/rust/registry/src/index.crates.io-6f17d22bba15001f/regex-syntax-0.6.25/src/utf8.rs

Source (jump to first uncovered line)
/*!
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`](../hir/struct.ClassUnicodeRange.html) 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.
*/

#![deny(missing_docs)]

use std::char;
use std::fmt;
use std::iter::FusedIterator;
use std::slice;

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().into_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 mut it = Utf8Sequences { range_stack: vec![] };
        it.push(start as u32, end as u32);
        it
    }

    /// 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(start as u32, end as u32);
    }

    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() {
            Some(Utf8Range::new(self.start as u8, self.end as u8))
        } 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 => 0x10FFFF,
        _ => unreachable!("invalid UTF-8 byte sequence size"),
    }
}

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

    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 {:?}",
                        start as u32, end as u32, 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..(0x10FFFF + 1) {
            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] = (cp >> 12 & 0x0F) as u8 | TAG_THREE_B;
        dst[1] = (cp >> 6 & 0x3F) as u8 | TAG_CONT;
        dst[2] = (cp & 0x3F) as u8 | TAG_CONT;
        dst
    }
}

Coverage Report

Created: 2023-04-25 07:07

Line	Count	Source (jump to first uncovered line)
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`](../hir/struct.ClassUnicodeRange.html) 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		#![deny(missing_docs)]
84
85		use std::char;
86		use std::fmt;
87		use std::iter::FusedIterator;
88		use std::slice;
89
90		const MAX_UTF8_BYTES: usize = 4;
91
92		/// Utf8Sequence represents a sequence of byte ranges.
93		///
94		/// To match a Utf8Sequence, a candidate byte sequence must match each
95		/// successive range.
96		///
97		/// For example, if there are two ranges, `[C2-DF][80-BF]`, then the byte
98		/// sequence `\xDD\x61` would not match because `0x61 < 0x80`.
99	0	#[derive(Copy, Clone, Eq, PartialEq, PartialOrd, Ord)]
100		pub enum Utf8Sequence {
101		/// One byte range.
102		One(Utf8Range),
103		/// Two successive byte ranges.
104		Two([Utf8Range; 2]),
105		/// Three successive byte ranges.
106		Three([Utf8Range; 3]),
107		/// Four successive byte ranges.
108		Four([Utf8Range; 4]),
109		}
110
111		impl Utf8Sequence {
112		/// Creates a new UTF-8 sequence from the encoded bytes of a scalar value
113		/// range.
114		///
115		/// This assumes that `start` and `end` have the same length.
116	0	fn from_encoded_range(start: &[u8], end: &[u8]) -> Self {
117	0	assert_eq!(start.len(), end.len());
118	0	match start.len() {
119	0	2 => Utf8Sequence::Two([
120	0	Utf8Range::new(start[0], end[0]),
121	0	Utf8Range::new(start[1], end[1]),
122	0	]),
123	0	3 => Utf8Sequence::Three([
124	0	Utf8Range::new(start[0], end[0]),
125	0	Utf8Range::new(start[1], end[1]),
126	0	Utf8Range::new(start[2], end[2]),
127	0	]),
128	0	4 => Utf8Sequence::Four([
129	0	Utf8Range::new(start[0], end[0]),
130	0	Utf8Range::new(start[1], end[1]),
131	0	Utf8Range::new(start[2], end[2]),
132	0	Utf8Range::new(start[3], end[3]),
133	0	]),
134	0	n => unreachable!("invalid encoded length: {}", n),
135		}
136	0	}
137
138		/// Returns the underlying sequence of byte ranges as a slice.
139	0	pub fn as_slice(&self) -> &[Utf8Range] {
140	0	use self::Utf8Sequence::*;
141	0	match *self {
142	0	One(ref r) => slice::from_ref(r),
143	0	Two(ref r) => &r[..],
144	0	Three(ref r) => &r[..],
145	0	Four(ref r) => &r[..],
146		}
147	0	}
148
149		/// Returns the number of byte ranges in this sequence.
150		///
151		/// The length is guaranteed to be in the closed interval `[1, 4]`.
152	0	pub fn len(&self) -> usize {
153	0	self.as_slice().len()
154	0	}
155
156		/// Reverses the ranges in this sequence.
157		///
158		/// For example, if this corresponds to the following sequence:
159		///
160		/// ```text
161		/// [D0-D3][80-BF]
162		/// ```
163		///
164		/// Then after reversal, it will be
165		///
166		/// ```text
167		/// [80-BF][D0-D3]
168		/// ```
169		///
170		/// This is useful when one is constructing a UTF-8 automaton to match
171		/// character classes in reverse.
172	0	pub fn reverse(&mut self) {
173	0	match *self {
174	0	Utf8Sequence::One(_) => {}
175	0	Utf8Sequence::Two(ref mut x) => x.reverse(),
176	0	Utf8Sequence::Three(ref mut x) => x.reverse(),
177	0	Utf8Sequence::Four(ref mut x) => x.reverse(),
178		}
179	0	}
180
181		/// Returns true if and only if a prefix of `bytes` matches this sequence
182		/// of byte ranges.
183	0	pub fn matches(&self, bytes: &[u8]) -> bool {
184	0	if bytes.len() < self.len() {
185	0	return false;
186	0	}
187	0	for (&b, r) in bytes.iter().zip(self) {
188	0	if !r.matches(b) {
189	0	return false;
190	0	}
191		}
192	0	true
193	0	}
194		}
195
196		impl<'a> IntoIterator for &'a Utf8Sequence {
197		type IntoIter = slice::Iter<'a, Utf8Range>;
198		type Item = &'a Utf8Range;
199
200	0	fn into_iter(self) -> Self::IntoIter {
201	0	self.as_slice().into_iter()
202	0	}
203		}
204
205		impl fmt::Debug for Utf8Sequence {
206	0	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
207	0	use self::Utf8Sequence::*;
208	0	match *self {
209	0	One(ref r) => write!(f, "{:?}", r),
210	0	Two(ref r) => write!(f, "{:?}{:?}", r[0], r[1]),
211	0	Three(ref r) => write!(f, "{:?}{:?}{:?}", r[0], r[1], r[2]),
212	0	Four(ref r) => {
213	0	write!(f, "{:?}{:?}{:?}{:?}", r[0], r[1], r[2], r[3])
214		}
215		}
216	0	}
217		}
218
219		/// A single inclusive range of UTF-8 bytes.
220	0	#[derive(Clone, Copy, Eq, PartialEq, PartialOrd, Ord)]
221		pub struct Utf8Range {
222		/// Start of byte range (inclusive).
223		pub start: u8,
224		/// End of byte range (inclusive).
225		pub end: u8,
226		}
227
228		impl Utf8Range {
229	0	fn new(start: u8, end: u8) -> Self {
230	0	Utf8Range { start, end }
231	0	}
232
233		/// Returns true if and only if the given byte is in this range.
234	0	pub fn matches(&self, b: u8) -> bool {
235	0	self.start <= b && b <= self.end
236	0	}
237		}
238
239		impl fmt::Debug for Utf8Range {
240	0	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
241	0	if self.start == self.end {
242	0	write!(f, "[{:X}]", self.start)
243		} else {
244	0	write!(f, "[{:X}-{:X}]", self.start, self.end)
245		}
246	0	}
247		}
248
249		/// An iterator over ranges of matching UTF-8 byte sequences.
250		///
251		/// The iteration represents an alternation of comprehensive byte sequences
252		/// that match precisely the set of UTF-8 encoded scalar values.
253		///
254		/// A byte sequence corresponds to one of the scalar values in the range given
255		/// if and only if it completely matches exactly one of the sequences of byte
256		/// ranges produced by this iterator.
257		///
258		/// Each sequence of byte ranges matches a unique set of bytes. That is, no two
259		/// sequences will match the same bytes.
260		///
261		/// # Example
262		///
263		/// This shows how to match an arbitrary byte sequence against a range of
264		/// scalar values.
265		///
266		/// ```rust
267		/// use regex_syntax::utf8::{Utf8Sequences, Utf8Sequence};
268		///
269		/// fn matches(seqs: &[Utf8Sequence], bytes: &[u8]) -> bool {
270		/// for range in seqs {
271		/// if range.matches(bytes) {
272		/// return true;
273		/// }
274		/// }
275		/// false
276		/// }
277		///
278		/// // Test the basic multilingual plane.
279		/// let seqs: Vec<_> = Utf8Sequences::new('\u{0}', '\u{FFFF}').collect();
280		///
281		/// // UTF-8 encoding of 'a'.
282		/// assert!(matches(&seqs, &[0x61]));
283		/// // UTF-8 encoding of '☃' (`\u{2603}`).
284		/// assert!(matches(&seqs, &[0xE2, 0x98, 0x83]));
285		/// // UTF-8 encoding of `\u{10348}` (outside the BMP).
286		/// assert!(!matches(&seqs, &[0xF0, 0x90, 0x8D, 0x88]));
287		/// // Tries to match against a UTF-8 encoding of a surrogate codepoint,
288		/// // which is invalid UTF-8, and therefore fails, despite the fact that
289		/// // the corresponding codepoint (0xD800) falls in the range given.
290		/// assert!(!matches(&seqs, &[0xED, 0xA0, 0x80]));
291		/// // And fails against plain old invalid UTF-8.
292		/// assert!(!matches(&seqs, &[0xFF, 0xFF]));
293		/// ```
294		///
295		/// If this example seems circuitous, that's because it is! It's meant to be
296		/// illustrative. In practice, you could just try to decode your byte sequence
297		/// and compare it with the scalar value range directly. However, this is not
298		/// always possible (for example, in a byte based automaton).
299	0	#[derive(Debug)]
300		pub struct Utf8Sequences {
301		range_stack: Vec<ScalarRange>,
302		}
303
304		impl Utf8Sequences {
305		/// Create a new iterator over UTF-8 byte ranges for the scalar value range
306		/// given.
307	0	pub fn new(start: char, end: char) -> Self {
308	0	let mut it = Utf8Sequences { range_stack: vec![] };
309	0	it.push(start as u32, end as u32);
310	0	it
311	0	}
312
313		/// reset resets the scalar value range.
314		/// Any existing state is cleared, but resources may be reused.
315		///
316		/// N.B. Benchmarks say that this method is dubious.
317		#[doc(hidden)]
318	0	pub fn reset(&mut self, start: char, end: char) {
319	0	self.range_stack.clear();
320	0	self.push(start as u32, end as u32);
321	0	}
322
323	0	fn push(&mut self, start: u32, end: u32) {
324	0	self.range_stack.push(ScalarRange { start, end });
325	0	}
326		}
327
328		struct ScalarRange {
329		start: u32,
330		end: u32,
331		}
332
333		impl fmt::Debug for ScalarRange {
334	0	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
335	0	write!(f, "ScalarRange({:X}, {:X})", self.start, self.end)
336	0	}
337		}
338
339		impl Iterator for Utf8Sequences {
340		type Item = Utf8Sequence;
341
342	0	fn next(&mut self) -> Option<Self::Item> {
343	0	'TOP: while let Some(mut r) = self.range_stack.pop() {
344		'INNER: loop {
345	0	if let Some((r1, r2)) = r.split() {
346	0	self.push(r2.start, r2.end);
347	0	r.start = r1.start;
348	0	r.end = r1.end;
349	0	continue 'INNER;
350	0	}
351	0	if !r.is_valid() {
352	0	continue 'TOP;
353	0	}
354	0	for i in 1..MAX_UTF8_BYTES {
355	0	let max = max_scalar_value(i);
356	0	if r.start <= max && max < r.end {
357	0	self.push(max + 1, r.end);
358	0	r.end = max;
359	0	continue 'INNER;
360	0	}
361		}
362	0	if let Some(ascii_range) = r.as_ascii() {
363	0	return Some(Utf8Sequence::One(ascii_range));
364	0	}
365	0	for i in 1..MAX_UTF8_BYTES {
366	0	let m = (1 << (6 * i)) - 1;
367	0	if (r.start & !m) != (r.end & !m) {
368	0	if (r.start & m) != 0 {
369	0	self.push((r.start \| m) + 1, r.end);
370	0	r.end = r.start \| m;
371	0	continue 'INNER;
372	0	}
373	0	if (r.end & m) != m {
374	0	self.push(r.end & !m, r.end);
375	0	r.end = (r.end & !m) - 1;
376	0	continue 'INNER;
377	0	}
378	0	}
379		}
380	0	let mut start = [0; MAX_UTF8_BYTES];
381	0	let mut end = [0; MAX_UTF8_BYTES];
382	0	let n = r.encode(&mut start, &mut end);
383	0	return Some(Utf8Sequence::from_encoded_range(
384	0	&start[0..n],
385	0	&end[0..n],
386	0	));
387		}
388		}
389	0	None
390	0	}
391		}
392
393		impl FusedIterator for Utf8Sequences {}
394
395		impl ScalarRange {
396		/// split splits this range if it overlaps with a surrogate codepoint.
397		///
398		/// Either or both ranges may be invalid.
399	0	fn split(&self) -> Option<(ScalarRange, ScalarRange)> {
400	0	if self.start < 0xE000 && self.end > 0xD7FF {
401	0	Some((
402	0	ScalarRange { start: self.start, end: 0xD7FF },
403	0	ScalarRange { start: 0xE000, end: self.end },
404	0	))
405		} else {
406	0	None
407		}
408	0	}
409
410		/// is_valid returns true if and only if start <= end.
411	0	fn is_valid(&self) -> bool {
412	0	self.start <= self.end
413	0	}
414
415		/// as_ascii returns this range as a Utf8Range if and only if all scalar
416		/// values in this range can be encoded as a single byte.
417	0	fn as_ascii(&self) -> Option<Utf8Range> {
418	0	if self.is_ascii() {
419	0	Some(Utf8Range::new(self.start as u8, self.end as u8))
420		} else {
421	0	None
422		}
423	0	}
424
425		/// is_ascii returns true if the range is ASCII only (i.e., takes a single
426		/// byte to encode any scalar value).
427	0	fn is_ascii(&self) -> bool {
428	0	self.is_valid() && self.end <= 0x7f
429	0	}
430
431		/// encode writes the UTF-8 encoding of the start and end of this range
432		/// to the corresponding destination slices, and returns the number of
433		/// bytes written.
434		///
435		/// The slices should have room for at least `MAX_UTF8_BYTES`.
436	0	fn encode(&self, start: &mut [u8], end: &mut [u8]) -> usize {
437	0	let cs = char::from_u32(self.start).unwrap();
438	0	let ce = char::from_u32(self.end).unwrap();
439	0	let ss = cs.encode_utf8(start);
440	0	let se = ce.encode_utf8(end);
441	0	assert_eq!(ss.len(), se.len());
442	0	ss.len()
443	0	}
444		}
445
446	0	fn max_scalar_value(nbytes: usize) -> u32 {
447	0	match nbytes {
448	0	1 => 0x007F,
449	0	2 => 0x07FF,
450	0	3 => 0xFFFF,
451	0	4 => 0x10FFFF,
452	0	_ => unreachable!("invalid UTF-8 byte sequence size"),
453		}
454	0	}
455
456		#[cfg(test)]
457		mod tests {
458		use std::char;
459
460		use crate::utf8::{Utf8Range, Utf8Sequences};
461
462		fn rutf8(s: u8, e: u8) -> Utf8Range {
463		Utf8Range::new(s, e)
464		}
465
466		fn never_accepts_surrogate_codepoints(start: char, end: char) {
467		for cp in 0xD800..0xE000 {
468		let buf = encode_surrogate(cp);
469		for r in Utf8Sequences::new(start, end) {
470		if r.matches(&buf) {
471		panic!(
472		"Sequence ({:X}, {:X}) contains range {:?}, \
473		which matches surrogate code point {:X} \
474		with encoded bytes {:?}",
475		start as u32, end as u32, r, cp, buf,
476		);
477		}
478		}
479		}
480		}
481
482		#[test]
483		fn codepoints_no_surrogates() {
484		never_accepts_surrogate_codepoints('\u{0}', '\u{FFFF}');
485		never_accepts_surrogate_codepoints('\u{0}', '\u{10FFFF}');
486		never_accepts_surrogate_codepoints('\u{0}', '\u{10FFFE}');
487		never_accepts_surrogate_codepoints('\u{80}', '\u{10FFFF}');
488		never_accepts_surrogate_codepoints('\u{D7FF}', '\u{E000}');
489		}
490
491		#[test]
492		fn single_codepoint_one_sequence() {
493		// Tests that every range of scalar values that contains a single
494		// scalar value is recognized by one sequence of byte ranges.
495		for i in 0x0..(0x10FFFF + 1) {
496		let c = match char::from_u32(i) {
497		None => continue,
498		Some(c) => c,
499		};
500		let seqs: Vec<_> = Utf8Sequences::new(c, c).collect();
501		assert_eq!(seqs.len(), 1);
502		}
503		}
504
505		#[test]
506		fn bmp() {
507		use crate::utf8::Utf8Sequence::*;
508
509		let seqs = Utf8Sequences::new('\u{0}', '\u{FFFF}').collect::<Vec<_>>();
510		assert_eq!(
511		seqs,
512		vec![
513		One(rutf8(0x0, 0x7F)),
514		Two([rutf8(0xC2, 0xDF), rutf8(0x80, 0xBF)]),
515		Three([
516		rutf8(0xE0, 0xE0),
517		rutf8(0xA0, 0xBF),
518		rutf8(0x80, 0xBF)
519		]),
520		Three([
521		rutf8(0xE1, 0xEC),
522		rutf8(0x80, 0xBF),
523		rutf8(0x80, 0xBF)
524		]),
525		Three([
526		rutf8(0xED, 0xED),
527		rutf8(0x80, 0x9F),
528		rutf8(0x80, 0xBF)
529		]),
530		Three([
531		rutf8(0xEE, 0xEF),
532		rutf8(0x80, 0xBF),
533		rutf8(0x80, 0xBF)
534		]),
535		]
536		);
537		}
538
539		#[test]
540		fn reverse() {
541		use crate::utf8::Utf8Sequence::*;
542
543		let mut s = One(rutf8(0xA, 0xB));
544		s.reverse();
545		assert_eq!(s.as_slice(), &[rutf8(0xA, 0xB)]);
546
547		let mut s = Two([rutf8(0xA, 0xB), rutf8(0xB, 0xC)]);
548		s.reverse();
549		assert_eq!(s.as_slice(), &[rutf8(0xB, 0xC), rutf8(0xA, 0xB)]);
550
551		let mut s = Three([rutf8(0xA, 0xB), rutf8(0xB, 0xC), rutf8(0xC, 0xD)]);
552		s.reverse();
553		assert_eq!(
554		s.as_slice(),
555		&[rutf8(0xC, 0xD), rutf8(0xB, 0xC), rutf8(0xA, 0xB)]
556		);
557
558		let mut s = Four([
559		rutf8(0xA, 0xB),
560		rutf8(0xB, 0xC),
561		rutf8(0xC, 0xD),
562		rutf8(0xD, 0xE),
563		]);
564		s.reverse();
565		assert_eq!(
566		s.as_slice(),
567		&[
568		rutf8(0xD, 0xE),
569		rutf8(0xC, 0xD),
570		rutf8(0xB, 0xC),
571		rutf8(0xA, 0xB)
572		]
573		);
574		}
575
576		fn encode_surrogate(cp: u32) -> [u8; 3] {
577		const TAG_CONT: u8 = 0b1000_0000;
578		const TAG_THREE_B: u8 = 0b1110_0000;
579
580		assert!(0xD800 <= cp && cp < 0xE000);
581		let mut dst = [0; 3];
582		dst[0] = (cp >> 12 & 0x0F) as u8 \| TAG_THREE_B;
583		dst[1] = (cp >> 6 & 0x3F) as u8 \| TAG_CONT;
584		dst[2] = (cp & 0x3F) as u8 \| TAG_CONT;
585		dst
586		}
587		}