Modernize high-performance logging docs to prioritize source-generated logging

[Copilot]

Documentation focused on LoggerMessage.Define() from .NET Core 3.x era. Modern .NET 6+ applications should use LoggerMessageAttribute with compile-time source generation for better performance and developer experience.

Changes

Restructured content hierarchy:

• Source-generated logging (LoggerMessageAttribute) now primary approach
• Legacy LoggerMessage.Define() moved to dedicated section for .NET Framework/Core 3.1 users
• Added benefits summary with concrete performance advantages (compile-time parsing, zero boxing, unlimited parameters)

Updated all examples:

Before (legacy):

public static class LoggerExtensions
{
    private static readonly Action<ILogger, WorkItem, Exception> s_processingPriorityItem;
    
    static LoggerExtensions()
    {
        s_processingPriorityItem = LoggerMessage.Define<WorkItem>(
            LogLevel.Information,
            new EventId(1, nameof(PriorityItemProcessed)),
            "Processing priority item: {Item}");
    }
    
    public static void PriorityItemProcessed(this ILogger logger, WorkItem workItem) =>
        s_processingPriorityItem(logger, workItem, default!);
}

After (modern):

public static partial class Log
{
    [LoggerMessage(
        EventId = 1,
        Level = LogLevel.Information,
        Message = "Processing priority item: {Item}")]
    public static partial void PriorityItemProcessed(
        ILogger logger, WorkItem item);
}

Cross-references:

• Added links to compile-time logging source generation documentation
• Scope examples use BeginScope with source-generated methods
• Legacy section explains migration path and limitations (6 parameter limit, no dynamic log level)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>update LoggerMessage.Define() to be source generated logging</issue_title>
<issue_description>### Type of issue

Outdated article

Description

Most of the content on that high perf logging page talks about LoggerMessage.Define() which may have been state of the art around .NET Core 3 but as soon as source generated logging came out. Please update this documentation to reflect the above.

Page URL

https://learn.microsoft.com/en-us/dotnet/core/extensions/high-performance-logging#define-a-logger-message

Content source URL

https://github.com/dotnet/docs/blob/main/docs/core/extensions/high-performance-logging.md

Document Version Independent Id

3f5f1b6e-06ac-cc07-48cd-b8b957a4abbb

Article author

@IEvangelist

Metadata

• ID: aa00c051-c047-bbcd-5e25-ca6a722b51c3
• Service: dotnet-fundamentals</issue_description>

Comments on the Issue (you are @copilot in this section)

@tarekgh We may need to copy the summary from the page https://learn.microsoft.com/en-us/dotnet/core/extensions/logger-message-generator#summary and refer to the page too.

• Fixes update LoggerMessage.Define() to be source generated logging #40870

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.