From bf39976d218cc31ed8efeb064a7ac9bf78d05075 Mon Sep 17 00:00:00 2001
From: Ivan Enderlin <ivan@mnt.io>
Date: Wed, 22 May 2024 09:36:15 +0200
Subject: [PATCH] doc(sdk): Add a useful inline documentation.

---
 crates/matrix-sdk/src/event_cache/linked_chunk/updates.rs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/crates/matrix-sdk/src/event_cache/linked_chunk/updates.rs b/crates/matrix-sdk/src/event_cache/linked_chunk/updates.rs
index bc0370528..bd711d994 100644
--- a/crates/matrix-sdk/src/event_cache/linked_chunk/updates.rs
+++ b/crates/matrix-sdk/src/event_cache/linked_chunk/updates.rs
@@ -291,9 +291,12 @@ impl<Item, Gap> Updates<Item, Gap> {
 
     pub(super) fn new_reader_token(&mut self) -> ReaderToken {
         let mut inner = self.inner.write().unwrap();
-        inner.last_token += 1;
 
+        // Add 1 before reading the `last_token`, in this particular order, because the
+        // 0 token is reserved by `MAIN_READER_TOKEN`.
+        inner.last_token += 1;
         let last_token = inner.last_token;
+
         inner.last_index_per_reader.insert(last_token, 0);
 
         last_token