Replace the BTreeMap by an IndexMap to return values in order

Cargo.lock

@@ -2731,6 +2731,7 @@ dependencies = [
  "grenad",
  "heed",
  "hnsw",
+ "indexmap",
  "insta",
  "itertools",
  "json-depth-checker",

meilisearch/Cargo.toml

@@ -14,14 +14,27 @@ default-run = "meilisearch"
 
 [dependencies]
 actix-cors = "0.6.4"
-actix-http = { version = "3.3.1", default-features = false, features = ["compress-brotli", "compress-gzip", "rustls"] }
-actix-web = { version = "4.3.1", default-features = false, features = ["macros", "compress-brotli", "compress-gzip", "cookies", "rustls"] }
+actix-http = { version = "3.3.1", default-features = false, features = [
+    "compress-brotli",
+    "compress-gzip",
+    "rustls",
+] }
+actix-web = { version = "4.3.1", default-features = false, features = [
+    "macros",
+    "compress-brotli",
+    "compress-gzip",
+    "cookies",
+    "rustls",
+] }
 actix-web-static-files = { git = "https://github.com/kilork/actix-web-static-files.git", rev = "2d3b6160", optional = true }
 anyhow = { version = "1.0.70", features = ["backtrace"] }
 async-stream = "0.3.5"
 async-trait = "0.1.68"
 bstr = "1.4.0"
-byte-unit = { version = "4.0.19", default-features = false, features = ["std", "serde"] }
+byte-unit = { version = "4.0.19", default-features = false, features = [
+    "std",
+    "serde",
+] }
 bytes = "1.4.0"
 clap = { version = "4.2.1", features = ["derive", "env"] }
 crossbeam-channel = "0.5.8"
@@ -57,7 +70,10 @@ prometheus = { version = "0.13.3", features = ["process"] }
 rand = "0.8.5"
 rayon = "1.7.0"
 regex = "1.7.3"
-reqwest = { version = "0.11.16", features = ["rustls-tls", "json"], default-features = false }
+reqwest = { version = "0.11.16", features = [
+    "rustls-tls",
+    "json",
+], default-features = false }
 rustls = "0.20.8"
 rustls-pemfile = "1.0.2"
 segment = { version = "0.2.2", optional = true }
@@ -71,7 +87,12 @@ sysinfo = "0.28.4"
 tar = "0.4.38"
 tempfile = "3.5.0"
 thiserror = "1.0.40"
-time = { version = "0.3.20", features = ["serde-well-known", "formatting", "parsing", "macros"] }
+time = { version = "0.3.20", features = [
+    "serde-well-known",
+    "formatting",
+    "parsing",
+    "macros",
+] }
 tokio = { version = "1.27.0", features = ["full"] }
 tokio-stream = "0.1.12"
 toml = "0.7.3"
@@ -99,7 +120,10 @@ yaup = "0.2.1"
 anyhow = { version = "1.0.70", optional = true }
 cargo_toml = { version = "0.15.2", optional = true }
 hex = { version = "0.4.3", optional = true }
-reqwest = { version = "0.11.16", features = ["blocking", "rustls-tls"], default-features = false, optional = true }
+reqwest = { version = "0.11.16", features = [
+    "blocking",
+    "rustls-tls",
+], default-features = false, optional = true }
 sha-1 = { version = "0.10.1", optional = true }
 static-files = { version = "0.2.3", optional = true }
 tempfile = { version = "3.5.0", optional = true }
@@ -109,7 +133,17 @@ zip = { version = "0.6.4", optional = true }
 [features]
 default = ["analytics", "meilisearch-types/all-tokenizations", "mini-dashboard"]
 analytics = ["segment"]
-mini-dashboard = ["actix-web-static-files", "static-files", "anyhow", "cargo_toml", "hex", "reqwest", "sha-1", "tempfile", "zip"]
+mini-dashboard = [
+    "actix-web-static-files",
+    "static-files",
+    "anyhow",
+    "cargo_toml",
+    "hex",
+    "reqwest",
+    "sha-1",
+    "tempfile",
+    "zip",
+]
 chinese = ["meilisearch-types/chinese"]
 hebrew = ["meilisearch-types/hebrew"]
 japanese = ["meilisearch-types/japanese"]

meilisearch/src/search.rs

@@ -6,6 +6,7 @@ use std::time::Instant;
 use deserr::Deserr;
 use either::Either;
 use index_scheduler::RoFeatures;
+use indexmap::IndexMap;
 use log::warn;
 use meilisearch_auth::IndexSearchRules;
 use meilisearch_types::deserr::DeserrJsonError;
@@ -279,7 +280,7 @@ pub struct SearchResult {
     #[serde(flatten)]
     pub hits_info: HitsInfo,
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub facet_distribution: Option<BTreeMap<String, BTreeMap<String, u64>>>,
+    pub facet_distribution: Option<BTreeMap<String, IndexMap<String, u64>>>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub facet_stats: Option<BTreeMap<String, FacetStats>>,
 }

milli/Cargo.toml

@@ -34,6 +34,7 @@ heed = { git = "https://github.com/meilisearch/heed", tag = "v0.12.6", default-f
     "sync-read-txn",
 ] }
 hnsw = { version = "0.11.0", features = ["serde1"] }
+indexmap = { version = "1.9.3", features = ["serde"] }
 json-depth-checker = { path = "../json-depth-checker" }
 levenshtein_automata = { version = "0.2.1", features = ["fst_automaton"] }
 memmap2 = "0.5.10"

milli/src/search/facet/facet_distribution.rs

@@ -4,6 +4,7 @@ use std::{fmt, mem};
 
 use heed::types::ByteSlice;
 use heed::BytesDecode;
+use indexmap::IndexMap;
 use roaring::RoaringBitmap;
 
 use crate::error::UserError;
@@ -83,7 +84,7 @@ impl<'a> FacetDistribution<'a> {
         field_id: FieldId,
         facet_type: FacetType,
         candidates: &RoaringBitmap,
-        distribution: &mut BTreeMap<String, u64>,
+        distribution: &mut IndexMap<String, u64>,
     ) -> heed::Result<()> {
         match facet_type {
             FacetType::Number => {
@@ -153,7 +154,7 @@ impl<'a> FacetDistribution<'a> {
         field_id: FieldId,
         candidates: &RoaringBitmap,
         order_by: OrderBy,
-        distribution: &mut BTreeMap<String, u64>,
+        distribution: &mut IndexMap<String, u64>,
     ) -> heed::Result<()> {
         let search_function = match order_by {
             OrderBy::Lexicographic => lexicographically_iterate_over_facet_distribution,
@@ -184,7 +185,7 @@ impl<'a> FacetDistribution<'a> {
         field_id: FieldId,
         candidates: &RoaringBitmap,
         order_by: OrderBy,
-        distribution: &mut BTreeMap<String, u64>,
+        distribution: &mut IndexMap<String, u64>,
     ) -> heed::Result<()> {
         let search_function = match order_by {
             OrderBy::Lexicographic => lexicographically_iterate_over_facet_distribution,
@@ -219,10 +220,10 @@ impl<'a> FacetDistribution<'a> {
         )
     }
 
-    fn facet_values(&self, field_id: FieldId) -> heed::Result<BTreeMap<String, u64>> {
+    fn facet_values(&self, field_id: FieldId) -> heed::Result<IndexMap<String, u64>> {
         use FacetType::{Number, String};
 
-        let mut distribution = BTreeMap::new();
+        let mut distribution = IndexMap::new();
         match (self.order_by, &self.candidates) {
             (OrderBy::Lexicographic, Some(cnd)) if cnd.len() <= CANDIDATES_THRESHOLD => {
                 // Classic search, candidates were specified, we must return facet values only related
@@ -318,7 +319,7 @@ impl<'a> FacetDistribution<'a> {
         Ok(distribution)
     }
 
-    pub fn execute(&self) -> Result<BTreeMap<String, BTreeMap<String, u64>>> {
+    pub fn execute(&self) -> Result<BTreeMap<String, IndexMap<String, u64>>> {
         let fields_ids_map = self.index.fields_ids_map(self.rtxn)?;
         let filterable_fields = self.index.filterable_fields(self.rtxn)?;