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

By default, RestSharp swallows deserialization and transport
exceptions into RestResponse.ErrorException, and the generated
ToApiResponse<T> in this template only carries ErrorText — the
actual exception is dropped. Combined with a generated GetXxxAsync
that returns Data directly, callers silently receive null on any
deserialization failure (e.g. a required property missing in the
upstream JSON). The error never reaches application logs or APM.

Add an opt-in `throwOnAnyError` switch (default false, restsharp
library only) that sets `ThrowOnAnyError = true` on RestClientOptions,
making RestSharp rethrow the original ApiException(500, ...) that
the generated deserializer already throws. The exception then
propagates to the caller and into normal application error handling.

Default kept off to preserve backwards compatibility — opt in when
you want bugs to surface instead of silently producing null/[].

Author: mjansrud

docs/generators/csharp.md

@@ -51,6 +51,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |useDateTimeForDate|Use DateTime to model date properties even if DateOnly supported. (.net 6.0+ only)| |false|
 |useDateTimeOffset|Use DateTimeOffset to model date-time properties| |false|
 |useIntForTimeout|Use int for Timeout (fall back to v7.9.0 templates). This option (for restsharp only) will be deprecated so please migrated to TimeSpan instead.| |false|
+|throwOnAnyError|Configure RestSharp to rethrow deserialization and transport errors instead of swallowing them into RestResponse.ErrorException (which the default ToApiResponse<T> discards as null Data). Recommended for production use to surface bugs that would otherwise be invisible. (restsharp only)| |false|
 |useOneOfDiscriminatorLookup|Use the discriminator's mapping in oneOf to speed up the model lookup. IMPORTANT: Validation (e.g. one and only one match in oneOf's schemas) will be skipped.| |false|
 |useSourceGeneration|Use source generation where available (only `generichost` library supports this option).| |false|
 |useVirtualForHooks|Generate code that exposes public virtual hooks on ApiClient to customize low-level HTTP requests (only `restsharp`. `httpclient` libraries support this option).| |false|

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpClientCodegen.java

@@ -122,6 +122,7 @@ public class CSharpClientCodegen extends AbstractCSharpCodegen {
     protected boolean supportsFileParameters = Boolean.TRUE;
     protected boolean supportsDateOnly = Boolean.FALSE;
     protected boolean useIntForTimeout = Boolean.FALSE;
+    protected boolean throwOnAnyError = Boolean.FALSE;
 
     @Setter protected boolean validatable = Boolean.TRUE;
     @Setter protected boolean equatable = Boolean.FALSE;
@@ -132,6 +133,7 @@ public class CSharpClientCodegen extends AbstractCSharpCodegen {
     private static final String OPERATION_PARAMETER_SORTING_KEY = "operationParameterSorting";
     private static final String MODEL_PROPERTY_SORTING_KEY = "modelPropertySorting";
     private static final String USE_INT_FOR_TIMEOUT = "useIntForTimeout";
+    private static final String THROW_ON_ANY_ERROR = "throwOnAnyError";
 
     enum SortingMethod {
         DEFAULT,
@@ -249,6 +251,10 @@ public CSharpClientCodegen() {
                 "Use int for Timeout (fall back to v7.9.0 templates). This option (for restsharp only) will be deprecated so please migrated to TimeSpan instead.",
                 String.valueOf(this.useIntForTimeout));
 
+        addSwitch(CSharpClientCodegen.THROW_ON_ANY_ERROR,
+                "Configure RestSharp to rethrow deserialization and transport errors instead of swallowing them into RestResponse.ErrorException (which the default ToApiResponse<T> discards as null Data). Recommended for production use to surface bugs that would otherwise be invisible. (restsharp only)",
+                this.throwOnAnyError);
+
         CliOption framework = new CliOption(
                 CodegenConstants.DOTNET_FRAMEWORK,
                 CodegenConstants.DOTNET_FRAMEWORK_DESC
@@ -871,6 +877,7 @@ public void processOpts() {
         syncBooleanProperty(additionalProperties, "useSourceGeneration", this::setUseSourceGeneration, this.useSourceGeneration);
         syncBooleanProperty(additionalProperties, "supportsDateOnly", this::setSupportsDateOnly, this.supportsDateOnly);
         syncBooleanProperty(additionalProperties, "useIntForTimeout", this::setUseIntForTimeout, this.useIntForTimeout);
+        syncBooleanProperty(additionalProperties, "throwOnAnyError", this::setThrowOnAnyError, this.throwOnAnyError);
 
         final String testPackageName = testPackageName();
         String packageFolder = sourceFolder + File.separator + packageName;
@@ -1244,6 +1251,10 @@ public void setUseIntForTimeout(Boolean useIntForTimeout) {
         this.useIntForTimeout = useIntForTimeout;
     }
 
+    public void setThrowOnAnyError(Boolean throwOnAnyError) {
+        this.throwOnAnyError = throwOnAnyError;
+    }
+
     public void setSupportsRetry(Boolean supportsRetry) {
         this.supportsRetry = supportsRetry;
     }

modules/openapi-generator/src/main/resources/csharp/ApiClient.mustache

@@ -467,7 +467,8 @@ namespace {{packageName}}.Client
                 Proxy = configuration.Proxy,
                 UserAgent = configuration.UserAgent,
                 UseDefaultCredentials = configuration.UseDefaultCredentials,
-                RemoteCertificateValidationCallback = configuration.RemoteCertificateValidationCallback
+                RemoteCertificateValidationCallback = configuration.RemoteCertificateValidationCallback{{#throwOnAnyError}},
+                ThrowOnAnyError = true{{/throwOnAnyError}}
             };
             setOptions(clientOptions);