[MPG C# Generator] Paging action operations should not resource-wrap return types

[haiyuazhang]

Bug Description

The MPG C# generator incorrectly wraps paging results in resource types for action operations. When a paging operation is an ARM action (not a list), the generator should return the raw data type (e.g., Pageable<ServerConfigurationData>), not the resource-wrapped type (e.g., Pageable<NodeConfigurationResource>).

Example TypeSpec: ServerConfiguration.tsp — the listByServer operation is an ArmResourceActionSync (action on ClusterServer), not a resource list on ServerConfiguration.

tspCodeModel evidence

The emitter correctly identifies the operation as an Action in the resource metadata:

{
    "methodId": "Microsoft.DBforPostgreSQL.Configurations.listByServer",
    "kind": "Action",
    "operationPath": ".../{clusterName}/servers/{serverName}/configurations",
    "resourceScope": ".../{clusterName}/servers/{serverName}"
}

However, the method-level metadata only says kind: "paging" — the Action vs List distinction is only in the resource operation metadata.

Expected behavior

Since the operation is an Action (not a List), the generated method should return:

public virtual Pageable<CosmosDBForPostgreSqlServerConfigurationData> GetConfigurations(...)

Actual behavior

The generator sees the paging kind + a matching NodeConfigurationResource class, and produces:

public virtual Pageable<CosmosDBForPostgreSqlNodeConfigurationResource> GetConfigurations(...)

Root cause

The generator does not check the ARM resource operation kind (Action vs List) when deciding whether to resource-wrap paging results. It only checks the method-level kind: "paging" and the existence of a matching resource class.

Current workaround

Use CodeGenSuppress in a Customized/ file to suppress the generated method and replace it with a hand-written version returning the raw data type.

[github-actions]

🎯 Agentic Issue Triage

Summary: This issue reports a bug in the MPG (Management Plane Generator) C# Generator where paging action operations are incorrectly resource-wrapping their return types. When a paging operation is an ARM action (not a list), the generator should return the raw data type (e.g., Pageable(ServerConfigurationData)), but instead produces a resource-wrapped type (e.g., Pageable(NodeConfigurationResource)).

Labels applied: Mgmt, Central-EngSys

📋 Issue Analysis

Root Cause

The generator checks kind: "paging" at the method level and the existence of a matching resource class, but does not check the ARM resource operation kind (Action vs List). The distinction between Action and List is only present in the resource operation metadata, not the method-level metadata.

Reproduction

• Service: CosmosDBForPostgreSQL (Microsoft.DBforPostgreSQL)
• The TypeSpec defines a @get @action("configurations") @list`` operation using ArmResourceActionSync, which is an action on `ClusterServer`, not a list operation on `ServerConfiguration`.
• The emitter correctly marks this as kind: "Action" in the resource metadata, but the C# generator ignores this distinction.

Fix Direction

The generator (in /eng/packages/http-client-csharp-mgmt) needs to:

1. Read the ARM resource operation kind field when deciding whether to resource-wrap paging return types.
2. Skip resource-wrapping when kind == "Action", even if a matching resource class exists.

Current Workaround

Use CodeGenSuppress in a Customized/ file to suppress the generated method and replace it with a hand-written version returning the raw data type.

🔗 Relevant Resources

• Generator source: /eng/packages/http-client-csharp-mgmt
• CodeGenSuppress workaround documentation
• Related TypeSpec decorator: @action from @azure-tools/typespec-azure-resource-manager

Generated by Agentic Triage for issue #57110 · ◷