Metalama Documentation Skill

This skill contains the complete Metalama documentation including conceptual guides, API reference, and sample code.

This skill pertains to Metalama 2026.0.

Directory Structure

Directory	Contents
content/conceptual/	Conceptual documentation (aspects, templates, fabrics, validation, etc.)
content/patterns/	Pattern libraries (contracts, caching, observability, memoization, DI)
content/api/	API documentation overview pages
code/	Sample code (.cs = source, .t.cs = transformed output, .Aspect.cs = aspect implementation)
api/	API reference YML files from DocFx

Finding Information

1. Search the index: Use grep with -B3 to search index.yml for keywords (each entry has: name, path, summary, keywords - so -B3 captures the path):

   grep -i -B3 "caching" index.yml
   grep -i -B3 "BuildAspect" index.yml
   

2. Browse by topic: Navigate the content/ directory structure.
3. API lookup: Use grep on api/.manifest to find API YML files by type or member name:

   grep -i "OverrideMethodAspect" api/.manifest
   

Key Entry Points

Topic	File	Description
Getting Started	content/conceptual/using/using-metalama.md	How to use Metalama in your projects
Creating Aspects	content/conceptual/aspects/aspects.md	Overview of aspect creation
Overriding Methods	content/conceptual/aspects/simple-aspects/overriding-methods.md	Basic method interception
Templates	content/conceptual/aspects/templates/templates.md	T# template syntax and patterns
Fabrics	content/conceptual/using/fabrics/fabrics.md	Bulk aspect application
Contracts	content/patterns/contracts/contract-patterns.md	Parameter/property validation
Caching	content/patterns/caching/caching.md	Method result caching
Observability	content/patterns/observability/observability.md	INotifyPropertyChanged implementation
Debugging Aspects	content/conceptual/aspects/testing/debugging-aspects.md	Debug compile-time code, breakpoints, meta.DebugBreak()
Debugging User Code	content/conceptual/using/debugging-aspect-oriented-code.md	Debug run-time transformed code, LamaDebug configuration

Common Patterns

Base Classes

Base Class	Target	Key Override	Use When
OverrideMethodAspect	Methods	OverrideMethod()	Wrap/intercept methods
OverrideFieldOrPropertyAspect	Fields/Properties	OverrideProperty	Wrap property access
ContractAspect	Parameters/Fields/Properties	Validate(dynamic? value)	Validate values
TypeAspect	Types	BuildAspect()	Introduce members, implement interfaces
MethodAspect	Methods	BuildAspect()	Programmatic method transformation
TypeFabric	Single type	AmendType()	Bulk changes to one type
ProjectFabric	Project	AmendProject()	Apply aspects across project

Template Fundamentals

[!IMPORTANT] T# templates look like C# but have different semantics. Code that works in normal C# may not work identically in a template. Always read the full template documentation at content/conceptual/aspects/templates/ before writing template code.

public override dynamic? OverrideMethod()
{
    // Pre-logic
    try
    {
        return meta.Proceed();  // Calls original method
    }
    finally
    {
        // Post-logic (always runs)
    }
}

• dynamic? handles any return type (void returns null)
• meta.Proceed() auto-transforms to await for async targets
• Use meta.Target.* to access compile-time information about the target declaration
• To debug templates, use meta.DebugBreak() (not Debugger.Break())

Debugging Quick Reference

Debugging compile-time code (aspects, fabrics, templates):

1. Add Debugger.Break() in BuildAspect/fabrics, or meta.DebugBreak() in templates
2. Build with: dotnet build -p:MetalamaDebugCompiler=True -p:MetalamaConcurrentBuildEnabled=False
3. Attach debugger when prompted, then set breakpoints in transformed code (obj/.../metalama/)

Debugging run-time code (transformed output):

1. Create a LamaDebug build configuration in Visual Studio
2. Use F11 to step into code, or add Debugger.Break()
3. Set breakpoints in transformed files under obj/<Config>/<TFM>/metalama/

Common Pitfalls

Mistake	Correct Approach
Using Debugger.Break() in templates	Use meta.DebugBreak() in templates; Debugger.Break() only works in BuildAspect and fabrics
Setting breakpoints in source files	Breakpoints don't work in Metalama-transformed projects; use Debugger.Break()/meta.DebugBreak() then set breakpoints in transformed code
Using nameof() for introduced members	Use string literals; nameof() resolves at aspect compile-time, not target compile-time
Filtering all types by namespace in fabrics	Use GlobalNamespace.GetDescendant("Ns") or a NamespaceFabric instead of SelectTypes().Where(t => t.Namespace...)
Forgetting partial on target classes	Classes receiving introduced members need the partial modifier

Sample Code Conventions

• Name.cs - Target code receiving the aspect
• Name.Aspect.cs - Aspect implementation
• Name.t.cs - Transformed output (what the compiler generates)
• Name.Dependency.cs - Referenced project code for multi-project examples

Metalama Markdown Directives

The documentation uses custom [!metalama-*] directives to include code samples. These are processed at build time to generate HTML, but in the skill files you see the raw directives.

Reading Directive References

When you see a directive in a Markdown file, extract the file path and read the referenced file directly.

Directive	Purpose	Example
[!metalama-file PATH]	Shows a single source file	[!metalama-file ~/code/Project/File.cs]
[!metalama-test PATH]	Shows test with input/output	[!metalama-test ~/code/Project/Test.cs]
[!metalama-compare PATH]	Shows side-by-side diff	[!metalama-compare ~/code/Project/File.cs]
[!metalama-vimeo ID]	Embeds Vimeo video	[!metalama-vimeo 842168905]

Path Resolution

• ~/ resolves to the SKILLS.md directory
• Example: ~/code/Metalama.Documentation.SampleCode.AspectFramework/GettingStarted/GettingStarted.cs → Read code/Metalama.Documentation.SampleCode.AspectFramework/GettingStarted/GettingStarted.cs

How to Read Referenced Code

When you encounter a directive like [!metalama-file ~/code/Project/File.cs]:

1. Read the main file: code/Project/File.cs
2. Check for related files (same name, different suffix):
   • File.Aspect.cs - Aspect implementation
   • File.t.cs - Transformed output
   • File.Fabric.cs - Fabric code

Markers: If you see marker="NAME", look for code between // [<snippet NAME>] and // [<endsnippet NAME>] in the file.

API Reference

The api/ directory contains DocFx-generated YML files for all public APIs.

Finding API Documentation

Use api/.manifest - a JSON index mapping all UIDs (types, members, overloads) to their YML files.

1. Search the manifest for the type or member name:

   "Metalama.Framework.Aspects.OverrideMethodAspect": "Metalama.Framework.Aspects.OverrideMethodAspect.yml"
   "Metalama.Framework.Aspects.OverrideMethodAspect.OverrideMethod": "Metalama.Framework.Aspects.OverrideMethodAspect.yml"
   "Metalama.Framework.Code.IMethod": "Metalama.Framework.Code.IMethod.yml"
   

2. Read the corresponding YML file to get full documentation.

3. Naming conventions:

   • Types: Namespace.TypeName.yml
   • Generic types: backtick becomes dash, e.g., IAspectBuilder<T> → Metalama.Framework.Aspects.IAspectBuilder-1.yml
   • All members of a type are in the same YML file as the type

YML File Structure

Each type's YML file contains all members of that type in a single file:

items:
- uid: Namespace.TypeName           # Type definition
  commentId: T:Namespace.TypeName
  type: Class|Interface|Enum|...
  summary: Type description
  remarks: Detailed explanation
  syntax:
    content: public class TypeName : BaseClass
  children:                         # List of member UIDs
  - Namespace.TypeName.Method1
  - Namespace.TypeName.Property1

- uid: Namespace.TypeName.Method1   # Member definition
  commentId: M:Namespace.TypeName.Method1
  type: Method|Property|Field|...
  summary: Member description
  syntax:
    content: public void Method1()
  parameters: [...]                 # For methods
  return: { type: ..., description: ... }

Key Namespaces

Namespace	Purpose
Metalama.Framework.Aspects	Aspect base classes, attributes, meta API
Metalama.Framework.Code	Code model interfaces (IMethod, IType, IParameter, etc.)
Metalama.Framework.Advising	Advice APIs for introducing members, implementing interfaces
Metalama.Framework.Eligibility	Eligibility builders for aspect targeting
Metalama.Framework.Diagnostics	Reporting warnings and errors
Metalama.Framework.Fabrics	Fabric base classes
Metalama.Patterns.Contracts	Contract validation aspects
Metalama.Patterns.Caching	Caching aspects and configuration
Metalama.Patterns.Observability	INotifyPropertyChanged implementation
Metalama.Extensions.DependencyInjection	Dependency injection
Metalama.Extensions.Architecture	Architecture enforcement/validation

Linking to Documentation

When referencing documentation articles, provide links to the live documentation at https://doc.metalama.net.

URL format: https://doc.metalama.net/<path> where <path> is derived from the file path under content/:

• Remove content/ prefix
• Remove .md suffix
• For index files where the filename matches the parent folder (e.g., path/leaf/leaf.md), use just path/leaf

Examples:

File Path	URL
content/conceptual/aspects/aspects.md	https://doc.metalama.net/conceptual/aspects
content/conceptual/aspects/templates/templates.md	https://doc.metalama.net/conceptual/aspects/templates
content/patterns/caching/caching.md	https://doc.metalama.net/patterns/caching
content/conceptual/aspects/simple-aspects/overriding-methods.md	https://doc.metalama.net/conceptual/aspects/simple-aspects/overriding-methods

External Resources

• Live documentation: https://doc.metalama.net
• Source repository: https://github.com/metalama/Metalama
• Samples repository: https://github.com/metalama/Metalama.Samples