error: variable 'count' set but not used [-Werror,-Wunused-but-set-variable]

[jahead]

On react native 0.74.3

With release mode we get

Execution failed for task ':react-native-leveldb:buildCMakeRelWithDebInfo[arm64-v8a]'.
> com.android.ide.common.process.ProcessException: ninja: Entering directory `/Users/jahead/projects/bcs/BcsInspectionsMobileApp/node_modules/react-native-leveldb/android/.cxx/RelWithDebInfo/306y1138/arm64-v8a'
  [1/4] Building CXX object leveldb/CMakeFiles/leveldb.dir/util/cache.cc.o
  FAILED: leveldb/CMakeFiles/leveldb.dir/util/cache.cc.o 
  /Users/jahead/Library/Android/sdk/ndk/26.1.10909125/toolchains/llvm/prebuilt/darwin-x86_64/bin/clang++ --target=aarch64-none-linux-android23 --sysroot=/Users/jahead/Library/Android/sdk/ndk/26.1.10909125/toolchains/llvm/prebuilt/darwin-x86_64/sysroot -DLEVELDB_COMPILE_LIBRARY -DLEVELDB_PLATFORM_POSIX=1 -I/Users/jahead/projects/bcs/BcsInspectionsMobileApp/node_modules/react-native-leveldb/android/.cxx/RelWithDebInfo/306y1138/arm64-v8a/leveldb/include -I/Users/jahead/projects/bcs/BcsInspectionsMobileApp/node_modules/react-native-leveldb/cpp/leveldb/. -I/Users/jahead/projects/bcs/BcsInspectionsMobileApp/node_modules/react-native-leveldb/cpp/leveldb/include -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security  -O2   -Wall -Wno-unused-variable -fstack-protector-all -fno-exceptions -fno-rtti -O2 -g -DNDEBUG -fPIC -Werror -Wthread-safety -pthread -std=c++11 -MD -MT leveldb/CMakeFiles/leveldb.dir/util/cache.cc.o -MF leveldb/CMakeFiles/leveldb.dir/util/cache.cc.o.d -o leveldb/CMakeFiles/leveldb.dir/util/cache.cc.o -c /Users/jahead/projects/bcs/BcsInspectionsMobileApp/node_modules/react-native-leveldb/cpp/leveldb/util/cache.cc
  /Users/jahead/projects/bcs/BcsInspectionsMobileApp/node_modules/react-native-leveldb/cpp/leveldb/util/cache.cc:130:14: error: variable 'count' set but not used [-Werror,-Wunused-but-set-variable]
      uint32_t count = 0;
               ^
  1 error generated.
  ninja: build stopped: subcommand failed.

From looking at the build this is likely from react-native-leveldb/cpp/leveldb/util/cache.cc:130:14

    uint32_t count = 0;
    for (uint32_t i = 0; i < length_; i++) {
      LRUHandle* h = list_[i];
      while (h != nullptr) {
        LRUHandle* next = h->next_hash;
        uint32_t hash = h->hash;
        LRUHandle** ptr = &new_list[hash & (new_length - 1)];
        h->next_hash = *ptr;
        *ptr = h;
        h = next;
        count++;
      }
    }
    assert(elems_ == count);

likely assert(elems_ == count); is being optimised out in release and therefore not being used. So in debug it complies fine, but release not.

The cppFlags are being controlled in build.gradle

     externalNativeBuild {
      cmake {
        cppFlags '-O2 -frtti -fexceptions -Wall -Wno-unused-variable -fstack-protector-all'
        arguments '-DANDROID_STL=c++_shared'
        abiFilters(*reactNativeArchitectures())
      }
    }

the -Wall and -Wno-unused-variable are the cause removing those two flags restores building in release

I'm not sure why it only just started breaking in 0.74.3

[shamilovtim]

Just hit this. Thanks OP for providing a patch.