Merge bitcoin/bitcoin#25017: validation: make CScriptCheck and prevector swap members noexcept

e5485e8e4be7f2ee0671f58c3dcce35c68ba0ee0 test, bench: make prevector and checkqueue swap member functions noexcept (Jon Atack)
abc1ee509025d92db5311c3f5df3b61c09cad24f validation: make CScriptCheck and prevector swap member functions noexcept (Jon Atack)

Pull request description:

  along with those seen elsewhere in the codebase (prevector and checkqueue units/fuzz/bench).

  A swap must not fail; when a class has a swap member function, it should be declared noexcept.
  https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c84-a-swap-function-must-not-fail

ACKs for top commit:
  pk-b2:
    ACK e5485e8e4b
  w0xlt:
    ACK e5485e8e4b

Tree-SHA512: c82359d5e13f9262ce45efdae9baf71e41ed26568e0aff620e2bfb0ab37a62b6d56ae9340a28a0332c902cc1fa87da3fb72d6f6d6f53a8b7e695a5011f71f7f1

src/bench/checkqueue.cpp

@@ -35,7 +35,10 @@ static void CCheckQueueSpeedPrevectorJob(benchmark::Bench& bench)
         {
             return true;
         }
-        void swap(PrevectorJob& x){p.swap(x.p);};
+        void swap(PrevectorJob& x) noexcept
+        {
+            p.swap(x.p);
+        };
     };
     CCheckQueue<PrevectorJob> queue {QUEUE_BATCH_SIZE};
 

src/hdchain.h

@@ -70,7 +70,7 @@ public:
                 );
     }
 
-    void swap(CHDChain& first, CHDChain& second) // nothrow
+    void swap(CHDChain& first, CHDChain& second) noexcept
     {
         // enable ADL (not necessary in our case, but good practice)
         using std::swap;

src/prevector.h

@@ -475,7 +475,8 @@ public:
         return *item_ptr(size() - 1);
     }
 
-    void swap(prevector<N, T, Size, Diff>& other) {
+    void swap(prevector<N, T, Size, Diff>& other) noexcept
+    {
         std::swap(_union, other._union);
         std::swap(_size, other._size);
     }

src/test/checkqueue_tests.cpp

@@ -27,7 +27,7 @@ struct FakeCheck {
     {
         return true;
     }
-    void swap(FakeCheck& x){};
+    void swap(FakeCheck& x) noexcept {};
 };
 
 struct FakeCheckCheckCompletion {
@@ -37,7 +37,7 @@ struct FakeCheckCheckCompletion {
         n_calls.fetch_add(1, std::memory_order_relaxed);
         return true;
     }
-    void swap(FakeCheckCheckCompletion& x){};
+    void swap(FakeCheckCheckCompletion& x) noexcept {};
 };
 
 struct FailingCheck {
@@ -48,7 +48,7 @@ struct FailingCheck {
     {
         return !fails;
     }
-    void swap(FailingCheck& x)
+    void swap(FailingCheck& x) noexcept
     {
         std::swap(fails, x.fails);
     };
@@ -66,7 +66,10 @@ struct UniqueCheck {
         results.insert(check_id);
         return true;
     }
-    void swap(UniqueCheck& x) { std::swap(x.check_id, check_id); };
+    void swap(UniqueCheck& x) noexcept
+    {
+        std::swap(x.check_id, check_id);
+    };
 };
 
 
@@ -94,7 +97,10 @@ struct MemoryCheck {
     {
         fake_allocated_memory.fetch_sub(b, std::memory_order_relaxed);
     };
-    void swap(MemoryCheck& x) { std::swap(b, x.b); };
+    void swap(MemoryCheck& x) noexcept
+    {
+        std::swap(b, x.b);
+    };
 };
 
 struct FrozenCleanupCheck {
@@ -118,7 +124,10 @@ struct FrozenCleanupCheck {
             cv.wait(l, []{ return nFrozen.load(std::memory_order_relaxed) == 0;});
         }
     }
-    void swap(FrozenCleanupCheck& x){std::swap(should_freeze, x.should_freeze);};
+    void swap(FrozenCleanupCheck& x) noexcept
+    {
+        std::swap(should_freeze, x.should_freeze);
+    };
 };
 
 // Static Allocations

src/test/fuzz/checkqueue.cpp

@@ -26,7 +26,7 @@ struct DumbCheck {
         return result;
     }
 
-    void swap(DumbCheck& x)
+    void swap(DumbCheck& x) noexcept
     {
     }
 };

src/test/fuzz/prevector.cpp

@@ -161,7 +161,7 @@ public:
         pre_vector.shrink_to_fit();
     }
 
-    void swap()
+    void swap() noexcept
     {
         real_vector.swap(real_vector_alt);
         pre_vector.swap(pre_vector_alt);

src/test/prevector_tests.cpp

@@ -165,7 +165,8 @@ public:
         test();
     }
 
-    void swap() {
+    void swap() noexcept
+    {
         real_vector.swap(real_vector_alt);
         pre_vector.swap(pre_vector_alt);
         test();

src/validation.h

@@ -289,7 +289,8 @@ public:
 
     bool operator()();
 
-    void swap(CScriptCheck &check) {
+    void swap(CScriptCheck& check) noexcept
+    {
         std::swap(ptxTo, check.ptxTo);
         std::swap(m_tx_out, check.m_tx_out);
         std::swap(nIn, check.nIn);