Merge #658

658: Add proximity calculation for the same word r=ManyTheFish a=msvaljek

# Pull Request

## Related issue
Fixes https://github.com/meilisearch/milli/issues/647

## What does this PR do?
- During [the increase of the current word position](d94339a858/milli/src/update/index_documents/extract/extract_word_pair_proximity_docids.rs (L129-L135)) we extract the proximity between the current position and the next one.

## PR checklist
Please check if your PR fulfills the following requirements:
- [x] Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
- [x] Have you read the contributing guidelines?
- [x] Have you made sure that the title is accurate and descriptive of the changes?

Thank you so much for contributing to Meilisearch!


Co-authored-by: msvaljek <marko.svaljek@commercetools.com>

milli/src/update/index_documents/extract/extract_word_pair_proximity_docids.rs

@@ -127,6 +127,17 @@ fn document_word_positions_into_sorter<'b>(
             // Advance the head and push it in the heap.
             if let Some(mut head) = ordered_peeked_word_positions.pop() {
                 if let Some(next_position) = head.iter.next() {
+                    let prox = positions_proximity(head.position, next_position);
+
+                    if prox > 0 && prox < MAX_DISTANCE {
+                        word_pair_proximity
+                            .entry((head.word.clone(), head.word.clone()))
+                            .and_modify(|p| {
+                                *p = cmp::min(*p, prox);
+                            })
+                            .or_insert(prox);
+                    }
+
                     word_positions_heap.push(PeekedWordPosition {
                         word: head.word,
                         position: next_position,