Update AG0041LogTemplateAnalyzer.cs (#193)

* Update AG0041LogTemplateAnalyzer.cs

* Create AG0041.md

Author: joeldickson

doc/AG0041.md

@@ -0,0 +1,68 @@
+# AG0041: Use message templates in logging
+
+Structured logging should be employed instead of string interpolation or concatenation.
+
+## Why is this an issue?
+
+Logging is a critical aspect of any application, providing insights into its behavior and facilitating debugging.
+However, not all logging approaches are created equal. Using string interpolation or concatenation for log messages is
+a common pitfall that can lead to performance issues and hinder log analysis.
+
+Consider the following problematic code:
+
+```csharp
+logger.Information($"User {userId} logged in at {DateTime.Now}");  // Noncompliant
+logger.Information("Error occurred: " + errorMessage);  // Noncompliant
+```
+
+Instead, you should use message templates:
+
+```csharp
+logger.Information("User {UserId} logged in at {LoginTime}", userId, DateTime.Now);  // Compliant
+logger.Information("Error occurred: {ErrorMessage}", errorMessage);  // Compliant
+```
+
+## Benefits of using message templates
+
+The use of message templates in logging offers several significant advantages over traditional string interpolation or 
+concatenation methods. Firstly, message templates can provide a notable performance boost, particularly in scenarios where 
+log messages aren't actually written due to log level settings. This efficiency is crucial in high-volume logging environments 
+where every millisecond counts.
+
+Structured logging, enabled by message templates, is another key benefit. It allows variables to be captured as separate entities 
+rather than being merged into a single string. This separation enables powerful log analysis capabilities, making it easier to search, 
+filter, and aggregate log data based on specific parameters. The ability to maintain consistent log formats across an application 
+is also greatly enhanced with message templates, leading to more uniform and easily interpretable logs.
+
+Message templates also facilitate semantic logging, allowing developers to attach additional metadata to log events. This extra 
+context can be invaluable when debugging complex issues or analyzing application behavior. Furthermore, modern logging frameworks such 
+as Serilog and Microsoft.Extensions.Logging are optimized for template-style logging. By using message templates, developers can 
+take full advantage of these frameworks' features and performance optimizations, ensuring their logging strategy is future-proof 
+and aligned with industry best practices.
+
+## More Info
+
+This analyzer checks for the use of string interpolation (`$"..."`) or string concatenation in logging method calls. It specifically targets methods of `ILogger` from both `Microsoft.Extensions.Logging` and `Serilog`.
+
+### Noncompliant Code Examples
+
+```csharp
+_logger.LogInformation($"Processing order {orderId}");
+_logger.LogError("Error: " + exception.Message);
+```
+
+### Compliant Solution
+
+```csharp
+_logger.LogInformation("Processing order {OrderId}", orderId);
+_logger.LogError("Error: {ErrorMessage}", exception.Message);
+```
+
+### Exceptions
+
+This rule doesn't apply to non-logging methods or to logging methods that explicitly expect formatted strings.
+
+## Resources
+
+* [Structured logging with ILogger in .NET](https://docs.microsoft.com/en-us/aspnet/core/fundamentals/logging/?view=aspnetcore-5.0#log-message-template)
+* [Serilog message templates](https://github.com/serilog/serilog/wiki/Writing-Log-Events#message-templates)

src/Agoda.Analyzers/AgodaCustom/AG0041LogTemplateAnalyzer.cs

@@ -22,7 +22,7 @@ public class AG0041LogTemplateAnalyzer : DiagnosticAnalyzer
             Category, 
             DiagnosticSeverity.Warning, 
             isEnabledByDefault: true, 
-            helpLinkUri: "https://github.com/agoda-com/AgodaAnalyzers/issues/183");
+            helpLinkUri: "https://github.com/agoda-com/AgodaAnalyzers/blob/master/doc/AG0041.md");
 
         public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(Rule);
 
@@ -87,4 +87,4 @@ private static bool ContainsStringConcatenation(ExpressionSyntax expression)
                              bes.Right.IsKind(SyntaxKind.StringLiteralExpression)));
         }
     }
-}
+}