feat!: ship the attributes in a public library instead of generating them into each project

CLAUDE.md

@@ -26,7 +26,24 @@ Each versioned project links all `.cs` files from `ReactiveUI.SourceGenerators.R
 
 `#if ROSYLN_412 || ROSYLN_500` guards inside the shared source enable partial-property pipelines only on the newer Roslyn builds.
 
-The `ReactiveUI.SourceGenerators` NuGet project packages all three DLLs under separate `analyzers/dotnet/roslyn4.8/cs`, `analyzers/dotnet/roslyn4.14/cs`, and `analyzers/dotnet/roslyn5.0/cs` paths, so NuGet/MSBuild automatically selects the right build based on the host compiler.
+Each versioned project builds `ReactiveUI.SourceGenerators.Roslyn.dll`. The `ReactiveUI.SourceGenerators` project is
+the package consumers install: it builds the attributes into `ReactiveUI.SourceGenerators.dll` under `lib/`, and bundles
+the three generator DLLs, each with the code fixes, under `analyzers/dotnet/roslyn4.8/cs`, `analyzers/dotnet/roslyn4.14/cs`,
+and `analyzers/dotnet/roslyn5.0/cs`, so NuGet/MSBuild automatically selects the right build based on the host compiler.
+
+### Generated code never declares a shared type
+
+The attributes and the enums they take (`AccessModifier`, `PropertyAccessModifier`, `InheritanceModifier`) are public
+types in `ReactiveUI.SourceGenerators`, which targets `$(LibraryTfms)` (net8.0-net11.0, net462-net481). A type
+declared into each consumer would repeat in every assembly, and an assembly granted `InternalsVisibleTo` would see two
+copies (CS0436).
+
+- **Do not use `RegisterPostInitializationOutput`**, or emit any type whose fully qualified name another assembly
+  could also declare.
+- A new attribute goes in `ReactiveUI.SourceGenerators` and is `[Conditional(KeepAttributes.Symbol)]`: the generators
+  read it from source, so a consumer keeps no reference to the attributes assembly.
+- Generators, analyzers and code fixes stay `netstandard2.0`, the Roslyn host's framework. Only the attributes library
+  targets `$(LibraryTfms)`.
 
 Generators report only the `RXUISG*` diagnostics about input they cannot generate from (see
 [Analyzer Separation](#analyzer-separation-roslyn-best-practice)). Diagnostics about how code should be written, and
@@ -37,7 +54,7 @@ their code fixes, live in the separate `ReactiveUI.SourceGenerators.Analyzers.Co
 ```
 src/
 ├── ReactiveUI.SourceGenerators.Roslyn/          # Shared source (linked into all versioned projects)
-│   ├── AttributeDefinitions.cs                  # Injected attribute source texts
+│   ├── AttributeDefinitions.cs                  # Metadata names of the attributes the generators read
 │   ├── Reactive/                                # [Reactive] generator + Execute + models
 │   ├── ReactiveCommand/                         # [ReactiveCommand] generator + Execute + models
 │   ├── RoutedControlHost/                       # [RoutedControlHost] generator
@@ -52,11 +69,11 @@ src/
 │       ├── Extensions/                          # ISymbol*, ITypeSymbol*, INamedTypeSymbol*, AttributeData extensions
 │       ├── Helpers/                             # ImmutableArrayBuilder<T>, EquatableArray<T>, HashCode, etc.
 │       └── Models/                              # Result<T>, DiagnosticInfo, TargetInfo, etc.
-├── ReactiveUI.SourceGenerators.Roslyn480/       # Roslyn 4.8 build (no define)
+├── ReactiveUI.SourceGenerators.Roslyn480/       # Roslyn 4.8 build (no define) of ReactiveUI.SourceGenerators.Roslyn.dll
 ├── ReactiveUI.SourceGenerators.Roslyn4140/      # Roslyn 4.14 build (ROSYLN_412)
 ├── ReactiveUI.SourceGenerators.Roslyn5000/      # Roslyn 5.0 build (ROSYLN_500)
 ├── ReactiveUI.SourceGenerators.Analyzers.CodeFixes/  # Analyzers + code fixers
-├── ReactiveUI.SourceGenerators/                 # NuGet packaging project (bundles all three DLLs)
+├── ReactiveUI.SourceGenerators/                 # The package: public attributes, with the Roslyn builds bundled
 ├── ReactiveUI.SourceGenerator.Tests/            # TUnit tests with generator snapshots (GeneratorSnapshot)
 ├── benchmarks/                                  # BenchmarkDotNet generation benchmarks with EventPipe tracing
 ├── ReactiveUI.SourceGenerators.Execute*/        # Compile-time execution verification projects
@@ -98,24 +115,20 @@ _ = writer.Lines("""
 nothing), `OpenContainingTypes`, `OpenPartialType`, `CloseBlocks`, `InheritDoc`, `ExcludeFromCodeCoverage`. Build a
 generator's `GeneratedCode` attribute once, in a static field, with `SourceWriterExtensions.GeneratedCodeAttribute`.
 
-The injected attribute source texts (in `AttributeDefinitions.cs`) are fixed `$$"""..."""` raw strings, each built once
-per process.
-
 A change to an emitter must keep the output token-for-token the same unless it deliberately changes generated code;
 compare changed snapshots with whitespace removed to prove it.
 
 ## Roslyn Incremental Pipeline Pattern
 
 Each generator follows this structure:
 
-1. **`Initialize`** — registers post-initialization output (inject attribute source), then calls one or more `Run*` methods.
+1. **`Initialize`** — calls one or more `Run*` methods. It registers no post-initialization output.
 2. **`Run*`** — builds the `IncrementalValuesProvider` using `ForAttributeWithMetadataName` + a syntax predicate + a semantic extraction function.
 3. **`Get*Info` (Execute file)** — stateless extraction function. Returns `Result<TModel?>` with embedded diagnostics. Must be pure; must not capture any `ISymbol` or `SyntaxNode` beyond this call.
 4. **`GenerateSource` (Execute file)** — pure function that writes a model through `SourceWriter`. No Roslyn symbols allowed here.
 
 ```
 Initialize()
-  ├─ RegisterPostInitializationOutput → inject attribute definitions
   └─ SyntaxProvider.ForAttributeWithMetadataName
        ├─ syntax predicate (fast, node-type check only)
        ├─ semantic extraction → Get*Info() → Result<Model>
@@ -220,7 +233,8 @@ Analyzer and helper tests use direct `CSharpCompilation` / `CompilationWithAnaly
 ### Adding a New Generator
 
 1. Create a value-equatable model record in `Core/Models/` or the generator's own `Models/` folder.
-2. Add attribute source text to `AttributeDefinitions.cs` as a `$$"""..."""` raw string property initialised once.
+2. Add the attribute as a public `[Conditional(KeepAttributes.Symbol)]` type in `ReactiveUI.SourceGenerators`, and its
+   metadata name to `AttributeDefinitions.cs`.
 3. Create `<Name>Generator.cs` with `Initialize` wiring up `ForAttributeWithMetadataName`.
 4. Create `<Name>Generator.Execute.cs` with `Get*Info` (extraction) and `GenerateSource` (writes through `SourceWriter`).
 5. Add snapshot tests in `ReactiveUI.SourceGenerator.Tests/UnitTests/`.

README.md

@@ -26,6 +26,15 @@ dotnet add package ReactiveUI.SourceGenerators
 
 Ensure the package is loaded with `PrivateAssets="all"` to avoid issues with generated code in consuming projects.
 
+The attributes (`[Reactive]`, `[ReactiveCommand]` and the rest) are public types in the package's
+`ReactiveUI.SourceGenerators` assembly; the generators no longer declare them in your project, so assemblies
+that share internals through `InternalsVisibleTo` no longer see two copies. Your project compiles against that assembly
+but keeps no reference to it. If an older install added an `<IncludeAssets>` line without `compile`, remove it:
+
+```xml
+<PackageReference Include="ReactiveUI.SourceGenerators" Version="..." PrivateAssets="all" />
+```
+
 ReactiveUI V24.x.x consumers can reference either `ReactiveUI` for the primitives-based API without
 System.Reactive, or `ReactiveUI.Reactive` for the System.Reactive-based API. The generators detect
 the referenced API surface automatically. ReactiveUI releases from 23.2.28 remain supported.
@@ -40,7 +49,8 @@ ReactiveUI Source Generators automatically generate ReactiveUI objects to stream
 - `[Reactive(UseRequired = true)]` With field and access modifiers. This will generate a required property, (Not Required for partial properties, use required keyword for property declaration).
 - `[Reactive(nameof(RaiseProperty1), nameof(RaiseProperty2))]` With field and property changed notification for additional properties.
 - `[ReactiveCommand]`
-- `[ReactiveCommand(RunInBackground = true)]` runs a synchronous command on ReactiveUI's background scheduler
+- `[ReactiveCommand(RunInBackground = true)]` runs a synchronous command on ReactiveUI's background scheduler, and starts a task-returning command with `Task.Run`
+- `[ReactiveCommand(BackgroundScheduler = nameof(_scheduler))]` runs a synchronous command on the given scheduler
 - `[ReactiveCommand(CanExecute = nameof(IObservableBoolName))]` with CanExecute
 - `[ReactiveCommand(OutputScheduler = "RxSchedulers.MainThreadScheduler")]` using a ReactiveUI Scheduler
 - `[ReactiveCommand(OutputScheduler = nameof(_isheduler))]` using a Scheduler defined in the class
@@ -325,7 +335,9 @@ public partial class MyReactiveClass
 
 ### Usage ReactiveCommand on the background scheduler
 
-Use `RunInBackground` for synchronous command methods that should be created with `ReactiveCommand.CreateRunInBackground`. Task- and observable-returning methods continue to use their asynchronous ReactiveCommand factories.
+Use `RunInBackground` to run a command's method off the calling thread. A synchronous method's command is created with `ReactiveCommand.CreateRunInBackground`. A task-returning method is started with `Task.Run`, so the code before its first `await` no longer runs on the calling thread; the command parameter and `CancellationToken` are passed through. Observable-returning methods are unaffected.
+
+`BackgroundScheduler` chooses the scheduler a synchronous method runs on, from a scheduler member of the class or a built-in ReactiveUI scheduler, and implies `RunInBackground`. A task-returning method always starts on the thread pool.
 
 ```csharp
 using ReactiveUI.SourceGenerators;
@@ -334,6 +346,12 @@ public partial class MyReactiveClass
 {
     [ReactiveCommand(RunInBackground = true)]
     private void ExecuteExpensiveWork() { }
+
+    [ReactiveCommand(RunInBackground = true)]
+    private async Task<int> LoadAsync(int id, CancellationToken token) => await _repository.LoadAsync(id, token);
+
+    [ReactiveCommand(BackgroundScheduler = nameof(_workScheduler))]
+    private void Crunch() { }
 }
 ```
 

src/Directory.Build.props

@@ -42,6 +42,8 @@
   <PropertyGroup>
     <!-- Roslyn projects target netstandard2.0 -->
     <RoslynTfm>netstandard2.0</RoslynTfm>
+    <!-- The ReactiveUI.SourceGenerators attributes library consumers compile against: modern .NET and .NET Framework -->
+    <LibraryTfms>net8.0;net9.0;net10.0;net11.0;net462;net47;net471;net472;net48;net481</LibraryTfms>
     <!-- Test projects multi-target net8.0, net9.0, and net10.0 -->
     <TestTfms>net8.0;net9.0;net10.0</TestTfms>
   </PropertyGroup>

src/ReactiveUI.SourceGenerator.Tests/DERIVEDLIST/BDLG.FRxProps#TestNs.TestVM.Bdl.verified.cs

@@ -1,7 +1,6 @@
 //HintName: TestNs.TestVM.BindableDerivedList.g.cs
 // <auto-generated/>
 using System.Collections.ObjectModel;
-using DynamicData;
 using ReactiveUI;
 
 #pragma warning disable

src/ReactiveUI.SourceGenerator.Tests/DERIVEDLIST/DLE.AccMods#TestNs.TestVM.Bdl.verified.cs

@@ -1,7 +1,6 @@
 //HintName: TestNs.TestVM.BindableDerivedList.g.cs
 // <auto-generated/>
 using System.Collections.ObjectModel;
-using DynamicData;
 using ReactiveUI;
 
 #pragma warning disable

src/ReactiveUI.SourceGenerator.Tests/DERIVEDLIST/DLE.CplxGen#TestNs.TestVM.Bdl.verified.cs

@@ -1,7 +1,6 @@
 //HintName: TestNs.TestVM.BindableDerivedList.g.cs
 // <auto-generated/>
 using System.Collections.ObjectModel;
-using DynamicData;
 using ReactiveUI;
 
 #pragma warning disable

src/ReactiveUI.SourceGenerator.Tests/DERIVEDLIST/DLE.DateTimeT#TestNs.TestVM.Bdl.verified.cs

@@ -1,7 +1,6 @@
 //HintName: TestNs.TestVM.BindableDerivedList.g.cs
 // <auto-generated/>
 using System.Collections.ObjectModel;
-using DynamicData;
 using ReactiveUI;
 
 #pragma warning disable

src/ReactiveUI.SourceGenerator.Tests/DERIVEDLIST/DLE.DiffNss#Ns1.TestVM.Bdl.verified.cs

@@ -1,7 +1,6 @@
 //HintName: Namespace1.TestVM.BindableDerivedList.g.cs
 // <auto-generated/>
 using System.Collections.ObjectModel;
-using DynamicData;
 using ReactiveUI;
 
 #pragma warning disable

src/ReactiveUI.SourceGenerator.Tests/DERIVEDLIST/DLE.DiffNss#Ns2.TestVM.Bdl.verified.cs

@@ -1,7 +1,6 @@
 //HintName: Namespace2.TestVM.BindableDerivedList.g.cs
 // <auto-generated/>
 using System.Collections.ObjectModel;
-using DynamicData;
 using ReactiveUI;
 
 #pragma warning disable

src/ReactiveUI.SourceGenerator.Tests/DERIVEDLIST/DLE.EnumT#TestNs.TestVM.Bdl.verified.cs

@@ -1,7 +1,6 @@
 //HintName: TestNs.TestVM.BindableDerivedList.g.cs
 // <auto-generated/>
 using System.Collections.ObjectModel;
-using DynamicData;
 using ReactiveUI;
 
 #pragma warning disable