From 138c9b56ae957458cdf71ad00412c53c0948b2db Mon Sep 17 00:00:00 2001
From: Matteo Merli <mmerli@apache.org>
Date: Wed, 24 Jun 2026 12:43:06 -0700
Subject: [PATCH] fix: silence pulsar warnings under no-compression feature
 sets

Building the pulsar crate without the `compression` feature (e.g.
`--no-default-features --features tokio-runtime`) produces three warnings
that are masked under the default feature set, which enables `compression`:

  - unused `io::Write` import in producer.rs
  - unnecessary `mut` on compress_message's `message` parameter
  - unnecessary `mut` on process_payload's `payload` parameter

Gate the import and the `mut` bindings on the individual compression
sub-features (lz4/flate2/zstd/snap) that actually use them, so the crate
is warning-free across every feature combination -- including
single-sub-feature builds like `--features lz4` -- without changing
behavior under any feature. `io::Write` moves into the flate2/snap match
arms, matching the existing `use std::io::Read;` convention in engine.rs.
---
 src/consumer/engine.rs | 12 +++++++++++-
 src/producer.rs        | 17 +++++++++++++++--
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/src/consumer/engine.rs b/src/consumer/engine.rs
index 46144205..3d3d92cb 100644
--- a/src/consumer/engine.rs
+++ b/src/consumer/engine.rs
@@ -437,8 +437,18 @@ impl<Exe: Executor> ConsumerEngine<Exe> {
     async fn process_payload(
         &mut self,
         message: CommandMessage,
-        mut payload: Payload,
+        payload: Payload,
     ) -> Result<(), Error> {
+        // Only the compression arms below mutate `payload`; without any of those
+        // features the binding stays immutable, so gate the `mut` to avoid an
+        // `unused_mut` warning.
+        #[cfg(any(
+            feature = "lz4",
+            feature = "flate2",
+            feature = "zstd",
+            feature = "snap"
+        ))]
+        let mut payload = payload;
         let compression = match payload.metadata.compression {
             None => proto::CompressionType::None,
             Some(compression) => proto::CompressionType::try_from(compression).map_err(|err| {
diff --git a/src/producer.rs b/src/producer.rs
index b21790f1..5f31d1ce 100644
--- a/src/producer.rs
+++ b/src/producer.rs
@@ -1,7 +1,6 @@
 //! Message publication
 use std::{
     collections::{btree_map::Entry, BTreeMap, HashMap, VecDeque},
-    io::Write,
     pin::Pin,
     sync::{
         atomic::{AtomicU64, Ordering},
@@ -832,9 +831,19 @@ impl<Exe: Executor> TopicProducer<Exe> {
 
 #[cfg_attr(feature = "telemetry", tracing::instrument(skip_all))]
 fn compress_message(
-    mut message: ProducerMessage,
+    message: ProducerMessage,
     compression: &Option<Compression>,
 ) -> Result<ProducerMessage, Error> {
+    // Only the compression arms below mutate `message`; without any of those
+    // features the binding stays immutable, so gate the `mut` to avoid an
+    // `unused_mut` warning.
+    #[cfg(any(
+        feature = "lz4",
+        feature = "flate2",
+        feature = "zstd",
+        feature = "snap"
+    ))]
+    let mut message = message;
     let compressed_message = match compression {
         None | Some(Compression::None) => message,
         #[cfg(feature = "lz4")]
@@ -850,6 +859,8 @@ fn compress_message(
         }
         #[cfg(feature = "flate2")]
         Some(Compression::Zlib(compression)) => {
+            use std::io::Write;
+
             let mut e = flate2::write::ZlibEncoder::new(Vec::new(), compression.level);
             e.write_all(&message.payload[..])
                 .map_err(ProducerError::Io)?;
@@ -871,6 +882,8 @@ fn compress_message(
         }
         #[cfg(feature = "snap")]
         Some(Compression::Snappy(..)) => {
+            use std::io::Write;
+
             let mut compressed_payload = Vec::new();
             {
                 let mut encoder = snap::write::FrameEncoder::new(&mut compressed_payload);