feat: Add Decorator pattern source generator

[Copilot]

Decorator Pattern Source Generator - PR Review Round 9 ✅

✅ All PR Review Comments Addressed (5/5)

1. DecoratorIgnoreAttribute Documentation (comment 2719557357)

• ✅ Updated XML summary to clarify behavior for interface vs abstract class contracts
• ✅ For abstract classes: emits sealed override
• ✅ For interfaces: emits non-virtual implementation
• ✅ More accurate description of actual generator behavior

2. Misleading Test Comment (comment 2719557371)

• ✅ Changed "sealed" to "non-virtual (i.e., not declared as virtual)"
• ✅ Clarifies that interface members marked with DecoratorIgnore are simply non-virtual, not sealed
• ✅ Prevents confusion for future maintainers

3. Unused Context Parameter in GenerateBaseDecorator (comment 2719557378)

• ✅ Renamed context parameter to _ to indicate intentionally unused
• ✅ Prevents IDE0060 warnings
• ✅ Reserved for potential future use (e.g., diagnostics during generation)

4. Unused Config Parameter in GenerateForwardingMethod (comment 2719557389)

• ✅ Renamed config parameter to _ to indicate intentionally unused
• ✅ Prevents IDE0060 warnings
• ✅ Reserved for potential future configuration options

5. Unused Config Parameter in GenerateForwardingProperty (comment 2719557397)

• ✅ Renamed config parameter to _ to indicate intentionally unused
• ✅ Prevents IDE0060 warnings
• ✅ Reserved for potential future configuration options

📊 Test Results

• 28/28 decorator tests passing (100%)
• 173/173 total tests passing (100%)
• Zero compilation errors
• No analyzer warnings (IDE0060)

🔧 Code Quality Improvements

• More accurate documentation reflecting actual behavior
• Clearer test comments
• Warning-free codebase (unused parameter warnings suppressed with _ naming)
• All unused parameters properly marked as intentionally unused for future extensibility

All feedback addressed with zero test failures and clean compilation!

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Generator: Create Decorator Pattern</issue_title>
<issue_description>## Summary

Add a source generator that produces boilerplate-free, GoF-consistent Decorator pattern implementations for interfaces and abstract classes.

The generator lives in PatternKit.Generators and emits self-contained, readable C# with no runtime PatternKit dependency.

Primary goals:

• Generate typed decorators without reflection.
• Make ordering explicit and deterministic.
• Support both “wrapper class” style and “pipeline” (next) style.
• Support sync + async members (favor ValueTask for generated hooks).

---

Motivation / Problem

Decorator chains are frequently hand-written and drift:

• missing forwarding members
• inconsistent ordering semantics
• repeated logging/timing/retry boilerplate
• async gets messy quickly

Source generation can emit correct forwarding + consistent hooks once.

---

Supported Targets (must-have)

Decorator generation must support:

• interface
• abstract class (virtual/abstract members only)

Decorator generation is opt-in via attribute on the contract.

---

Proposed User Experience

A) Generate base decorator + optional pipeline builder

[GenerateDecorator]
public partial interface IStorage
{
    Stream OpenRead(string path);
    ValueTask<Stream> OpenReadAsync(string path, CancellationToken ct = default);
}

Generated (representative shape):

public abstract partial class StorageDecoratorBase : IStorage
{
    protected StorageDecoratorBase(IStorage inner);

    protected IStorage Inner { get; }

    public virtual Stream OpenRead(string path) => Inner.OpenRead(path);
    public virtual ValueTask<Stream> OpenReadAsync(string path, CancellationToken ct = default)
        => Inner.OpenReadAsync(path, ct);
}

public static partial class StorageDecorators
{
    public static IStorage Compose(IStorage inner, params Func<IStorage, IStorage>[] decorators);
}

B) Typed decorators written by users

public sealed class CachingStorage : StorageDecoratorBase
{
    public CachingStorage(IStorage inner) : base(inner) { }

    public override Stream OpenRead(string path) { /* cache */ }
}

The generator ensures the base class always stays in sync with the contract.

---

Attributes / Surface Area

Namespace: PatternKit.Generators.Decorator

• [GenerateDecorator] on contract type

  • string? BaseTypeName (default: <ContractName>DecoratorBase)
  • string? HelpersTypeName (default: <ContractName>Decorators)
  • DecoratorCompositionMode Composition (default: HelpersOnly)
  • bool GenerateAsync (default: inferred)
  • bool ForceAsync (default: false)

Optional:

• [DecoratorIgnore] for members to exclude.

Enums:

• DecoratorCompositionMode: None, HelpersOnly, PipelineNextStyle (v2)

---

Semantics (must-have)

Forwarding correctness

• Base decorator forwards all included members to Inner.
• For abstract class contracts, only virtual/abstract members are forwarded.

Composition helper ordering

If helper Compose is generated:

• decorators applied in array order.

• ordering must be documented:

  • decorators[0] is outermost by default.

Async

• Base decorator preserves exact signature from contract.
• No signature rewriting.

---

Diagnostics (must-have)

• PKDEC001 Type marked [GenerateDecorator] must be partial.
• PKDEC002 Unsupported member kind (e.g., event) for v1.
• PKDEC003 Name conflict for generated base/helper types.
• PKDEC004 Member not accessible for generation.

---

Generated Code Layout

• ContractName.Decorator.g.cs

Determinism:

• stable emission order by fully-qualified member name.

---

Testing Expectations

• Base decorator forwards calls correctly.
• Composition helper wraps in deterministic order.
• Async forwarding works.
• Diagnostics: unsupported members, naming conflicts.

---

Acceptance Criteria

• [GenerateDecorator] works for interfaces and abstract classes.
• Generated base decorator forwards all members correctly.
• Optional composition helpers generated with deterministic ordering.
• Async members supported without signature rewriting.
• Diagnostics and tests included.
  </issue_description>

<agent_instructions>Ensure complete BDD code coverage, comprehensive realworld usage examples and demos, user guides, and congruence with our existing implementations.</agent_instructions>

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

• Fixes Generator: Create Decorator Pattern #36

---

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[github-actions]

⚠️ Deprecation Warning: The deny-licenses option is deprecated for possible removal in the next major release. For more information, see issue 997.

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[github-actions]

Test Results

173 tests   173 ✅  1m 27s ⏱️
  1 suites    0 💤
  1 files      0 ❌

Results for commit ed8fac9.

♻️ This comment has been updated with latest results.

[github-actions]

🔍 PR Validation Results

Version: ``

✅ Validation Steps

• Build solution
• Run tests
• Build documentation
• Dry-run NuGet packaging

📊 Artifacts

Dry-run artifacts have been uploaded and will be available for 7 days.

---

This comment was automatically generated by the PR validation workflow.

[codecov]

Codecov Report

❌ Patch coverage is 72.34679% with 185 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.19%. Comparing base (c658faa) to head (ed8fac9).

Files with missing lines	Patch %	Lines
...Kit.Examples/Decorators/StorageDecoratorExample.cs	0.00%	91 Missing ⚠️
src/PatternKit.Generators/DecoratorGenerator.cs	84.46%	55 Missing and 34 partials ⚠️
...stractions/Decorator/GenerateDecoratorAttribute.cs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #91      +/-   ##
==========================================
- Coverage   85.83%   85.19%   -0.65%     
==========================================
  Files         143      146       +3     
  Lines       12288    12957     +669     
  Branches     1641     1749     +108     
==========================================
+ Hits        10548    11039     +491     
- Misses       1329     1480     +151     
- Partials      411      438      +27     

Flag	Coverage Δ
unittests	85.19% <72.34%> (-0.65%)	⬇️

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[Copilot]

Pull request overview

Adds a new Decorator-pattern source generator to produce base decorator implementations (plus optional composition helpers) for interfaces and abstract classes, backed by new attributes, tests, and an example.

Changes:

• Introduces [GenerateDecorator], [DecoratorIgnore], and DecoratorCompositionMode in the abstractions package.
• Adds DecoratorGenerator to emit forwarding base decorator types and (optionally) a Compose helper.
• Adds a new test suite and an examples/demo file showcasing generated decorators.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 17 comments.

Show a summary per file

File	Description
src/PatternKit.Generators/DecoratorGenerator.cs	Implements the incremental source generator and code emission for decorators/helpers.
src/PatternKit.Generators.Abstractions/Decorator/GenerateDecoratorAttribute.cs	Adds public generator surface area (attribute + enum) to configure decorator generation.
src/PatternKit.Generators.Abstractions/Decorator/DecoratorIgnoreAttribute.cs	Adds attribute for per-member generation behavior control.
src/PatternKit.Generators/AnalyzerReleases.Unshipped.md	Registers new diagnostic IDs for the decorator generator.
test/PatternKit.Generators.Tests/DecoratorGeneratorTests.cs	Adds compilation-based tests for generated output.
src/PatternKit.Examples/Decorators/StorageDecoratorExample.cs	Adds a real-world example demonstrating decorator chaining and usage.

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[JerrettDavis]

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[JerrettDavis]

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[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

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Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

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Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

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