Fix the return of equal candidates in different pages

milli/src/search/criteria/attribute.rs

@@ -1,5 +1,6 @@
 use std::{borrow::Cow, cmp::{self, Ordering}, collections::BinaryHeap};
 use std::collections::{BTreeMap, HashMap, btree_map};
+use std::collections::binary_heap::PeekMut;
 use std::mem::take;
 
 use roaring::RoaringBitmap;
@@ -332,13 +333,26 @@ struct Branch<'t, 'q> {
 }
 
 impl<'t, 'q> Branch<'t, 'q> {
-    fn cmp(&self, other: &Self) -> Ordering {
-        let compute_rank = |left: u32, branch_size: u32| left.saturating_sub((0..branch_size).sum()) / branch_size;
-        let (s_left, _, _) = self.last_result;
-        let (o_left, _, _) = other.last_result;
+    fn next(&mut self) -> heed::Result<bool> {
+        match self.query_level_iterator.next()? {
+            (tree_level, Some(last_result)) => {
+                self.last_result = last_result;
+                self.tree_level = tree_level;
+                Ok(true)
+            },
+            (_, None) => Ok(false),
+        }
+    }
+
+    fn compute_rank(&self) -> u32 {
         // we compute a rank from the left interval.
-        let self_rank = compute_rank(s_left, self.branch_size);
-        let other_rank = compute_rank(o_left, other.branch_size);
+        let (left, _, _) = self.last_result;
+        left.saturating_sub((0..self.branch_size).sum()) * 60 / self.branch_size
+    }
+
+    fn cmp(&self, other: &Self) -> Ordering {
+        let self_rank = self.compute_rank();
+        let other_rank = other.compute_rank();
         let left_cmp = self_rank.cmp(&other_rank).reverse();
         // on level: higher is better,
         // we want to reduce highest levels first.
@@ -426,44 +440,53 @@ fn set_compute_candidates<'t>(
 {
     let mut branches_heap = initialize_query_level_iterators(ctx, branches, wdcache)?;
     let lowest_level = TreeLevel::min_value();
-    let mut final_candidates = None;
+    let mut final_candidates: Option<(u32, RoaringBitmap)> = None;
 
     while let Some(mut branch) = branches_heap.peek_mut() {
         let is_lowest_level = branch.tree_level == lowest_level;
+        let branch_rank = branch.compute_rank();
         let (_, _, candidates) = &mut branch.last_result;
         candidates.intersect_with(&allowed_candidates);
         if candidates.is_empty() {
             // we don't have candidates, get next interval.
-            match branch.query_level_iterator.next()? {
-                (_, Some(last_result)) => {
-                    branch.last_result = last_result;
-                },
-                // TODO clean up this
-                (_, None) => { std::collections::binary_heap::PeekMut::<'_, Branch<'_, '_>>::pop(branch); },
-            }
-
+            if !branch.next()? { PeekMut::pop(branch); }
         }
         else if is_lowest_level {
             // we have candidates, but we can't dig deeper, return candidates.
-            final_candidates = Some(take(candidates));
-            break;
+            final_candidates = match final_candidates.take() {
+                Some((best_rank, mut best_candidates)) => {
+                    // if current is worst than best we break to return
+                    // candidates that correspond to the best rank
+                    if branch_rank > best_rank {
+                        final_candidates = Some((best_rank, best_candidates));
+                        break;
+                    // else we add current candidates to best candidates
+                    // and we fetch the next page
+                    } else {
+                        best_candidates.union_with(candidates);
+                        if !branch.next()? { PeekMut::pop(branch); }
+                        Some((best_rank, best_candidates))
+                    }
+                },
+                // we take current candidates as best candidates
+                // and we fetch the next page
+                None => {
+                    let candidates = take(candidates);
+                    if !branch.next()? { PeekMut::pop(branch); }
+                    Some((branch_rank, candidates))
+                },
+            };
         } else {
             // we have candidates, lets dig deeper in levels.
-            let mut query_level_iterator = branch.query_level_iterator.dig(ctx)?;
-            match query_level_iterator.next()? {
-                (tree_level, Some(last_result)) => {
-                    branch.query_level_iterator = query_level_iterator;
-                    branch.tree_level = tree_level;
-                    branch.last_result = last_result;
-                },
-                // TODO clean up this
-                (_, None) => { std::collections::binary_heap::PeekMut::<'_, Branch<'_, '_>>::pop(branch); },
-            }
+            branch.query_level_iterator = branch.query_level_iterator.dig(ctx)?;
+            if !branch.next()? { PeekMut::pop(branch); }
         }
 
     }
 
-    Ok(final_candidates)
+    Ok(final_candidates.map(|(_rank, candidates)| {
+        candidates
+    }))
 }
 
 fn linear_compute_candidates(