[Bug]: Missing Extension Methods for Extensible Enums in Collections

[efrainretana]

Describe the bug

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Bug 1: Missing Extension Methods for Extensible Enums in Collections

Description

The TypeSpec C# generator produces serialization code that calls ToSerialString() and To<EnumName>() extension methods for extensible enum types (readonly structs with string backing), but these extension methods are never generated.

Reproduction

When generating code for CjkBigramTokenFilterScripts (an extensible enum defined as a readonly partial struct), the generated serialization file CjkBigramTokenFilter.Serialization.cs contains:

// Line 46 - serialization
writer.WriteStringValue(item.ToSerialString());

// Line 107 - deserialization  
array.Add(item.GetString().ToCjkBigramTokenFilterScripts());

However, the generated CjkBigramTokenFilterScripts.cs file only contains the struct definition with a ToString() method no ToSerialString() or ToCjkBigramTokenFilterScripts() extension methods are generated.

Expected Behavior

For extensible enums (readonly structs), the generator should either:

1. Generate the extension methods in a separate *.Serialization.cs file (like it does for fixed enums), OR
2. Use ToString() and the constructor directly in the serialization code:

   writer.WriteStringValue(item.ToString());
   array.Add(new CjkBigramTokenFilterScripts(item.GetString()));

Workaround

Manually create the missing extension methods:

internal static class CjkBigramTokenFilterScriptsExtensions
{
    public static string ToSerialString(this CjkBigramTokenFilterScripts value) => value.ToString();
    public static CjkBigramTokenFilterScripts ToCjkBigramTokenFilterScripts(this string value) => new(value);
}

Affected Types

This likely affects all extensible enums used in collection properties. Known affected types:

• CjkBigramTokenFilterScripts
• EdgeNGramTokenizer

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Reproduction

steps: Regenerate SDK on Azure.Search.Documents.

Example PREVIOUS autorest file: https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/search/Azure.Search.Documents/src/Generated/Models/CjkBigramTokenFilterScripts.Serialization.cs

Repo: https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/search/Azure.Search.Documents/src

Checklist

• Follow our Code of Conduct
• Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion.
• The provided reproduction is a minimal reproducible example of the bug.

[efrainretana]

Example repro: https://github.com/Azure/azure-sdk-for-net/blob/3df80e71cc22102f60910e9d188ca864ea18849d/sdk/search/Azure.Search.Documents/src/Generated/Models/CjkBigramTokenFilter.Serialization.cs#L111