Add decorator registration support with compile-time validation

[pwelter34]

Summary

This PR adds comprehensive decorator registration support to Injectio, allowing services to be wrapped with decorators without runtime dependencies. The implementation includes a new RegisterDecorator attribute, compile-time diagnostics for decorator validation, and code generation for decorator application.

Key Changes

• New RegisterDecorator Attribute: Added RegisterDecoratorAttribute to mark classes as decorators for existing services, supporting:

  • Generic and non-generic service type specification
  • Keyed service decoration (with specific keys or AnyKey)
  • Custom factory methods for decorator instantiation
  • Decorator ordering via Order property
  • Tag-based filtering
  • Open generic service decoration

• Compile-Time Validation: Extended ServiceRegistrationAnalyzer with decorator-specific diagnostics:

  • INJ0010: Decorator does not implement service type
  • INJ0011: Missing service type specification
  • INJ0012: Missing inner service constructor parameter
  • INJ0013: Factory method not found
  • INJ0014: Factory method has invalid signature
  • INJ0015: Open-generic + keyed combination (unsupported)
  • INJ0016: Decorated service not registered (when no dynamic modules present)

• Code Generation:

  • Extended ServiceRegistrationWriter to generate decorator registration calls
  • Added GenerateDecorationHelper() to emit decoration extension methods (Decorate<T>, DecorateKeyed<T>, DecorateOpenGeneric)
  • Decorators are applied in order and inherit the lifetime of the decorated service
  • Support for both automatic instantiation via ActivatorUtilities and custom factory methods

• Analyzer Enhancement: Implemented AnalyzeCompilation to perform cross-symbol analysis:

  • Collects all decorator registrations and registered service types
  • Validates decorator constraints at compilation end
  • Detects unregistered service targets (when no dynamic modules exist)

• Test Coverage: Added comprehensive test suite (ServiceRegistrationDecoratorTests) with:

  • Simple decorator registration
  • Generic attribute syntax
  • Chained decorators with ordering
  • Keyed service decoration
  • AnyKey decoration
  • Custom factory methods
  • Open generic decorators
  • Tag-based filtering
  • All diagnostic scenarios

Notable Implementation Details

• Decorators use a thread-safe collection pattern with locks during compilation analysis
• The decoration helper is only emitted when decorators are present
• Decorator ordering is deterministic (by service type, order value, then decorator type name)
• Open generic + keyed combination is explicitly rejected as unsupported
• Unregistered service detection only applies when no service modules could dynamically register services

https://claude.ai/code/session_01DFMTsCCwsWoYM7vWumE6mw

[coveralls]

Coverage Report for CI Build 25031366509

Warning

Build has drifted: This PR's base is out of sync with its target branch, so coverage data may include unrelated changes.
Quick fix: rebase this PR. Learn more →

Coverage increased (+2.7%) to 89.254%

Details

• Coverage increased (+2.7%) from the base build.
• Patch coverage: 46 uncovered changes across 4 files (675 of 721 lines covered, 93.62%).
• 3 coverage regressions across 2 files.

Uncovered Changes

File	Changed	Covered	%
src/Injectio.Generators/ServiceRegistrationAnalyzer.cs	277	251	90.61%
src/Injectio.Generators/ServiceRegistrationGenerator.cs	253	239	94.47%
src/Injectio.Generators/ServiceRegistrationWriter.cs	106	101	95.28%
src/Injectio.Generators/Infrastructure/CollectionBuilderAttribute.cs	1	0	0.0%

Coverage Regressions

3 previously-covered lines in 2 files lost coverage.

File	Lines Losing Coverage	Coverage
src/Injectio.Generators/SymbolHelpers.cs	2	88.32%
src/Injectio.Generators/ServiceRegistrationGenerator.cs	1	88.8%

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Coverage Stats

Relevant Lines:	1501
Covered Lines:	1407
Line Coverage:	93.74%
Relevant Branches:	872
Covered Branches:	711
Branch Coverage:	81.54%
Branches in Coverage %:	Yes
Coverage Strength:	75.36 hits per line

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💛 - Coveralls