Use pattern matching where appropriate

* Simpler code
* Uncovers some untested code paths

Author: 0xced

src/Log4NetTextFormatter.cs

@@ -106,7 +106,7 @@ private void WriteEvent(LogEvent logEvent, XmlWriter writer)
             WriteEventAttribute(logEvent, writer, "thread", ThreadIdPropertyName);
             WriteDomainAndUserName(logEvent, writer);
             var properties = logEvent.Properties.Where(e => !SpecialProperties.Contains(e.Key)).ToList();
-            var hasMachineNameProperty = logEvent.Properties.TryGetValue(MachineNamePropertyName, out var machineNameProperty) && machineNameProperty is ScalarValue scalarValue && scalarValue.Value != null;
+            var hasMachineNameProperty = logEvent.Properties.TryGetValue(MachineNamePropertyName, out var machineNameProperty) && machineNameProperty is ScalarValue { Value: not null };
             if (properties.Any() || hasMachineNameProperty)
             {
                 WriteProperties(logEvent, writer, properties, machineNameProperty);
@@ -123,7 +123,7 @@ private void WriteEvent(LogEvent logEvent, XmlWriter writer)
         /// <param name="writer">The XML writer.</param>
         private static void WriteDomainAndUserName(LogEvent logEvent, XmlWriter writer)
         {
-            if (logEvent.Properties.TryGetValue(UserNamePropertyName, out var propertyValue) && propertyValue is ScalarValue scalarValue && scalarValue.Value is string userNameProperty)
+            if (logEvent.Properties.TryGetValue(UserNamePropertyName, out var propertyValue) && propertyValue is ScalarValue { Value: string userNameProperty })
             {
                 // See https://github.com/serilog/serilog-enrichers-environment/blob/3fc7cf78c5f34816633000ae74d846033498e44b/src/Serilog.Enrichers.Environment/Enrichers/EnvironmentUserNameEnricher.cs#L53
                 var parts = userNameProperty.Split('\\');
@@ -149,9 +149,9 @@ private static void WriteDomainAndUserName(LogEvent logEvent, XmlWriter writer)
         /// <remarks>Only properties with a non null <see cref="ScalarValue"/> are supported, other types are ignored.</remarks>
         private void WriteEventAttribute(LogEvent logEvent, XmlWriter writer, string attributeName, string propertyName)
         {
-            if (logEvent.Properties.TryGetValue(propertyName, out var propertyValue) && propertyValue is ScalarValue scalarValue && scalarValue.Value != null)
+            if (logEvent.Properties.TryGetValue(propertyName, out var propertyValue) && propertyValue is ScalarValue { Value: not null })
             {
-                writer.WriteAttributeString(attributeName, RenderValue(scalarValue));
+                writer.WriteAttributeString(attributeName, RenderValue(propertyValue));
             }
         }
 
@@ -225,7 +225,7 @@ private string RenderValue(LogEventPropertyValue value)
         {
             using var valueWriter = new StringWriter();
             // The "l" format specifier switches off quoting of strings, see https://github.com/serilog/serilog/wiki/Formatting-Output#formatting-plain-text
-            value.Render(valueWriter, value is ScalarValue scalarValue && scalarValue.Value is string ? "l" : null, _options.FormatProvider);
+            value.Render(valueWriter, value is ScalarValue { Value: string } ? "l" : null, _options.FormatProvider);
             return valueWriter.ToString();
         }
 
@@ -321,7 +321,7 @@ private void WritePropertyElement(XmlWriter writer, string name, LogEventPropert
         {
             WriteStartElement(writer, "data");
             writer.WriteAttributeString("name", name);
-            var isNullValue = value is ScalarValue scalarValue && scalarValue.Value == null;
+            var isNullValue = value is ScalarValue { Value: null };
             if (!isNullValue)
             {
                 writer.WriteAttributeString("value", RenderValue(value));

src/Serilog.Formatting.Log4Net.csproj

@@ -5,7 +5,7 @@
   </PropertyGroup>
 
   <PropertyGroup Label="Compiling">
-    <LangVersion>8.0</LangVersion>
+    <LangVersion>9.0</LangVersion>
     <Nullable>enable</Nullable>
     <AnalysisLevel>latest</AnalysisLevel>
     <AnalysisMode>AllEnabledByDefault</AnalysisMode>

tests/Log4NetTextFormatterTest.DomainAndUserNamePropertyStructureValue.approved.xml

@@ -0,0 +1,3 @@
+<log4net:event timestamp="2003-01-04T15:09:26.535+01:00" level="INFO" xmlns:log4net="http://logging.apache.org/log4net/schemas/log4net-events-1.2/">
+  <log4net:message><![CDATA[Hello from Serilog]]></log4net:message>
+</log4net:event>

tests/Log4NetTextFormatterTest.LoggerNameStructureValue.approved.xml

@@ -0,0 +1,3 @@
+<log4net:event timestamp="2003-01-04T15:09:26.535+01:00" level="INFO" xmlns:log4net="http://logging.apache.org/log4net/schemas/log4net-events-1.2/">
+  <log4net:message><![CDATA[Hello from Serilog]]></log4net:message>
+</log4net:event>

tests/Log4NetTextFormatterTest.MachineNamePropertyStructureValue.approved.xml

@@ -0,0 +1,3 @@
+<log4net:event timestamp="2003-01-04T15:09:26.535+01:00" level="INFO" xmlns:log4net="http://logging.apache.org/log4net/schemas/log4net-events-1.2/">
+  <log4net:message><![CDATA[Hello from Serilog]]></log4net:message>
+</log4net:event>

tests/Log4NetTextFormatterTest.cs

@@ -258,6 +258,21 @@ public void LoggerName()
             Approvals.VerifyWithExtension(output.ToString(), "xml");
         }
 
+        [Fact]
+        public void LoggerNameStructureValue()
+        {
+            // Arrange
+            using var output = new StringWriter();
+            var logEvent = CreateLogEvent(properties: new LogEventProperty(Constants.SourceContextPropertyName, new StructureValue(new List<LogEventProperty>())));
+            var formatter = new Log4NetTextFormatter();
+
+            // Act
+            formatter.Format(logEvent, output);
+
+            // Assert
+            Approvals.VerifyWithExtension(output.ToString(), "xml");
+        }
+
         [Fact]
         public void DefaultFormatProvider()
         {
@@ -503,6 +518,21 @@ public void DomainAndUserNameProperty(string? environmentUserName)
             Approvals.VerifyWithExtension(output.ToString(), "xml");
         }
 
+        [Fact]
+        public void DomainAndUserNamePropertyStructureValue()
+        {
+            // Arrange
+            using var output = new StringWriter();
+            var logEvent = CreateLogEvent(properties: new LogEventProperty(EnvironmentUserNameEnricher.EnvironmentUserNamePropertyName, new StructureValue(new List<LogEventProperty>())));
+            var formatter = new Log4NetTextFormatter();
+
+            // Act
+            formatter.Format(logEvent, output);
+
+            // Assert
+            Approvals.VerifyWithExtension(output.ToString(), "xml");
+        }
+
         [Theory]
         [InlineData(null)]
         [InlineData("TheMachineName")]
@@ -522,6 +552,21 @@ public void MachineNameProperty(string? machineName)
             Approvals.VerifyWithExtension(output.ToString(), "xml");
         }
 
+        [Fact]
+        public void MachineNamePropertyStructureValue()
+        {
+            // Arrange
+            using var output = new StringWriter();
+            var logEvent = CreateLogEvent(properties: new LogEventProperty(MachineNameEnricher.MachineNamePropertyName, new StructureValue(new List<LogEventProperty>())));
+            var formatter = new Log4NetTextFormatter();
+
+            // Act
+            formatter.Format(logEvent, output);
+
+            // Assert
+            Approvals.VerifyWithExtension(output.ToString(), "xml");
+        }
+
         [Fact]
         public void SequenceProperty()
         {