feat: interface-based observation plugin system with ReactiveUI-aligned affinities by glennawatson · Pull Request #14 · reactiveui/ReactiveUI.Binding.SourceGenerators

glennawatson · 2026-03-09T00:44:39Z

Summary

Replaces 7 static observation generators with an interface-based plugin system where plugins compete by affinity to generate platform-specific, reflection-free observation code
Affinity values now match ReactiveUI's exact runtime values — KVO (15), ReactiveObject (10), WinForms (8), WinUI (6), INPC (5), Android (5), WPF (4) — meaning the source generator now mirrors how ReactiveUI itself selects observation strategies at runtime, but resolved entirely at compile time
Platform-specific code generation replaces generic INPC-only output: WPF uses DependencyPropertyDescriptor.AddValueChanged, WinUI uses RegisterPropertyChangedCallback, WinForms uses direct {Property}Changed event subscription, KVO uses NSObject.AddObserver with compile-time resolved key paths
New EventObservable<T> runtime type provides platform-agnostic event-based observation using pure BCL types (Action<EventHandler> add/remove pattern), used by WPF and WinForms plugins
Pipeline A simplified from 7 separate filter calls + Consolidate() to a single ObservationPluginRegistry.GetBestPlugin() dispatch
User-extensible architecture — because the source generator uses the same affinity values as ReactiveUI's runtime, user-registered ICreatesObservableForProperty implementations with higher affinity will naturally override the generated observation at runtime

Test plan

7,236 tests passing across all TFMs (net8.0, net9.0, net10.0)
100% line coverage, 100% branch coverage
Build succeeds with zero warnings (-warnaserror)
Snapshot tests updated and verified for all platform types
Platform test stubs include full API surface (WinUI DP registration, KVO NSObject stubs, WinForms events)

…ed selection Replace 7 static observation generator classes with an interface-based plugin system where plugins compete by affinity to generate platform-specific, reflection-free observation code. Affinity values now match ReactiveUI's exact runtime values (KVO=15, ReactiveObject=10, WinForms=8, WinUI=6, INPC=5, Android=5, WPF=4). Each plugin generates code that mirrors the corresponding ReactiveUI runtime implementation but without reflection: - WPF: EventObservable with DependencyPropertyDescriptor.AddValueChanged - WinUI: inline __WinUIDPObservable with RegisterPropertyChangedCallback - WinForms: EventObservable with direct {Property}Changed event subscription - KVO: inline __KVOObservable with NSObject.AddObserver and compile-time resolved key paths (lowercase first char, boolean "is" prefix) - INPC/ReactiveObject: PropertyObservable/PropertyChangingObservable - Android: ReturnObservable fallback (no INPC on Android View) Pipeline A simplified from 7 separate filter calls + Consolidate() to a single plugin-based step via ObservationPluginRegistry.GetBestPlugin(). New runtime type EventObservable<T> provides platform-agnostic event-based observation using pure BCL types (Action<EventHandler> add/remove pattern). 100% line and branch coverage maintained across the full solution (7236 tests).

codecov · 2026-03-09T00:58:03Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (f6d518b) to head (be14d5e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #14   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          118       121    +3     
  Lines         1949      2014   +65     
  Branches       364       375   +11     
=========================================
+ Hits          1949      2014   +65

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Copilot

Pull request overview

This PR refactors the ReactiveUI.Binding source generator’s property observation pipeline from multiple static, per-platform generators into an interface-based observation plugin system, and introduces new platform-specific observation outputs (WinUI DP callbacks, WPF DP descriptor hooks, WinForms {Property}Changed events, Apple KVO) that align with ReactiveUI’s runtime affinity model.

Changes:

Added an IObservationPlugin abstraction with concrete platform plugins and a central ObservationPluginRegistry to select the best strategy by affinity.
Introduced EventObservable<T> (runtime) to support platform-agnostic event-based observation (used by WPF/WinForms strategies).
Updated generator logic and snapshot tests to reflect new platform-specific observation code and simplified dispatch.

Reviewed changes

Copilot reviewed 51 out of 53 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/tests/ReactiveUI.Binding.Tests/Observables/EventObservableTests.cs	Adds unit tests for the new `EventObservable<T>` runtime type.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WhenChangedGeneratorTests.cs	Updates platform stubs (WinForms/WinUI/KVO) used by generator tests.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCnG.SP_ReactiveObject#WhenChangingDispatch.g.verified.cs	Snapshot update for `WhenChanging` dispatch output formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCnG.SP_INPC_CFP#WhenChangingDispatch.g.verified.cs	Snapshot update for `WhenChanging` dispatch output formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCnG.SP_INPC#WhenChangingDispatch.g.verified.cs	Snapshot update for `WhenChanging` dispatch output formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCnG.ReactiveObject_Changing_Property#WhenChangingDispatch.g.verified.cs	Snapshot update for `WhenChanging` dispatch output formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCnG.INPChangingOnly_Property#WhenChangingDispatch.g.verified.cs	Snapshot update for `WhenChanging` dispatch output formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.WpfDependencyObject_Property#WhenChangedDispatch.g.verified.cs	Snapshot update for WPF `WhenChanged` output formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.WpfDependencyObject_Property#GeneratedBinderRegistration.g.verified.cs	Snapshot update reflecting plugin-based kind detection comments.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.WinUIDependencyObject_Property#WhenChangedDispatch.g.verified.cs	Snapshot update switching WinUI DP observation to generated `__WinUIDPObservable`.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.WinUIDependencyObject_Property#GeneratedBinderRegistration.g.verified.cs	Snapshot update reflecting plugin-based kind detection comments.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.WinFormsComponent_Property#WhenChangedDispatch.g.verified.cs	Snapshot update switching WinForms observation to `EventObservable<T>` on `{Property}Changed`.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.WinFormsComponent_Property#GeneratedBinderRegistration.g.verified.cs	Snapshot update reflecting plugin-based kind detection comments.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.SP_ReactiveObject#WhenChangedDispatch.g.verified.cs	Snapshot update for `WhenChanged` dispatch output formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.SP_INPC_CFP#WhenChangedDispatch.g.verified.cs	Snapshot update for `WhenChanged` dispatch output formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.SP_INPC#WhenChangedDispatch.g.verified.cs	Snapshot update for `WhenChanged` dispatch output formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.NullableProperty#WhenChangedDispatch.g.verified.cs	Snapshot update for nullable property observation output formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.MultipleViewModels#WhenChangedDispatch.g.verified.cs	Snapshot update for multiple view-model dispatch formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.MI_SameViewModel#WhenChangedDispatch.g.verified.cs	Snapshot update for multiple invocations formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.KVO_NSObject_Property#WhenChangedDispatch.g.verified.cs	Snapshot update switching Apple observation to generated `__KVOObservable`.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.KVO_NSObject_Property#GeneratedBinderRegistration.g.verified.cs	Snapshot update reflecting plugin-based kind detection comments.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.IntProperty#WhenChangedDispatch.g.verified.cs	Snapshot update for value-type observation output formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.AndroidView_Property#WhenChangedDispatch.g.verified.cs	Snapshot update for Android view observation output formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WCG.AndroidView_Property#GeneratedBinderRegistration.g.verified.cs	Snapshot update reflecting plugin-based kind detection comments.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WAVG.SP_INPC_CFP#WhenAnyValueDispatch.g.verified.cs	Snapshot update for `WhenAnyValue` formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WAVG.SP_INPC#WhenAnyValueDispatch.g.verified.cs	Snapshot update for `WhenAnyValue` formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WAVG.NullableProperties#WhenAnyValueDispatch.g.verified.cs	Snapshot update for nullable `WhenAnyValue` formatting.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/Plugins/ObservationPluginTests.cs	Adds targeted unit tests for plugin emit methods not covered by snapshots.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/CodeGeneration/ObservationCodeGeneratorHelperTests.cs	Updates/extends generator helper tests for new fallback behavior.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/BOG.ReactiveObject_Source#GeneratedBinderRegistration.g.verified.cs	Snapshot update for kind ordering/printing changes.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/BIG.DeepPropertyPath#BindInteractionDispatch.g.verified.cs	Snapshot indentation/formatting changes for deep interaction binding code.
src/tests/ReactiveUI.Binding.SourceGenerators.Tests/BCG.DeepCommandPath#BindCommandDispatch.g.verified.cs	Snapshot indentation/formatting changes for deep command binding code.
src/ReactiveUI.Binding/Observables/EventObservable.cs	Adds new fused event-based observable implementation used by generated code.
src/ReactiveUI.Binding.SourceGenerators/Plugins/ObservationPluginRegistry.cs	Adds plugin registry + best-match dispatch by affinity/kind.
src/ReactiveUI.Binding.SourceGenerators/Plugins/Observation/WpfObservationPlugin.cs	Adds WPF DP plugin emitting `EventObservable<T>` with `DependencyPropertyDescriptor`.
src/ReactiveUI.Binding.SourceGenerators/Plugins/Observation/WinUIObservationPlugin.cs	Adds WinUI DP plugin emitting `__WinUIDPObservable<T>` helper class and usage.
src/ReactiveUI.Binding.SourceGenerators/Plugins/Observation/WinFormsObservationPlugin.cs	Adds WinForms plugin emitting `EventObservable<T>` for `{Property}Changed`.
src/ReactiveUI.Binding.SourceGenerators/Plugins/Observation/ReactiveObjectObservationPlugin.cs	Adds ReactiveObject plugin emitting `PropertyObservable` / `PropertyChangingObservable`.
src/ReactiveUI.Binding.SourceGenerators/Plugins/Observation/KVOObservationPlugin.cs	Adds Apple KVO plugin emitting `__KVOObservable<T>` + `__KVOObserver` helper classes.
src/ReactiveUI.Binding.SourceGenerators/Plugins/Observation/INPCObservationPlugin.cs	Adds INPC plugin emitting `PropertyObservable` / `PropertyChangingObservable`.
src/ReactiveUI.Binding.SourceGenerators/Plugins/Observation/AndroidObservationPlugin.cs	Adds Android plugin (currently ReturnObservable fallback).
src/ReactiveUI.Binding.SourceGenerators/Plugins/IObservationPlugin.cs	Introduces the observation plugin interface contract for codegen.
src/ReactiveUI.Binding.SourceGenerators/Plugins/ICommandBindingPlugin.cs	Introduces a command binding plugin interface (foundation for extensibility).
src/ReactiveUI.Binding.SourceGenerators/Generators/RegistrationGenerator.cs	Simplifies registration pipeline by removing old consolidation method.
src/ReactiveUI.Binding.SourceGenerators/BindingGenerator.cs	Switches from 7 per-kind filters to single plugin-based observable type selection.
src/ReactiveUI.Binding.SourceGenerators/Generators/Observation/WpfBindingGenerator.cs	Removes legacy static WPF observation generator filter.
src/ReactiveUI.Binding.SourceGenerators/Generators/Observation/WinUIBindingGenerator.cs	Removes legacy static WinUI observation generator filter.
src/ReactiveUI.Binding.SourceGenerators/Generators/Observation/WinFormsBindingGenerator.cs	Removes legacy static WinForms observation generator filter.
src/ReactiveUI.Binding.SourceGenerators/Generators/Observation/ReactiveObjectBindingGenerator.cs	Removes legacy static ReactiveObject observation generator filter.
src/ReactiveUI.Binding.SourceGenerators/Generators/Observation/KVOBindingGenerator.cs	Removes legacy static KVO observation generator filter.
src/ReactiveUI.Binding.SourceGenerators/Generators/Observation/INPCBindingGenerator.cs	Removes legacy static INPC observation generator filter.
src/ReactiveUI.Binding.SourceGenerators/Generators/Observation/AndroidBindingGenerator.cs	Removes legacy static Android observation generator filter.
src/ReactiveUI.Binding.SourceGenerators/CodeGeneration/ObservationCodeGenerator.cs	Updates observation codegen to use plugin dispatch + emits plugin helper classes when needed.

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src/tests/ReactiveUI.Binding.SourceGenerators.Tests/WhenChangedGeneratorTests.cs

src/ReactiveUI.Binding.SourceGenerators/CodeGeneration/ObservationCodeGenerator.cs

…ride - Move command binding plugins from Generators/CommandBinding/ to Plugins/CommandBinding/ mirroring the observation plugin folder structure - Create CommandBindingPluginRegistry for affinity-based plugin selection - Convert CommandPropertyBindingPlugin, EventEnabledBindingPlugin, and DefaultEventBindingPlugin from static classes to ICommandBindingPlugin implementations with Affinity properties (5, 4, 3) - Add CommandBindingAffinityChecker runtime class allowing user-registered ICreatesCommandBinding plugins to override generated bindings when they have higher affinity (mirrors ObservationAffinityChecker pattern) - Add ObservationAffinityChecker for property observation user override - Replace EmitCustomBinderFallback with EmitCommandAffinityCheck in BindCommandCodeGenerator for affinity-aware runtime fallback - Add RuntimeObservationFallback multi-property WhenChanging/WhenAnyValue overloads (2 and 3 properties) - Sort usedPluginKinds for deterministic helper class emission order - Add comprehensive tests: CommandBindingAffinityCheckerTests, ObservationAffinityCheckerTests, CommandBindingPluginTests - 7365 tests pass, 100% line/branch/method coverage

Copilot

Pull request overview

Copilot reviewed 99 out of 100 changed files in this pull request and generated 3 comments.

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src/ReactiveUI.Binding/Fallback/ObservationAffinityChecker.cs

src/ReactiveUI.Binding/Observables/EventObservable.cs

src/ReactiveUI.Binding.SourceGenerators/Plugins/Observation/KVOObservationPlugin.cs

…y starting with "Is"

glennawatson and others added 2 commits March 9, 2026 11:42

Merge branch 'main' into feature/affinity-backup

6ca6561

glennawatson requested a review from Copilot March 9, 2026 00:57

Copilot started reviewing on behalf of glennawatson March 9, 2026 00:57 View session

ChrisPulman approved these changes Mar 9, 2026

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Copilot AI reviewed Mar 9, 2026

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glennawatson requested a review from Copilot March 9, 2026 02:06

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src/ReactiveUI.Binding/Fallback/ObservationAffinityChecker.cs Show resolved Hide resolved

src/ReactiveUI.Binding/Observables/EventObservable.cs Show resolved Hide resolved

src/ReactiveUI.Binding.SourceGenerators/Plugins/Observation/KVOObservationPlugin.cs Show resolved Hide resolved

fix: prevent KVO key path double-prefixing for bool properties alread…

be14d5e

…y starting with "Is"

glennawatson merged commit ac1f5a1 into main Mar 9, 2026
6 checks passed

glennawatson deleted the feature/affinity-backup branch March 9, 2026 02:32

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feat: interface-based observation plugin system with ReactiveUI-aligned affinities#14

feat: interface-based observation plugin system with ReactiveUI-aligned affinities#14
glennawatson merged 4 commits intomainfrom
feature/affinity-backup

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glennawatson commented Mar 9, 2026

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