pika compile error with gcc 9.3 which is default in ubuntu 20.04

[kernelai]

env：

➜  rocksdb git:(004237e62) hostnamectl
   Static hostname: ubuntu
         Icon name: computer-vm
           Chassis: vm
        Machine ID: 0cf4eb7841d1420ca74911c50be49e02
           Boot ID: d712388d9098445986b53c13bb4d70d9
    Virtualization: oracle
  Operating System: Ubuntu 20.04.3 LTS
            Kernel: Linux 5.4.0-89-generic
      Architecture: x86-64

compiler：

➜  rocksdb git:(004237e62) g++ --version
g++ (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

error:

./db/version_edit.h: In constructor ‘rocksdb::FdWithKeyRange::FdWithKeyRange(rocksdb::FileDescriptor, rocksdb::Slice, rocksdb::Slice, rocksdb::FileMetaData*)’:
**./db/version_edit.h:156:33: error: implicitly-declared ‘constexpr rocksdb::FileDescriptor::FileDescriptor(const rocksdb::FileDescriptor&)’ is deprecated [-Werror=deprecated-copy]**
  156 |         largest_key(_largest_key) {}
      |                                 ^
./db/version_edit.h:47:19: note: because ‘rocksdb::FileDescriptor’ has user-provided ‘rocksdb::FileDescriptor& rocksdb::FileDescriptor::operator=(const rocksdb::FileD
escriptor&)’
   47 |   FileDescriptor& operator=(const FileDescriptor& fd) {
      |                   ^~~~~~~~
./db/version_edit.h: In instantiation of ‘constexpr std::pair<_T1, _T2>::pair(_U1&&, _U2&&) [with _U1 = int&; _U2 = rocksdb::FileMetaData; typename std::enable_if<(std::_PCC<true, _T1, _T2>::_MoveConstructiblePair<_U1, _U2>() && std::_PCC<true, _T1, _T2>::_ImplicitlyMoveConvertiblePair<_U1, _U2>()), bool>::type <anonymous> = true; _T1 = int; _T2 = rocksdb::FileMetaData]’:
/usr/include/c++/9/ext/new_allocator.h:147:4:   required from ‘void __gnu_cxx::new_allocator<_Tp>::construct(_Up*, _Args&& ...) [with _Up = std::pair<int, rocksdb::FileMetaData>; _Args = {int&, rocksdb::FileMetaData}; _Tp = std::pair<int, rocksdb::FileMetaData>]’
/usr/include/c++/9/bits/alloc_traits.h:484:4:   required from ‘static void std::allocator_traits<std::allocator<_CharT> >::construct(std::allocator_traits<std::allocator<_CharT> >::allocator_type&, _Up*, _Args&& ...) [with _Up = std::pair<int, rocksdb::FileMetaData>; _Args = {int&, rocksdb::FileMetaData}; _Tp = std::pair<int, rocksdb::FileMetaData>; std::allocator_traits<std::allocator<_CharT> >::allocator_type = std::allocator<std::pair<int, rocksdb::FileMetaData> >]’
/usr/include/c++/9/bits/vector.tcc:115:30:   required from ‘void std::vector<_Tp, _Alloc>::emplace_back(_Args&& ...) [with _Args = {int&, rocksdb::FileMetaData}; _Tp = std::pair<int, rocksdb::FileMetaData>; _Alloc = std::allocator<std::pair<int, rocksdb::FileMetaData> >]’
./db/version_edit.h:218:48:   required from here
./db/version_edit.h:76:8: error: implicitly-declared ‘constexpr rocksdb::FileDescriptor::FileDescriptor(const rocksdb::FileDescriptor&)’ is deprecated [-Werror=deprecated-copy]

[kernelai]

facebook rocksdb try to fix it. #issue

[kernelai]

编译报错的原因是 comment总结起来是声明了拷贝赋值函数，而没有声明拷贝构造函数，当隐式使用拷贝构造函数时，编译器会报错。早期的编译器不报错，但gcc 8 9 会强制报错。

方案：
1， rocksdb修复了这个问题pull。升级新版本rocksdb。
2， 使用编译选项CXXFLAGS='-Wno-error=deprecated-copy -Wno-error=pessimizing-move'

[kernelai]

新的报错：

./memtable/inlineskiplist.h:282:11: error: ‘void* memcpy(void*, const void*, size_t)’ writing to an object of type ‘struct std::atomic<rocksdb::InlineSkipList<const rocksdb::MemTableRep::KeyComparator&>::Node*>’ with no trivial copy-assignment [-Werror=class-memaccess]
  282 |     memcpy(&next_[0], &height, sizeof(int));
      |     ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ./memtable/inlineskiplist.h:47,
                 from memtable/skiplistrep.cc:6:
/usr/include/c++/9/atomic:356:12: note: ‘struct std::atomic<rocksdb::InlineSkipList<const rocksdb::MemTableRep::KeyComparator&>::Node*>’ declared here
  356 |     struct atomic<_Tp*>
      |            ^~~~~~~~~~~~
In file included from ./db/range_del_aggregator.h:15,
                 from ./db/memtable.h:19,
                 from memtable/skiplistrep.cc:7:
./db/version_edit.h: In instantiation of ‘constexpr std::pair<_T1, _T2>::pair(_U1&&, _U2&&) [with _U1 = int&; _U2 = rocksdb::FileMetaData; typename std::enable_if<(std::_PCC<true, _T1, _T2>::_MoveConstructiblePair<_U1, _U2>() && std::_PCC<true, _T1, _T2>::_ImplicitlyMoveConvertiblePair<_U1, _U2>()), bool>::type <anonymous> = true; _T1 = int; _T2 = rocksdb::FileMetaData]’:
/usr/include/c++/9/ext/new_allocator.h:147:4:   required from ‘void __gnu_cxx::new_allocator<_Tp>::construct(_Up*, _Args&& ...) [with _Up = std::pair<int, rocksdb::FileMetaData>; _Args = {int&, rocksdb::FileMetaData}; _Tp = std::pair<int, rocksdb::FileMetaData>]’
/usr/include/c++/9/bits/alloc_traits.h:484:4:   required from ‘static void std::allocator_traits<std::allocator<_Tp> >::construct(std::allocator_traits<std::allocator<_Tp> >::allocator_type&, _Up*, _Args&& ...) [with _Up = std::pair<int, rocksdb::FileMetaData>; _Args = {int&, rocksdb::FileMetaData}; _Tp = std::pair<int, rocksdb::FileMetaData>; std::allocator_traits<std::allocator<_Tp> >::allocator_type = std::allocator<std::pair<int, rocksdb::FileMetaData> >]’
/usr/include/c++/9/bits/vector.tcc:115:30:   required from ‘void std::vector<_Tp, _Alloc>::emplace_back(_Args&& ...) [with _Args = {int&, rocksdb::FileMetaData}; _Tp = std::pair<int, rocksdb::FileMetaData>; _Alloc = std::allocator<std::pair<int, rocksdb::FileMetaData> >]’

对象没有普通拷贝复制函数。
rocksdb fix it pr.
可以使用-Wno-error=class-memaccess 忽略掉该错误。

报错：

./memtable/inlineskiplist.h:302:54: error: array subscript -1 is below array bounds of ‘std::atomic<rocksdb::InlineSkipList<rocksdb::TestComparator>::Node*> [1]’ [-Werror=array-bounds]
  302 |     return (next_[-n].load(std::memory_order_acquire));
      |                                                      ^

数组越界。但其实node是个指针，使用[]操作。
使用-Wno-error=array-bounds屏蔽报错。