Enable nullable reference types

Directory.Build.props

@@ -6,5 +6,6 @@
     <AssemblyOriginatorKeyFile>$(MSBuildThisFileDirectory)assets/Serilog.snk</AssemblyOriginatorKeyFile>
     <ImplicitUsings>enable</ImplicitUsings>
     <CheckEolTargetFramework>false</CheckEolTargetFramework>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 </Project>

sample/Sample/Program.cs

@@ -73,14 +73,14 @@ public bool IsEnabled(LogEvent logEvent)
 
 public class LoginData
 {
-    public string Username;
+    public string? Username;
     // ReSharper disable once NotAccessedField.Global
-    public string Password;
+    public string? Password;
 }
 
 public class CustomPolicy : IDestructuringPolicy
 {
-    public bool TryDestructure(object value, ILogEventPropertyValueFactory propertyValueFactory, out LogEventPropertyValue result)
+    public bool TryDestructure(object value, ILogEventPropertyValueFactory propertyValueFactory, out LogEventPropertyValue? result)
     {
         result = null;
 

src/Serilog.Settings.Configuration/ConfigurationLoggerConfigurationExtensions.cs

@@ -47,7 +47,7 @@ public static LoggerConfiguration Configuration(
         this LoggerSettingsConfiguration settingConfiguration,
         IConfiguration configuration,
         string sectionName,
-        DependencyContext dependencyContext = null)
+        DependencyContext? dependencyContext = null)
     {
         if (settingConfiguration == null) throw new ArgumentNullException(nameof(settingConfiguration));
         if (configuration == null) throw new ArgumentNullException(nameof(configuration));
@@ -87,7 +87,7 @@ public static LoggerConfiguration Configuration(
     public static LoggerConfiguration ConfigurationSection(
         this LoggerSettingsConfiguration settingConfiguration,
         IConfigurationSection configSection,
-        DependencyContext dependencyContext = null)
+        DependencyContext? dependencyContext = null)
     {
         if (settingConfiguration == null) throw new ArgumentNullException(nameof(settingConfiguration));
         if (configSection == null) throw new ArgumentNullException(nameof(configSection));
@@ -214,7 +214,7 @@ public static LoggerConfiguration Configuration(
     public static LoggerConfiguration Configuration(
         this LoggerSettingsConfiguration settingConfiguration,
         IConfiguration configuration,
-        ConfigurationReaderOptions readerOptions = null)
+        ConfigurationReaderOptions? readerOptions = null)
     {
         var configurationReader = readerOptions switch
         {
@@ -225,7 +225,7 @@ public static LoggerConfiguration Configuration(
         return settingConfiguration.Settings(configurationReader);
     }
 
-    static ConfigurationReader GetConfigurationReader(IConfiguration configuration, ConfigurationReaderOptions readerOptions, DependencyContext dependencyContext)
+    static ConfigurationReader GetConfigurationReader(IConfiguration configuration, ConfigurationReaderOptions readerOptions, DependencyContext? dependencyContext)
     {
         var assemblyFinder = dependencyContext == null ? AssemblyFinder.Auto() : AssemblyFinder.ForDependencyContext(dependencyContext);
         var section = string.IsNullOrWhiteSpace(readerOptions.SectionName) ? configuration : configuration.GetSection(readerOptions.SectionName);

src/Serilog.Settings.Configuration/Settings/Configuration/Assemblies/DllScanningAssemblyFinder.cs

@@ -46,7 +46,7 @@ where IsCaseInsensitiveMatch(assemblyFileName, nameToFind)
 
         return query.ToList().AsReadOnly();
 
-        static AssemblyName TryGetAssemblyNameFrom(string path)
+        static AssemblyName? TryGetAssemblyNameFrom(string path)
         {
             try
             {

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

@@ -20,9 +20,9 @@ class ConfigurationReader : IConfigurationReader
     readonly IConfiguration _section;
     readonly IReadOnlyCollection<Assembly> _configurationAssemblies;
     readonly ResolutionContext _resolutionContext;
-    readonly IConfigurationRoot _configurationRoot;
+    readonly IConfigurationRoot? _configurationRoot;
 
-    public ConfigurationReader(IConfiguration configSection, AssemblyFinder assemblyFinder, ConfigurationReaderOptions readerOptions, IConfiguration configuration = null)
+    public ConfigurationReader(IConfiguration configSection, AssemblyFinder assemblyFinder, ConfigurationReaderOptions readerOptions, IConfiguration? configuration = null)
     {
         _section = configSection ?? throw new ArgumentNullException(nameof(configSection));
         _configurationAssemblies = LoadConfigurationAssemblies(_section, assemblyFinder);
@@ -145,8 +145,8 @@ void ApplyMinimumLevel(LoggerConfiguration loggerConfiguration)
     {
         var minimumLevelDirective = _section.GetSection("MinimumLevel");
 
-        IConfigurationSection defaultMinLevelDirective = GetDefaultMinLevelDirective();
-        if (defaultMinLevelDirective.Value != null)
+        IConfigurationSection? defaultMinLevelDirective = GetDefaultMinLevelDirective();
+        if (defaultMinLevelDirective?.Value != null)
         {
             ApplyMinimumLevelConfiguration(defaultMinLevelDirective, (configuration, levelSwitch) => configuration.ControlledBy(levelSwitch));
         }
@@ -189,7 +189,7 @@ void ApplyMinimumLevelConfiguration(IConfigurationSection directive, Action<Logg
             SubscribeToLoggingLevelChanges(directive, levelSwitch);
         }
 
-        IConfigurationSection GetDefaultMinLevelDirective()
+        IConfigurationSection? GetDefaultMinLevelDirective()
         {
             var defaultLevelDirective = minimumLevelDirective.GetSection("Default");
             if (_configurationRoot != null && minimumLevelDirective.Value != null && defaultLevelDirective.Value != null)
@@ -439,7 +439,7 @@ object GetImplicitValueForNotSpecifiedKey(ParameterInfo parameter, MethodInfo me
         return parameter.DefaultValue;
     }
 
-    internal static MethodInfo SelectConfigurationMethod(IReadOnlyCollection<MethodInfo> candidateMethods, string name, IReadOnlyCollection<string> suppliedArgumentNames)
+    internal static MethodInfo? SelectConfigurationMethod(IReadOnlyCollection<MethodInfo> candidateMethods, string name, IReadOnlyCollection<string> suppliedArgumentNames)
     {
         // Per issue #111, it is safe to use case-insensitive matching on argument names. The CLR doesn't permit this type
         // of overloading, and the Microsoft.Extensions.Configuration keys are case-insensitive (case is preserved with some

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

@@ -38,7 +38,7 @@ public ConfigurationReaderOptions() : this(dependencyContext: null)
     /// The dependency context from which sink/enricher packages can be located. If <see langword="null"/>, the platform default will be used.
     /// </param>
     /// <remarks>Prefer the constructor taking explicit assemblies: <see cref="ConfigurationReaderOptions(System.Reflection.Assembly[])"/>. It's the only one supporting single-file publishing.</remarks>
-    public ConfigurationReaderOptions(DependencyContext dependencyContext) => DependencyContext = dependencyContext;
+    public ConfigurationReaderOptions(DependencyContext? dependencyContext) => DependencyContext = dependencyContext;
 
     /// <summary>
     /// Initialize a new instance of the <see cref="ConfigurationReaderOptions"/> class.
@@ -50,12 +50,12 @@ public ConfigurationReaderOptions() : this(dependencyContext: null)
     /// <summary>
     /// The section name for section which contains a Serilog section. Defaults to <c>Serilog</c>.
     /// </summary>
-    public string SectionName { get; init; } = ConfigurationLoggerConfigurationExtensions.DefaultSectionName;
+    public string? SectionName { get; init; } = ConfigurationLoggerConfigurationExtensions.DefaultSectionName;
 
     /// <summary>
     /// The <see cref="IFormatProvider"/> used when converting strings to other object types. Defaults to the invariant culture.
     /// </summary>
-    public IFormatProvider FormatProvider { get; init; } = CultureInfo.InvariantCulture;
+    public IFormatProvider? FormatProvider { get; init; } = CultureInfo.InvariantCulture;
 
     /// <summary>
     /// Called when a log level switch is created while reading the configuration.
@@ -65,9 +65,9 @@ public ConfigurationReaderOptions() : this(dependencyContext: null)
     ///   <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> OnLevelSwitchCreated { get; init; }
+    public Action<string, LoggingLevelSwitch>? OnLevelSwitchCreated { get; init; }
 
-    internal Assembly[] Assemblies { get; }
-    internal DependencyContext DependencyContext { get; }
+    internal Assembly[]? Assemblies { get; }
+    internal DependencyContext? DependencyContext { get; }
     internal ConfigurationAssemblySource? ConfigurationAssemblySource { get; }
 }

src/Serilog.Settings.Configuration/Settings/Configuration/IConfigurationArgumentValue.cs

@@ -2,5 +2,5 @@
 
 interface IConfigurationArgumentValue
 {
-    object ConvertTo(Type toType, ResolutionContext resolutionContext);
+    object? ConvertTo(Type toType, ResolutionContext resolutionContext);
 }

src/Serilog.Settings.Configuration/Settings/Configuration/LoggingFilterSwitchProxy.cs

@@ -2,8 +2,8 @@
 
 class LoggingFilterSwitchProxy
 {
-    readonly Action<string> _setProxy;
-    readonly Func<string> _getProxy;
+    readonly Action<string?> _setProxy;
+    readonly Func<string?> _getProxy;
 
     LoggingFilterSwitchProxy(object realSwitch)
     {
@@ -12,26 +12,26 @@ class LoggingFilterSwitchProxy
         var type = realSwitch.GetType();
         var expressionProperty = type.GetProperty("Expression") ?? throw new MissingMemberException(type.FullName, "Expression");
 
-        _setProxy = (Action<string>)Delegate.CreateDelegate(
-            typeof(Action<string>),
+        _setProxy = (Action<string?>)Delegate.CreateDelegate(
+            typeof(Action<string?>),
             realSwitch,
             expressionProperty.GetSetMethod());
 
-        _getProxy = (Func<string>)Delegate.CreateDelegate(
-            typeof(Func<string>),
+        _getProxy = (Func<string?>)Delegate.CreateDelegate(
+            typeof(Func<string?>),
             realSwitch,
             expressionProperty.GetGetMethod());
     }
 
     public object RealSwitch { get; }
 
-    public string Expression
+    public string? Expression
     {
         get => _getProxy();
         set => _setProxy(value);
     }
 
-    public static LoggingFilterSwitchProxy Create(string expression = null)
+    public static LoggingFilterSwitchProxy? Create(string? expression = null)
     {
         var filterSwitchType =
             Type.GetType("Serilog.Expressions.LoggingFilterSwitch, Serilog.Expressions") ??

src/Serilog.Settings.Configuration/Settings/Configuration/ObjectArgumentValue.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics.CodeAnalysis;
 using System.Linq.Expressions;
 using System.Reflection;
 
@@ -20,7 +21,7 @@ public ObjectArgumentValue(IConfigurationSection section, IReadOnlyCollection<As
         _configurationAssemblies = configurationAssemblies ?? throw new ArgumentNullException(nameof(configurationAssemblies));
     }
 
-    public object ConvertTo(Type toType, ResolutionContext resolutionContext)
+    public object? ConvertTo(Type toType, ResolutionContext resolutionContext)
     {
         // return the entire section for internal processing
         if (toType == typeof(IConfigurationSection)) return _section;
@@ -71,7 +72,7 @@ object CreateArray()
             return array;
         }
 
-        bool TryCreateContainer(out object result)
+        bool TryCreateContainer([NotNullWhen(true)] out object? result)
         {
             result = null;
 
@@ -98,7 +99,7 @@ bool TryCreateContainer(out object result)
     }
 
     internal static bool TryBuildCtorExpression(
-        IConfigurationSection section, Type parameterType, ResolutionContext resolutionContext, out NewExpression ctorExpression)
+        IConfigurationSection section, Type parameterType, ResolutionContext resolutionContext, [NotNullWhen(true)] out NewExpression? ctorExpression)
     {
         ctorExpression = null;
 
@@ -138,11 +139,11 @@ internal static bool TryBuildCtorExpression(
              from p in c.GetParameters()
              let argumentBindResult = suppliedArguments.TryGetValue(p.Name, out var argValue) switch
              {
-                 true => new { success = true, hasMatch = true, value = (object)argValue },
+                 true => new { success = true, hasMatch = true, value = (object?)argValue },
                  false => p.HasDefaultValue switch
                  {
-                     true  => new { success = true,  hasMatch = false, value = p.DefaultValue },
-                     false => new { success = false, hasMatch = false, value = (object)null },
+                     true  => new { success = true,  hasMatch = false, value = (object?)p.DefaultValue },
+                     false => new { success = false, hasMatch = false, value = (object?)null },
                  },
              }
              group new { argumentBindResult, p.ParameterType } by c into gr
@@ -178,7 +179,7 @@ where gr.All(z => z.argumentBindResult.success)
         ctorExpression = Expression.New(ctor.ConstructorInfo, ctorArguments);
         return true;
 
-        static bool TryBindToCtorArgument(object value, Type type, ResolutionContext resolutionContext, out Expression argumentExpression)
+        static bool TryBindToCtorArgument(object value, Type type, ResolutionContext resolutionContext, [NotNullWhen(true)] out Expression? argumentExpression)
         {
             argumentExpression = null;
 
@@ -217,7 +218,7 @@ static bool TryBindToCtorArgument(object value, Type type, ResolutionContext res
         }
     }
 
-    static bool IsContainer(Type type, out Type elementType)
+    static bool IsContainer(Type type, [NotNullWhen(true)] out Type? elementType)
     {
         elementType = null;
         foreach (var iface in type.GetInterfaces())

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

@@ -11,9 +11,9 @@ sealed class ResolutionContext
 {
     readonly IDictionary<string, LoggingLevelSwitch> _declaredLevelSwitches;
     readonly IDictionary<string, LoggingFilterSwitchProxy> _declaredFilterSwitches;
-    readonly IConfiguration _appConfiguration;
+    readonly IConfiguration? _appConfiguration;
 
-    public ResolutionContext(IConfiguration appConfiguration = null, ConfigurationReaderOptions readerOptions = null)
+    public ResolutionContext(IConfiguration? appConfiguration = null, ConfigurationReaderOptions? readerOptions = null)
     {
         _declaredLevelSwitches = new Dictionary<string, LoggingLevelSwitch>();
         _declaredFilterSwitches = new Dictionary<string, LoggingFilterSwitchProxy>();
@@ -51,18 +51,7 @@ public LoggingFilterSwitchProxy LookUpFilterSwitchByName(string switchName)
 
     public bool HasAppConfiguration => _appConfiguration != null;
 
-    public IConfiguration AppConfiguration
-    {
-        get
-        {
-            if (!HasAppConfiguration)
-            {
-                throw new InvalidOperationException("AppConfiguration is not available");
-            }
-
-            return _appConfiguration;
-        }
-    }
+    public IConfiguration AppConfiguration => _appConfiguration ?? throw new InvalidOperationException("AppConfiguration is not available");
 
     public string AddLevelSwitch(string levelSwitchName, LoggingLevelSwitch levelSwitch)
     {

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

@@ -1,4 +1,5 @@
-using System.Reflection;
+using System.Diagnostics.CodeAnalysis;
+using System.Reflection;
 using System.Text.RegularExpressions;
 
 using Serilog.Core;
@@ -23,7 +24,7 @@ public StringArgumentValue(string providedValue)
             { typeof(Type), s => Type.GetType(s, throwOnError:true) },
         };
 
-    public object ConvertTo(Type toType, ResolutionContext resolutionContext)
+    public object? ConvertTo(Type toType, ResolutionContext resolutionContext)
     {
         var argumentValue = Environment.ExpandEnvironmentVariables(_providedValue);
 
@@ -158,7 +159,7 @@ public object ConvertTo(Type toType, ResolutionContext resolutionContext)
         return Convert.ChangeType(argumentValue, toType, resolutionContext.ReaderOptions.FormatProvider);
     }
 
-    internal static Type FindType(string typeName)
+    internal static Type? FindType(string typeName)
     {
         var type = Type.GetType(typeName);
         if (type == null)
@@ -172,7 +173,7 @@ internal static Type FindType(string typeName)
         return type;
     }
 
-    internal static bool TryParseStaticMemberAccessor(string input, out string accessorTypeName, out string memberName)
+    internal static bool TryParseStaticMemberAccessor(string input, [NotNullWhen(true)] out string? accessorTypeName, [NotNullWhen(true)] out string? memberName)
     {
         if (input == null)
         {

src/Serilog.Settings.Configuration/Settings/Configuration/SurrogateConfigurationMethods.cs

@@ -45,14 +45,14 @@ static LoggerConfiguration Sink(
         LoggerSinkConfiguration loggerSinkConfiguration,
         ILogEventSink sink,
         LogEventLevel restrictedToMinimumLevel = LevelAlias.Minimum,
-        LoggingLevelSwitch levelSwitch = null)
+        LoggingLevelSwitch? levelSwitch = null)
         => loggerSinkConfiguration.Sink(sink, restrictedToMinimumLevel, levelSwitch);
 
     static LoggerConfiguration Logger(
         LoggerSinkConfiguration loggerSinkConfiguration,
         Action<LoggerConfiguration> configureLogger,
         LogEventLevel restrictedToMinimumLevel = LevelAlias.Minimum,
-        LoggingLevelSwitch levelSwitch = null)
+        LoggingLevelSwitch? levelSwitch = null)
         => loggerSinkConfiguration.Logger(configureLogger, restrictedToMinimumLevel, levelSwitch);
 
     // .AuditTo...
@@ -61,14 +61,14 @@ static LoggerConfiguration Sink(
         LoggerAuditSinkConfiguration auditSinkConfiguration,
         ILogEventSink sink,
         LogEventLevel restrictedToMinimumLevel = LevelAlias.Minimum,
-        LoggingLevelSwitch levelSwitch = null)
+        LoggingLevelSwitch? levelSwitch = null)
         => auditSinkConfiguration.Sink(sink, restrictedToMinimumLevel, levelSwitch);
 
     static LoggerConfiguration Logger(
         LoggerAuditSinkConfiguration auditSinkConfiguration,
         Action<LoggerConfiguration> configureLogger,
         LogEventLevel restrictedToMinimumLevel = LevelAlias.Minimum,
-        LoggingLevelSwitch levelSwitch = null)
+        LoggingLevelSwitch? levelSwitch = null)
         => auditSinkConfiguration.Logger(configureLogger, restrictedToMinimumLevel, levelSwitch);
 
     // .Filter...
@@ -109,7 +109,7 @@ static LoggerConfiguration AtLevel(
         LoggerEnrichmentConfiguration loggerEnrichmentConfiguration,
         Action<LoggerEnrichmentConfiguration> configureEnricher,
         LogEventLevel enrichFromLevel = LevelAlias.Minimum,
-        LoggingLevelSwitch levelSwitch = null)
+        LoggingLevelSwitch? levelSwitch = null)
         => levelSwitch != null ? loggerEnrichmentConfiguration.AtLevel(levelSwitch, configureEnricher)
                                : loggerEnrichmentConfiguration.AtLevel(enrichFromLevel, configureEnricher);
 

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

@@ -154,7 +154,7 @@ public void CallableMethodsAreSelected()
         var suppliedArgumentNames = new[] { "pathFormat" };
 
         var selected = ConfigurationReader.SelectConfigurationMethod(options, "DummyRollingFile", suppliedArgumentNames);
-        Assert.Equal(typeof(string), selected.GetParameters()[1].ParameterType);
+        Assert.Equal(typeof(string), selected?.GetParameters()[1].ParameterType);
     }
 
     [Fact]
@@ -166,7 +166,7 @@ public void MethodsAreSelectedBasedOnCountOfMatchedArguments()
         var suppliedArgumentNames = new[] { "pathFormat", "formatter" };
 
         var selected = ConfigurationReader.SelectConfigurationMethod(options, "DummyRollingFile", suppliedArgumentNames);
-        Assert.Equal(typeof(ITextFormatter), selected.GetParameters()[1].ParameterType);
+        Assert.Equal(typeof(ITextFormatter), selected?.GetParameters()[1].ParameterType);
     }
 
     [Fact]
@@ -178,7 +178,7 @@ public void MethodsAreSelectedBasedOnCountOfMatchedArgumentsAndThenStringType()
         var suppliedArgumentNames = new[] { "pathFormat", "formatter" };
 
         var selected = ConfigurationReader.SelectConfigurationMethod(options, "DummyRollingFile", suppliedArgumentNames);
-        Assert.Equal(typeof(string), selected.GetParameters()[2].ParameterType);
+        Assert.Equal(typeof(string), selected?.GetParameters()[2].ParameterType);
     }
 
     public static IEnumerable<object[]> FlatMinimumLevel => new List<object[]>