/// The iteration represents an alternation of comprehensive byte sequences
/// that match precisely the set of UTF-8 encoded scalar values.
///
/// A byte sequence corresponds to one of the scalar values in the range given
/// if and only if it completely matches exactly one of the sequences of byte
/// ranges produced by this iterator.
///
/// Each sequence of byte ranges matches a unique set of bytes. That is, no two
/// sequences will match the same bytes.
///
/// # Example
///
/// This shows how to match an arbitrary byte sequence against a range of
/// scalar values.
///
/// ```rust
/// use regex_syntax::utf8::{Utf8Sequences, Utf8Sequence};
///
/// fn matches(seqs: &[Utf8Sequence], bytes: &[u8]) -> bool {
///     for range in seqs {
///         if range.matches(bytes) {
///             return true;
///         }
///     }
///     false
/// }
///
/// // Test the basic multilingual plane.
/// let seqs: Vec<_> = Utf8Sequences::new('\u{0}', '\u{FFFF}').collect();
///
/// // UTF-8 encoding of 'a'.
/// assert!(matches(&seqs, &[0x61]));
/// // UTF-8 encoding of '☃' (`\u{2603}`).
/// assert!(matches(&seqs, &[0xE2, 0x98, 0x83]));
/// // UTF-8 encoding of `\u{10348}` (outside the BMP).
/// assert!(!matches(&seqs, &[0xF0, 0x90, 0x8D, 0x88]));
/// // Tries to match against a UTF-8 encoding of a surrogate codepoint,
/// // which is invalid UTF-8, and therefore fails, despite the fact that
/// // the corresponding codepoint (0xD800) falls in the range given.
/// assert!(!matches(&seqs, &[0xED, 0xA0, 0x80]));
/// // And fails against plain old invalid UTF-8.
/// assert!(!matches(&seqs, &[0xFF, 0xFF]));
/// ```
///
/// If this example seems circuitous, that's because it is! It's meant to be
/// illustrative. In practice, you could just try to decode your byte sequence
/// and compare it with the scalar value range directly. However, this is not
/// always possible (for example, in a byte based automaton).
#[derive(Debug)]
pub struct Utf8Sequences {
    range_stack: Vec<ScalarRange>,
}

impl Utf8Sequences {
    /// Create a new iterator over UTF-8 byte ranges for the scalar value range
    /// given.
    pub fn new(start: char, end: char) -> Self {
        let range =
            ScalarRange { start: u32::from(start), end: u32::from(end) };
        Utf8Sequences { range_stack: vec![range] }
    }

    /// reset resets the scalar value range.
    /// Any existing state is cleared, but resources may be reused.
    ///
    /// N.B. Benchmarks say that this method is dubious.
    #[doc(hidden)]
    pub fn reset(&mut self, start: char, end: char) {
        self.range_stack.clear();
        self.push(u32::from(start), u32::from(end));
    }

    fn push(&mut self, start: u32, end: u32) {
        self.range_stack.push(ScalarRange { start, end });
    }
}

struct ScalarRange {
    start: u32,
    end: u32,
}

impl fmt::Debug for ScalarRange {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "ScalarRange({:X}, {:X})", self.start, self.end)
    }
}

impl Iterator for Utf8Sequences {
    type Item = Utf8Sequence;

    fn next(&mut self) -> Option<Self::Item> {
        'TOP: while let Some(mut r) = self.range_stack.pop() {
            'INNER: loop {
                if let Some((r1, r2)) = r.split() {
                    self.push(r2.start, r2.end);
                    r.start = r1.start;
                    r.end = r1.end;
                    continue 'INNER;
                }
                if !r.is_valid() {
                    continue 'TOP;
                }
                for i in 1..MAX_UTF8_BYTES {
                    let max = max_scalar_value(i);
                    if r.start <= max && max < r.end {
                        self.push(max + 1, r.end);
                        r.end = max;
                        continue 'INNER;
                    }
                }
                if let Some(ascii_range) = r.as_ascii() {
                    return Some(Utf8Sequence::One(ascii_range));
                }
                for i in 1..MAX_UTF8_BYTES {
                    let m = (1 << (6 * i)) - 1;
                    if (r.start & !m) != (r.end & !m) {
                        if (r.start & m) != 0 {
                            self.push((r.start | m) + 1, r.end);
                            r.end = r.start | m;
                            continue 'INNER;
                        }
                        if (r.end & m) != m {
                            self.push(r.end & !m, r.end);
                            r.end = (r.end & !m) - 1;
                            continue 'INNER;
                        }
                    }
                }
                let mut start = [0; MAX_UTF8_BYTES];
                let mut end = [0; MAX_UTF8_BYTES];
                let n = r.encode(&mut start, &mut end);
                return Some(Utf8Sequence::from_encoded_range(
                    &start[0..n],
                    &end[0..n],
                ));
            }
        }
        None
    }
}

impl FusedIterator for Utf8Sequences {}

impl ScalarRange {
    /// split splits this range if it overlaps with a surrogate codepoint.
    ///
    /// Either or both ranges may be invalid.
    fn split(&self) -> Option<(ScalarRange, ScalarRange)> {
        if self.start < 0xE000 && self.end > 0xD7FF {
            Some((
                ScalarRange { start: self.start, end: 0xD7FF },
                ScalarRange { start: 0xE000, end: self.end },
            ))
        } else {
            None
        }
    }

    /// is_valid returns true if and only if start <= end.
    fn is_valid(&self) -> bool {
        self.start <= self.end
    }

    /// as_ascii returns this range as a Utf8Range if and only if all scalar
    /// values in this range can be encoded as a single byte.
    fn as_ascii(&self) -> Option<Utf8Range> {
        if self.is_ascii() {
            let start = u8::try_from(self.start).unwrap();
            let end = u8::try_from(self.end).unwrap();
            Some(Utf8Range::new(start, end))
        } else {
            None
        }
    }

    /// is_ascii returns true if the range is ASCII only (i.e., takes a single
    /// byte to encode any scalar value).
    fn is_ascii(&self) -> bool {
        self.is_valid() && self.end <= 0x7f
    }

    /// encode writes the UTF-8 encoding of the start and end of this range
    /// to the corresponding destination slices, and returns the number of
    /// bytes written.
    ///
    /// The slices should have room for at least `MAX_UTF8_BYTES`.
    fn encode(&self, start: &mut [u8], end: &mut [u8]) -> usize {
        let cs = char::from_u32(self.start).unwrap();
        let ce = char::from_u32(self.end).unwrap();
        let ss = cs.encode_utf8(start);
        let se = ce.encode_utf8(end);
        assert_eq!(ss.len(), se.len());
        ss.len()
    }
}

fn max_scalar_value(nbytes: usize) -> u32 {
    match nbytes {
        1 => 0x007F,
        2 => 0x07FF,
        3 => 0xFFFF,
        4 => 0x0010_FFFF,
        _ => unreachable!("invalid UTF-8 byte sequence size"),
    }
}

#[cfg(test)]
mod tests {
    use core::char;

    use alloc::{vec, vec::Vec};

    use crate::utf8::{Utf8Range, Utf8Sequences};

    fn rutf8(s: u8, e: u8) -> Utf8Range {
        Utf8Range::new(s, e)
    }

    fn never_accepts_surrogate_codepoints(start: char, end: char) {
        for cp in 0xD800..0xE000 {
            let buf = encode_surrogate(cp);
            for r in Utf8Sequences::new(start, end) {
                if r.matches(&buf) {
                    panic!(
                        "Sequence ({:X}, {:X}) contains range {:?}, \
                         which matches surrogate code point {:X} \
                         with encoded bytes {:?}",
                        u32::from(start),
                        u32::from(end),
                        r,
                        cp,
                        buf,
                    );
                }
            }
        }
    }

    #[test]
    fn codepoints_no_surrogates() {
        never_accepts_surrogate_codepoints('\u{0}', '\u{FFFF}');
        never_accepts_surrogate_codepoints('\u{0}', '\u{10FFFF}');
        never_accepts_surrogate_codepoints('\u{0}', '\u{10FFFE}');
        never_accepts_surrogate_codepoints('\u{80}', '\u{10FFFF}');
        never_accepts_surrogate_codepoints('\u{D7FF}', '\u{E000}');
    }

    #[test]
    fn single_codepoint_one_sequence() {
        // Tests that every range of scalar values that contains a single
        // scalar value is recognized by one sequence of byte ranges.
        for i in 0x0..=0x0010_FFFF {
            let c = match char::from_u32(i) {
                None => continue,
                Some(c) => c,
            };
            let seqs: Vec<_> = Utf8Sequences::new(c, c).collect();
            assert_eq!(seqs.len(), 1);
        }
    }

    #[test]
    fn bmp() {
        use crate::utf8::Utf8Sequence::*;

        let seqs = Utf8Sequences::new('\u{0}', '\u{FFFF}').collect::<Vec<_>>();
        assert_eq!(
            seqs,
            vec![
                One(rutf8(0x0, 0x7F)),
                Two([rutf8(0xC2, 0xDF), rutf8(0x80, 0xBF)]),
                Three([
                    rutf8(0xE0, 0xE0),
                    rutf8(0xA0, 0xBF),
                    rutf8(0x80, 0xBF)
                ]),
                Three([
                    rutf8(0xE1, 0xEC),
                    rutf8(0x80, 0xBF),
                    rutf8(0x80, 0xBF)
                ]),
                Three([
                    rutf8(0xED, 0xED),
                    rutf8(0x80, 0x9F),
                    rutf8(0x80, 0xBF)
                ]),
                Three([
                    rutf8(0xEE, 0xEF),
                    rutf8(0x80, 0xBF),
                    rutf8(0x80, 0xBF)
                ]),
            ]
        );
    }

    #[test]
    fn reverse() {
        use crate::utf8::Utf8Sequence::*;

        let mut s = One(rutf8(0xA, 0xB));
        s.reverse();
        assert_eq!(s.as_slice(), &[rutf8(0xA, 0xB)]);

        let mut s = Two([rutf8(0xA, 0xB), rutf8(0xB, 0xC)]);
        s.reverse();
        assert_eq!(s.as_slice(), &[rutf8(0xB, 0xC), rutf8(0xA, 0xB)]);

        let mut s = Three([rutf8(0xA, 0xB), rutf8(0xB, 0xC), rutf8(0xC, 0xD)]);
        s.reverse();
        assert_eq!(
            s.as_slice(),
            &[rutf8(0xC, 0xD), rutf8(0xB, 0xC), rutf8(0xA, 0xB)]
        );

        let mut s = Four([
            rutf8(0xA, 0xB),
            rutf8(0xB, 0xC),
            rutf8(0xC, 0xD),
            rutf8(0xD, 0xE),
        ]);
        s.reverse();
        assert_eq!(
            s.as_slice(),
            &[
                rutf8(0xD, 0xE),
                rutf8(0xC, 0xD),
                rutf8(0xB, 0xC),
                rutf8(0xA, 0xB)
            ]
        );
    }

    fn encode_surrogate(cp: u32) -> [u8; 3] {
        const TAG_CONT: u8 = 0b1000_0000;
        const TAG_THREE_B: u8 = 0b1110_0000;

        assert!(0xD800 <= cp && cp < 0xE000);
        let mut dst = [0; 3];
        dst[0] = u8::try_from(cp >> 12 & 0x0F).unwrap() | TAG_THREE_B;
        dst[1] = u8::try_from(cp >> 6 & 0x3F).unwrap() | TAG_CONT;
        dst[2] = u8::try_from(cp & 0x3F).unwrap() | TAG_CONT;
        dst
    }
}

Coverage Report

Created: 2025-09-27 07:40

Line	Count	Source
1		/*!
2		Converts ranges of Unicode scalar values to equivalent ranges of UTF-8 bytes.
3
4		This is sub-module is useful for constructing byte based automatons that need
5		to embed UTF-8 decoding. The most common use of this module is in conjunction
6		with the [`hir::ClassUnicodeRange`](crate::hir::ClassUnicodeRange) type.
7
8		See the documentation on the `Utf8Sequences` iterator for more details and
9		an example.
10
11		# Wait, what is this?
12
13		This is simplest to explain with an example. Let's say you wanted to test
14		whether a particular byte sequence was a Cyrillic character. One possible
15		scalar value range is `[0400-04FF]`. The set of allowed bytes for this
16		range can be expressed as a sequence of byte ranges:
17
18		```text
19		[D0-D3][80-BF]
20		```
21
22		This is simple enough: simply encode the boundaries, `0400` encodes to
23		`D0 80` and `04FF` encodes to `D3 BF`, and create ranges from each
24		corresponding pair of bytes: `D0` to `D3` and `80` to `BF`.
25
26		However, what if you wanted to add the Cyrillic Supplementary characters to
27		your range? Your range might then become `[0400-052F]`. The same procedure
28		as above doesn't quite work because `052F` encodes to `D4 AF`. The byte ranges
29		you'd get from the previous transformation would be `[D0-D4][80-AF]`. However,
30		this isn't quite correct because this range doesn't capture many characters,
31		for example, `04FF` (because its last byte, `BF` isn't in the range `80-AF`).
32
33		Instead, you need multiple sequences of byte ranges:
34
35		```text
36		[D0-D3][80-BF] # matches codepoints 0400-04FF
37		[D4][80-AF] # matches codepoints 0500-052F
38		```
39
40		This gets even more complicated if you want bigger ranges, particularly if
41		they naively contain surrogate codepoints. For example, the sequence of byte
42		ranges for the basic multilingual plane (`[0000-FFFF]`) look like this:
43
44		```text
45		[0-7F]
46		[C2-DF][80-BF]
47		[E0][A0-BF][80-BF]
48		[E1-EC][80-BF][80-BF]
49		[ED][80-9F][80-BF]
50		[EE-EF][80-BF][80-BF]
51		```
52
53		Note that the byte ranges above will not match any erroneous encoding of
54		UTF-8, including encodings of surrogate codepoints.
55
56		And, of course, for all of Unicode (`[000000-10FFFF]`):
57
58		```text
59		[0-7F]
60		[C2-DF][80-BF]
61		[E0][A0-BF][80-BF]
62		[E1-EC][80-BF][80-BF]
63		[ED][80-9F][80-BF]
64		[EE-EF][80-BF][80-BF]
65		[F0][90-BF][80-BF][80-BF]
66		[F1-F3][80-BF][80-BF][80-BF]
67		[F4][80-8F][80-BF][80-BF]
68		```
69
70		This module automates the process of creating these byte ranges from ranges of
71		Unicode scalar values.
72
73		# Lineage
74
75		I got the idea and general implementation strategy from Russ Cox in his
76		[article on regexps](https://web.archive.org/web/20160404141123/https://swtch.com/~rsc/regexp/regexp3.html) and RE2.
77		Russ Cox got it from Ken Thompson's `grep` (no source, folk lore?).
78		I also got the idea from
79		[Lucene](https://github.com/apache/lucene-solr/blob/ae93f4e7ac6a3908046391de35d4f50a0d3c59ca/lucene/core/src/java/org/apache/lucene/util/automaton/UTF32ToUTF8.java),
80		which uses it for executing automata on their term index.
81		*/
82
83		use core::{char, fmt, iter::FusedIterator, slice};
84
85		use alloc::{vec, vec::Vec};
86
87		const MAX_UTF8_BYTES: usize = 4;
88
89		/// Utf8Sequence represents a sequence of byte ranges.
90		///
91		/// To match a Utf8Sequence, a candidate byte sequence must match each
92		/// successive range.
93		///
94		/// For example, if there are two ranges, `[C2-DF][80-BF]`, then the byte
95		/// sequence `\xDD\x61` would not match because `0x61 < 0x80`.
96		#[derive(Copy, Clone, Eq, PartialEq, PartialOrd, Ord)]
97		pub enum Utf8Sequence {
98		/// One byte range.
99		One(Utf8Range),
100		/// Two successive byte ranges.
101		Two([Utf8Range; 2]),
102		/// Three successive byte ranges.
103		Three([Utf8Range; 3]),
104		/// Four successive byte ranges.
105		Four([Utf8Range; 4]),
106		}
107
108		impl Utf8Sequence {
109		/// Creates a new UTF-8 sequence from the encoded bytes of a scalar value
110		/// range.
111		///
112		/// This assumes that `start` and `end` have the same length.
113	0	fn from_encoded_range(start: &[u8], end: &[u8]) -> Self {
114	0	assert_eq!(start.len(), end.len());
115	0	match start.len() {
116	0	2 => Utf8Sequence::Two([
117	0	Utf8Range::new(start[0], end[0]),
118	0	Utf8Range::new(start[1], end[1]),
119	0	]),
120	0	3 => Utf8Sequence::Three([
121	0	Utf8Range::new(start[0], end[0]),
122	0	Utf8Range::new(start[1], end[1]),
123	0	Utf8Range::new(start[2], end[2]),
124	0	]),
125	0	4 => Utf8Sequence::Four([
126	0	Utf8Range::new(start[0], end[0]),
127	0	Utf8Range::new(start[1], end[1]),
128	0	Utf8Range::new(start[2], end[2]),
129	0	Utf8Range::new(start[3], end[3]),
130	0	]),
131	0	n => unreachable!("invalid encoded length: {}", n),
132		}
133	0	}
134
135		/// Returns the underlying sequence of byte ranges as a slice.
136	0	pub fn as_slice(&self) -> &[Utf8Range] {
137		use self::Utf8Sequence::*;
138	0	match *self {
139	0	One(ref r) => slice::from_ref(r),
140	0	Two(ref r) => &r[..],
141	0	Three(ref r) => &r[..],
142	0	Four(ref r) => &r[..],
143		}
144	0	}
145
146		/// Returns the number of byte ranges in this sequence.
147		///
148		/// The length is guaranteed to be in the closed interval `[1, 4]`.
149	0	pub fn len(&self) -> usize {
150	0	self.as_slice().len()
151	0	}
152
153		/// Reverses the ranges in this sequence.
154		///
155		/// For example, if this corresponds to the following sequence:
156		///
157		/// ```text
158		/// [D0-D3][80-BF]
159		/// ```
160		///
161		/// Then after reversal, it will be
162		///
163		/// ```text
164		/// [80-BF][D0-D3]
165		/// ```
166		///
167		/// This is useful when one is constructing a UTF-8 automaton to match
168		/// character classes in reverse.
169	0	pub fn reverse(&mut self) {
170	0	match *self {
171	0	Utf8Sequence::One(_) => {}
172	0	Utf8Sequence::Two(ref mut x) => x.reverse(),
173	0	Utf8Sequence::Three(ref mut x) => x.reverse(),
174	0	Utf8Sequence::Four(ref mut x) => x.reverse(),
175		}
176	0	}
177
178		/// Returns true if and only if a prefix of `bytes` matches this sequence
179		/// of byte ranges.
180	0	pub fn matches(&self, bytes: &[u8]) -> bool {
181	0	if bytes.len() < self.len() {
182	0	return false;
183	0	}
184	0	for (&b, r) in bytes.iter().zip(self) {
185	0	if !r.matches(b) {
186	0	return false;
187	0	}
188		}
189	0	true
190	0	}
191		}
192
193		impl<'a> IntoIterator for &'a Utf8Sequence {
194		type IntoIter = slice::Iter<'a, Utf8Range>;
195		type Item = &'a Utf8Range;
196
197	0	fn into_iter(self) -> Self::IntoIter {
198	0	self.as_slice().iter()
199	0	}
200		}
201
202		impl fmt::Debug for Utf8Sequence {
203	0	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
204		use self::Utf8Sequence::*;
205	0	match *self {
206	0	One(ref r) => write!(f, "{:?}", r),
207	0	Two(ref r) => write!(f, "{:?}{:?}", r[0], r[1]),
208	0	Three(ref r) => write!(f, "{:?}{:?}{:?}", r[0], r[1], r[2]),
209	0	Four(ref r) => {
210	0	write!(f, "{:?}{:?}{:?}{:?}", r[0], r[1], r[2], r[3])
211		}
212		}
213	0	}
214		}
215
216		/// A single inclusive range of UTF-8 bytes.
217		#[derive(Clone, Copy, Eq, PartialEq, PartialOrd, Ord)]
218		pub struct Utf8Range {
219		/// Start of byte range (inclusive).
220		pub start: u8,
221		/// End of byte range (inclusive).
222		pub end: u8,
223		}
224
225		impl Utf8Range {
226	0	fn new(start: u8, end: u8) -> Self {
227	0	Utf8Range { start, end }
228	0	}
229
230		/// Returns true if and only if the given byte is in this range.
231	0	pub fn matches(&self, b: u8) -> bool {
232	0	self.start <= b && b <= self.end
233	0	}
234		}
235
236		impl fmt::Debug for Utf8Range {
237	0	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
238	0	if self.start == self.end {
239	0	write!(f, "[{:X}]", self.start)
240		} else {
241	0	write!(f, "[{:X}-{:X}]", self.start, self.end)
242		}
243	0	}
244		}
245
246		/// An iterator over ranges of matching UTF-8 byte sequences.
247		///
248		/// The iteration represents an alternation of comprehensive byte sequences
249		/// that match precisely the set of UTF-8 encoded scalar values.
250		///
251		/// A byte sequence corresponds to one of the scalar values in the range given
252		/// if and only if it completely matches exactly one of the sequences of byte
253		/// ranges produced by this iterator.
254		///
255		/// Each sequence of byte ranges matches a unique set of bytes. That is, no two
256		/// sequences will match the same bytes.
257		///
258		/// # Example
259		///
260		/// This shows how to match an arbitrary byte sequence against a range of
261		/// scalar values.
262		///
263		/// ```rust
264		/// use regex_syntax::utf8::{Utf8Sequences, Utf8Sequence};
265		///
266		/// fn matches(seqs: &[Utf8Sequence], bytes: &[u8]) -> bool {
267		/// for range in seqs {
268		/// if range.matches(bytes) {
269		/// return true;
270		/// }
271		/// }
272		/// false
273		/// }
274		///
275		/// // Test the basic multilingual plane.
276		/// let seqs: Vec<_> = Utf8Sequences::new('\u{0}', '\u{FFFF}').collect();
277		///
278		/// // UTF-8 encoding of 'a'.
279		/// assert!(matches(&seqs, &[0x61]));
280		/// // UTF-8 encoding of '☃' (`\u{2603}`).
281		/// assert!(matches(&seqs, &[0xE2, 0x98, 0x83]));
282		/// // UTF-8 encoding of `\u{10348}` (outside the BMP).
283		/// assert!(!matches(&seqs, &[0xF0, 0x90, 0x8D, 0x88]));
284		/// // Tries to match against a UTF-8 encoding of a surrogate codepoint,
285		/// // which is invalid UTF-8, and therefore fails, despite the fact that
286		/// // the corresponding codepoint (0xD800) falls in the range given.
287		/// assert!(!matches(&seqs, &[0xED, 0xA0, 0x80]));
288		/// // And fails against plain old invalid UTF-8.
289		/// assert!(!matches(&seqs, &[0xFF, 0xFF]));
290		/// ```
291		///
292		/// If this example seems circuitous, that's because it is! It's meant to be
293		/// illustrative. In practice, you could just try to decode your byte sequence
294		/// and compare it with the scalar value range directly. However, this is not
295		/// always possible (for example, in a byte based automaton).
296		#[derive(Debug)]
297		pub struct Utf8Sequences {
298		range_stack: Vec<ScalarRange>,
299		}
300
301		impl Utf8Sequences {
302		/// Create a new iterator over UTF-8 byte ranges for the scalar value range
303		/// given.
304	0	pub fn new(start: char, end: char) -> Self {
305	0	let range =
306	0	ScalarRange { start: u32::from(start), end: u32::from(end) };
307	0	Utf8Sequences { range_stack: vec![range] }
308	0	}
309
310		/// reset resets the scalar value range.
311		/// Any existing state is cleared, but resources may be reused.
312		///
313		/// N.B. Benchmarks say that this method is dubious.
314		#[doc(hidden)]
315	0	pub fn reset(&mut self, start: char, end: char) {
316	0	self.range_stack.clear();
317	0	self.push(u32::from(start), u32::from(end));
318	0	}
319
320	0	fn push(&mut self, start: u32, end: u32) {
321	0	self.range_stack.push(ScalarRange { start, end });
322	0	}
323		}
324
325		struct ScalarRange {
326		start: u32,
327		end: u32,
328		}
329
330		impl fmt::Debug for ScalarRange {
331	0	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
332	0	write!(f, "ScalarRange({:X}, {:X})", self.start, self.end)
333	0	}
334		}
335
336		impl Iterator for Utf8Sequences {
337		type Item = Utf8Sequence;
338
339	0	fn next(&mut self) -> Option<Self::Item> {
340	0	'TOP: while let Some(mut r) = self.range_stack.pop() {
341		'INNER: loop {
342	0	if let Some((r1, r2)) = r.split() {
343	0	self.push(r2.start, r2.end);
344	0	r.start = r1.start;
345	0	r.end = r1.end;
346	0	continue 'INNER;
347	0	}
348	0	if !r.is_valid() {
349	0	continue 'TOP;
350	0	}
351	0	for i in 1..MAX_UTF8_BYTES {
352	0	let max = max_scalar_value(i);
353	0	if r.start <= max && max < r.end {
354	0	self.push(max + 1, r.end);
355	0	r.end = max;
356	0	continue 'INNER;
357	0	}
358		}
359	0	if let Some(ascii_range) = r.as_ascii() {
360	0	return Some(Utf8Sequence::One(ascii_range));
361	0	}
362	0	for i in 1..MAX_UTF8_BYTES {
363	0	let m = (1 << (6 * i)) - 1;
364	0	if (r.start & !m) != (r.end & !m) {
365	0	if (r.start & m) != 0 {
366	0	self.push((r.start \| m) + 1, r.end);
367	0	r.end = r.start \| m;
368	0	continue 'INNER;
369	0	}
370	0	if (r.end & m) != m {
371	0	self.push(r.end & !m, r.end);
372	0	r.end = (r.end & !m) - 1;
373	0	continue 'INNER;
374	0	}
375	0	}
376		}
377	0	let mut start = [0; MAX_UTF8_BYTES];
378	0	let mut end = [0; MAX_UTF8_BYTES];
379	0	let n = r.encode(&mut start, &mut end);
380	0	return Some(Utf8Sequence::from_encoded_range(
381	0	&start[0..n],
382	0	&end[0..n],
383	0	));
384		}
385		}
386	0	None
387	0	}
388		}
389
390		impl FusedIterator for Utf8Sequences {}
391
392		impl ScalarRange {
393		/// split splits this range if it overlaps with a surrogate codepoint.
394		///
395		/// Either or both ranges may be invalid.
396	0	fn split(&self) -> Option<(ScalarRange, ScalarRange)> {
397	0	if self.start < 0xE000 && self.end > 0xD7FF {
398	0	Some((
399	0	ScalarRange { start: self.start, end: 0xD7FF },
400	0	ScalarRange { start: 0xE000, end: self.end },
401	0	))
402		} else {
403	0	None
404		}
405	0	}
406
407		/// is_valid returns true if and only if start <= end.
408	0	fn is_valid(&self) -> bool {
409	0	self.start <= self.end
410	0	}
411
412		/// as_ascii returns this range as a Utf8Range if and only if all scalar
413		/// values in this range can be encoded as a single byte.
414	0	fn as_ascii(&self) -> Option<Utf8Range> {
415	0	if self.is_ascii() {
416	0	let start = u8::try_from(self.start).unwrap();
417	0	let end = u8::try_from(self.end).unwrap();
418	0	Some(Utf8Range::new(start, end))
419		} else {
420	0	None
421		}
422	0	}
423
424		/// is_ascii returns true if the range is ASCII only (i.e., takes a single
425		/// byte to encode any scalar value).
426	0	fn is_ascii(&self) -> bool {
427	0	self.is_valid() && self.end <= 0x7f
428	0	}
429
430		/// encode writes the UTF-8 encoding of the start and end of this range
431		/// to the corresponding destination slices, and returns the number of
432		/// bytes written.
433		///
434		/// The slices should have room for at least `MAX_UTF8_BYTES`.
435	0	fn encode(&self, start: &mut [u8], end: &mut [u8]) -> usize {
436	0	let cs = char::from_u32(self.start).unwrap();
437	0	let ce = char::from_u32(self.end).unwrap();
438	0	let ss = cs.encode_utf8(start);
439	0	let se = ce.encode_utf8(end);
440	0	assert_eq!(ss.len(), se.len());
441	0	ss.len()
442	0	}
443		}
444
445	0	fn max_scalar_value(nbytes: usize) -> u32 {
446	0	match nbytes {
447	0	1 => 0x007F,
448	0	2 => 0x07FF,
449	0	3 => 0xFFFF,
450	0	4 => 0x0010_FFFF,
451	0	_ => unreachable!("invalid UTF-8 byte sequence size"),
452		}
453	0	}
454
455		#[cfg(test)]
456		mod tests {
457		use core::char;
458
459		use alloc::{vec, vec::Vec};
460
461		use crate::utf8::{Utf8Range, Utf8Sequences};
462
463		fn rutf8(s: u8, e: u8) -> Utf8Range {
464		Utf8Range::new(s, e)
465		}
466
467		fn never_accepts_surrogate_codepoints(start: char, end: char) {
468		for cp in 0xD800..0xE000 {
469		let buf = encode_surrogate(cp);
470		for r in Utf8Sequences::new(start, end) {
471		if r.matches(&buf) {
472		panic!(
473		"Sequence ({:X}, {:X}) contains range {:?}, \
474		which matches surrogate code point {:X} \
475		with encoded bytes {:?}",
476		u32::from(start),
477		u32::from(end),
478		r,
479		cp,
480		buf,
481		);
482		}
483		}
484		}
485		}
486
487		#[test]
488		fn codepoints_no_surrogates() {
489		never_accepts_surrogate_codepoints('\u{0}', '\u{FFFF}');
490		never_accepts_surrogate_codepoints('\u{0}', '\u{10FFFF}');
491		never_accepts_surrogate_codepoints('\u{0}', '\u{10FFFE}');
492		never_accepts_surrogate_codepoints('\u{80}', '\u{10FFFF}');
493		never_accepts_surrogate_codepoints('\u{D7FF}', '\u{E000}');
494		}
495
496		#[test]
497		fn single_codepoint_one_sequence() {
498		// Tests that every range of scalar values that contains a single
499		// scalar value is recognized by one sequence of byte ranges.
500		for i in 0x0..=0x0010_FFFF {
501		let c = match char::from_u32(i) {
502		None => continue,
503		Some(c) => c,
504		};
505		let seqs: Vec<_> = Utf8Sequences::new(c, c).collect();
506		assert_eq!(seqs.len(), 1);
507		}
508		}
509
510		#[test]
511		fn bmp() {
512		use crate::utf8::Utf8Sequence::*;
513
514		let seqs = Utf8Sequences::new('\u{0}', '\u{FFFF}').collect::<Vec<_>>();
515		assert_eq!(
516		seqs,
517		vec![
518		One(rutf8(0x0, 0x7F)),
519		Two([rutf8(0xC2, 0xDF), rutf8(0x80, 0xBF)]),
520		Three([
521		rutf8(0xE0, 0xE0),
522		rutf8(0xA0, 0xBF),
523		rutf8(0x80, 0xBF)
524		]),
525		Three([
526		rutf8(0xE1, 0xEC),
527		rutf8(0x80, 0xBF),
528		rutf8(0x80, 0xBF)
529		]),
530		Three([
531		rutf8(0xED, 0xED),
532		rutf8(0x80, 0x9F),
533		rutf8(0x80, 0xBF)
534		]),
535		Three([
536		rutf8(0xEE, 0xEF),
537		rutf8(0x80, 0xBF),
538		rutf8(0x80, 0xBF)
539		]),
540		]
541		);
542		}
543
544		#[test]
545		fn reverse() {
546		use crate::utf8::Utf8Sequence::*;
547
548		let mut s = One(rutf8(0xA, 0xB));
549		s.reverse();
550		assert_eq!(s.as_slice(), &[rutf8(0xA, 0xB)]);
551
552		let mut s = Two([rutf8(0xA, 0xB), rutf8(0xB, 0xC)]);
553		s.reverse();
554		assert_eq!(s.as_slice(), &[rutf8(0xB, 0xC), rutf8(0xA, 0xB)]);
555
556		let mut s = Three([rutf8(0xA, 0xB), rutf8(0xB, 0xC), rutf8(0xC, 0xD)]);
557		s.reverse();
558		assert_eq!(
559		s.as_slice(),
560		&[rutf8(0xC, 0xD), rutf8(0xB, 0xC), rutf8(0xA, 0xB)]
561		);
562
563		let mut s = Four([
564		rutf8(0xA, 0xB),
565		rutf8(0xB, 0xC),
566		rutf8(0xC, 0xD),
567		rutf8(0xD, 0xE),
568		]);
569		s.reverse();
570		assert_eq!(
571		s.as_slice(),
572		&[
573		rutf8(0xD, 0xE),
574		rutf8(0xC, 0xD),
575		rutf8(0xB, 0xC),
576		rutf8(0xA, 0xB)
577		]
578		);
579		}
580
581		fn encode_surrogate(cp: u32) -> [u8; 3] {
582		const TAG_CONT: u8 = 0b1000_0000;
583		const TAG_THREE_B: u8 = 0b1110_0000;
584
585		assert!(0xD800 <= cp && cp < 0xE000);
586		let mut dst = [0; 3];
587		dst[0] = u8::try_from(cp >> 12 & 0x0F).unwrap() \| TAG_THREE_B;
588		dst[1] = u8::try_from(cp >> 6 & 0x3F).unwrap() \| TAG_CONT;
589		dst[2] = u8::try_from(cp & 0x3F).unwrap() \| TAG_CONT;
590		dst
591		}
592		}