avoid redundant set.Contains before Add/Remove

Author: Pathoschild

src/SMAPI.Toolkit/Framework/Clients/CompatibilityRepo/ChangeDescriptor.cs

@@ -111,11 +111,8 @@ public void Apply(List<string> values)
             HashSet<string> curValues = new(values.Select(p => p.Trim()), StringComparer.OrdinalIgnoreCase);
             foreach (string add in this.Add)
             {
-                if (!curValues.Contains(add))
-                {
+                if (curValues.Add(add))
                     values.Add(add);
-                    curValues.Add(add);
-                }
             }
         }
     }

src/SMAPI/Framework/Extensions/MonitorExtensions.cs

@@ -14,11 +14,8 @@ internal static class MonitorExtensions
         /// <param name="level">The log severity level.</param>
         public void LogOnce(HashSet<string> hash, string message, LogLevel level = LogLevel.Trace)
         {
-            if (!hash.Contains(message))
-            {
+            if (hash.Add(message))
                 monitor.Log(message, level);
-                hash.Add(message);
-            }
         }
     }
 }

src/SMAPI/Framework/ModLoading/Finders/FieldFinder.cs

@@ -50,10 +50,8 @@ public override bool Handle(ModuleDefinition module, ILProcessor cil, Instructio
         if (this.FieldNames.Count > 0)
         {
             FieldReference? fieldRef = RewriteHelper.AsFieldReference(instruction);
-            if (fieldRef != null && fieldRef.DeclaringType.FullName == this.FullTypeName && this.FieldNames.Contains(fieldRef.Name))
+            if (fieldRef != null && fieldRef.DeclaringType.FullName == this.FullTypeName && this.FieldNames.Remove(fieldRef.Name))
             {
-                this.FieldNames.Remove(fieldRef.Name);
-
                 this.MarkFlag(this.Result);
                 this.Phrases.Add($"{this.FullTypeName}.{fieldRef.Name} field");
             }

src/SMAPI/Framework/StateTracking/FieldWatchers/InventoryWatcher.cs

@@ -120,11 +120,8 @@ private void Add(Item? value)
         if (value == null)
             return;
 
-        if (this.RemovedImpl.Contains(value))
-        {
+        if (this.RemovedImpl.Remove(value))
             this.AddedImpl.Remove(value);
-            this.RemovedImpl.Remove(value);
-        }
         else
             this.AddedImpl.Add(value);
     }
@@ -136,11 +133,8 @@ private void Remove(Item? value)
         if (value == null)
             return;
 
-        if (this.AddedImpl.Contains(value))
-        {
-            this.AddedImpl.Remove(value);
+        if (this.AddedImpl.Remove(value))
             this.RemovedImpl.Remove(value);
-        }
         else
             this.RemovedImpl.Add(value);
     }