[csharp][restsharp] add throwOnAnyError option to surface client errors

[mjansrud]

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Description

By default the C# restsharp client silently drops deserialization failures. The chain:

1. Deserializer.Deserialize<T> throws ApiException(500, e.Message) on parse failure.
2. RestSharp's Execute<T> catches the exception and stuffs it into response.ErrorException, leaving response.Data = null.
3. The generated ToApiResponse<T> carries ErrorText but discards ErrorException.
4. ExceptionFactory only fires on non-2xx HTTP status, so a 200 with a deserialization failure passes through silently.
5. The generated GetXxxAsync returns localVarResponse.Data directly — callers receive null with no signal in logs or APM.

We hit this in production when an upstream service started returning JSON missing a property our schema marked as required. Endpoints quietly returned empty lists — clients rendered nothing — there was no error to investigate. Discovering the cause required adding ad-hoc logging to the generated code.

Fix

This PR adds an opt-in switch throwOnAnyError (restsharp library only, default false) that sets RestClientOptions.ThrowOnAnyError = true. RestSharp then rethrows the original ApiException instead of swallowing it. No template logic changes, no behaviour change for existing users.

Verification

Tested locally on 14 generated clients in our monorepo. Before:

• GET /candidates → 200 [] (silent — required field missing in upstream JSON)
• No error in logs or App Insights.

After enabling throwOnAnyError=true:

• GET /candidates → 500 with Required property 'track' not found in JSON. Path '[0]'
• Function logger emits ApiException → propagates to APM.

Why default off

Keeping the default false to preserve backwards compatibility for users who may rely on the current null-on-deserialization-failure behaviour. Opt-in via --additional-properties throwOnAnyError=true.

---

Summary by cubic

Adds an opt-in throwOnAnyError option for C# restsharp clients to rethrow deserialization and transport errors so client failures surface instead of returning null. Default is false; existing behavior is unchanged.

• New Features

  • Adds generator switch throwOnAnyError (C# restsharp) that sets RestClientOptions.ThrowOnAnyError = true so exceptions bubble up.
  • With a retry policy, rethrows PolicyResult.FinalException (or InvalidOperationException if it’s null) from DeserializeRestResponseFromPolicyAsync for consistent behavior.

• Migration

  • Opt in via --additional-properties throwOnAnyError=true (or configOptions).

^{Written for commit 65b15cc. Summary will update on new commits. Review in cubic}

[cubic-dev-ai]

1 issue found across 3 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/ApiClient.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/csharp/ApiClient.mustache:471">
P2: `throwOnAnyError` is lost when retry policies are enabled: Polly captures the exception, the fallback response only stores `ErrorException`, and `ToApiResponse` does not surface it, so the generated `ApiResponse` still hides the client error.</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 2 files (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/ApiClient.v790.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/csharp/ApiClient.v790.mustache:562">
P2: `throwOnAnyError` can throw `null` for handled-result policy failures, causing a `NullReferenceException` instead of surfacing the actual policy failure.</violation>
</file>

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