From a95c41f463681eda15a89115f6f95aa20e55afa3 Mon Sep 17 00:00:00 2001
From: Joonas Koivunen <joonas@neon.tech>
Date: Thu, 21 Mar 2024 00:42:38 +0200
Subject: [PATCH] fix(heavier_once_cell): take_and_deinit should take ownership
 (#7185)

Small fix to remove confusing `mut` bindings.

Builds upon #7175, split off from #7030. Cc: #5331.
---
 libs/utils/src/sync/heavier_once_cell.rs     | 4 ++--
 pageserver/src/tenant/storage_layer/layer.rs | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/libs/utils/src/sync/heavier_once_cell.rs b/libs/utils/src/sync/heavier_once_cell.rs
index a3aee45b58..8eee1f72a6 100644
--- a/libs/utils/src/sync/heavier_once_cell.rs
+++ b/libs/utils/src/sync/heavier_once_cell.rs
@@ -245,7 +245,7 @@ impl<'a, T> Guard<'a, T> {
     ///
     /// The permit will be on a semaphore part of the new internal value, and any following
     /// [`OnceCell::get_or_init`] will wait on it to complete.
-    pub fn take_and_deinit(&mut self) -> (T, InitPermit) {
+    pub fn take_and_deinit(mut self) -> (T, InitPermit) {
         let mut swapped = Inner::default();
         let sem = swapped.init_semaphore.clone();
         // acquire and forget right away, moving the control over to InitPermit
@@ -543,7 +543,7 @@ mod tests {
         target.set(42, permit);
 
         let (_answer, permit) = {
-            let mut guard = target
+            let guard = target
                 .get_or_init(|permit| async { Ok::<_, Infallible>((11, permit)) })
                 .await
                 .unwrap();
diff --git a/pageserver/src/tenant/storage_layer/layer.rs b/pageserver/src/tenant/storage_layer/layer.rs
index 626fd69ef3..c503d0d454 100644
--- a/pageserver/src/tenant/storage_layer/layer.rs
+++ b/pageserver/src/tenant/storage_layer/layer.rs
@@ -729,7 +729,7 @@ impl LayerInner {
 
                     return Ok(strong);
                 }
-                Ok(Err(mut guard)) => {
+                Ok(Err(guard)) => {
                     // path to here: the evict_blocking is stuck on spawn_blocking queue.
                     //
                     // reset the contents, deactivating the eviction and causing a
@@ -1128,7 +1128,7 @@ impl LayerInner {
             let maybe_downloaded = self.inner.get();
 
             let (_weak, permit) = match maybe_downloaded {
-                Some(mut guard) => {
+                Some(guard) => {
                     if let ResidentOrWantedEvicted::WantedEvicted(_weak, version) = &*guard {
                         if *version == only_version {
                             guard.take_and_deinit()