fix(csharp): use enum rendering functions for array-of-enum properties in JSON converter

[Neokil]

Description

Array-typed properties whose items are enums were serialized and deserialized
using the generic JsonSerializer.Serialize/Deserialize path in the generated
JsonConverter. This ignored the *ValueConverter.ToJsonValue /
*ValueConverter.FromStringOrDefault functions that are used correctly for
scalar enum properties, and caused enum values to be written using the default
.NET JSON behaviour — which outputs the PascalCase enum member name — instead
of the casing defined in the OpenAPI spec.

Example: An OpenAPI spec defining ShippingMethod with value express would
be serialized as "Express" instead of "express" when that enum appeared as
an array item.

Root cause

JsonConverter.mustache had no {{#items.isEnum}} branches in either the read
or write path. Scalar enum properties ({{#isEnum}}) were handled correctly, but
array-of-enum properties fell through to the generic JsonSerializer path.

Changes

• modules/openapi-generator/src/main/resources/csharp/libraries/generichost/JsonConverter.mustache
  • Read path: added {{#items.isEnum}} branch inside the fallback
    deserialize block — iterates the JSON array and calls
    *ValueConverter.FromStringOrDefault (external enum) or
    *FromStringOrDefault (inner enum) per item.
  • Write path: added {{#items.isEnum}} branch in all four
    required/optional × nullable/non-nullable write cases — emits
    WriteStartArray, calls *ValueConverter.ToJsonValue /
    *ToJsonValue per item (using WriteStringValue for string enums and
    WriteNumberValue for numeric enums), then WriteEndArray.
• modules/openapi-generator/src/test/resources/3_0/csharp/enum-array.yaml
  — new OpenAPI spec with a model containing both a scalar enum property
  (preferredMethod) and an array-of-enum property (allowedMethods) to
  exercise both the working and previously broken cases.

How to reproduce

Generate a C# client from an OpenAPI spec that contains a model with an
array property whose items are a string enum. Serialize an instance of that
model and observe that the enum values in the array are written in PascalCase
("Express") rather than the value defined in the spec ("express").

Generator

• Language: C# (csharp)
• Library: generichost
• Template file: libraries/generichost/JsonConverter.mustache

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---

Summary by cubic

Fixes C# generichost JSON converter to handle array-of-enum properties using the enum rendering functions, so clients honor OpenAPI casing (e.g., "express" not "Express"). Also guards JSON null values for enum arrays to keep the reader in sync.

• Bug Fixes
  • Add items.isEnum handling in the read path to iterate arrays and use *ValueConverter.FromStringOrDefault (or inner enum equivalent); skip processing when the token is Null to avoid Utf8JsonReader desync.
  • Add items.isEnum handling in the write path for all required/optional and nullable cases, emitting arrays and using *ValueConverter.ToJsonValue per item (string or numeric).
  • Add test spec 3_0/csharp/enum-array.yaml covering scalar enum and array-of-enum serialization/deserialization.

^{Written for commit d0ba616. Summary will update on new commits.}

[Neokil]

FYI: @mandrean (2017/08) @shibayan (2020/02) @Blackclaws (2021/03) @lucamazzanti (2021/05) @iBicha (2023/07)

[cubic-dev-ai]

1 issue found across 2 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="modules/openapi-generator/src/main/resources/csharp/libraries/generichost/JsonConverter.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/csharp/libraries/generichost/JsonConverter.mustache:256">
P1: Enum-array deserialization lacks token-type/null guard before manual array loop, risking reader desynchronization and invalid token reads.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

1 issue found across 1 file (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="modules/openapi-generator/src/main/resources/csharp/libraries/generichost/JsonConverter.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/csharp/libraries/generichost/JsonConverter.mustache:255">
P2: Enum-array null handling now skips setting the Option property when the JSON token is Null, so explicit nulls are treated as “not set.” This can cause required-property checks to throw and omit explicit nulls on re-serialization.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

P2: Enum-array null handling now skips setting the Option property when the JSON token is Null, so explicit nulls are treated as “not set.” This can cause required-property checks to throw and omit explicit nulls on re-serialization.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At modules/openapi-generator/src/main/resources/csharp/libraries/generichost/JsonConverter.mustache, line 255:

<comment>Enum-array null handling now skips setting the Option property when the JSON token is Null, so explicit nulls are treated as “not set.” This can cause required-property checks to throw and omit explicit nulls on re-serialization.</comment>

<file context>
@@ -252,16 +252,19 @@
                             {{#items.isEnum}}
-                            var {{#lambda.camelcase_sanitize_param}}{{name}}{{/lambda.camelcase_sanitize_param}}Items = new List<{{#items.isInnerEnum}}{{classname}}.{{/items.isInnerEnum}}{{{items.datatypeWithEnum}}}>();
-                            while (utf8JsonReader.Read())
+                            if (utf8JsonReader.TokenType != JsonTokenType.Null)
                             {
-                                if (utf8JsonReader.TokenType == JsonTokenType.EndArray)
</file context>

[devhl-labs]

Good find, please keep working this. cubic-dev-ai seems to be raising a good point. Also consider exploring the isContainer property and moving your code out of the fallback. Also, a new yaml sample for this isn't really necessary. You can append to the existing Petstore.