Merge bitcoin/bitcoin#24971: tidy: modernize-use-nullptr

9c96f1008b4997aea31f293fed31f98ed3becfcf tidy: enable modernize-use-nullptr (fanquake)
e53274868e0ec35156349826b0995bc444287690 Don't use zero as null pointer constant (-Wzero-as-null-pointer-constant) (practicalswift)

Pull request description:

  Alternative to #15112 which uses `clang-tidy` to do perform the checking, rather than `-Wzero-as-null-pointer-constant`, and avoids having to uses pragmas, i.e:
  ```cpp
  #if defined(HAVE_CONFIG_H)
  #include <config/bitcoin-config.h>
  #endif

  #if defined(HAVE_W_ZERO_AS_NULL_POINTER_CONSTANT)
  #pragma GCC diagnostic push
  #pragma GCC diagnostic ignored "-Wzero-as-null-pointer-constant"
  #pragma GCC diagnostic ignored "-Wunknown-pragmas"
  #pragma clang diagnostic push
  #pragma clang diagnostic ignored "-Wzero-as-null-pointer-constant"
  #endif
  ```
  to suppress warnings coming from upstream code.

  Can be tested by dropping the preceding commit. Should produce errors like:
  ```bash
  clang-tidy-14 --use-color -p=/home/ubuntu/ci_scratch/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu /home/ubuntu/ci_scratch/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/src/netbase.cpp
  /home/ubuntu/ci_scratch/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/src/netbase.cpp:678:36: error: use nullptr [modernize-use-nullptr,-warnings-as-errors]
          if (!Socks5(strDest, port, 0, sock)) {
                                     ^
                                     nullptr

  ```

ACKs for top commit:
  laanwj:
    Concept and code review ACK 9c96f1008b4997aea31f293fed31f98ed3becfcf

Tree-SHA512: d822a354e44ba8f7fc53da9a4be7de5c25cc4ffc7c57651b76fdd1a030764b0390cfd79fca94685b8a3ff4f4d13054764f12d1f0d8c2a1b9ba519a7524f7f5bf

10 files changed, 27 insertions, 12 deletions

diff --git a/src/.bear-tidy-config b/src/.bear-tidy-config
new file mode 100644
index 0000000000..111ef6ee44
--- /dev/null
+++ b/src/.bear-tidy-config
@@ -0,0 +1,15 @@
+{
+  "output": {
+    "content": {
+      "include_only_existing_source": true,
+      "paths_to_include": [],
+      "paths_to_exclude": [
+        "src/leveldb"
+      ]
+    },
+    "format": {
+      "command_as_array": true,
+      "drop_output_field": false
+    }
+  }
+}
diff --git a/src/.clang-tidy b/src/.clang-tidy
index 27616ad072..fda95967f5 100644
--- a/src/.clang-tidy
+++ b/src/.clang-tidy
@@ -1,2 +1,2 @@
-Checks:          '-*,bugprone-argument-comment'
-WarningsAsErrors: bugprone-argument-comment
+Checks:          '-*,bugprone-argument-comment,modernize-use-nullptr'
+WarningsAsErrors: 'bugprone-argument-comment,modernize-use-nullptr'
diff --git a/src/mapport.cpp b/src/mapport.cpp
index 42ca366089..235e6f904c 100644
--- a/src/mapport.cpp
+++ b/src/mapport.cpp
@@ -193,7 +193,7 @@ static bool ProcessUpnp()
         std::string strDesc = PACKAGE_NAME " " + FormatFullVersion();
 
         do {
-            r = UPNP_AddPortMapping(urls.controlURL, data.first.servicetype, port.c_str(), port.c_str(), lanaddr, strDesc.c_str(), "TCP", 0, "0");
+            r = UPNP_AddPortMapping(urls.controlURL, data.first.servicetype, port.c_str(), port.c_str(), lanaddr, strDesc.c_str(), "TCP", nullptr, "0");
 
             if (r != UPNPCOMMAND_SUCCESS) {
                 ret = false;
@@ -206,7 +206,7 @@ static bool ProcessUpnp()
         } while (g_mapport_interrupt.sleep_for(PORT_MAPPING_REANNOUNCE_PERIOD));
         g_mapport_interrupt.reset();
 
-        r = UPNP_DeletePortMapping(urls.controlURL, data.first.servicetype, port.c_str(), "TCP", 0);
+        r = UPNP_DeletePortMapping(urls.controlURL, data.first.servicetype, port.c_str(), "TCP", nullptr);
         LogPrintf("UPNP_DeletePortMapping() returned: %d\n", r);
         freeUPNPDevlist(devlist); devlist = nullptr;
         FreeUPNPUrls(&urls);
diff --git a/src/netbase.cpp b/src/netbase.cpp
index 9557297df1..ce23f7e4ad 100644
--- a/src/netbase.cpp
+++ b/src/netbase.cpp
@@ -675,7 +675,7 @@ bool ConnectThroughProxy(const Proxy& proxy, const std::string& strDest, uint16_
             return false;
         }
     } else {
-        if (!Socks5(strDest, port, 0, sock)) {
+        if (!Socks5(strDest, port, nullptr, sock)) {
             return false;
         }
     }
diff --git a/src/qt/intro.cpp b/src/qt/intro.cpp
index 63b4055092..f4928951fe 100644
--- a/src/qt/intro.cpp
+++ b/src/qt/intro.cpp
@@ -226,7 +226,7 @@ bool Intro::showIfNeeded(bool& did_show_intro, int64_t& prune_MiB)
         }
 
         /* If current default data directory does not exist, let the user choose one */
-        Intro intro(0, Params().AssumedBlockchainSize(), Params().AssumedChainStateSize());
+        Intro intro(nullptr, Params().AssumedBlockchainSize(), Params().AssumedChainStateSize());
         intro.setDataDirectory(dataDir);
         intro.setWindowIcon(QIcon(":icons/bitcoin"));
         did_show_intro = true;
diff --git a/src/randomenv.cpp b/src/randomenv.cpp
index 388841289a..53ebeb31cd 100644
--- a/src/randomenv.cpp
+++ b/src/randomenv.cpp
@@ -363,10 +363,10 @@ void RandAddStaticEnv(CSHA512& hasher)
 
 #if HAVE_DECL_GETIFADDRS && HAVE_DECL_FREEIFADDRS
     // Network interfaces
-    struct ifaddrs *ifad = NULL;
+    struct ifaddrs *ifad = nullptr;
     getifaddrs(&ifad);
     struct ifaddrs *ifit = ifad;
-    while (ifit != NULL) {
+    while (ifit != nullptr) {
         hasher.Write((const unsigned char*)&ifit, sizeof(ifit));
         hasher.Write((const unsigned char*)ifit->ifa_name, strlen(ifit->ifa_name) + 1);
         hasher.Write((const unsigned char*)&ifit->ifa_flags, sizeof(ifit->ifa_flags));
diff --git a/src/support/allocators/secure.h b/src/support/allocators/secure.h
index a9aa928082..c6bd685189 100644
--- a/src/support/allocators/secure.h
+++ b/src/support/allocators/secure.h
@@ -37,7 +37,7 @@ struct secure_allocator : public std::allocator<T> {
         typedef secure_allocator<_Other> other;
     };
 
-    T* allocate(std::size_t n, const void* hint = 0)
+    T* allocate(std::size_t n, const void* hint = nullptr)
     {
         T* allocation = static_cast<T*>(LockedPoolManager::Instance().alloc(sizeof(T) * n));
         if (!allocation) {
diff --git a/src/test/fuzz/crypto_diff_fuzz_chacha20.cpp b/src/test/fuzz/crypto_diff_fuzz_chacha20.cpp
index fcc96c6418..1b89d55773 100644
--- a/src/test/fuzz/crypto_diff_fuzz_chacha20.cpp
+++ b/src/test/fuzz/crypto_diff_fuzz_chacha20.cpp
@@ -128,7 +128,7 @@ void ECRYPT_encrypt_bytes(ECRYPT_ctx* x, const u8* m, u8* c, u32 bytes)
 {
     u32 x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15;
     u32 j0, j1, j2, j3, j4, j5, j6, j7, j8, j9, j10, j11, j12, j13, j14, j15;
-    u8* ctarget = NULL;
+    u8* ctarget = nullptr;
     u8 tmp[64];
     uint32_t i;
 
diff --git a/src/torcontrol.cpp b/src/torcontrol.cpp
index 287de9c794..e2a7cb4066 100644
--- a/src/torcontrol.cpp
+++ b/src/torcontrol.cpp
@@ -306,7 +306,7 @@ std::map<std::string,std::string> ParseTorReplyMapping(const std::string &s)
 
 TorController::TorController(struct event_base* _base, const std::string& tor_control_center, const CService& target):
     base(_base),
-    m_tor_control_center(tor_control_center), conn(base), reconnect(true), reconnect_ev(0),
+    m_tor_control_center(tor_control_center), conn(base), reconnect(true), reconnect_ev(nullptr),
     reconnect_timeout(RECONNECT_TIMEOUT_START),
     m_target(target)
 {
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 0d7075810d..489599e2a0 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -2768,7 +2768,7 @@ std::shared_ptr<CWallet> CWallet::Create(WalletContext& context, const std::stri
     } else if (wallet_creation_flags & WALLET_FLAG_DISABLE_PRIVATE_KEYS) {
         // Make it impossible to disable private keys after creation
         error = strprintf(_("Error loading %s: Private keys can only be disabled during creation"), walletFile);
-        return NULL;
+        return nullptr;
     } else if (walletInstance->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
         for (auto spk_man : walletInstance->GetActiveScriptPubKeyMans()) {
             if (spk_man->HavePrivateKeys()) {