build: Disable deprecated-copy warning only when external warnings are enabled #22258

Fixes #18967

Alternative to https://github.com/bitcoin/bitcoin/pull/22240

Tested warnings-free on Focal with:

• clang (./configure --with-incompatible-bdb --enable-suppress-external-warnings CC=clang CXX=clang++ && make clean && make -j $(nproc))
• gcc (./configure --with-incompatible-bdb --enable-suppress-external-warnings && make clean && make -j $(nproc))
• depends (CONFIG_SITE="$PWD/depends/x86_64-pc-linux-gnu/share/config.site" ./configure --enable-suppress-external-warnings && make clean && make -j $(nproc))

Also tested on Fedora 34 with clang and gcc.

@fanquake (or someone else) Can you test this one please: #18738 (comment)

Concept ACK

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #21430 (build: Add -Werror=implicit-fallthrough compile flag by hebasto)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

tACK 1111457d7433c2cca1d7e98946f6954e3a0280ef

According to Clang 13.0.0 we have deprecated-copy warnings in our code too:

clang++-devel -std=c++17 -DHAVE_CONFIG_H -I. -I../src/config  -DDEBUG -DDEBUG_LOCKORDER -DABORT_ON_FAILED_ASSUME  -I. -I./secp256k1/include -isystem /usr/local/include/db5 -DBOOST_SP_USE_STD_ATOMIC -DBOOST_AC_USE_STD_ATOMIC -isystem /usr/local/include -I./leveldb/include -I./leveldb/helpers/memenv -I./univalue/include   -isystem /usr/local/include -I/usr/local/include -D_THREAD_SAFE -pthread  -I/usr/local/include -Wno-deprecated-declarations -Werror -DHAVE_BUILD_INFO -D__STDC_FORMAT_MACROS -DPROVIDE_FUZZ_MAIN_FUNCTION -O0 -g3 -ftrapv -Wstack-protector -fstack-protector-all -fcf-protection=full -Wall -Wextra -Wgnu -Wformat -Wformat-security -Wvla -Wshadow-field -Wswitch -Wthread-safety -Wrange-loop-analysis -Wredundant-decls -Wunused-variable -Wunused-member-function -Wdate-time -Wconditional-uninitialized -Wsign-compare -Woverloaded-virtual -Wsuggest-override -Wunreachable-code-loop-increment -Wdocumentation -Wno-unused-parameter -Wno-self-assign -Wno-unused-local-typedef -Wno-implicit-fallthrough    -fPIE  -MT policy/libbitcoin_server_a-rbf.o -MD -MP -MF policy/.deps/libbitcoin_server_a-rbf.Tpo -c -o policy/libbitcoin_server_a-rbf.o `test -f 'policy/rbf.cpp' || echo './'`policy/rbf.cpp

In file included from policy/rbf.cpp:5:
In file included from ./policy/rbf.h:8:
In file included from ./txmempool.h:24:
./util/epochguard.h:53:17: error: definition of implicit copy constructor for 'Marker' is deprecated because it has a user-declared copy assignment operator [-Werror,-Wdeprecated-copy]
        Marker& operator=(const Marker&) = delete;
                ^
./txmempool.h:81:7: note: in implicit copy constructor for 'Epoch::Marker' first required here
class CTxMemPoolEntry
      ^
policy/rbf.cpp:29:29: note: in implicit copy constructor for 'CTxMemPoolEntry' first required here
    CTxMemPoolEntry entry = *pool.mapTx.find(tx.GetHash());
                            ^
1 error generated.




In file included from test/fuzz/policy_estimator.cpp:9:
In file included from ./test/fuzz/util.h:27:
In file included from ./txmempool.h:24:
./util/epochguard.h:53:17: error: definition of implicit copy constructor for 'Marker' is deprecated because it has a user-declared copy assignment operator [-Werror,-Wdeprecated-copy]
        Marker& operator=(const Marker&) = delete;
                ^
./txmempool.h:81:7: note: in implicit copy constructor for 'Epoch::Marker' first required here
class CTxMemPoolEntry
      ^
/usr/include/c++/v1/memory:1876:31: note: in implicit move constructor for 'CTxMemPoolEntry' first required here
            ::new((void*)__p) _Up(_VSTD::forward<_Args>(__args)...);
                              ^
/usr/include/c++/v1/memory:1768:18: note: in instantiation of function template specialization 'std::allocator<CTxMemPoolEntry>::construct<CTxMemPoolEntry, CTxMemPoolEntry>' requested here
            {__a.construct(__p, _VSTD::forward<_Args>(__args)...);}
                 ^
/usr/include/c++/v1/memory:1595:14: note: in instantiation of function template specialization 'std::allocator_traits<std::allocator<CTxMemPoolEntry>>::__construct<CTxMemPoolEntry, CTxMemPoolEntry>' requested here
            {__construct(__has_construct<allocator_type, _Tp*, _Args...>(),
             ^
/usr/include/c++/v1/vector:924:21: note: in instantiation of function template specialization 'std::allocator_traits<std::allocator<CTxMemPoolEntry>>::construct<CTxMemPoolEntry, CTxMemPoolEntry>' requested here
    __alloc_traits::construct(this->__alloc(), _VSTD::__to_address(__tx.__pos_),
                    ^
/usr/include/c++/v1/vector:1652:9: note: in instantiation of function template specialization 'std::vector<CTxMemPoolEntry>::__construct_one_at_end<CTxMemPoolEntry>' requested here
        __construct_one_at_end(_VSTD::move(__x));
        ^
test/fuzz/policy_estimator.cpp:49:37: note: in instantiation of member function 'std::vector<CTxMemPoolEntry>::push_back' requested here
                    mempool_entries.push_back(ConsumeTxMemPoolEntry(fuzzed_data_provider, tx));
                                    ^
1 error generated.

cc @ajtowns the below fixes it:

diff --git i/src/policy/rbf.cpp w/src/policy/rbf.cpp
index 8125b41c41..10859d256d 100644
--- i/src/policy/rbf.cpp
+++ w/src/policy/rbf.cpp
@@ -23,13 +23,13 @@ RBFTransactionState IsRBFOptIn(const CTransaction& tx, const CTxMemPool& pool)
     }
 
     // If all the inputs have nSequence >= maxint-1, it still might be
     // signaled for RBF if any unconfirmed parents have signaled.
     uint64_t noLimit = std::numeric_limits<uint64_t>::max();
     std::string dummy;
-    CTxMemPoolEntry entry = *pool.mapTx.find(tx.GetHash());
+    const CTxMemPoolEntry& entry = *pool.mapTx.find(tx.GetHash());
     pool.CalculateMemPoolAncestors(entry, setAncestors, noLimit, noLimit, noLimit, noLimit, dummy, false);
 
     for (CTxMemPool::txiter it : setAncestors) {
         if (SignalsOptInRBF(it->GetTx())) {
             return RBFTransactionState::REPLACEABLE_BIP125;
         }
diff --git i/src/util/epochguard.h w/src/util/epochguard.h
index 1570ec4eb4..79c0abb4eb 100644
--- i/src/util/epochguard.h
+++ w/src/util/epochguard.h
@@ -42,12 +42,16 @@ public:
     Epoch& operator=(const Epoch&) = delete;
 
     bool guarded() const { return m_guarded; }
 
     class Marker
     {
+    public:
+        Marker() = default;
+        Marker(const Marker& other) = default;
+
     private:
         uint64_t m_marker = 0;
 
         // only allow modification via Epoch member functions
         friend class Epoch;
         Marker& operator=(const Marker&) = delete;