Native: properly activate native methods/events (#4524)

#4520 fixes false-positive
activation in case if DeprecatedIn hardfork is passed. However,
it's not enough for proper ActiveIn work because there's a case of
false-positive activation in case if both DeprecatedIn and ActiveIn
hardforks are not yet passed.

This commit rewrites ActiveIn condition: the method/event IS active if
and only if ActiveIn hardfork IS active AND DeprecatedIn hardfork IS NOT
active. ActiveIn hardfork IS active if it's null OR it's already passed.
DeprecatedIn hardfork IS NOT active if it's null OR it's not yet passed.

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

Author: AnnaShaleva

src/Neo/SmartContract/Native/NativeContract.cs

@@ -225,12 +225,8 @@ private NativeContractsCache.CacheEntry GetAllowedMethods(IsHardforkEnabledDeleg
 
         internal static bool IsActive(IHardforkActivable u, IsHardforkEnabledDelegate hfChecker, uint blockHeight)
         {
-            return  // no hardfork is involved
-                    u.ActiveIn is null && u.DeprecatedIn is null ||
-                    // deprecated method hardfork is involved
-                    u.DeprecatedIn is not null && hfChecker(u.DeprecatedIn.Value, blockHeight) == false ||
-                    // active method hardfork is involved
-                    (u.DeprecatedIn is null && u.ActiveIn is not null && hfChecker(u.ActiveIn.Value, blockHeight));
+            // Method/event is active iff ActiveIn hardfork IS active AND DeprecatedIn hardfork IS NOT active.
+            return (u.ActiveIn is null || hfChecker(u.ActiveIn.Value, blockHeight)) && (u.DeprecatedIn is null || !hfChecker(u.DeprecatedIn.Value, blockHeight));
         }
 
         /// <summary>

tests/Neo.UnitTests/SmartContract/Native/UT_NativeContract.cs

@@ -76,6 +76,8 @@ public void TestActiveDeprecatedIn()
             Assert.IsTrue(NativeContract.IsActive(new active() { ActiveIn = null, DeprecatedIn = Hardfork.HF_Cockatrice }, settings.IsHardforkEnabled, 1));
             Assert.IsFalse(NativeContract.IsActive(new active() { ActiveIn = null, DeprecatedIn = Hardfork.HF_Cockatrice }, settings.IsHardforkEnabled, 20));
 
+            Assert.IsFalse(NativeContract.IsActive(new active() { ActiveIn = Hardfork.HF_Basilisk, DeprecatedIn = Hardfork.HF_Cockatrice }, settings.IsHardforkEnabled, 9));
+            Assert.IsTrue(NativeContract.IsActive(new active() { ActiveIn = Hardfork.HF_Basilisk, DeprecatedIn = Hardfork.HF_Cockatrice }, settings.IsHardforkEnabled, 10));
             Assert.IsTrue(NativeContract.IsActive(new active() { ActiveIn = Hardfork.HF_Basilisk, DeprecatedIn = Hardfork.HF_Cockatrice }, settings.IsHardforkEnabled, 19));
             Assert.IsFalse(NativeContract.IsActive(new active() { ActiveIn = Hardfork.HF_Basilisk, DeprecatedIn = Hardfork.HF_Cockatrice }, settings.IsHardforkEnabled, 20));
         }