Merging upstream version 1.70.0+dfsg2.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 415 insertions, 0 deletions

diff --git a/vendor/similar/src/algorithms/myers.rs b/vendor/similar/src/algorithms/myers.rs
new file mode 100644
index 000000000..542c7ed75
--- /dev/null
+++ b/vendor/similar/src/algorithms/myers.rs
@@ -0,0 +1,415 @@
+//! Myers' diff algorithm.
+//!
+//! * time: `O((N+M)D)`
+//! * space `O(N+M)`
+//!
+//! See [the original article by Eugene W. Myers](http://www.xmailserver.org/diff2.pdf)
+//! describing it.
+//!
+//! The implementation of this algorithm is based on the implementation by
+//! Brandon Williams.
+//!
+//! # Heuristics
+//!
+//! At present this implementation of Myers' does not implement any more advanced
+//! heuristics that would solve some pathological cases.  For instane passing two
+//! large and completely distinct sequences to the algorithm will make it spin
+//! without making reasonable progress.  Currently the only protection in the
+//! library against this is to pass a deadline to the diffing algorithm.
+//!
+//! For potential improvements here see [similar#15](https://github.com/mitsuhiko/similar/issues/15).
+
+use std::ops::{Index, IndexMut, Range};
+use std::time::Instant;
+
+use crate::algorithms::utils::{common_prefix_len, common_suffix_len, is_empty_range};
+use crate::algorithms::DiffHook;
+
+/// Myers' diff algorithm.
+///
+/// Diff `old`, between indices `old_range` and `new` between indices `new_range`.
+pub fn diff<Old, New, D>(
+    d: &mut D,
+    old: &Old,
+    old_range: Range<usize>,
+    new: &New,
+    new_range: Range<usize>,
+) -> Result<(), D::Error>
+where
+    Old: Index<usize> + ?Sized,
+    New: Index<usize> + ?Sized,
+    D: DiffHook,
+    New::Output: PartialEq<Old::Output>,
+{
+    diff_deadline(d, old, old_range, new, new_range, None)
+}
+
+/// Myers' diff algorithm with deadline.
+///
+/// Diff `old`, between indices `old_range` and `new` between indices `new_range`.
+///
+/// This diff is done with an optional deadline that defines the maximal
+/// execution time permitted before it bails and falls back to an approximation.
+pub fn diff_deadline<Old, New, D>(
+    d: &mut D,
+    old: &Old,
+    old_range: Range<usize>,
+    new: &New,
+    new_range: Range<usize>,
+    deadline: Option<Instant>,
+) -> Result<(), D::Error>
+where
+    Old: Index<usize> + ?Sized,
+    New: Index<usize> + ?Sized,
+    D: DiffHook,
+    New::Output: PartialEq<Old::Output>,
+{
+    let max_d = max_d(old_range.len(), new_range.len());
+    let mut vb = V::new(max_d);
+    let mut vf = V::new(max_d);
+    conquer(
+        d, old, old_range, new, new_range, &mut vf, &mut vb, deadline,
+    )?;
+    d.finish()
+}
+
+// A D-path is a path which starts at (0,0) that has exactly D non-diagonal
+// edges. All D-paths consist of a (D - 1)-path followed by a non-diagonal edge
+// and then a possibly empty sequence of diagonal edges called a snake.
+
+/// `V` contains the endpoints of the furthest reaching `D-paths`. For each
+/// recorded endpoint `(x,y)` in diagonal `k`, we only need to retain `x` because
+/// `y` can be computed from `x - k`. In other words, `V` is an array of integers
+/// where `V[k]` contains the row index of the endpoint of the furthest reaching
+/// path in diagonal `k`.
+///
+/// We can't use a traditional Vec to represent `V` since we use `k` as an index
+/// and it can take on negative values. So instead `V` is represented as a
+/// light-weight wrapper around a Vec plus an `offset` which is the maximum value
+/// `k` can take on in order to map negative `k`'s back to a value >= 0.
+#[derive(Debug)]
+struct V {
+    offset: isize,
+    v: Vec<usize>, // Look into initializing this to -1 and storing isize
+}
+
+impl V {
+    fn new(max_d: usize) -> Self {
+        Self {
+            offset: max_d as isize,
+            v: vec![0; 2 * max_d],
+        }
+    }
+
+    fn len(&self) -> usize {
+        self.v.len()
+    }
+}
+
+impl Index<isize> for V {
+    type Output = usize;
+
+    fn index(&self, index: isize) -> &Self::Output {
+        &self.v[(index + self.offset) as usize]
+    }
+}
+
+impl IndexMut<isize> for V {
+    fn index_mut(&mut self, index: isize) -> &mut Self::Output {
+        &mut self.v[(index + self.offset) as usize]
+    }
+}
+
+fn max_d(len1: usize, len2: usize) -> usize {
+    // XXX look into reducing the need to have the additional '+ 1'
+    (len1 + len2 + 1) / 2 + 1
+}
+
+#[inline(always)]
+fn split_at(range: Range<usize>, at: usize) -> (Range<usize>, Range<usize>) {
+    (range.start..at, at..range.end)
+}
+
+/// A `Snake` is a sequence of diagonal edges in the edit graph.  Normally
+/// a snake has a start end end point (and it is possible for a snake to have
+/// a length of zero, meaning the start and end points are the same) however
+/// we do not need the end point which is why it's not implemented here.
+///
+/// The divide part of a divide-and-conquer strategy. A D-path has D+1 snakes
+/// some of which may be empty. The divide step requires finding the ceil(D/2) +
+/// 1 or middle snake of an optimal D-path. The idea for doing so is to
+/// simultaneously run the basic algorithm in both the forward and reverse
+/// directions until furthest reaching forward and reverse paths starting at
+/// opposing corners 'overlap'.
+fn find_middle_snake<Old, New>(
+    old: &Old,
+    old_range: Range<usize>,
+    new: &New,
+    new_range: Range<usize>,
+    vf: &mut V,
+    vb: &mut V,
+    deadline: Option<Instant>,
+) -> Option<(usize, usize)>
+where
+    Old: Index<usize> + ?Sized,
+    New: Index<usize> + ?Sized,
+    New::Output: PartialEq<Old::Output>,
+{
+    let n = old_range.len();
+    let m = new_range.len();
+
+    // By Lemma 1 in the paper, the optimal edit script length is odd or even as
+    // `delta` is odd or even.
+    let delta = n as isize - m as isize;
+    let odd = delta & 1 == 1;
+
+    // The initial point at (0, -1)
+    vf[1] = 0;
+    // The initial point at (N, M+1)
+    vb[1] = 0;
+
+    // We only need to explore ceil(D/2) + 1
+    let d_max = max_d(n, m);
+    assert!(vf.len() >= d_max);
+    assert!(vb.len() >= d_max);
+
+    for d in 0..d_max as isize {
+        // are we running for too long?
+        if let Some(deadline) = deadline {
+            if Instant::now() > deadline {
+                break;
+            }
+        }
+
+        // Forward path
+        for k in (-d..=d).rev().step_by(2) {
+            let mut x = if k == -d || (k != d && vf[k - 1] < vf[k + 1]) {
+                vf[k + 1]
+            } else {
+                vf[k - 1] + 1
+            };
+            let y = (x as isize - k) as usize;
+
+            // The coordinate of the start of a snake
+            let (x0, y0) = (x, y);
+            //  While these sequences are identical, keep moving through the
+            //  graph with no cost
+            if x < old_range.len() && y < new_range.len() {
+                let advance = common_prefix_len(
+                    old,
+                    old_range.start + x..old_range.end,
+                    new,
+                    new_range.start + y..new_range.end,
+                );
+                x += advance;
+            }
+
+            // This is the new best x value
+            vf[k] = x;
+
+            // Only check for connections from the forward search when N - M is
+            // odd and when there is a reciprocal k line coming from the other
+            // direction.
+            if odd && (k - delta).abs() <= (d - 1) {
+                // TODO optimize this so we don't have to compare against n
+                if vf[k] + vb[-(k - delta)] >= n {
+                    // Return the snake
+                    return Some((x0 + old_range.start, y0 + new_range.start));
+                }
+            }
+        }
+
+        // Backward path
+        for k in (-d..=d).rev().step_by(2) {
+            let mut x = if k == -d || (k != d && vb[k - 1] < vb[k + 1]) {
+                vb[k + 1]
+            } else {
+                vb[k - 1] + 1
+            };
+            let mut y = (x as isize - k) as usize;
+
+            // The coordinate of the start of a snake
+            if x < n && y < m {
+                let advance = common_suffix_len(
+                    old,
+                    old_range.start..old_range.start + n - x,
+                    new,
+                    new_range.start..new_range.start + m - y,
+                );
+                x += advance;
+                y += advance;
+            }
+
+            // This is the new best x value
+            vb[k] = x;
+
+            if !odd && (k - delta).abs() <= d {
+                // TODO optimize this so we don't have to compare against n
+                if vb[k] + vf[-(k - delta)] >= n {
+                    // Return the snake
+                    return Some((n - x + old_range.start, m - y + new_range.start));
+                }
+            }
+        }
+
+        // TODO: Maybe there's an opportunity to optimize and bail early?
+    }
+
+    // deadline reached
+    None
+}
+
+#[allow(clippy::too_many_arguments)]
+fn conquer<Old, New, D>(
+    d: &mut D,
+    old: &Old,
+    mut old_range: Range<usize>,
+    new: &New,
+    mut new_range: Range<usize>,
+    vf: &mut V,
+    vb: &mut V,
+    deadline: Option<Instant>,
+) -> Result<(), D::Error>
+where
+    Old: Index<usize> + ?Sized,
+    New: Index<usize> + ?Sized,
+    D: DiffHook,
+    New::Output: PartialEq<Old::Output>,
+{
+    // Check for common prefix
+    let common_prefix_len = common_prefix_len(old, old_range.clone(), new, new_range.clone());
+    if common_prefix_len > 0 {
+        d.equal(old_range.start, new_range.start, common_prefix_len)?;
+    }
+    old_range.start += common_prefix_len;
+    new_range.start += common_prefix_len;
+
+    // Check for common suffix
+    let common_suffix_len = common_suffix_len(old, old_range.clone(), new, new_range.clone());
+    let common_suffix = (
+        old_range.end - common_suffix_len,
+        new_range.end - common_suffix_len,
+    );
+    old_range.end -= common_suffix_len;
+    new_range.end -= common_suffix_len;
+
+    if is_empty_range(&old_range) && is_empty_range(&new_range) {
+        // Do nothing
+    } else if is_empty_range(&new_range) {
+        d.delete(old_range.start, old_range.len(), new_range.start)?;
+    } else if is_empty_range(&old_range) {
+        d.insert(old_range.start, new_range.start, new_range.len())?;
+    } else if let Some((x_start, y_start)) = find_middle_snake(
+        old,
+        old_range.clone(),
+        new,
+        new_range.clone(),
+        vf,
+        vb,
+        deadline,
+    ) {
+        let (old_a, old_b) = split_at(old_range, x_start);
+        let (new_a, new_b) = split_at(new_range, y_start);
+        conquer(d, old, old_a, new, new_a, vf, vb, deadline)?;
+        conquer(d, old, old_b, new, new_b, vf, vb, deadline)?;
+    } else {
+        d.delete(
+            old_range.start,
+            old_range.end - old_range.start,
+            new_range.start,
+        )?;
+        d.insert(
+            old_range.start,
+            new_range.start,
+            new_range.end - new_range.start,
+        )?;
+    }
+
+    if common_suffix_len > 0 {
+        d.equal(common_suffix.0, common_suffix.1, common_suffix_len)?;
+    }
+
+    Ok(())
+}
+
+#[test]
+fn test_find_middle_snake() {
+    let a = &b"ABCABBA"[..];
+    let b = &b"CBABAC"[..];
+    let max_d = max_d(a.len(), b.len());
+    let mut vf = V::new(max_d);
+    let mut vb = V::new(max_d);
+    let (x_start, y_start) =
+        find_middle_snake(a, 0..a.len(), b, 0..b.len(), &mut vf, &mut vb, None).unwrap();
+    assert_eq!(x_start, 4);
+    assert_eq!(y_start, 1);
+}
+
+#[test]
+fn test_diff() {
+    let a: &[usize] = &[0, 1, 2, 3, 4];
+    let b: &[usize] = &[0, 1, 2, 9, 4];
+
+    let mut d = crate::algorithms::Replace::new(crate::algorithms::Capture::new());
+    diff(&mut d, a, 0..a.len(), b, 0..b.len()).unwrap();
+    insta::assert_debug_snapshot!(d.into_inner().ops());
+}
+
+#[test]
+fn test_contiguous() {
+    let a: &[usize] = &[0, 1, 2, 3, 4, 4, 4, 5];
+    let b: &[usize] = &[0, 1, 2, 8, 9, 4, 4, 7];
+
+    let mut d = crate::algorithms::Replace::new(crate::algorithms::Capture::new());
+    diff(&mut d, a, 0..a.len(), b, 0..b.len()).unwrap();
+    insta::assert_debug_snapshot!(d.into_inner().ops());
+}
+
+#[test]
+fn test_pat() {
+    let a: &[usize] = &[0, 1, 3, 4, 5];
+    let b: &[usize] = &[0, 1, 4, 5, 8, 9];
+
+    let mut d = crate::algorithms::Capture::new();
+    diff(&mut d, a, 0..a.len(), b, 0..b.len()).unwrap();
+    insta::assert_debug_snapshot!(d.ops());
+}
+
+#[test]
+fn test_deadline_reached() {
+    use std::ops::Index;
+    use std::time::Duration;
+
+    let a = (0..100).collect::<Vec<_>>();
+    let mut b = (0..100).collect::<Vec<_>>();
+    b[10] = 99;
+    b[50] = 99;
+    b[25] = 99;
+
+    struct SlowIndex<'a>(&'a [usize]);
+
+    impl<'a> Index<usize> for SlowIndex<'a> {
+        type Output = usize;
+
+        fn index(&self, index: usize) -> &Self::Output {
+            std::thread::sleep(Duration::from_millis(1));
+            &self.0[index]
+        }
+    }
+
+    let slow_a = SlowIndex(&a);
+    let slow_b = SlowIndex(&b);
+
+    // don't give it enough time to do anything interesting
+    let mut d = crate::algorithms::Replace::new(crate::algorithms::Capture::new());
+    diff_deadline(
+        &mut d,
+        &slow_a,
+        0..a.len(),
+        &slow_b,
+        0..b.len(),
+        Some(Instant::now() + Duration::from_millis(50)),
+    )
+    .unwrap();
+    insta::assert_debug_snapshot!(d.into_inner().ops());
+}