Add WriteTo.FallbackChain and WriteTo.Fallible support in configuration#474
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nblumhardt merged 2 commits intoserilog:devfrom Apr 30, 2026
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FallbackChain and Fallible were introduced as instance methods on LoggerSinkConfiguration in Serilog 4.1, so they weren't discovered by the extension-method scanner. Expose them through the same surrogate pattern already used for Sink/Logger. Sample project demonstrates both features against an AlwaysFailingSink so the fallback path and failure listener are actually exercised at runtime. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Mention Conditional/FallbackChain/Fallible in the nested-configuration section of the README, and extend the sample appsettings.json with WithComputed, ByExcluding, ExpressionTemplate, AuditTo, and a MinimumLevel ControlledBy switch to exercise more of the supported surface. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Looks good, thanks @ArieGato.
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Closes #473.
Summary
FallbackChainandFalliblesurrogates toSurrogateConfigurationMethodsso the twoLoggerSinkConfigurationinstance methods introduced in Serilog 4.1 can be used fromappsettings.json/IConfiguration.Sampleproject with anAlwaysFailingSinkplus aSampleFailureListenerso both sections in the sampleappsettings.jsonexercise the fallback path and failure-listener path at runtime.paramsarray, andFalliblerouting failures to a listener.Implementation notes
Both methods are instance methods on
LoggerSinkConfigurationrather than extension methods, so the extension-method scanner inConfigurationReader.FindConfigurationExtensionMethodsdoesn't discover them — same as the existingSink/Loggersurrogates.FallbackChain's third parameter isparams Action<LoggerSinkConfiguration>[]. Becauseparamsdoes not setParameterInfo.HasDefaultValue = true, it isn't treated as omittable byHasImplicitValueWhenNotSpecified, so the surrogate uses= nullexplicitly. Same underlying mechanical issue as #441; that broader fix would let the surrogate drop the?? []workaround later.LoggerAuditSinkConfigurationdoes not expose these methods in Serilog (by design — audit pipelines are meant to fail loudly), so no correspondingAuditTosurrogates are added.Test plan
dotnet buildpasses on net462 / netstandard2.0 / net8.0 / net9.0 / net10.0coverlet.collectorlocally)[fallback ...]lines in console and[SampleFailureListener]lines inSelfLog)