refactor: disallow setting flags in CCoinsCacheEntry constructors

No behavior change because any entries that are added in EmplaceCoinInternalDANGER
have DIRTY assigned to them after, and if they
are not inserted then they will not be
modified as before.
This prepares moving the cache entry
flags field to private access.

Co-Authored-By: Martin Leitner-Ankerl <[email protected]>

Author: andrewtoth

src/coins.cpp

@@ -108,10 +108,13 @@ void CCoinsViewCache::AddCoin(const COutPoint &outpoint, Coin&& coin, bool possi
 
 void CCoinsViewCache::EmplaceCoinInternalDANGER(COutPoint&& outpoint, Coin&& coin) {
     cachedCoinsUsage += coin.DynamicMemoryUsage();
-    cacheCoins.emplace(
+    auto [it, inserted] = cacheCoins.emplace(
         std::piecewise_construct,
         std::forward_as_tuple(std::move(outpoint)),
-        std::forward_as_tuple(std::move(coin), CCoinsCacheEntry::DIRTY));
+        std::forward_as_tuple(std::move(coin)));
+    if (inserted) {
+        it->second.AddFlags(CCoinsCacheEntry::DIRTY);
+    }
 }
 
 void AddCoins(CCoinsViewCache& cache, const CTransaction &tx, int nHeight, bool check_for_overwrite) {

src/coins.h

@@ -104,7 +104,7 @@ class Coin
 struct CCoinsCacheEntry
 {
     Coin coin; // The actual cached data.
-    unsigned char flags;
+    unsigned char flags{0};
 
     enum Flags {
         /**
@@ -127,9 +127,8 @@ struct CCoinsCacheEntry
         FRESH = (1 << 1),
     };
 
-    CCoinsCacheEntry() : flags(0) {}
-    explicit CCoinsCacheEntry(Coin&& coin_) : coin(std::move(coin_)), flags(0) {}
-    CCoinsCacheEntry(Coin&& coin_, unsigned char flag) : coin(std::move(coin_)), flags(flag) {}
+    CCoinsCacheEntry() noexcept = default;
+    explicit CCoinsCacheEntry(Coin&& coin_) noexcept : coin(std::move(coin_)) {}
 
     inline void AddFlags(unsigned char flags) noexcept { this->flags |= flags; }
     inline void ClearFlags() noexcept