cmake: make unused-variables an error and fix them

CMakeLists.txt

@@ -23,7 +23,7 @@ else()
 endif()
 
 # Top-level CMake config
-set(CMAKE_CXX_FLAGS "-Wall -Werror=vla")
+set(CMAKE_CXX_FLAGS "-Wall -Werror=vla -Werror=unused-variable")
 set(CMAKE_CXX_FLAGS_DEBUG "-g")
 set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)

src/executor/Executor.cpp

@@ -183,7 +183,8 @@ void Executor::executeTasks(std::vector<int> msgIdxs,
     // one-to-one with thread pool threads. Only once the pool is exhausted
     // do we start overloading
     for (int msgIdx : msgIdxs) {
-        const faabric::Message& msg = req->messages().at(msgIdx);
+        [[maybe_unused]] const faabric::Message& msg =
+          req->messages().at(msgIdx);
 
         if (availablePoolThreads.empty()) {
             SPDLOG_ERROR("No available thread pool threads (size: {})",

src/transport/PointToPointBroker.cpp

@@ -467,7 +467,8 @@ void PointToPointBroker::sendMappingsFromSchedulingDecision(
         msg.set_appid(decision.appId);
         msg.set_groupid(decision.groupId);
 
-        std::set<int>& indexes = groupIdIdxsMap[decision.groupId];
+        [[maybe_unused]] std::set<int>& indexes =
+          groupIdIdxsMap[decision.groupId];
 
         for (int i = 0; i < decision.nFunctions; i++) {
             auto* mapping = msg.add_mappings();

src/util/snapshot.cpp

@@ -421,7 +421,7 @@ void SnapshotData::applyDiff(const SnapshotDiff& diff)
         return;
     }
 
-    uint8_t* copyTarget = validatedOffsetPtr(diff.getOffset());
+    [[maybe_unused]] uint8_t* copyTarget = validatedOffsetPtr(diff.getOffset());
     switch (diff.getDataType()) {
         case (faabric::util::SnapshotDataType::Int): {
             int32_t finalValue =
@@ -762,7 +762,7 @@ void SnapshotMergeRegion::addDiffs(std::vector<SnapshotDiff>& diffs,
     bool changed = false;
     switch (dataType) {
         case (SnapshotDataType::Int): {
-            int preUpdate = unalignedRead<int>(updated);
+            [[maybe_unused]] int preUpdate = unalignedRead<int>(updated);
             changed = calculateDiffValue<int>(original, updated, operation);
 
             SPDLOG_TRACE("Calculated int {} merge: {} {} -> {}",
@@ -773,7 +773,7 @@ void SnapshotMergeRegion::addDiffs(std::vector<SnapshotDiff>& diffs,
             break;
         }
         case (SnapshotDataType::Long): {
-            long preUpdate = unalignedRead<long>(updated);
+            [[maybe_unused]] long preUpdate = unalignedRead<long>(updated);
             changed = calculateDiffValue<long>(original, updated, operation);
 
             SPDLOG_TRACE("Calculated long {} merge: {} {} -> {}",
@@ -784,7 +784,7 @@ void SnapshotMergeRegion::addDiffs(std::vector<SnapshotDiff>& diffs,
             break;
         }
         case (SnapshotDataType::Float): {
-            float preUpdate = unalignedRead<float>(updated);
+            [[maybe_unused]] float preUpdate = unalignedRead<float>(updated);
             changed = calculateDiffValue<float>(original, updated, operation);
 
             SPDLOG_TRACE("Calculated float {} merge: {} {} -> {}",
@@ -795,7 +795,7 @@ void SnapshotMergeRegion::addDiffs(std::vector<SnapshotDiff>& diffs,
             break;
         }
         case (SnapshotDataType::Double): {
-            double preUpdate = unalignedRead<double>(updated);
+            [[maybe_unused]] double preUpdate = unalignedRead<double>(updated);
             changed = calculateDiffValue<double>(original, updated, operation);
 
             SPDLOG_TRACE("Calculated double {} merge: {} {} -> {}",

tests/dist/mpi/mpi_native.cpp

@@ -72,7 +72,7 @@ int MPI_Init(int* argc, char*** argv)
     }
 
     // Initialise MPI-specific logging
-    int thisRank = executingContext.getRank();
+    [[maybe_unused]] int thisRank = executingContext.getRank();
     SPDLOG_DEBUG(
       "Initialised world (id: {}) for rank: {}", call->mpiworldid(), thisRank);
 
@@ -98,7 +98,7 @@ int MPI_Comm_size(MPI_Comm comm, int* size)
 
 int MPI_Finalize()
 {
-    int rank = executingContext.getRank();
+    [[maybe_unused]] int rank = executingContext.getRank();
     SPDLOG_DEBUG("MPI - MPI_Finalize (rank: {})", rank);
 
     return terminateMpi();

tests/dist/scheduler/functions.cpp

@@ -31,7 +31,8 @@ int handleSimpleThread(tests::DistTestExecutor* exec,
     // Return a distinctive value
     int returnValue = msg.id() / 2;
 
-    const faabric::util::SystemConfig& conf = faabric::util::getSystemConfig();
+    [[maybe_unused]] const faabric::util::SystemConfig& conf =
+      faabric::util::getSystemConfig();
     SPDLOG_DEBUG("Thread {} executed on host {}. Returning {}",
                  msg.id(),
                  conf.endpointHost,

tests/test/mpi/test_mpi_world.cpp

@@ -194,6 +194,7 @@ TEST_CASE_METHOD(MpiBaseTestFixture, "Test local barrier", "[mpi]")
 
         world.barrier(rankA1);
         assert(sendData == recvData);
+        UNUSED(recvData);
     });
 
     world.recv(rankA1,

tests/test/util/test_queue.cpp

@@ -214,7 +214,7 @@ TEST_CASE("Stress test fixed capacity queue", "[util]")
             startLatch->wait();
 
             for (int j = 0; j < numMessages; j++) {
-                int result = queues.at(i)->dequeue();
+                [[maybe_unused]] int result = queues.at(i)->dequeue();
                 assert(result == i * j);
             }
         });