Import 'regex-syntax' package vesion 0.6.17
* Add OWNERS
Bug: 152884384
Test: make
Change-Id: I760a69ffc851039ceaff58980deece308a426aed
diff --git a/src/utf8.rs b/src/utf8.rs
new file mode 100644
index 0000000..489729e
--- /dev/null
+++ b/src/utf8.rs
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+/*!
+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:
+
+```ignore
+[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:
+
+```ignore
+[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:
+
+```ignore
+[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]`):
+
+```ignore
+[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::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:
+ ///
+ /// ```ignore
+ /// [D0-D3][80-BF]
+ /// ```
+ ///
+ /// Then after reversal, it will be
+ ///
+ /// ```ignore
+ /// [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).
+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 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 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 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 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
+ }
+}