feat: add view registration attributes and attribute-aware dispatch

[glennawatson]

What's New

Three new attributes give you compile-time control over how views are registered and resolved — no runtime reflection needed.

Exclude a view from auto-registration

[ExcludeFromViewRegistration]
public class DesignTimeView : IViewFor<MyViewModel> { ... }

The source generator skips this class entirely. Useful for design-time views, test doubles, or platform-specific views you register manually.

Cache a view as a singleton

[SingleInstanceView]
public class ShellView : IViewFor<ShellViewModel> { ... }

The generator emits a static field and lazy-initialization pattern so the same instance is returned on every resolution:

// Generated code (simplified)
private static ShellView __singletonView_0;

if (__singletonView_0 == null)
    __singletonView_0 = new ShellView();
return __singletonView_0;

Register a view under a contract

[ViewContract("compact")]
public class CompactView : IViewFor<DashboardViewModel> { ... }

The generated dispatch only matches when the caller requests that exact contract:

// Generated code (simplified)
if (instance is DashboardViewModel)
{
    if (contract == "compact")
        return __ResolveView_0(contract);
}

This lets you have multiple views for the same ViewModel, selected at resolution time:

viewLocator.ResolveView(vm);             // default view
viewLocator.ResolveView(vm, "compact");  // compact view

Fluent mapping builder

DefaultViewLocator now exposes a CreateMappingBuilder() factory for fluent runtime registration:

var locator = new DefaultViewLocator();
locator.CreateMappingBuilder()
    .Map<LoginViewModel, LoginView>()
    .Map<SettingsViewModel, SettingsView>("admin");

---

Maintainer Notes

Attributes

• ExcludeFromViewRegistrationAttribute, SingleInstanceViewAttribute, ViewContractAttribute added to ReactiveUI.Binding/View/
• Namespace is ReactiveUI.Binding (not ReactiveUI) — ReactiveUI will delete its copies and consume these via global using
• Metadata name constants added to Constants.cs

Source Generator Changes

• ViewRegistrationExtractor reads all three attributes during IViewFor<T> extraction; excluded views return null before reaching the pipeline
• ViewRegistrationInfo record gains Contract (string?) and IsSingleInstance (bool) properties
• ViewLocatorDispatchGenerator deduplicates by (ViewModel FQN, Contract) pair, emits contract-guarded dispatch branches, and emits singleton cache fields + lazy init for [SingleInstanceView] views
• Generator rewritten to use $$""" raw string literals matching project conventions

Cleanup

• Removed redundant : IEquatable<Self> from all 10 sealed record model types (records implement this automatically)
• Defensive null guards in extractor refactored to use InvalidOperationExceptionHelper.EnsureNotNull (attribute types co-exist with IViewFor<T> in the same assembly, so null is unreachable)

Coverage

• 100% line and branch coverage maintained

[Copilot]

Pull request overview

Adds compile-time attributes and generator support to control view auto-registration/resolution (exclude, singleton caching, and contract-based dispatch), plus a fluent runtime mapping builder on DefaultViewLocator.

Changes:

• Introduces ExcludeFromViewRegistrationAttribute, SingleInstanceViewAttribute, and ViewContractAttribute in ReactiveUI.Binding.
• Updates the source generator pipeline to extract these attributes and emit contract-aware dispatch + optional singleton caching fields.
• Adds DefaultViewLocator.CreateMappingBuilder() and expands unit/snapshot coverage; removes redundant IEquatable<T> from model records.

Reviewed changes

Copilot reviewed 36 out of 36 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/ReactiveUI.Binding/View/ViewContractAttribute.cs	Adds contract attribute for view resolution specificity.
src/ReactiveUI.Binding/View/SingleInstanceViewAttribute.cs	Adds marker attribute for singleton view caching generation.
src/ReactiveUI.Binding/View/ExcludeFromViewRegistrationAttribute.cs	Adds marker attribute to skip view auto-registration.
src/ReactiveUI.Binding/View/DefaultViewLocator.cs	Exposes CreateMappingBuilder() factory for fluent runtime mappings.
src/ReactiveUI.Binding.SourceGenerators/Constants.cs	Adds metadata name constants for new attributes.
src/ReactiveUI.Binding.SourceGenerators/Helpers/ViewRegistrationExtractor.cs	Extracts contract/singleton/exclusion metadata into ViewRegistrationInfo.
src/ReactiveUI.Binding.SourceGenerators/Generators/ViewLocatorDispatchGenerator.cs	Emits contract-aware dispatch branches and singleton cache fields.
src/ReactiveUI.Binding.SourceGenerators/Models/ViewRegistrationInfo.cs	Extends model with Contract and IsSingleInstance.
src/ReactiveUI.Binding.SourceGenerators/Models/WhenAnyObservableInvocationInfo.cs	Removes redundant IEquatable<> from record.
src/ReactiveUI.Binding.SourceGenerators/Models/PropertyPathSegment.cs	Removes redundant IEquatable<> from record.
src/ReactiveUI.Binding.SourceGenerators/Models/ObservableTypeInfo.cs	Removes redundant IEquatable<> from record.
src/ReactiveUI.Binding.SourceGenerators/Models/ObservablePropertyInfo.cs	Removes redundant IEquatable<> from record.
src/ReactiveUI.Binding.SourceGenerators/Models/InvocationInfo.cs	Removes redundant IEquatable<> from record.
src/ReactiveUI.Binding.SourceGenerators/Models/ClassBindingInfo.cs	Removes redundant IEquatable<> from record.
src/ReactiveUI.Binding.SourceGenerators/Models/BindingInvocationInfo.cs	Removes redundant IEquatable<> from record.
src/ReactiveUI.Binding.SourceGenerators/Models/BindInteractionInvocationInfo.cs	Removes redundant IEquatable<> from record.
src/ReactiveUI.Binding.SourceGenerators/Models/BindCommandInvocationInfo.cs	Removes redundant IEquatable<> from record.
src/tests/ReactiveUI.Binding.Tests/View/ViewAttributeTests.cs	Adds basic tests for new attribute types.
src/tests/ReactiveUI.Binding.Tests/View/DefaultViewLocatorTests.cs	Tests CreateMappingBuilder() registers mappings on the locator instance.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/ViewLocatorDispatchGeneratorTests.cs	Adds snapshot tests for exclusion, singleton, and contract dispatch generation.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.ViewWithoutParameterlessConstructor#ViewDispatch.g.verified.cs	Updates snapshots for new generator output formatting/behavior.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.ViewWithPrivateConstructor#ViewDispatch.g.verified.cs	Updates snapshots for new generator output formatting/behavior.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.ViewContractGeneratesContractDispatch#ViewDispatch.g.verified.cs	Adds snapshot for contract-aware dispatch output.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.ViewContractGeneratesContractDispatch#GeneratedBindingsAttributes.g.verified.cs	Snapshot for generated bindings attributes file.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.ViewContractGeneratesContractDispatch#GeneratedBinderRegistration.g.verified.cs	Snapshot for generated binder registration file.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.SingleViewForImplementation#ViewDispatch.g.verified.cs	Updates snapshot for generator formatting changes.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.SingleInstanceViewWithoutParameterlessCtor#ViewDispatch.g.verified.cs	Adds snapshot for singleton attribute without direct construction case.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.SingleInstanceViewWithoutParameterlessCtor#GeneratedBindingsAttributes.g.verified.cs	Snapshot for generated bindings attributes file.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.SingleInstanceViewWithoutParameterlessCtor#GeneratedBinderRegistration.g.verified.cs	Snapshot for generated binder registration file.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.SingleInstanceViewGeneratesSingletonCache#ViewDispatch.g.verified.cs	Adds snapshot for singleton-cache output.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.SingleInstanceViewGeneratesSingletonCache#GeneratedBindingsAttributes.g.verified.cs	Snapshot for generated bindings attributes file.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.SingleInstanceViewGeneratesSingletonCache#GeneratedBinderRegistration.g.verified.cs	Snapshot for generated binder registration file.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.MultipleViewForImplementations#ViewDispatch.g.verified.cs	Updates snapshot for generator formatting changes.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.ExclAttr#GeneratedBindingsAttributes.g.verified.cs	Snapshot for exclusion-only generation case.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.ExclAttr#GeneratedBinderRegistration.g.verified.cs	Snapshot for exclusion-only generation case.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/VDG.DuplicateViewModelsAreDeduplicated#ViewDispatch.g.verified.cs	Updates snapshot for new deduplication key and formatting changes.

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (3c0fe71) to head (3979338).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #17   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          125       126    +1     
  Lines         2116      2119    +3     
  Branches       395       395           
=========================================
+ Hits          2116      2119    +3     

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