Merge pull request #246 from meilisearch/better-highlighting-area

Make the highlight system much better

meilidb-core/src/levenshtein.rs

@@ -0,0 +1,134 @@
+use std::cmp::min;
+use std::collections::BTreeMap;
+use std::ops::{Index, IndexMut};
+
+// A simple wrapper around vec so we can get contiguous but index it like it's 2D array.
+struct N2Array<T> {
+    y_size: usize,
+    buf: Vec<T>,
+}
+
+impl<T: Clone> N2Array<T> {
+    fn new(x: usize, y: usize, value: T) -> N2Array<T> {
+        N2Array {
+            y_size: y,
+            buf: vec![value; x * y],
+        }
+    }
+}
+
+impl<T> Index<(usize, usize)> for N2Array<T> {
+    type Output = T;
+
+    #[inline]
+    fn index(&self, (x, y): (usize, usize)) -> &T {
+        &self.buf[(x * self.y_size) + y]
+    }
+}
+
+impl<T> IndexMut<(usize, usize)> for N2Array<T> {
+    #[inline]
+    fn index_mut(&mut self, (x, y): (usize, usize)) -> &mut T {
+        &mut self.buf[(x * self.y_size) + y]
+    }
+}
+
+pub fn prefix_damerau_levenshtein(source: &[u8], target: &[u8]) -> (u32, usize) {
+    let (n, m) = (source.len(), target.len());
+
+    assert!(
+        n <= m,
+        "the source string must be shorter than the target one"
+    );
+
+    if n == 0 {
+        return (m as u32, 0);
+    }
+    if m == 0 {
+        return (n as u32, 0);
+    }
+
+    if n == m && source == target {
+        return (0, m);
+    }
+
+    let inf = n + m;
+    let mut matrix = N2Array::new(n + 2, m + 2, 0);
+
+    matrix[(0, 0)] = inf;
+    for i in 0..n + 1 {
+        matrix[(i + 1, 0)] = inf;
+        matrix[(i + 1, 1)] = i;
+    }
+    for j in 0..m + 1 {
+        matrix[(0, j + 1)] = inf;
+        matrix[(1, j + 1)] = j;
+    }
+
+    let mut last_row = BTreeMap::new();
+
+    for (row, char_s) in source.iter().enumerate() {
+        let mut last_match_col = 0;
+        let row = row + 1;
+
+        for (col, char_t) in target.iter().enumerate() {
+            let col = col + 1;
+            let last_match_row = *last_row.get(&char_t).unwrap_or(&0);
+            let cost = if char_s == char_t { 0 } else { 1 };
+
+            let dist_add = matrix[(row, col + 1)] + 1;
+            let dist_del = matrix[(row + 1, col)] + 1;
+            let dist_sub = matrix[(row, col)] + cost;
+            let dist_trans = matrix[(last_match_row, last_match_col)]
+                + (row - last_match_row - 1)
+                + 1
+                + (col - last_match_col - 1);
+
+            let dist = min(min(dist_add, dist_del), min(dist_sub, dist_trans));
+
+            matrix[(row + 1, col + 1)] = dist;
+
+            if cost == 0 {
+                last_match_col = col;
+            }
+        }
+
+        last_row.insert(char_s, row);
+    }
+
+    let mut minimum = (u32::max_value(), 0);
+
+    for x in n..=m {
+        let dist = matrix[(n + 1, x + 1)] as u32;
+        if dist < minimum.0 {
+            minimum = (dist, x)
+        }
+    }
+
+    minimum
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn matched_length() {
+        let query = "Levenste";
+        let text = "Levenshtein";
+
+        let (dist, length) = prefix_damerau_levenshtein(query.as_bytes(), text.as_bytes());
+        assert_eq!(dist, 1);
+        assert_eq!(&text[..length], "Levenshte");
+    }
+
+    #[test]
+    #[should_panic]
+    fn matched_length_panic() {
+        let query = "Levenshtein";
+        let text = "Levenste";
+
+        // this function will panic if source if longer than target
+        prefix_damerau_levenshtein(query.as_bytes(), text.as_bytes());
+    }
+}

meilidb-core/src/lib.rs

@@ -7,6 +7,7 @@ pub mod criterion;
 mod database;
 mod distinct_map;
 mod error;
+mod levenshtein;
 mod number;
 mod query_builder;
 mod ranked_map;

meilidb-core/src/query_builder.rs

@@ -11,6 +11,7 @@ use slice_group_by::{GroupBy, GroupByMut};
 
 use crate::automaton::{Automaton, AutomatonGroup, AutomatonProducer, QueryEnhancer};
 use crate::distinct_map::{BufferedDistinctMap, DistinctMap};
+use crate::levenshtein::prefix_damerau_levenshtein;
 use crate::raw_document::{raw_documents_from, RawDocument};
 use crate::{criterion::Criteria, Document, DocumentId, Highlight, TmpMatch};
 use crate::{reordered_attrs::ReorderedAttrs, store, MResult};
@@ -162,6 +163,7 @@ fn fetch_raw_documents(
                 index,
                 is_exact,
                 query_len,
+                query,
                 ..
             } = automaton;
             let dfa = automaton.dfa();
@@ -176,6 +178,12 @@ fn fetch_raw_documents(
                 let distance = dfa.eval(input).to_u8();
                 let is_exact = *is_exact && distance == 0 && input.len() == *query_len;
 
+                let covered_area = if query.len() > input.len() {
+                    query.len()
+                } else {
+                    prefix_damerau_levenshtein(query.as_bytes(), input).1
+                };
+
                 let doc_indexes = match postings_lists_store.postings_list(reader, input)? {
                     Some(doc_indexes) => doc_indexes,
                     None => continue,
@@ -197,7 +205,7 @@ fn fetch_raw_documents(
                         let highlight = Highlight {
                             attribute: di.attribute,
                             char_index: di.char_index,
-                            char_length: u16::try_from(*query_len).unwrap_or(u16::max_value()),
+                            char_length: u16::try_from(covered_area).unwrap_or(u16::max_value()),
                         };
 
                         tmp_matches.push((di.document_id, id, match_, highlight));