Add Composer pattern source generator #103
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Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
…nc support Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
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[WIP] Add source generator for Composer pattern implementation
Add Composer pattern source generator
Jan 30, 2026
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Dependency Review✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.Scanned FilesNone |
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Test Results292 tests 292 ✅ 1m 19s ⏱️ Results for commit 2c64338. ♻️ This comment has been updated with latest results. |
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🔍 PR Validation ResultsVersion: `` ✅ Validation Steps
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Codecov Report❌ Patch coverage is Additional details and impacted files@@ Coverage Diff @@
## main #103 +/- ##
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+ Coverage 82.67% 87.37% +4.70%
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Files 166 169 +3
Lines 15767 16150 +383
Branches 2199 2273 +74
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+ Hits 13035 14111 +1076
+ Misses 2155 2039 -116
+ Partials 577 0 -577
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Pull request overview
This PR adds a comprehensive source generator for the Composer pattern, enabling deterministic composition of ordered pipeline components (middleware, handlers, policies) into executable pipelines. The generator supports both synchronous and asynchronous execution with compile-time validation.
Changes:
- Adds
ComposerGeneratorwith incremental generation usingForAttributeWithMetadataNamefor efficient compilation - Implements 9 diagnostics (PKCOM001-009) covering partial validation, ordering, signatures, and async mismatches
- Provides attributes for pipeline configuration:
[Composer],[ComposeStep],[ComposeTerminal],[ComposeIgnore] - Generates both sync (
Invoke) and async (InvokeAsync) methods withValueTask<T>support - Supports class, struct, record class, and record struct as pipeline hosts
- Handles struct pipelines specially to avoid lambda capture issues
Reviewed changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated 13 comments.
Show a summary per file
| File | Description |
|---|---|
| src/PatternKit.Generators/ComposerGenerator.cs | Main generator implementation with validation, diagnostics, and code generation for sync/async pipelines |
| src/PatternKit.Generators.Abstractions/Composer/ComposerAttribute.cs | Pipeline host attribute with configuration options for method names, async generation, and wrap order |
| src/PatternKit.Generators.Abstractions/Composer/ComposeStepAttribute.cs | Step marking attribute with order and optional name properties |
| src/PatternKit.Generators.Abstractions/Composer/ComposeTerminalAttribute.cs | Terminal step marker requiring exactly one per pipeline |
| src/PatternKit.Generators.Abstractions/Composer/ComposeIgnoreAttribute.cs | Exclusion marker for methods that should not be composed |
| test/PatternKit.Generators.Tests/ComposerGeneratorTests.cs | Comprehensive test suite covering basic scenarios, diagnostics, type variants, and configuration options |
| test/PatternKit.Generators.Tests/packages.lock.json | Updated lock file with transitive dependency System.Reflection.Metadata from test infrastructure |
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…generation logic Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
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Pull request overview
Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.
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Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
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Pull request overview
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Minor Cleanup from PR Review
Changes
Removed unused import (line 5)
System.Collections.Immutableimport that was not used anywhere in the fileFixed misleading test name (line 775)
TrulyMixedSyncAndAsync_GeneratesBothtoTrulyMixedSyncAndAsync_GeneratesAsyncOnlynameof()reference to match new test nameTest Results
Original prompt
This section details on the original issue you should resolve
<issue_title>Generator: Create Composer Pattern</issue_title>
<issue_description># Generator: Create Composer Pattern
Summary
Add a source generator that produces a boilerplate-free Composer pattern implementation: a deterministic way to compose ordered components (steps, middleware, handlers, policies) into a single executable pipeline.
This is not a classic GoF pattern, but it’s an extremely common architectural pattern in modern .NET systems (middleware pipelines, validation pipelines, retry stacks, message processing chains, etc.). The goal is to provide a canonical, strongly-typed composition primitive that other PatternKit generators can reuse.
The generator lives in
PatternKit.Generatorsand emits self-contained C# with no runtime PatternKit dependency.Primary goals:
Compose) and an executor (Invoke).ValueTask).Motivation / Problem
Teams repeatedly re-implement composition:
next-style)Hand-rolled composition leads to:
A generator can:
Supported Targets (must-have)
The generator must support:
partial classpartial structpartial record classpartial record structThe annotated type represents a pipeline host that declares:
Proposed User Experience
A) Request → Response middleware composition
Generated (representative shape):
B) Void pipeline (actions)
V1 can restrict to pipelines with an explicit input type; void pipelines can be v2 if you prefer.
Attributes / Surface Area
Namespace:
PatternKit.Generators.ComposerCore
[Composer]on the pipeline hoststring InvokeMethodName = "Invoke"string InvokeAsyncMethodName = "InvokeAsync"bool GenerateAsync(default: inferred)bool ForceAsync(default: false)ComposerWrapOrder WrapOrder(default: OuterFirst)[ComposeStep]on component methodsint Orderstring? Name[ComposeTerminal]on terminal methodEnums:
ComposerWrapOrder:OuterFirst|InnerFirstOptional:
[ComposeIgnore](exclude method)Semantics (must-have)
Ordering
Order.Wrapping
next.Order=0is outermost (documented).Signatures
Pipeline step signature must match one of:
TOut Step(in TIn input, Func<TIn, TOut> next)ValueTask<TOut> StepAsync(TIn input, Func<TIn, ValueTask<TOut>> next, CancellationToken ct = default)Terminal signature must match:
TOut Terminal(in TIn input)ValueTask<TOut> TerminalAsync(TIn input, CancellationToken ct = default)Rules:
ForceAsync=true.Allocation expectations
Invokeshould not allocate per call in sync mode.Diagnostics (must-have)
Stable IDs, actionable:
PKCOM001Type marked[Composer]must bepartial.PKCOM002No[ComposeStep]methods f...💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.