[csharp][restsharp] add throwOnAnyError option to surface client errors (OpenAPITools#23663)

* [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/[].

* docs: regenerate csharp.md to alphabetical order

* [csharp][restsharp] honour throwOnAnyError when retry policy is configured

Polly's ExecuteAndCapture catches the rethrown ApiException, so without
this change the option is silently neutralized whenever
RetryConfiguration.RetryPolicy != null: the exception ends up in
RestResponse.ErrorException, which ToApiResponse discards.

When throwOnAnyError is enabled, rethrow PolicyResult.FinalException
from DeserializeRestResponseFromPolicyAsync so the contract is
consistent across both the no-retry and retry paths. Default-off branch
is byte-identical to the previous output.

* [csharp][restsharp] guard throwOnAnyError against null FinalException

Polly's PolicyResult.FinalException is null when Outcome is Failure but
the failure type is ResultHandledByThisPolicy (e.g. a retry policy
configured with .HandleResult(...) that gives up after N retries).
Throwing it directly would NRE; fall back to InvalidOperationException
so the option still surfaces an error.

Also restores the trailing whitespace on the if line so existing
restsharp samples don't all need regenerating.

Author: mjansrud

docs/generators/csharp.md

@@ -47,6 +47,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |returnICollection|Return ICollection<T> instead of the concrete type.| |false|
 |sourceFolder|source folder for generated code| |src|
 |targetFramework|The target .NET framework version. To target multiple frameworks, use `;` as the separator, e.g. `netstandard2.1;netcoreapp3.1`|<dl><dt>**netstandard1.3**</dt><dd>.NET Standard 1.3</dd><dt>**netstandard1.4**</dt><dd>.NET Standard 1.4</dd><dt>**netstandard1.5**</dt><dd>.NET Standard 1.5</dd><dt>**netstandard1.6**</dt><dd>.NET Standard 1.6</dd><dt>**netstandard2.0**</dt><dd>.NET Standard 2.0</dd><dt>**netstandard2.1**</dt><dd>.NET Standard 2.1</dd><dt>**net47**</dt><dd>.NET Framework 4.7</dd><dt>**net48**</dt><dd>.NET Framework 4.8</dd><dt>**net8.0**</dt><dd>.NET 8.0 (End of Support 10 November 2026)</dd><dt>**net9.0**</dt><dd>.NET 9.0 (End of Support 10 November 2026)</dd><dt>**net10.0**</dt><dd>.NET 10.0 (End of Support 14 November 2028)</dd></dl>|net10.0|
+|throwOnAnyError|Configure RestSharp to rethrow deserialization and transport errors instead of swallowing them into RestResponse.ErrorException (which the default ToApiResponse&lt;T&gt; discards as null Data). Recommended for production use to surface bugs that would otherwise be invisible. (restsharp only)| |false|
 |useCollection|Deserialize array types to Collection&lt;T&gt; instead of List&lt;T&gt;.| |false|
 |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|

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);
             
@@ -566,10 +567,15 @@ namespace {{packageName}}.Client
             }
             else
             {
+                {{#throwOnAnyError}}
+                throw policyResult.FinalException ?? new InvalidOperationException("The retry policy failed without an exception.");
+                {{/throwOnAnyError}}
+                {{^throwOnAnyError}}
                 return new RestResponse<T>(request)
                 {
                     ErrorException = policyResult.FinalException
                 };
+                {{/throwOnAnyError}}
             }
         }
                 

modules/openapi-generator/src/main/resources/csharp/ApiClient.v790.mustache

@@ -558,10 +558,15 @@ namespace {{packageName}}.Client
             }
             else
             {
+                {{#throwOnAnyError}}
+                throw policyResult.FinalException ?? new InvalidOperationException("The retry policy failed without an exception.");
+                {{/throwOnAnyError}}
+                {{^throwOnAnyError}}
                 return new RestResponse<T>(request)
                 {
                     ErrorException = policyResult.FinalException
                 };
+                {{/throwOnAnyError}}
             }
         }