From fc433159e2f31fa6e3200023f0ab382de08e4681 Mon Sep 17 00:00:00 2001
From: Sam Zhou <samzhou19815@meta.com>
Date: Tue, 18 Feb 2025 12:21:00 -0800
Subject: [PATCH] [flow][indexing] Diff the `new_available_exports_index` and
 `old_available_exports_index`

Summary:
This stack aims to fix the bug that incremental update of exports will incorrectly drop some export count to zero, because the current subtract function will incorrectly remove the entire export even through it will be added back.

This diff fixes the issue by first diffing the available export index into two disjoint index for additional and removal, which are then passes to `Export_index.merge` and `Export_index.subtract`. This ensures that for the overlapping old and new available index that's supposed to cancel out, they won't incorrectly nuke the usage count entry.

Changelog: [fix] Fixed a bug that causes incorrect updates to our index that tracks usage of exports, which leads to incorrect autoimport-ranked-by-usage results.

Reviewed By: panagosg7

Differential Revision: D69694640

fbshipit-source-id: 9f777f69db78d05b49b373f68531b1d777590763
---
 src/services/export/index/export_index.ml   | 23 +++++++++++++++++++++
 src/services/export/index/export_index.mli  |  4 ++++
 src/services/export/search/export_search.ml | 12 +++++++----
 3 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/src/services/export/index/export_index.ml b/src/services/export/index/export_index.ml
index 0a6a7e6d383..0bf3183aabb 100644
--- a/src/services/export/index/export_index.ml
+++ b/src/services/export/index/export_index.ml
@@ -132,6 +132,29 @@ let fold ~f ~init t =
 
 let map ~f t = SMap.map (ExportMap.map f) t
 
+let diff ~old_index ~new_index =
+  let exist_in_index export_name export_key map =
+    match SMap.find_opt export_name map with
+    | None -> false
+    | Some map -> ExportMap.mem export_key map
+  in
+  let diff_index l r =
+    SMap.fold
+      (fun export_name map acc ->
+        ExportMap.fold
+          (fun export_key _ acc ->
+            if exist_in_index export_name export_key r then
+              acc
+            else
+              let (s, k) = export_key in
+              add export_name s k acc)
+          map
+          acc)
+      l
+      SMap.empty
+  in
+  (diff_index new_index old_index, diff_index old_index new_index)
+
 let subtract old_t t =
   let (t, dead_names) =
     SMap.fold
diff --git a/src/services/export/index/export_index.mli b/src/services/export/index/export_index.mli
index e801cbb8719..7fae329a0a0 100644
--- a/src/services/export/index/export_index.mli
+++ b/src/services/export/index/export_index.mli
@@ -37,6 +37,10 @@ val merge : t -> t -> t
 
 val merge_export_import : t -> t -> t
 
+(* Returns tuple of two disjoint index: (addition_index, removal_index),
+ * to be passed to [merge] and `[subtract]`. *)
+val diff : old_index:t -> new_index:t -> t * t
+
 (** [subtract to_remove t] removes all of the exports in [to_remove] from [t], and
     also returns a list of keys that no longer are exported by any file. *)
 val subtract : t -> t -> t * string list
diff --git a/src/services/export/search/export_search.ml b/src/services/export/search/export_search.ml
index 3c55aac76dc..4f6d7b1efed 100644
--- a/src/services/export/search/export_search.ml
+++ b/src/services/export/search/export_search.ml
@@ -67,12 +67,16 @@ let init index =
   let type_matcher = Fuzzy_path.init types in
   { index; value_matcher; type_matcher }
 
-let merge_available_exports old_index new_index { index; value_matcher; type_matcher } =
-  let (index, dead_candidates) = Export_index.subtract old_index index in
+let merge_available_exports
+    old_available_exports_index new_available_exports_index { index; value_matcher; type_matcher } =
+  let (addition_index, removal_index) =
+    Export_index.diff ~old_index:old_available_exports_index ~new_index:new_available_exports_index
+  in
+  let (index, dead_candidates) = Export_index.subtract removal_index index in
   let value_matcher = Fuzzy_path.remove_candidates value_matcher dead_candidates in
   let type_matcher = Fuzzy_path.remove_candidates type_matcher dead_candidates in
-  let index = Export_index.merge new_index index in
-  let { values; types } = partition_candidates new_index in
+  let index = Export_index.merge addition_index index in
+  let { values; types } = partition_candidates addition_index in
   let value_matcher = Fuzzy_path.add_candidates value_matcher values in
   let type_matcher = Fuzzy_path.add_candidates type_matcher types in
   { index; value_matcher; type_matcher }