fix: gracefully handle unknown properties for C# (#2239)

rmaced0 · web-flow · commit 0629fabc531d · 2025-04-20T19:32:42.000+02:00
diff --git a/examples/csharp-generate-json-serializer/__snapshots__/index.spec.ts.snap b/examples/csharp-generate-json-serializer/__snapshots__/index.spec.ts.snap
@@ -36,7 +36,7 @@ internal class RootConverter : JsonConverter<Root>
   {
     if (reader.TokenType != JsonTokenType.StartObject)
     {
-      throw new JsonException();
+      throw new JsonException(\\"Unexpected start of JSON\\");
     }
 
     var instance = new Root();
@@ -51,7 +51,7 @@ internal class RootConverter : JsonConverter<Root>
       // Get the key.
       if (reader.TokenType != JsonTokenType.PropertyName)
       {
-        throw new JsonException();
+        throw new JsonException(\\"Unexpected property name token in JSON\\");
       }
 
       string propertyName = reader.GetString();
@@ -61,9 +61,11 @@ internal class RootConverter : JsonConverter<Root>
           instance.Email = value;
           continue;
         }
+      // Gracefully handle/ignore unknown fields
+      JsonSerializer.Deserialize<JsonElement>(ref reader, options);
     }
   
-    throw new JsonException();
+    throw new JsonException(\\"Unexpected end of JSON\\");
   }
   public override void Write(Utf8JsonWriter writer, Root value, JsonSerializerOptions options)
   {
diff --git a/src/generators/csharp/presets/JsonSerializerPreset.ts b/src/generators/csharp/presets/JsonSerializerPreset.ts
@@ -177,7 +177,7 @@ function renderDeserialize({
 {
   if (reader.TokenType != JsonTokenType.StartObject)
   {
-    throw new JsonException();
+    throw new JsonException("Unexpected start of JSON");
   }
 
   var instance = new ${model.name}();
@@ -192,14 +192,16 @@ function renderDeserialize({
     // Get the key.
     if (reader.TokenType != JsonTokenType.PropertyName)
     {
-      throw new JsonException();
+      throw new JsonException("Unexpected property name token in JSON");
     }
 
     string propertyName = reader.GetString();
 ${renderer.indent(deserializeProperties, 4)}
+    // Gracefully handle/ignore unknown fields
+    JsonSerializer.Deserialize<JsonElement>(ref reader, options);
   }
   
-  throw new JsonException();
+  throw new JsonException("Unexpected end of JSON");
 }`;
 }
 
diff --git a/test/generators/csharp/presets/__snapshots__/JsonSerializerPreset.spec.ts.snap b/test/generators/csharp/presets/__snapshots__/JsonSerializerPreset.spec.ts.snap
@@ -69,7 +69,7 @@ internal class TestConverter : JsonConverter<Test>
   {
     if (reader.TokenType != JsonTokenType.StartObject)
     {
-      throw new JsonException();
+      throw new JsonException(\\"Unexpected start of JSON\\");
     }
 
     var instance = new Test();
@@ -84,7 +84,7 @@ internal class TestConverter : JsonConverter<Test>
       // Get the key.
       if (reader.TokenType != JsonTokenType.PropertyName)
       {
-        throw new JsonException();
+        throw new JsonException(\\"Unexpected property name token in JSON\\");
       }
 
       string propertyName = reader.GetString();
@@ -116,9 +116,11 @@ internal class TestConverter : JsonConverter<Test>
             var deserializedValue = JsonSerializer.Deserialize<Dictionary<string, dynamic>?>(ref reader, options);
             instance.AdditionalProperties.Add(propertyName, deserializedValue);
             continue;
+      // Gracefully handle/ignore unknown fields
+      JsonSerializer.Deserialize<JsonElement>(ref reader, options);
     }
   
-    throw new JsonException();
+    throw new JsonException(\\"Unexpected end of JSON\\");
   }
   public override void Write(Utf8JsonWriter writer, Test value, JsonSerializerOptions options)
   {
@@ -258,7 +260,7 @@ internal class NestedTestConverter : JsonConverter<NestedTest>
   {
     if (reader.TokenType != JsonTokenType.StartObject)
     {
-      throw new JsonException();
+      throw new JsonException(\\"Unexpected start of JSON\\");
     }
 
     var instance = new NestedTest();
@@ -273,7 +275,7 @@ internal class NestedTestConverter : JsonConverter<NestedTest>
       // Get the key.
       if (reader.TokenType != JsonTokenType.PropertyName)
       {
-        throw new JsonException();
+        throw new JsonException(\\"Unexpected property name token in JSON\\");
       }
 
       string propertyName = reader.GetString();
@@ -287,9 +289,11 @@ internal class NestedTestConverter : JsonConverter<NestedTest>
             var deserializedValue = JsonSerializer.Deserialize<Dictionary<string, dynamic>?>(ref reader, options);
             instance.AdditionalProperties.Add(propertyName, deserializedValue);
             continue;
+      // Gracefully handle/ignore unknown fields
+      JsonSerializer.Deserialize<JsonElement>(ref reader, options);
     }
   
-    throw new JsonException();
+    throw new JsonException(\\"Unexpected end of JSON\\");
   }
   public override void Write(Utf8JsonWriter writer, NestedTest value, JsonSerializerOptions options)
   {

Original file line number	Diff line number	Diff line change
`@@ -36,7 +36,7 @@ internal class RootConverter : JsonConverter<Root>`
`36`	`36`	`{`
`37`	`37`	`if (reader.TokenType != JsonTokenType.StartObject)`
`38`	`38`	`{`
`39`		`- throw new JsonException();`
	`39`	`+ throw new JsonException(\\"Unexpected start of JSON\\");`
`40`	`40`	`}`
`41`	`41`
`42`	`42`	`var instance = new Root();`
`@@ -51,7 +51,7 @@ internal class RootConverter : JsonConverter<Root>`
`51`	`51`	`// Get the key.`
`52`	`52`	`if (reader.TokenType != JsonTokenType.PropertyName)`
`53`	`53`	`{`
`54`		`- throw new JsonException();`
	`54`	`+ throw new JsonException(\\"Unexpected property name token in JSON\\");`
`55`	`55`	`}`
`56`	`56`
`57`	`57`	`string propertyName = reader.GetString();`
`@@ -61,9 +61,11 @@ internal class RootConverter : JsonConverter<Root>`
`61`	`61`	`instance.Email = value;`
`62`	`62`	`continue;`
`63`	`63`	`}`
	`64`	`+ // Gracefully handle/ignore unknown fields`
	`65`	`+ JsonSerializer.Deserialize<JsonElement>(ref reader, options);`
`64`	`66`	`}`
`65`	`67`
`66`		`- throw new JsonException();`
	`68`	`+ throw new JsonException(\\"Unexpected end of JSON\\");`
`67`	`69`	`}`
`68`	`70`	`public override void Write(Utf8JsonWriter writer, Root value, JsonSerializerOptions options)`
`69`	`71`	`{`
Original file line number	Diff line number	Diff line change
`@@ -177,7 +177,7 @@ function renderDeserialize({`
`177`	`177`	`{`
`178`	`178`	`if (reader.TokenType != JsonTokenType.StartObject)`
`179`	`179`	`{`
`180`		`- throw new JsonException();`
	`180`	`+ throw new JsonException("Unexpected start of JSON");`
`181`	`181`	`}`
`182`	`182`
`183`	`183`	`var instance = new ${model.name}();`
`@@ -192,14 +192,16 @@ function renderDeserialize({`
`192`	`192`	`// Get the key.`
`193`	`193`	`if (reader.TokenType != JsonTokenType.PropertyName)`
`194`	`194`	`{`
`195`		`- throw new JsonException();`
	`195`	`+ throw new JsonException("Unexpected property name token in JSON");`
`196`	`196`	`}`
`197`	`197`
`198`	`198`	`string propertyName = reader.GetString();`
`199`	`199`	`${renderer.indent(deserializeProperties, 4)}`
	`200`	`+ // Gracefully handle/ignore unknown fields`
	`201`	`+ JsonSerializer.Deserialize<JsonElement>(ref reader, options);`
`200`	`202`	`}`
`201`	`203`
`202`		`- throw new JsonException();`
	`204`	`+ throw new JsonException("Unexpected end of JSON");`
`203`	`205`	}`;
`204`	`206`	`}`
`205`	`207`
Original file line number	Diff line number	Diff line change
`@@ -69,7 +69,7 @@ internal class TestConverter : JsonConverter<Test>`
`69`	`69`	`{`
`70`	`70`	`if (reader.TokenType != JsonTokenType.StartObject)`
`71`	`71`	`{`
`72`		`- throw new JsonException();`
	`72`	`+ throw new JsonException(\\"Unexpected start of JSON\\");`
`73`	`73`	`}`
`74`	`74`
`75`	`75`	`var instance = new Test();`
`@@ -84,7 +84,7 @@ internal class TestConverter : JsonConverter<Test>`
`84`	`84`	`// Get the key.`
`85`	`85`	`if (reader.TokenType != JsonTokenType.PropertyName)`
`86`	`86`	`{`
`87`		`- throw new JsonException();`
	`87`	`+ throw new JsonException(\\"Unexpected property name token in JSON\\");`
`88`	`88`	`}`
`89`	`89`
`90`	`90`	`string propertyName = reader.GetString();`
`@@ -116,9 +116,11 @@ internal class TestConverter : JsonConverter<Test>`
`116`	`116`	`var deserializedValue = JsonSerializer.Deserialize<Dictionary<string, dynamic>?>(ref reader, options);`
`117`	`117`	`instance.AdditionalProperties.Add(propertyName, deserializedValue);`
`118`	`118`	`continue;`
	`119`	`+ // Gracefully handle/ignore unknown fields`
	`120`	`+ JsonSerializer.Deserialize<JsonElement>(ref reader, options);`
`119`	`121`	`}`
`120`	`122`
`121`		`- throw new JsonException();`
	`123`	`+ throw new JsonException(\\"Unexpected end of JSON\\");`
`122`	`124`	`}`
`123`	`125`	`public override void Write(Utf8JsonWriter writer, Test value, JsonSerializerOptions options)`
`124`	`126`	`{`
`@@ -258,7 +260,7 @@ internal class NestedTestConverter : JsonConverter<NestedTest>`
`258`	`260`	`{`
`259`	`261`	`if (reader.TokenType != JsonTokenType.StartObject)`
`260`	`262`	`{`
`261`		`- throw new JsonException();`
	`263`	`+ throw new JsonException(\\"Unexpected start of JSON\\");`
`262`	`264`	`}`
`263`	`265`
`264`	`266`	`var instance = new NestedTest();`
`@@ -273,7 +275,7 @@ internal class NestedTestConverter : JsonConverter<NestedTest>`
`273`	`275`	`// Get the key.`
`274`	`276`	`if (reader.TokenType != JsonTokenType.PropertyName)`
`275`	`277`	`{`
`276`		`- throw new JsonException();`
	`278`	`+ throw new JsonException(\\"Unexpected property name token in JSON\\");`
`277`	`279`	`}`
`278`	`280`
`279`	`281`	`string propertyName = reader.GetString();`
`@@ -287,9 +289,11 @@ internal class NestedTestConverter : JsonConverter<NestedTest>`
`287`	`289`	`var deserializedValue = JsonSerializer.Deserialize<Dictionary<string, dynamic>?>(ref reader, options);`
`288`	`290`	`instance.AdditionalProperties.Add(propertyName, deserializedValue);`
`289`	`291`	`continue;`
	`292`	`+ // Gracefully handle/ignore unknown fields`
	`293`	`+ JsonSerializer.Deserialize<JsonElement>(ref reader, options);`
`290`	`294`	`}`
`291`	`295`
`292`		`- throw new JsonException();`
	`296`	`+ throw new JsonException(\\"Unexpected end of JSON\\");`
`293`	`297`	`}`
`294`	`298`	`public override void Write(Utf8JsonWriter writer, NestedTest value, JsonSerializerOptions options)`
`295`	`299`	`{`