Add a callback on the reader options to expose the log level switches

Fixes #206

README.md

@@ -186,6 +186,22 @@ You can also declare `LoggingLevelSwitch`-es in custom section and reference the
 
 Level updates to switches are also respected for a dynamic update.
 
+Since version 4.0.0, both declared switches (i.e. `Serilog:LevelSwitches` section) and minimum level override switches (i.e. `Serilog:MinimumLevel:Override` section) are exposed through a callback on the reader options so that a reference can be kept:
+
+```csharp
+var allSwitches = new Dictionary<string, LoggingLevelSwitch>();
+var options = new ConfigurationReaderOptions
+{
+    OnAddedLevelSwitch = (switchName, logLevelSwitch) => allSwitches[switchName] = logLevelSwitch
+};
+
+var logger = new LoggerConfiguration()
+    .ReadFrom.Configuration(configuration, options)
+    .CreateLogger();
+
+LoggingLevelSwitch controlSwitch = allSwitches["$controlSwitch"];
+```
+
 ### WriteTo, Enrich, AuditTo, Destructure sections
 
 These sections support simplified syntax, for example the following is valid if no arguments are needed by the sinks:

src/Serilog.Settings.Configuration/ConfigurationLoggerConfigurationExtensions.cs

@@ -100,8 +100,8 @@ public static LoggerConfiguration ConfigurationSection(
             new ConfigurationReader(
                 configSection,
                 assemblyFinder,
-                configuration: null,
-                formatProvider: null));
+                new ConfigurationReaderOptions { FormatProvider = null },
+                configuration: null));
     }
 
     /// <summary>
@@ -164,7 +164,7 @@ public static LoggerConfiguration ConfigurationSection(
 
         var assemblyFinder = AssemblyFinder.ForSource(configurationAssemblySource);
 
-        return settingConfiguration.Settings(new ConfigurationReader(configSection, assemblyFinder, configuration: null, formatProvider: null));
+        return settingConfiguration.Settings(new ConfigurationReader(configSection, assemblyFinder, new ConfigurationReaderOptions { FormatProvider = null }, configuration: null));
     }
 
     /// <summary>
@@ -229,19 +229,19 @@ static ConfigurationReader GetConfigurationReader(IConfiguration configuration,
     {
         var assemblyFinder = dependencyContext == null ? AssemblyFinder.Auto() : AssemblyFinder.ForDependencyContext(dependencyContext);
         var section = configuration.GetSection(readerOptions.SectionName);
-        return new ConfigurationReader(section, assemblyFinder, readerOptions.FormatProvider, configuration);
+        return new ConfigurationReader(section, assemblyFinder, readerOptions, configuration);
     }
 
     static ConfigurationReader GetConfigurationReader(IConfiguration configuration, ConfigurationReaderOptions readerOptions, ConfigurationAssemblySource source)
     {
         var assemblyFinder = AssemblyFinder.ForSource(source);
         var section = configuration.GetSection(readerOptions.SectionName);
-        return new ConfigurationReader(section, assemblyFinder, readerOptions.FormatProvider, configuration);
+        return new ConfigurationReader(section, assemblyFinder, readerOptions, configuration);
     }
 
     static ConfigurationReader GetConfigurationReader(IConfiguration configuration, ConfigurationReaderOptions readerOptions, IReadOnlyCollection<Assembly> assemblies)
     {
         var section = configuration.GetSection(readerOptions.SectionName);
-        return new ConfigurationReader(section, assemblies, new ResolutionContext(configuration, readerOptions.FormatProvider));
+        return new ConfigurationReader(section, assemblies, new ResolutionContext(configuration, readerOptions));
     }
 }

src/Serilog.Settings.Configuration/Settings/Configuration/ConfigurationReader.cs

@@ -22,11 +22,11 @@ class ConfigurationReader : IConfigurationReader
     readonly ResolutionContext _resolutionContext;
     readonly IConfigurationRoot _configurationRoot;
 
-    public ConfigurationReader(IConfigurationSection configSection, AssemblyFinder assemblyFinder, IFormatProvider formatProvider, IConfiguration configuration = null)
+    public ConfigurationReader(IConfigurationSection configSection, AssemblyFinder assemblyFinder, ConfigurationReaderOptions readerOptions, IConfiguration configuration = null)
     {
         _section = configSection ?? throw new ArgumentNullException(nameof(configSection));
         _configurationAssemblies = LoadConfigurationAssemblies(_section, assemblyFinder);
-        _resolutionContext = new ResolutionContext(configuration, formatProvider);
+        _resolutionContext = new ResolutionContext(configuration, readerOptions);
         _configurationRoot = configuration as IConfigurationRoot;
     }
 
@@ -136,7 +136,8 @@ void ProcessLevelSwitchDeclarations()
             SubscribeToLoggingLevelChanges(levelSwitchDeclaration, newSwitch);
 
             // make them available later on when resolving argument values
-            _resolutionContext.AddLevelSwitch(switchName, newSwitch);
+            var referenceName = _resolutionContext.AddLevelSwitch(switchName, newSwitch);
+            _resolutionContext.ReaderOptions.OnAddedLevelSwitch?.Invoke(referenceName, newSwitch);
         }
     }
 
@@ -164,7 +165,11 @@ void ApplyMinimumLevel(LoggerConfiguration loggerConfiguration)
             var overridenLevelOrSwitch = overrideDirective.Value;
             if (Enum.TryParse(overridenLevelOrSwitch, out LogEventLevel _))
             {
-                ApplyMinimumLevelConfiguration(overrideDirective, (configuration, levelSwitch) => configuration.Override(overridePrefix, levelSwitch));
+                ApplyMinimumLevelConfiguration(overrideDirective, (configuration, levelSwitch) =>
+                {
+                    configuration.Override(overridePrefix, levelSwitch);
+                    _resolutionContext.ReaderOptions.OnAddedLevelSwitch?.Invoke(overridePrefix, levelSwitch);
+                });
             }
             else
             {

src/Serilog.Settings.Configuration/Settings/Configuration/ConfigurationReaderOptions.cs

@@ -1,6 +1,7 @@
 using System.Globalization;
 using System.Reflection;
 using Microsoft.Extensions.DependencyModel;
+using Serilog.Core;
 
 namespace Serilog.Settings.Configuration;
 
@@ -56,6 +57,16 @@ public ConfigurationReaderOptions() : this(dependencyContext: null)
     /// </summary>
     public IFormatProvider FormatProvider { get; init; } = CultureInfo.InvariantCulture;
 
+    /// <summary>
+    /// Called when a log level switch is created while reading the configuration.
+    /// Log level switches are created either from the <c>Serilog:LevelSwitches</c> section (declared switches) or the <c>Serilog:MinimumLevel:Override</c> section (minimum level override switches).
+    /// <list type="bullet">
+    ///   <item>For declared switches, the switch name includes the leading <c>$</c> character.</item>
+    ///   <item>For minimum level override switches, the switch name is the (partial) namespace or type name of the override.</item>
+    /// </list>
+    /// </summary>
+    public Action<string, LoggingLevelSwitch> OnAddedLevelSwitch { get; init; }
+
     internal Assembly[] Assemblies { get; }
     internal DependencyContext DependencyContext { get; }
     internal ConfigurationAssemblySource? ConfigurationAssemblySource { get; }

src/Serilog.Settings.Configuration/Settings/Configuration/ResolutionContext.cs

@@ -13,15 +13,15 @@ sealed class ResolutionContext
     readonly IDictionary<string, LoggingFilterSwitchProxy> _declaredFilterSwitches;
     readonly IConfiguration _appConfiguration;
 
-    public ResolutionContext(IConfiguration appConfiguration = null, IFormatProvider formatProvider = null)
+    public ResolutionContext(IConfiguration appConfiguration = null, ConfigurationReaderOptions readerOptions = null)
     {
         _declaredLevelSwitches = new Dictionary<string, LoggingLevelSwitch>();
         _declaredFilterSwitches = new Dictionary<string, LoggingFilterSwitchProxy>();
         _appConfiguration = appConfiguration;
-        FormatProvider = formatProvider;
+        ReaderOptions = readerOptions ?? new ConfigurationReaderOptions();
     }
 
-    public IFormatProvider FormatProvider { get; }
+    public ConfigurationReaderOptions ReaderOptions { get; }
 
     /// <summary>
     /// Looks up a switch in the declared LoggingLevelSwitches
@@ -64,18 +64,22 @@ public IConfiguration AppConfiguration
         }
     }
 
-    public void AddLevelSwitch(string levelSwitchName, LoggingLevelSwitch levelSwitch)
+    public string AddLevelSwitch(string levelSwitchName, LoggingLevelSwitch levelSwitch)
     {
         if (levelSwitchName == null) throw new ArgumentNullException(nameof(levelSwitchName));
         if (levelSwitch == null) throw new ArgumentNullException(nameof(levelSwitch));
-        _declaredLevelSwitches[ToSwitchReference(levelSwitchName)] = levelSwitch;
+        var referenceName = ToSwitchReference(levelSwitchName);
+        _declaredLevelSwitches[referenceName] = levelSwitch;
+        return referenceName;
     }
 
-    public void AddFilterSwitch(string filterSwitchName, LoggingFilterSwitchProxy filterSwitch)
+    public string AddFilterSwitch(string filterSwitchName, LoggingFilterSwitchProxy filterSwitch)
     {
         if (filterSwitchName == null) throw new ArgumentNullException(nameof(filterSwitchName));
         if (filterSwitch == null) throw new ArgumentNullException(nameof(filterSwitch));
-        _declaredFilterSwitches[ToSwitchReference(filterSwitchName)] = filterSwitch;
+        var referenceName = ToSwitchReference(filterSwitchName);
+        _declaredFilterSwitches[referenceName] = filterSwitch;
+        return referenceName;
     }
 
     string ToSwitchReference(string switchName)

src/Serilog.Settings.Configuration/Settings/Configuration/StringArgumentValue.cs

@@ -155,7 +155,7 @@ public object ConvertTo(Type toType, ResolutionContext resolutionContext)
             }
         }
 
-        return Convert.ChangeType(argumentValue, toType, resolutionContext.FormatProvider);
+        return Convert.ChangeType(argumentValue, toType, resolutionContext.ReaderOptions.FormatProvider);
     }
 
     internal static Type FindType(string typeName)

test/Serilog.Settings.Configuration.Tests/ConfigurationReaderTests.cs

@@ -1,4 +1,4 @@
-using System.Globalization;
+using System.Globalization;
 using System.Reflection;
 using Microsoft.Extensions.Configuration;
 using Serilog.Events;
@@ -18,7 +18,7 @@ public ConfigurationReaderTests()
         _configurationReader = new ConfigurationReader(
             JsonStringConfigSource.LoadSection("{ 'Serilog': {  } }", "Serilog"),
             AssemblyFinder.ForSource(ConfigurationAssemblySource.UseLoadedAssemblies),
-            CultureInfo.InvariantCulture);
+            new ConfigurationReaderOptions());
     }
 
     [Fact]
@@ -197,7 +197,7 @@ public void MethodsAreSelectedBasedOnCountOfMatchedArgumentsAndThenStringType()
     [MemberData(nameof(FlatMinimumLevel))]
     public void FlatMinimumLevelCorrectOneIsEnabledOnLogger(IConfigurationRoot root, LogEventLevel expectedMinimumLevel)
     {
-        var reader = new ConfigurationReader(root.GetSection("Serilog"), AssemblyFinder.ForSource(ConfigurationAssemblySource.UseLoadedAssemblies), CultureInfo.InvariantCulture, root);
+        var reader = new ConfigurationReader(root.GetSection("Serilog"), AssemblyFinder.ForSource(ConfigurationAssemblySource.UseLoadedAssemblies), new ConfigurationReaderOptions(), root);
         var loggerConfig = new LoggerConfiguration();
 
         reader.Configure(loggerConfig);
@@ -221,7 +221,7 @@ public void FlatMinimumLevelCorrectOneIsEnabledOnLogger(IConfigurationRoot root,
     [MemberData(nameof(ObjectMinimumLevel))]
     public void ObjectMinimumLevelCorrectOneIsEnabledOnLogger(IConfigurationRoot root, LogEventLevel expectedMinimumLevel)
     {
-        var reader = new ConfigurationReader(root.GetSection("Serilog"), AssemblyFinder.ForSource(ConfigurationAssemblySource.UseLoadedAssemblies), CultureInfo.InvariantCulture, root);
+        var reader = new ConfigurationReader(root.GetSection("Serilog"), AssemblyFinder.ForSource(ConfigurationAssemblySource.UseLoadedAssemblies), new ConfigurationReaderOptions(), root);
         var loggerConfig = new LoggerConfiguration();
 
         reader.Configure(loggerConfig);
@@ -263,7 +263,7 @@ public void ObjectMinimumLevelCorrectOneIsEnabledOnLogger(IConfigurationRoot roo
     [MemberData(nameof(MixedMinimumLevel))]
     public void MixedMinimumLevelCorrectOneIsEnabledOnLogger(IConfigurationRoot root, LogEventLevel expectedMinimumLevel)
     {
-        var reader = new ConfigurationReader(root.GetSection("Serilog"), AssemblyFinder.ForSource(ConfigurationAssemblySource.UseLoadedAssemblies), CultureInfo.InvariantCulture, root);
+        var reader = new ConfigurationReader(root.GetSection("Serilog"), AssemblyFinder.ForSource(ConfigurationAssemblySource.UseLoadedAssemblies), new ConfigurationReaderOptions(), root);
         var loggerConfig = new LoggerConfiguration();
 
         reader.Configure(loggerConfig);
@@ -275,7 +275,7 @@ public void MixedMinimumLevelCorrectOneIsEnabledOnLogger(IConfigurationRoot root
     public void NoConfigurationRootUsedStillValid()
     {
         var section = JsonStringConfigSource.LoadSection("{ 'Nest': { 'Serilog': { 'MinimumLevel': 'Error' } } }", "Nest");
-        var reader = new ConfigurationReader(section.GetSection("Serilog"), AssemblyFinder.ForSource(ConfigurationAssemblySource.UseLoadedAssemblies), CultureInfo.InvariantCulture, section);
+        var reader = new ConfigurationReader(section.GetSection("Serilog"), AssemblyFinder.ForSource(ConfigurationAssemblySource.UseLoadedAssemblies), new ConfigurationReaderOptions(), section);
         var loggerConfig = new LoggerConfiguration();
 
         reader.Configure(loggerConfig);

test/Serilog.Settings.Configuration.Tests/ConfigurationSettingsTests.cs

@@ -11,24 +11,24 @@ namespace Serilog.Settings.Configuration.Tests;
 
 public class ConfigurationSettingsTests
 {
-    static LoggerConfiguration ConfigFromJson(string jsonString, string secondJsonSource = null)
+    static LoggerConfiguration ConfigFromJson(string jsonString, string secondJsonSource = null, ConfigurationReaderOptions options = null)
     {
-        return ConfigFromJson(jsonString, secondJsonSource, out _);
+        return ConfigFromJson(jsonString, secondJsonSource, out _, options);
     }
 
-    static LoggerConfiguration ConfigFromJson(string jsonString, out IConfiguration configuration)
+    static LoggerConfiguration ConfigFromJson(string jsonString, out IConfiguration configuration, ConfigurationReaderOptions options = null)
     {
-        return ConfigFromJson(jsonString, null, out configuration);
+        return ConfigFromJson(jsonString, null, out configuration, options);
     }
 
-    static LoggerConfiguration ConfigFromJson(string jsonString, string secondJsonSource, out IConfiguration configuration)
+    static LoggerConfiguration ConfigFromJson(string jsonString, string secondJsonSource, out IConfiguration configuration, ConfigurationReaderOptions options)
     {
         var builder = new ConfigurationBuilder().AddJsonString(jsonString);
         if (secondJsonSource != null)
             builder.AddJsonString(secondJsonSource);
         configuration = builder.Build();
         return new LoggerConfiguration()
-            .ReadFrom.Configuration(configuration);
+            .ReadFrom.Configuration(configuration, options);
     }
 
     [Fact]
@@ -1345,4 +1345,37 @@ public void FilterWithIsAppliedWithCustomFilter()
         log.ForContext("User", "the user").Write(Some.InformationEvent());
         Assert.NotNull(evt);
     }
+
+    [Theory]
+    [InlineData("$switch1")]
+    [InlineData("switch1")]
+    public void TestLogLevelSwitchesCallback(string switchName)
+    {
+        var json = $@"{{
+                'Serilog': {{
+                    'LevelSwitches': {{ '{switchName}': 'Information' }},
+                    'MinimumLevel': {{
+                        'Override': {{
+                            'System': 'Warning',
+                            'System.Threading': 'Debug'
+                        }}
+                    }}
+                }}
+            }}";
+
+        IDictionary<string, LoggingLevelSwitch> switches = new Dictionary<string, LoggingLevelSwitch>();
+        var readerOptions = new ConfigurationReaderOptions { OnAddedLevelSwitch = (name, levelSwitch) => switches[name] = levelSwitch };
+        ConfigFromJson(json, options: readerOptions);
+
+        Assert.Equal(3, switches.Count);
+
+        var switch1 = Assert.Contains("$switch1", switches);
+        Assert.Equal(LogEventLevel.Information, switch1.MinimumLevel);
+
+        var system = Assert.Contains("System", switches);
+        Assert.Equal(LogEventLevel.Warning, system.MinimumLevel);
+
+        var systemThreading = Assert.Contains("System.Threading", switches);
+        Assert.Equal(LogEventLevel.Debug, systemThreading.MinimumLevel);
+    }
 }