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

1. 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

1. 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); } ``

1. 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

1. Replace inline logging calls with extension method calls

- Before: logger.LogWarning("Validation failed for {entityType}: {errors}", type, errs) - After: logger.ValidationFailed(type, errs)

1. Verify with build

``bash dotnet build ``

1. If build fails, review errors:

- Missing using statements for the extension class namespace - Parameter type mismatches - Duplicate EventIds

1. 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);