Make JSON support required properties

src/libraries/System.Text.Json/src/Resources/Strings.resx

@@ -660,12 +660,12 @@
     <value>Parameter already associated with a different JsonTypeInfo instance.</value>
   </data>
   <data name="JsonPropertyRequiredAndNotDeserializable" xml:space="preserve">
-    <value>JsonPropertyInfo with name '{0}' for type '{1}' is required but is not deserializable.</value>
+    <value>JsonPropertyInfo '{0}' defined in type '{1}' is marked required but does not specify a setter.</value>
   </data>
   <data name="JsonPropertyRequiredAndExtensionData" xml:space="preserve">
-    <value>JsonPropertyInfo with name '{0}' for type '{1}' cannot be required and be an extension data property.</value>
+    <value>JsonPropertyInfo '{0}' defined in type '{1}' is marked both as required and as an extension data property. This combination is not supported.</value>
   </data>
   <data name="JsonRequiredPropertiesMissing" xml:space="preserve">
-    <value>Type '{0}' contains required properties which were not set during deserialization: {1}</value>
+    <value>JSON deserialization for type '{0}' was missing required properties, including the following: {1}</value>
   </data>
-</root>
+</root>

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ReadStackFrame.cs

@@ -68,8 +68,8 @@ public JsonTypeInfo BaseJsonTypeInfo
         // Whether to use custom number handling.
         public JsonNumberHandling? NumberHandling;
 
-        // Required properties left
-        public BitArray? RequiredPropertiesLeft;
+        // Required properties which have value assigned
+        public BitArray? RequiredPropertiesSet;
 
         public void EndConstructorParameter()
         {
@@ -117,19 +117,19 @@ public void MarkRequiredPropertyAsRead(JsonPropertyInfo propertyInfo)
         {
             if (propertyInfo.IsRequired)
             {
-                Debug.Assert(RequiredPropertiesLeft != null);
-                RequiredPropertiesLeft[propertyInfo.RequiredPropertyIndex] = false;
+                Debug.Assert(RequiredPropertiesSet != null);
+                RequiredPropertiesSet[propertyInfo.RequiredPropertyIndex] = true;
             }
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal void InitializeRequiredPropertiesValidationState(JsonTypeInfo typeInfo)
         {
-            Debug.Assert(RequiredPropertiesLeft == null);
+            Debug.Assert(RequiredPropertiesSet == null);
 
             if (typeInfo.NumberOfRequiredProperties > 0)
             {
-                RequiredPropertiesLeft = new BitArray(typeInfo.NumberOfRequiredProperties, defaultValue: true);
+                RequiredPropertiesSet = new BitArray(typeInfo.NumberOfRequiredProperties, defaultValue: false);
             }
         }
 
@@ -138,11 +138,11 @@ internal void ValidateAllRequiredPropertiesAreRead(JsonTypeInfo typeInfo)
         {
             if (typeInfo.NumberOfRequiredProperties > 0)
             {
-                Debug.Assert(RequiredPropertiesLeft != null);
+                Debug.Assert(RequiredPropertiesSet != null);
 
-                if (!RequiredPropertiesLeft.AllBitsEqual(false))
+                if (!RequiredPropertiesSet.AllBitsEqual(true))
                 {
-                    ThrowHelper.ThrowJsonException_JsonRequiredPropertyMissing(typeInfo, RequiredPropertiesLeft);
+                    ThrowHelper.ThrowJsonException_JsonRequiredPropertyMissing(typeInfo, RequiredPropertiesSet);
                 }
             }
         }

src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs

@@ -216,18 +216,21 @@ public static void ThrowInvalidOperationException_JsonPropertyRequiredAndExtensi
         }
 
         [DoesNotReturn]
-        public static void ThrowJsonException_JsonRequiredPropertyMissing(JsonTypeInfo parent, BitArray missingJsonProperties)
+        public static void ThrowJsonException_JsonRequiredPropertyMissing(JsonTypeInfo parent, BitArray requiredPropertiesSet)
         {
             StringBuilder listOfMissingPropertiesBuilder = new();
             bool first = true;
 
             Debug.Assert(parent.PropertyCache != null);
 
+            // Soft cut-off length - once message becomes longer than that we won't be adding more elements
+            const int CutOffLength = 50;
+
             for (int propertyIdx = 0; propertyIdx < parent.PropertyCache.List.Count; propertyIdx++)
             {
                 JsonPropertyInfo property = parent.PropertyCache.List[propertyIdx].Value;
 
-                if (!property.IsRequired || !missingJsonProperties[property.RequiredPropertyIndex])
+                if (!property.IsRequired || requiredPropertiesSet[property.RequiredPropertyIndex])
                 {
                     continue;
                 }
@@ -240,6 +243,11 @@ public static void ThrowJsonException_JsonRequiredPropertyMissing(JsonTypeInfo p
 
                 listOfMissingPropertiesBuilder.Append(property.Name);
                 first = false;
+
+                if (listOfMissingPropertiesBuilder.Length >= CutOffLength)
+                {
+                    break;
+                }
             }
 
             throw new JsonException(SR.Format(SR.JsonRequiredPropertiesMissing, parent.Type, listOfMissingPropertiesBuilder.ToString()));