feat: Extend Visitor generator to support interface and struct hierarchies #90
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- Support interface-based hierarchies (e.g., IShape) - Support struct types that implement visitor interfaces - Intelligent visitor interface naming (IShape -> IShapeVisitor, not IIShapeVisitor) - Enhanced type discovery to find classes, structs, records, and interfaces - Add comprehensive tests for interface and struct hierarchies Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
- Add PKVIS001: Warning for no concrete types found - Add PKVIS002: Error for non-partial base types - Add PKVIS003: Warning for inaccessible types - Add PKVIS004: Error for non-partial derived types - Update AnalyzerReleases.Unshipped.md with new diagnostic IDs - Add IsPartial helper method for checking partial keyword Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
- Add comprehensive section on supported hierarchy types - Document interface-based hierarchies with examples - Document struct-based hierarchies for allocation-free patterns - Document record types support - Add Diagnostics section with all PKVIS001-004 errors - Update overview to mention support for all type kinds Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
- Add test for PKVIS001 (no concrete types found) - Add test for PKVIS002 (base type not partial) - Add test for PKVIS004 (derived type not partial) - Add test for valid hierarchy with no diagnostics - All 34 visitor generator tests passing Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
- Add using statement for Microsoft.CodeAnalysis.CSharp - Extract interface naming logic into GetDefaultVisitorInterfaceName method - Improve code maintainability and testability - All tests passing, CodeQL clean Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
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[WIP] Add source generator for Visitor pattern implementation
feat: Extend Visitor generator to support interface and struct hierarchies
Jan 22, 2026
JerrettDavis
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Jan 22, 2026
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Dependency Review✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.Scanned FilesNone |
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Test Results145 tests 145 ✅ 25s ⏱️ Results for commit eb05aaa. ♻️ This comment has been updated with latest results. |
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🔍 PR Validation ResultsVersion: `` ✅ Validation Steps
📊 ArtifactsDry-run artifacts have been uploaded and will be available for 7 days. This comment was automatically generated by the PR validation workflow. |
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #90 +/- ##
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+ Coverage 85.75% 90.09% +4.33%
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Files 143 143
Lines 12205 12288 +83
Branches 1623 1641 +18
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+ Hits 10467 11071 +604
+ Misses 1329 1217 -112
+ Partials 409 0 -409
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Pull request overview
This pull request extends the Visitor Pattern Generator to support interface, struct, and record hierarchies, not just class-based hierarchies. The generator now produces visitor infrastructure for any type hierarchy marked with [GenerateVisitor], enabling value-type visitors without boxing and interface-based polymorphism patterns.
Changes:
- Extended type discovery to accept interfaces, structs, and records as base types for visitor hierarchies
- Implemented intelligent visitor interface naming that avoids double-I prefixes for interface base types (IShape → IShapeVisitor)
- Added four new diagnostics (PKVIS001-004) to validate hierarchy structure and partial keyword requirements
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 9 comments.
Show a summary per file
| File | Description |
|---|---|
| src/PatternKit.Generators/VisitorGenerator.cs | Core generator logic extended with interface/struct support, type discovery helpers, and diagnostic reporting |
| test/PatternKit.Generators.Tests/VisitorGeneratorTests.cs | Added 6 new tests covering interface/struct hierarchies and diagnostic validation |
| src/PatternKit.Generators.Abstractions/Visitors/VisitorAttributes.cs | Updated AttributeUsage to allow Interface and Struct targets |
| docs/generators/visitor-generator.md | Comprehensive documentation of new hierarchy types and diagnostic codes |
| src/PatternKit.Generators/AnalyzerReleases.Unshipped.md | Documented four new diagnostic codes |
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@copilot apply changes based on the comments in this thread |
- Remove interface exclusion from partial check (fixes PKVIS002 for interfaces) - Add proper record type keyword detection (record/record struct) - Remove unused PKVIS003 diagnostic - Add explicit .Where() and .Select() for better readability - Simplify IsPartial method with LINQ - Add tests for record hierarchies - Add test for non-partial interface base types - Update documentation to remove PKVIS003 All 37 tests passing. Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
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All review feedback addressed in commit 99942b4. Changes include: ✅ Fixed interface partial validation (PKVIS002 now applies to interfaces) All 37 tests passing. |
JerrettDavis
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Jan 22, 2026
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
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@copilot apply changes based on the comments in this thread |
- Use IsDerivedFrom instead of ImplementsInterface for struct discovery (consistency) - Update documentation to clarify interfaces also require partial keyword - All 37 tests passing Co-authored-by: JerrettDavis <2610199+JerrettDavis@users.noreply.github.com>
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Both issues addressed in commit eb05aaa: ✅ Structs now use All 37 tests passing. |
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Code Coverage |
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.
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Comment on lines
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| if (type.IsRecord) | ||
| { | ||
| typeKeyword = type.TypeKind == TypeKind.Struct | ||
| ? "record struct" | ||
| : "record"; | ||
| } | ||
| else | ||
| { | ||
| typeKeyword = type.TypeKind switch | ||
| { | ||
| TypeKind.Interface => "interface", | ||
| TypeKind.Struct => "struct", | ||
| _ => "class" | ||
| }; | ||
| } |
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Both branches of this 'if' statement write to the same variable - consider using '?' to express intent better.
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Visitor Pattern Generator Enhancement Plan
Analysis Complete
Implementation Plan
Phase 1: Core Enhancements
Phase 2: Advanced Features
Phase 3: Documentation & Testing
Phase 4: Quality & Coverage
Completed Features
PR Review Feedback Addressed
First Review (99942b4):
Second Review (this commit):
Original prompt
This section details on the original issue you should resolve
<issue_title>Generator: Create Visitor Pattern</issue_title>
<issue_description>## Summary
Implement a source generator that emits all the boilerplate normally required for the Visitor design pattern, including:
All generated code should be:
Motivation & Context
The Visitor pattern is a classic behavioral design pattern that separates algorithms from the objects on which they operate, enabling new operations to be added without modifying the object structure. ([refactoring.guru][2])
In C#, implementing a visitor typically requires:
Visitmethod for each concrete elementAcceptmethod in every elementSource generation can make this automatic, safe, and ergonomic.
Goals
G1 — Source-gen visitor interfaces and accept methods
From minimal input, generate a visitor interface (or interfaces) and implement the required accept methods on all participating types.
G2 — Support multiple visitor families
Allow multiple independent visitor sets within a single project.
For example, one family for validation logic and another for serialization logic.
G3 — Support void and generic visitors
Visitor operations should optionally return values (
TResult) and accept context parameters.G4 — Make the generated API ergonomic
Prefer compile-time dispatch over
switch/if/ type casting. Avoid reflection entirely.G5 — Deterministic ordering & diagnostics
The generator should provide diagnostics if new concrete types are introduced but not included in visitors, and deterministic visit order where applicable.
User Experience
Opt-in Model
Users mark a base type and, optionally, concrete types they want included in a visitor family.
Example: Interface base
User defines shapes:
The generator produces:
IShapeVisitorinterface withVisit(Circle),Visit(Rectangle),Visit(Triangle)Accept(visitor)on each concrete typeExample: Abstract base class
User defines:
Generated code augments both with
Accept.Generated Output (Desired Shape)
Visitor Interface
Generated on the base type:
Generic Visitor
Optionally support returning a result:
Accept Methods
Multiple Visitor Families Supported
Example with diagnostics:
Each family emits:
IAstNodeVisitor_ValidationIAstNodeVisitor_RenderingOptions & Extensions
Support for Interface Segregation
Allow optional base visitor interfaces to group common visit methods:
Generated visitors implement the base.
Context Parameters
Visitors may accept a context parameter:
This allows stateful visitors without external state capture.
Default Implementation Hooks
Generated partial visitor interface stub could contain no-op defaults:
Optional generator flag to emit defaults.
Diagnostics
Provide generator diagnostics for:
| ID | Meaning |
| -------- | -------------------...
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