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Support C# 13 params collections (IEnumerable<T>, List<T>) #478

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Merged
nblumhardt merged 5 commits into from
May 26, 2026
Merged

Support C# 13 params collections (IEnumerable<T>, List<T>) #478

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feb587d
support params collections for generic interfaces and classes, ref st…
gyurebalint May 20, 2026
ec026bf
add log when CreateInstance throws
gyurebalint May 22, 2026
052ceaf
add unit test when CreateInstance throws
gyurebalint May 22, 2026
7879ae3
make log a one liner
gyurebalint May 22, 2026
dcc2467
removed diagnostics from assert, updated selflog in catch block
gyurebalint May 26, 2026
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39 changes: 35 additions & 4 deletions src/Serilog.Settings.Configuration/Settings/Configuration/ConfigurationReader.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -404,8 +404,13 @@ static bool HasImplicitValueWhenNotSpecified(ParameterInfo paramInfo)
return paramInfo.HasDefaultValue
// parameters of type IConfiguration are implicitly populated with provided Configuration
|| paramInfo.ParameterType == typeof(IConfiguration)
|| paramInfo.IsDefined(typeof(ParamArrayAttribute), false)
|| paramInfo.CustomAttributes.Any(a => a.AttributeType.FullName == "System.Runtime.CompilerServices.ParamCollectionAttribute");
|| IsParamCollection(paramInfo);
}

static bool IsParamCollection(ParameterInfo paramInfo)
{
return paramInfo.IsDefined(typeof(ParamArrayAttribute), false)
|| paramInfo.CustomAttributes.Any(a => a.AttributeType.FullName == "System.Runtime.CompilerServices.ParamCollectionAttribute");
}

internal object? GetImplicitValueForNotSpecifiedKey(ParameterInfo parameter, MethodInfo methodToInvoke)
Expand All @@ -431,9 +436,35 @@ static bool HasImplicitValueWhenNotSpecified(ParameterInfo paramInfo)
$"This is not supported when only a `IConfigSection` has been provided. (method '{methodToInvoke}')");
}

if (parameter.IsDefined(typeof(ParamArrayAttribute), false) && parameter.ParameterType.GetElementType() is { } elementType)
if (IsParamCollection(parameter))
{
return Array.CreateInstance(elementType, 0);
var paramType = parameter.ParameterType;

bool isByRefLike = paramType.CustomAttributes.Any(a => a.AttributeType.FullName == "System.Runtime.CompilerServices.IsByRefLikeAttribute");
if (isByRefLike)
{
return parameter.HasDefaultValue ? parameter.DefaultValue : null;
}

if (paramType.GetElementType() is { } elementType)
{
return Array.CreateInstance(elementType, 0);
}

if (paramType.IsGenericType && paramType.IsInterface)
{
var genericTypeArg = paramType.GetGenericArguments()[0];
return Array.CreateInstance(genericTypeArg, 0);
}

if (paramType.IsGenericType && !paramType.IsAbstract)
{
try
{
return Activator.CreateInstance(paramType);
}
catch { }

@nblumhardt nblumhardt May 22, 2026

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In the catch block here, it might be worth pointing out:

https://github.com/dotnet/csharplang/blob/main/proposals/csharp-12.0/collection-expressions.md#create-methods

which describes the cases in which Activator.CreateInstance is unlikely to succeed, and also the reflection-driven API we'd need to use in order to extend capability to them.

A Serilog.Debugging.SelfLog.WriteLine(...) call that includes the exception message and as much information as possible about the parameter being constructed would help users figure out why these might fail.

@gyurebalint gyurebalint May 22, 2026

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Hello,
I updated the PR, here is what the log produces:

Unable to create an implicit instance of the params collection type 'Serilog.Settings.Configuration.Tests.BrokenCollection`1[System.String]' for parameter 'list' on method 'DummyBrokenCollection'.
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
 ---> System.InvalidOperationException: I am broken by design!
   at Serilog.Settings.Configuration.Tests.BrokenCollection`1..ctor() in C:\Development\serilog-settings-configuration\test\Serilog.Settings.Configuration.Tests\DummyLoggerConfigurationExtensions.cs:line 72
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean wrapExceptions)
   --- End of inner exception stack trace ---
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean wrapExceptions)
   at Serilog.Settings.Configuration.ConfigurationReader.GetImplicitValueForNotSpecifiedKey(ParameterInfo parameter, MethodInfo methodToInvoke) in C:\Development\serilog-settings-configuration\src\Serilog.Settings.Configuration\Settings\Configuration\ConfigurationReader.cs:line 464

Let me know if this works for you.

}
}

return parameter.HasDefaultValue ? parameter.DefaultValue : null;
Expand Down
20 changes: 19 additions & 1 deletion test/Serilog.Settings.Configuration.Tests/ConfigurationReaderTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -373,8 +373,26 @@ public void ParamsEnumerableParameter_GracefullyReturnsDefaultValue()
var param = method.GetParameters().Last(); // params IEnumerable<string>

var result = reader.GetImplicitValueForNotSpecifiedKey(param, method);
var array = Assert.IsType<string[]>(result);
Assert.Empty(array);
}

Assert.Null(result);
[Fact]
public void ParamsListParameter_ReturnsEmptyList()
{
var reader = new ConfigurationReader(
JsonStringConfigSource.LoadSection("{}", "Serilog"),
AssemblyFinder.ForSource(ConfigurationAssemblySource.UseLoadedAssemblies),
new ConfigurationReaderOptions());

// Assuming you have a DummyParamsList method in your TestDummies
var method = typeof(DummyLoggerConfigurationExtensions).GetMethod("DummyParamsList")!;
var param = method.GetParameters().Last(); // params List<string>

var result = reader.GetImplicitValueForNotSpecifiedKey(param, method);

var list = Assert.IsType<List<string>>(result);
Assert.Empty(list);
}

[Fact]
Expand Down
7 changes: 7 additions & 0 deletions test/Serilog.Settings.Configuration.Tests/DummyLoggerConfigurationExtensions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,13 @@ public static LoggerConfiguration DummyParamsEnumerable(
return loggerSinkConfiguration.Sink(new DummyParamsSink(values.ToArray()));
}

public static LoggerConfiguration DummyParamsList(
this LoggerSinkConfiguration loggerSinkConfiguration,
params System.Collections.Generic.List<string> list)
{
return loggerSinkConfiguration.Sink(new DummyParamsSink(list.ToArray()));
}

public static LoggerConfiguration DummyParamsSpan(
this LoggerSinkConfiguration loggerSinkConfiguration,
params ReadOnlySpan<string> values)
Expand Down
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