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Diffstat (limited to 'third_party/rust/regex-syntax/src/hir/interval.rs')
| -rw-r--r-- | third_party/rust/regex-syntax/src/hir/interval.rs | 520 |
1 files changed, 520 insertions, 0 deletions
diff --git a/third_party/rust/regex-syntax/src/hir/interval.rs b/third_party/rust/regex-syntax/src/hir/interval.rs new file mode 100644 index 0000000000..56698c53af --- /dev/null +++ b/third_party/rust/regex-syntax/src/hir/interval.rs @@ -0,0 +1,520 @@ +use std::char; +use std::cmp; +use std::fmt::Debug; +use std::slice; +use std::u8; + +use crate::unicode; + +// This module contains an *internal* implementation of interval sets. +// +// The primary invariant that interval sets guards is canonical ordering. That +// is, every interval set contains an ordered sequence of intervals where +// no two intervals are overlapping or adjacent. While this invariant is +// occasionally broken within the implementation, it should be impossible for +// callers to observe it. +// +// Since case folding (as implemented below) breaks that invariant, we roll +// that into this API even though it is a little out of place in an otherwise +// generic interval set. (Hence the reason why the `unicode` module is imported +// here.) +// +// Some of the implementation complexity here is a result of me wanting to +// preserve the sequential representation without using additional memory. +// In many cases, we do use linear extra memory, but it is at most 2x and it +// is amortized. If we relaxed the memory requirements, this implementation +// could become much simpler. The extra memory is honestly probably OK, but +// character classes (especially of the Unicode variety) can become quite +// large, and it would be nice to keep regex compilation snappy even in debug +// builds. (In the past, I have been careless with this area of code and it has +// caused slow regex compilations in debug mode, so this isn't entirely +// unwarranted.) +// +// Tests on this are relegated to the public API of HIR in src/hir.rs. + +#[derive(Clone, Debug, Eq, PartialEq)] +pub struct IntervalSet<I> { + ranges: Vec<I>, +} + +impl<I: Interval> IntervalSet<I> { + /// Create a new set from a sequence of intervals. Each interval is + /// specified as a pair of bounds, where both bounds are inclusive. + /// + /// The given ranges do not need to be in any specific order, and ranges + /// may overlap. + pub fn new<T: IntoIterator<Item = I>>(intervals: T) -> IntervalSet<I> { + let mut set = IntervalSet { ranges: intervals.into_iter().collect() }; + set.canonicalize(); + set + } + + /// Add a new interval to this set. + pub fn push(&mut self, interval: I) { + // TODO: This could be faster. e.g., Push the interval such that + // it preserves canonicalization. + self.ranges.push(interval); + self.canonicalize(); + } + + /// Return an iterator over all intervals in this set. + /// + /// The iterator yields intervals in ascending order. + pub fn iter(&self) -> IntervalSetIter<'_, I> { + IntervalSetIter(self.ranges.iter()) + } + + /// Return an immutable slice of intervals in this set. + /// + /// The sequence returned is in canonical ordering. + pub fn intervals(&self) -> &[I] { + &self.ranges + } + + /// Expand this interval set such that it contains all case folded + /// characters. For example, if this class consists of the range `a-z`, + /// then applying case folding will result in the class containing both the + /// ranges `a-z` and `A-Z`. + /// + /// This returns an error if the necessary case mapping data is not + /// available. + pub fn case_fold_simple(&mut self) -> Result<(), unicode::CaseFoldError> { + let len = self.ranges.len(); + for i in 0..len { + let range = self.ranges[i]; + if let Err(err) = range.case_fold_simple(&mut self.ranges) { + self.canonicalize(); + return Err(err); + } + } + self.canonicalize(); + Ok(()) + } + + /// Union this set with the given set, in place. + pub fn union(&mut self, other: &IntervalSet<I>) { + // This could almost certainly be done more efficiently. + self.ranges.extend(&other.ranges); + self.canonicalize(); + } + + /// Intersect this set with the given set, in place. + pub fn intersect(&mut self, other: &IntervalSet<I>) { + if self.ranges.is_empty() { + return; + } + if other.ranges.is_empty() { + self.ranges.clear(); + return; + } + + // There should be a way to do this in-place with constant memory, + // but I couldn't figure out a simple way to do it. So just append + // the intersection to the end of this range, and then drain it before + // we're done. + let drain_end = self.ranges.len(); + + let mut ita = 0..drain_end; + let mut itb = 0..other.ranges.len(); + let mut a = ita.next().unwrap(); + let mut b = itb.next().unwrap(); + loop { + if let Some(ab) = self.ranges[a].intersect(&other.ranges[b]) { + self.ranges.push(ab); + } + let (it, aorb) = + if self.ranges[a].upper() < other.ranges[b].upper() { + (&mut ita, &mut a) + } else { + (&mut itb, &mut b) + }; + match it.next() { + Some(v) => *aorb = v, + None => break, + } + } + self.ranges.drain(..drain_end); + } + + /// Subtract the given set from this set, in place. + pub fn difference(&mut self, other: &IntervalSet<I>) { + if self.ranges.is_empty() || other.ranges.is_empty() { + return; + } + + // This algorithm is (to me) surprisingly complex. A search of the + // interwebs indicate that this is a potentially interesting problem. + // Folks seem to suggest interval or segment trees, but I'd like to + // avoid the overhead (both runtime and conceptual) of that. + // + // The following is basically my Shitty First Draft. Therefore, in + // order to grok it, you probably need to read each line carefully. + // Simplifications are most welcome! + // + // Remember, we can assume the canonical format invariant here, which + // says that all ranges are sorted, not overlapping and not adjacent in + // each class. + let drain_end = self.ranges.len(); + let (mut a, mut b) = (0, 0); + 'LOOP: while a < drain_end && b < other.ranges.len() { + // Basically, the easy cases are when neither range overlaps with + // each other. If the `b` range is less than our current `a` + // range, then we can skip it and move on. + if other.ranges[b].upper() < self.ranges[a].lower() { + b += 1; + continue; + } + // ... similarly for the `a` range. If it's less than the smallest + // `b` range, then we can add it as-is. + if self.ranges[a].upper() < other.ranges[b].lower() { + let range = self.ranges[a]; + self.ranges.push(range); + a += 1; + continue; + } + // Otherwise, we have overlapping ranges. + assert!(!self.ranges[a].is_intersection_empty(&other.ranges[b])); + + // This part is tricky and was non-obvious to me without looking + // at explicit examples (see the tests). The trickiness stems from + // two things: 1) subtracting a range from another range could + // yield two ranges and 2) after subtracting a range, it's possible + // that future ranges can have an impact. The loop below advances + // the `b` ranges until they can't possible impact the current + // range. + // + // For example, if our `a` range is `a-t` and our next three `b` + // ranges are `a-c`, `g-i`, `r-t` and `x-z`, then we need to apply + // subtraction three times before moving on to the next `a` range. + let mut range = self.ranges[a]; + while b < other.ranges.len() + && !range.is_intersection_empty(&other.ranges[b]) + { + let old_range = range; + range = match range.difference(&other.ranges[b]) { + (None, None) => { + // We lost the entire range, so move on to the next + // without adding this one. + a += 1; + continue 'LOOP; + } + (Some(range1), None) | (None, Some(range1)) => range1, + (Some(range1), Some(range2)) => { + self.ranges.push(range1); + range2 + } + }; + // It's possible that the `b` range has more to contribute + // here. In particular, if it is greater than the original + // range, then it might impact the next `a` range *and* it + // has impacted the current `a` range as much as possible, + // so we can quit. We don't bump `b` so that the next `a` + // range can apply it. + if other.ranges[b].upper() > old_range.upper() { + break; + } + // Otherwise, the next `b` range might apply to the current + // `a` range. + b += 1; + } + self.ranges.push(range); + a += 1; + } + while a < drain_end { + let range = self.ranges[a]; + self.ranges.push(range); + a += 1; + } + self.ranges.drain(..drain_end); + } + + /// Compute the symmetric difference of the two sets, in place. + /// + /// This computes the symmetric difference of two interval sets. This + /// removes all elements in this set that are also in the given set, + /// but also adds all elements from the given set that aren't in this + /// set. That is, the set will contain all elements in either set, + /// but will not contain any elements that are in both sets. + pub fn symmetric_difference(&mut self, other: &IntervalSet<I>) { + // TODO(burntsushi): Fix this so that it amortizes allocation. + let mut intersection = self.clone(); + intersection.intersect(other); + self.union(other); + self.difference(&intersection); + } + + /// Negate this interval set. + /// + /// For all `x` where `x` is any element, if `x` was in this set, then it + /// will not be in this set after negation. + pub fn negate(&mut self) { + if self.ranges.is_empty() { + let (min, max) = (I::Bound::min_value(), I::Bound::max_value()); + self.ranges.push(I::create(min, max)); + return; + } + + // There should be a way to do this in-place with constant memory, + // but I couldn't figure out a simple way to do it. So just append + // the negation to the end of this range, and then drain it before + // we're done. + let drain_end = self.ranges.len(); + + // We do checked arithmetic below because of the canonical ordering + // invariant. + if self.ranges[0].lower() > I::Bound::min_value() { + let upper = self.ranges[0].lower().decrement(); + self.ranges.push(I::create(I::Bound::min_value(), upper)); + } + for i in 1..drain_end { + let lower = self.ranges[i - 1].upper().increment(); + let upper = self.ranges[i].lower().decrement(); + self.ranges.push(I::create(lower, upper)); + } + if self.ranges[drain_end - 1].upper() < I::Bound::max_value() { + let lower = self.ranges[drain_end - 1].upper().increment(); + self.ranges.push(I::create(lower, I::Bound::max_value())); + } + self.ranges.drain(..drain_end); + } + + /// Converts this set into a canonical ordering. + fn canonicalize(&mut self) { + if self.is_canonical() { + return; + } + self.ranges.sort(); + assert!(!self.ranges.is_empty()); + + // Is there a way to do this in-place with constant memory? I couldn't + // figure out a way to do it. So just append the canonicalization to + // the end of this range, and then drain it before we're done. + let drain_end = self.ranges.len(); + for oldi in 0..drain_end { + // If we've added at least one new range, then check if we can + // merge this range in the previously added range. + if self.ranges.len() > drain_end { + let (last, rest) = self.ranges.split_last_mut().unwrap(); + if let Some(union) = last.union(&rest[oldi]) { + *last = union; + continue; + } + } + let range = self.ranges[oldi]; + self.ranges.push(range); + } + self.ranges.drain(..drain_end); + } + + /// Returns true if and only if this class is in a canonical ordering. + fn is_canonical(&self) -> bool { + for pair in self.ranges.windows(2) { + if pair[0] >= pair[1] { + return false; + } + if pair[0].is_contiguous(&pair[1]) { + return false; + } + } + true + } +} + +/// An iterator over intervals. +#[derive(Debug)] +pub struct IntervalSetIter<'a, I>(slice::Iter<'a, I>); + +impl<'a, I> Iterator for IntervalSetIter<'a, I> { + type Item = &'a I; + + fn next(&mut self) -> Option<&'a I> { + self.0.next() + } +} + +pub trait Interval: + Clone + Copy + Debug + Default + Eq + PartialEq + PartialOrd + Ord +{ + type Bound: Bound; + + fn lower(&self) -> Self::Bound; + fn upper(&self) -> Self::Bound; + fn set_lower(&mut self, bound: Self::Bound); + fn set_upper(&mut self, bound: Self::Bound); + fn case_fold_simple( + &self, + intervals: &mut Vec<Self>, + ) -> Result<(), unicode::CaseFoldError>; + + /// Create a new interval. + fn create(lower: Self::Bound, upper: Self::Bound) -> Self { + let mut int = Self::default(); + if lower <= upper { + int.set_lower(lower); + int.set_upper(upper); + } else { + int.set_lower(upper); + int.set_upper(lower); + } + int + } + + /// Union the given overlapping range into this range. + /// + /// If the two ranges aren't contiguous, then this returns `None`. + fn union(&self, other: &Self) -> Option<Self> { + if !self.is_contiguous(other) { + return None; + } + let lower = cmp::min(self.lower(), other.lower()); + let upper = cmp::max(self.upper(), other.upper()); + Some(Self::create(lower, upper)) + } + + /// Intersect this range with the given range and return the result. + /// + /// If the intersection is empty, then this returns `None`. + fn intersect(&self, other: &Self) -> Option<Self> { + let lower = cmp::max(self.lower(), other.lower()); + let upper = cmp::min(self.upper(), other.upper()); + if lower <= upper { + Some(Self::create(lower, upper)) + } else { + None + } + } + + /// Subtract the given range from this range and return the resulting + /// ranges. + /// + /// If subtraction would result in an empty range, then no ranges are + /// returned. + fn difference(&self, other: &Self) -> (Option<Self>, Option<Self>) { + if self.is_subset(other) { + return (None, None); + } + if self.is_intersection_empty(other) { + return (Some(self.clone()), None); + } + let add_lower = other.lower() > self.lower(); + let add_upper = other.upper() < self.upper(); + // We know this because !self.is_subset(other) and the ranges have + // a non-empty intersection. + assert!(add_lower || add_upper); + let mut ret = (None, None); + if add_lower { + let upper = other.lower().decrement(); + ret.0 = Some(Self::create(self.lower(), upper)); + } + if add_upper { + let lower = other.upper().increment(); + let range = Self::create(lower, self.upper()); + if ret.0.is_none() { + ret.0 = Some(range); + } else { + ret.1 = Some(range); + } + } + ret + } + + /// Compute the symmetric difference the given range from this range. This + /// returns the union of the two ranges minus its intersection. + fn symmetric_difference( + &self, + other: &Self, + ) -> (Option<Self>, Option<Self>) { + let union = match self.union(other) { + None => return (Some(self.clone()), Some(other.clone())), + Some(union) => union, + }; + let intersection = match self.intersect(other) { + None => return (Some(self.clone()), Some(other.clone())), + Some(intersection) => intersection, + }; + union.difference(&intersection) + } + + /// Returns true if and only if the two ranges are contiguous. Two ranges + /// are contiguous if and only if the ranges are either overlapping or + /// adjacent. + fn is_contiguous(&self, other: &Self) -> bool { + let lower1 = self.lower().as_u32(); + let upper1 = self.upper().as_u32(); + let lower2 = other.lower().as_u32(); + let upper2 = other.upper().as_u32(); + cmp::max(lower1, lower2) <= cmp::min(upper1, upper2).saturating_add(1) + } + + /// Returns true if and only if the intersection of this range and the + /// other range is empty. + fn is_intersection_empty(&self, other: &Self) -> bool { + let (lower1, upper1) = (self.lower(), self.upper()); + let (lower2, upper2) = (other.lower(), other.upper()); + cmp::max(lower1, lower2) > cmp::min(upper1, upper2) + } + + /// Returns true if and only if this range is a subset of the other range. + fn is_subset(&self, other: &Self) -> bool { + let (lower1, upper1) = (self.lower(), self.upper()); + let (lower2, upper2) = (other.lower(), other.upper()); + (lower2 <= lower1 && lower1 <= upper2) + && (lower2 <= upper1 && upper1 <= upper2) + } +} + +pub trait Bound: + Copy + Clone + Debug + Eq + PartialEq + PartialOrd + Ord +{ + fn min_value() -> Self; + fn max_value() -> Self; + fn as_u32(self) -> u32; + fn increment(self) -> Self; + fn decrement(self) -> Self; +} + +impl Bound for u8 { + fn min_value() -> Self { + u8::MIN + } + fn max_value() -> Self { + u8::MAX + } + fn as_u32(self) -> u32 { + self as u32 + } + fn increment(self) -> Self { + self.checked_add(1).unwrap() + } + fn decrement(self) -> Self { + self.checked_sub(1).unwrap() + } +} + +impl Bound for char { + fn min_value() -> Self { + '\x00' + } + fn max_value() -> Self { + '\u{10FFFF}' + } + fn as_u32(self) -> u32 { + self as u32 + } + + fn increment(self) -> Self { + match self { + '\u{D7FF}' => '\u{E000}', + c => char::from_u32((c as u32).checked_add(1).unwrap()).unwrap(), + } + } + + fn decrement(self) -> Self { + match self { + '\u{E000}' => '\u{D7FF}', + c => char::from_u32((c as u32).checked_sub(1).unwrap()).unwrap(), + } + } +} + +// Tests for interval sets are written in src/hir.rs against the public API. |