From 7c6bf5c9a5860cdcdd40eabb9061a2412e7c7e68 Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@electriccoin.co>
Date: Fri, 26 Jul 2024 00:15:26 +0000
Subject: [PATCH] zcash_client_sqlite: Fix `--no-default-features` compilation

Closes zcash/librustzcash#1273.
---
 zcash_client_sqlite/src/lib.rs | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/zcash_client_sqlite/src/lib.rs b/zcash_client_sqlite/src/lib.rs
index ba98b988c..afb3d170b 100644
--- a/zcash_client_sqlite/src/lib.rs
+++ b/zcash_client_sqlite/src/lib.rs
@@ -33,10 +33,6 @@
 #![deny(rustdoc::broken_intra_doc_links)]
 
 use incrementalmerkletree::{Marking, Position, Retention};
-use maybe_rayon::{
-    prelude::{IndexedParallelIterator, ParallelIterator},
-    slice::ParallelSliceMut,
-};
 use nonempty::NonEmpty;
 use rusqlite::{self, Connection};
 use secrecy::{ExposeSecret, SecretVec};
@@ -95,6 +91,24 @@ use {
     },
 };
 
+#[cfg(feature = "multicore")]
+use maybe_rayon::{
+    prelude::{IndexedParallelIterator, ParallelIterator},
+    slice::ParallelSliceMut,
+};
+
+/// `maybe-rayon` doesn't provide this as a fallback, so we have to.
+#[cfg(not(feature = "multicore"))]
+trait ParallelSliceMut<T> {
+    fn par_chunks_mut(&mut self, chunk_size: usize) -> std::slice::ChunksMut<'_, T>;
+}
+#[cfg(not(feature = "multicore"))]
+impl<T> ParallelSliceMut<T> for [T] {
+    fn par_chunks_mut(&mut self, chunk_size: usize) -> std::slice::ChunksMut<'_, T> {
+        self.chunks_mut(chunk_size)
+    }
+}
+
 #[cfg(feature = "unstable")]
 use {
     crate::chain::{fsblockdb_with_blocks, BlockMeta},