Merge bitcoin/bitcoin#29775: Testnet4 including PoW difficulty adjustment fix

6bfa26048dbafb91e9ca63ea8d3960271e798098 testnet: Add timewarp attack prevention for Testnet4 (Fabian Jahr)
0100907ca168c53e8fe044bdda396f308825162c testnet: Add Testnet4 difficulty adjustment rules fix (Fabian Jahr)
74a04f9e7ad6a16988149cc3438b9ce13c91cdb9 testnet: Introduce Testnet4 (Fabian Jahr)

Pull request description:

  To supplement the [ongoing conceptual discussion about a testnet reset](https://groups.google.com/g/bitcoindev/c/9bL00vRj7OU/m/9yCPo3uUBwAJ) I have drafted a move to v4 including a fix to the difficulty adjustment mechanism, which was part of the motivation that started the discussion.

  Conceptual considerations:
  - The conceptual discussion about doing a testnet4 or softforking the fix into testnet3 is outside of the scope of this PR and I would ask reviewers to contribute their opinions on this on the ML instead. However, I am happy to adapt this PR to a softfork change on testnet3 if there is consensus for that instead.
  - The difficulty adjustment fix suggested here touches the `CalculateNextWorkRequired` function and uses the same logic used in `GetNextWorkRequired` to find the last previous block that was not mined with difficulty 1 under the exceptionf. An alternative fix briefly mentioned on the mailing list by Jameson Lopp would be to "restrict the special testnet minimum difficulty rule so that it can't be triggered on the block right before a difficulty retarget". That would also fix the issue but I find my suggestion here a bit more elegant.

ACKs for top commit:
  jsarenik:
    tACK 6bfa26048dba
  achow101:
    ACK 6bfa26048dbafb91e9ca63ea8d3960271e798098
  murchandamus:
    tACK 6bfa26048dbafb91e9ca63ea8d3960271e798098

Tree-SHA512: 0b8b69a621406a944da5be551b863d065358ba94d85dd3b80d83c412660e230ee93b27316081fbee9b4851cc4ff8585db64c7dfa26cb5148ac835663f2712c3d

3 files changed, 19 insertions, 6 deletions

diff --git a/src/test/argsman_tests.cpp b/src/test/argsman_tests.cpp
index 5f0318e8c4..297595a9cf 100644
--- a/src/test/argsman_tests.cpp
+++ b/src/test/argsman_tests.cpp
@@ -644,10 +644,12 @@ BOOST_AUTO_TEST_CASE(util_GetChainTypeString)
 {
     TestArgsManager test_args;
     const auto testnet = std::make_pair("-testnet", ArgsManager::ALLOW_ANY);
+    const auto testnet4 = std::make_pair("-testnet4", ArgsManager::ALLOW_ANY);
     const auto regtest = std::make_pair("-regtest", ArgsManager::ALLOW_ANY);
-    test_args.SetupArgs({testnet, regtest});
+    test_args.SetupArgs({testnet, testnet4, regtest});
 
     const char* argv_testnet[] = {"cmd", "-testnet"};
+    const char* argv_testnet4[] = {"cmd", "-testnet4"};
     const char* argv_regtest[] = {"cmd", "-regtest"};
     const char* argv_test_no_reg[] = {"cmd", "-testnet", "-noregtest"};
     const char* argv_both[] = {"cmd", "-testnet", "-regtest"};
@@ -663,6 +665,12 @@ BOOST_AUTO_TEST_CASE(util_GetChainTypeString)
     BOOST_CHECK(test_args.ParseParameters(2, argv_testnet, error));
     BOOST_CHECK_EQUAL(test_args.GetChainTypeString(), "test");
 
+    BOOST_CHECK(test_args.ParseParameters(0, argv_testnet4, error));
+    BOOST_CHECK_EQUAL(test_args.GetChainTypeString(), "main");
+
+    BOOST_CHECK(test_args.ParseParameters(2, argv_testnet4, error));
+    BOOST_CHECK_EQUAL(test_args.GetChainTypeString(), "testnet4");
+
     BOOST_CHECK(test_args.ParseParameters(2, argv_regtest, error));
     BOOST_CHECK_EQUAL(test_args.GetChainTypeString(), "regtest");
 
@@ -758,8 +766,8 @@ struct ArgsMergeTestingSetup : public BasicTestingSetup {
             ForEachNoDup(conf_actions, SET, SECTION_NEGATE, [&] {
                 for (bool soft_set : {false, true}) {
                     for (bool force_set : {false, true}) {
-                        for (const std::string& section : {ChainTypeToString(ChainType::MAIN), ChainTypeToString(ChainType::TESTNET), ChainTypeToString(ChainType::SIGNET)}) {
-                            for (const std::string& network : {ChainTypeToString(ChainType::MAIN), ChainTypeToString(ChainType::TESTNET), ChainTypeToString(ChainType::SIGNET)}) {
+                        for (const std::string& section : {ChainTypeToString(ChainType::MAIN), ChainTypeToString(ChainType::TESTNET), ChainTypeToString(ChainType::TESTNET4), ChainTypeToString(ChainType::SIGNET)}) {
+                            for (const std::string& network : {ChainTypeToString(ChainType::MAIN), ChainTypeToString(ChainType::TESTNET), ChainTypeToString(ChainType::TESTNET4), ChainTypeToString(ChainType::SIGNET)}) {
                                 for (bool net_specific : {false, true}) {
                                     fn(arg_actions, conf_actions, soft_set, force_set, section, network, net_specific);
                                 }
@@ -913,7 +921,7 @@ BOOST_FIXTURE_TEST_CASE(util_ArgsMerge, ArgsMergeTestingSetup)
     // Results file is formatted like:
     //
     //   <input> || <IsArgSet/IsArgNegated/GetArg output> | <GetArgs output> | <GetUnsuitable output>
-    BOOST_CHECK_EQUAL(out_sha_hex, "d1e436c1cd510d0ec44d5205d4b4e3bee6387d316e0075c58206cb16603f3d82");
+    BOOST_CHECK_EQUAL(out_sha_hex, "f1ee5ab094cc43d16a6086fa7f2c10389e0f99902616b31bbf29189972ad1473");
 }
 
 // Similar test as above, but for ArgsManager::GetChainTypeString function.
@@ -1016,7 +1024,7 @@ BOOST_FIXTURE_TEST_CASE(util_ChainMerge, ChainMergeTestingSetup)
     // Results file is formatted like:
     //
     //   <input> || <output>
-    BOOST_CHECK_EQUAL(out_sha_hex, "f263493e300023b6509963887444c41386f44b63bc30047eb8402e8c1144854c");
+    BOOST_CHECK_EQUAL(out_sha_hex, "9e60306e1363528bbc19a47f22bcede88e5d6815212f18ec8e6cdc4638dddab4");
 }
 
 BOOST_AUTO_TEST_CASE(util_ReadWriteSettings)
diff --git a/src/test/pow_tests.cpp b/src/test/pow_tests.cpp
index 9aadebbe63..4af66af283 100644
--- a/src/test/pow_tests.cpp
+++ b/src/test/pow_tests.cpp
@@ -198,6 +198,11 @@ BOOST_AUTO_TEST_CASE(ChainParams_TESTNET_sanity)
     sanity_check_chainparams(*m_node.args, ChainType::TESTNET);
 }
 
+BOOST_AUTO_TEST_CASE(ChainParams_TESTNET4_sanity)
+{
+    sanity_check_chainparams(*m_node.args, ChainType::TESTNET4);
+}
+
 BOOST_AUTO_TEST_CASE(ChainParams_SIGNET_sanity)
 {
     sanity_check_chainparams(*m_node.args, ChainType::SIGNET);
diff --git a/src/test/versionbits_tests.cpp b/src/test/versionbits_tests.cpp
index f462895edb..896840b0f3 100644
--- a/src/test/versionbits_tests.cpp
+++ b/src/test/versionbits_tests.cpp
@@ -419,7 +419,7 @@ BOOST_AUTO_TEST_CASE(versionbits_computeblockversion)
 
     // check that any deployment on any chain can conceivably reach both
     // ACTIVE and FAILED states in roughly the way we expect
-    for (const auto& chain_type: {ChainType::MAIN, ChainType::TESTNET, ChainType::SIGNET, ChainType::REGTEST}) {
+    for (const auto& chain_type: {ChainType::MAIN, ChainType::TESTNET, ChainType::TESTNET4, ChainType::SIGNET, ChainType::REGTEST}) {
         const auto chainParams = CreateChainParams(*m_node.args, chain_type);
         uint32_t chain_all_vbits{0};
         for (int i = 0; i < (int)Consensus::MAX_VERSION_BITS_DEPLOYMENTS; ++i) {