From fc2590fc9dfdf283a15851d367a4b30bcf09aee6 Mon Sep 17 00:00:00 2001
From: ManyTheFish <many@meilisearch.com>
Date: Tue, 8 Aug 2023 16:43:08 +0200
Subject: [PATCH 1/2] Add a test

---
 meilisearch/tests/search/mod.rs | 56 +++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/meilisearch/tests/search/mod.rs b/meilisearch/tests/search/mod.rs
index 6fcc33309..3aefe7e83 100644
--- a/meilisearch/tests/search/mod.rs
+++ b/meilisearch/tests/search/mod.rs
@@ -1104,3 +1104,59 @@ async fn camelcased_words() {
         })
         .await;
 }
+
+#[actix_rt::test]
+async fn simple_search_with_strange_synonyms() {
+    let server = Server::new().await;
+    let index = server.index("test");
+
+    index.update_settings(json!({ "synonyms": {"&": ["to"], "to": ["&"]} })).await;
+    let r = index.wait_task(0).await;
+    meili_snap::snapshot!(r["status"], @r###""succeeded""###);
+
+    let documents = DOCUMENTS.clone();
+    index.add_documents(documents, None).await;
+    index.wait_task(1).await;
+
+    index
+        .search(json!({"q": "How to train"}), |response, code| {
+            meili_snap::snapshot!(code, @"200 OK");
+            meili_snap::snapshot!(meili_snap::json_string!(response["hits"]), @r###"
+            [
+              {
+                "title": "How to Train Your Dragon: The Hidden World",
+                "id": "166428"
+              }
+            ]
+            "###);
+        })
+        .await;
+
+    index
+        .search(json!({"q": "How & train"}), |response, code| {
+            meili_snap::snapshot!(code, @"200 OK");
+            meili_snap::snapshot!(meili_snap::json_string!(response["hits"]), @r###"
+            [
+              {
+                "title": "How to Train Your Dragon: The Hidden World",
+                "id": "166428"
+              }
+            ]
+            "###);
+        })
+        .await;
+
+    index
+        .search(json!({"q": "to"}), |response, code| {
+            meili_snap::snapshot!(code, @"200 OK");
+            meili_snap::snapshot!(meili_snap::json_string!(response["hits"]), @r###"
+            [
+              {
+                "title": "How to Train Your Dragon: The Hidden World",
+                "id": "166428"
+              }
+            ]
+            "###);
+        })
+        .await;
+}

From 8dc5acf998a3f7caf0126983bfa45265e7efed94 Mon Sep 17 00:00:00 2001
From: ManyTheFish <many@meilisearch.com>
Date: Tue, 8 Aug 2023 16:52:36 +0200
Subject: [PATCH 2/2] Try fix

---
 milli/src/update/settings.rs | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/milli/src/update/settings.rs b/milli/src/update/settings.rs
index 33f86a4bb..d3fdac0c7 100644
--- a/milli/src/update/settings.rs
+++ b/milli/src/update/settings.rs
@@ -477,13 +477,18 @@ impl<'a, 't, 'u, 'i> Settings<'a, 't, 'u, 'i> {
                 for (word, synonyms) in synonyms {
                     // Normalize both the word and associated synonyms.
                     let normalized_word = normalize(&tokenizer, word);
-                    let normalized_synonyms =
-                        synonyms.iter().map(|synonym| normalize(&tokenizer, synonym));
+                    let normalized_synonyms: Vec<_> = synonyms
+                        .iter()
+                        .map(|synonym| normalize(&tokenizer, synonym))
+                        .filter(|synonym| !synonym.is_empty())
+                        .collect();
 
                     // Store the normalized synonyms under the normalized word,
                     // merging the possible duplicate words.
-                    let entry = new_synonyms.entry(normalized_word).or_insert_with(Vec::new);
-                    entry.extend(normalized_synonyms);
+                    if !normalized_word.is_empty() && !normalized_synonyms.is_empty() {
+                        let entry = new_synonyms.entry(normalized_word).or_insert_with(Vec::new);
+                        entry.extend(normalized_synonyms.into_iter());
+                    }
                 }
 
                 // Make sure that we don't have duplicate synonyms.