dotnet-source-gen-logging

Convert existing logging calls to use the LoggerMessage source generator for high-performance, AOT-compatible logging with no boxing overhead and compile-time template parsing.

When to Use

• •Optimizing logging performance in hot paths
• •Preparing for Native AOT deployment
• •Organizing scattered log messages into logical groupings
• •Standardizing EventIds across the codebase

Steps

1. •

   Find ILogger usages and logging calls

   • •Search for ILogger field/parameter declarations
   • •Find all logging calls: LogInformation, LogWarning, LogError, LogDebug, LogTrace, LogCritical
   • •Note the log message templates and parameters
2. •

   Organize into logical groupings by domain

   • •Group related log messages by their functional area, eg:
     • •LoggingValidationExtensions - validation-related logs
     • •LoggingAuthenticationExtensions - auth-related logs
     • •LoggingDatabaseExtensions - database-related logs
     • •LoggingHttpExtensions - HTTP-related logs
     • •LoggingCacheExtensions - caching-related logs
     • •LoggingMessagingExtensions - messaging/queue-related logs
3. •

   Create partial static classes with extension methods

   csharp

   public static partial class LoggingValidationExtensions
   {
       [LoggerMessage(
           EventId = 1001,
           Level = LogLevel.Warning,
           Message = "Validation failed for {EntityType}: {Errors}")]
       public static partial void ValidationFailed(
           this ILogger logger, string entityType, string errors);
   }
   

4. •

   Use EventId ranges per category

   • •1000-1999: Validation
   • •2000-2999: Authentication
   • •3000-3999: Database
   • •4000-4999: HTTP
   • •5000-5999: Cache
   • •6000-6999: Messaging
   • •7000-7999: General/Application
5. •

   Replace inline logging calls with extension method calls

   • •Before: _logger.LogWarning("Validation failed for {entityType}: {errors}", type, errs)
   • •After: _logger.ValidationFailed(type, errs)
6. •

   Verify with build

   bash

   dotnet build
   

7. •

   If build fails, review errors:

   • •Missing using statements for the extension class namespace
   • •Parameter type mismatches
   • •Duplicate EventIds
8. •

   Report results:

   • •List all created extension classes
   • •Show count of converted log messages per category
   • •Confirm build status

Key Notes

• •Requires .NET 6+ - the source generator is built into the SDK
• •Avoids boxing - value types are not boxed when passed to the generated methods
• •Template parsed once - message template is parsed at compile time, not runtime
• •Use PascalCase for placeholders - {EntityType} not {entityType} (matching is case-insensitive, but PascalCase is the recommended convention)
• •Extension methods - allows fluent logger.MethodName() syntax
• •Partial classes - required for source generator to emit the implementation

Example Conversion

Before:

_logger.LogInformation("User {UserId} logged in from {IpAddress}", userId, ip);
_logger.LogWarning("Failed login attempt for {Username}", username);

After:

// In LoggingAuthenticationExtensions.cs
public static partial class LoggingAuthenticationExtensions
{
    [LoggerMessage(
        EventId = 2001,
        Level = LogLevel.Information,
        Message = "User {UserId} logged in from {IpAddress}")]
    public static partial void UserLoggedIn(
        this ILogger logger, string userId, string ipAddress);

    [LoggerMessage(
        EventId = 2002,
        Level = LogLevel.Warning,
        Message = "Failed login attempt for {Username}")]
    public static partial void FailedLoginAttempt(
        this ILogger logger, string username);
}

// Usage
_logger.UserLoggedIn(userId, ip);
_logger.FailedLoginAttempt(username);