From 71f59749dca59bec6119da76cef5d984864b43fb Mon Sep 17 00:00:00 2001
From: ManyTheFish <many@meilisearch.com>
Date: Mon, 9 Dec 2024 15:44:06 +0100
Subject: [PATCH] Reduce union impact in merging

---
 crates/milli/src/update/new/merger.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/crates/milli/src/update/new/merger.rs b/crates/milli/src/update/new/merger.rs
index 9728f99d6..9e87388a2 100644
--- a/crates/milli/src/update/new/merger.rs
+++ b/crates/milli/src/update/new/merger.rs
@@ -235,8 +235,12 @@ fn merge_cbo_bitmaps(
         (Some(_current), None, None) => Ok(Operation::Ignore), // but it's strange
         (Some(current), None, Some(add)) => Ok(Operation::Write(current | add)),
         (Some(current), Some(del), add) => {
+            debug_assert!(
+                del.is_subset(&current),
+                "del is not a subset of current, which must be impossible."
+            );
             let output = match add {
-                Some(add) => (&current - del) | add,
+                Some(add) => (&current - (&del - &add)) | (add - del),
                 None => &current - del,
             };
             if output.is_empty() {