Summary

Bindings over the members ReactiveUI.SourceGenerators writes are now generated, and a binding call that nothing was generated for is reported when you build.

• Members ReactiveUI.SourceGenerators writes bind like any other. The generator reads [Reactive] (field and partial property), [ReactiveCollection], [BindableDerivedList], [ReactiveCommand] and [IReactiveObject] by metadata name, and follows that package's rules for the name, type and accessibility of what each writes. WhenAnyValue, WhenAny, Bind, OneWayBind, BindCommand, ToProperty and the rest now dispatch for those members in both runtime flavours, where they used to throw at run time.
• RXUIBIND021 (Warning) reports a binding call with no generated binding. It fires on any call that still resolves to a throwing runtime stub and that no interceptor claims, whatever the cause: a member another source generator adds, a stored lambda, an unreachable type. The call throws when it runs, so the build now says so.
• New docs page sourcegenerators observes, binds and runs the members a [Reactive] field, [IReactiveObject] and [ReactiveCommand] produce.
• UnsafeSetupExamples.PlainCallWithStoredPathThrows is now PlainCallNeedsAPathWrittenInTheCall. It called a stub on purpose to show the exception, which RXUIBIND021 now reports; it names the warning and shows the path the generator reads instead.

Why

No generator sees another generator's output. A call such as vm.WhenAnyValue(x => x.Nickname), where Nickname comes from a [Reactive] field, named a member that did not exist in the compilation this generator reads, so nothing was generated, no diagnostic was reported, and the call threw at run time. A class marked [IReactiveObject] looked as if it raised no notification. ReactiveUI.Core now depends on ReactiveUI.SourceGenerators (reactiveui/ReactiveUI#4516), so this is the common case rather than an edge.

Breaking changes

None. Calls that used to throw at run time now either run or are reported by RXUIBIND021.

How this was verified

• ReactiveUI.SourceGenerators' own generators run beside this one in the tests, against 4.0.0 in one test project and 4.0.1 in the other, and a scenario covering every attribute is compiled, loaded and executed for both runtime flavours, with and without interceptors. Declaration tests pin each naming and typing rule, including every setter and access modifier and each command shape.
• Analyzer tests cover a member added by an unknown generator, stored lambdas, ToProperty, extension-block stubs, and the methods that do their own work. The full solution builds with the new rule and reports nothing outside the one rewritten example.
• Ran the Linux examples suite and the Windows examples on a real Windows machine.

Notes for the reviewer

• Start with Generators/SourceGeneratorsCompilation.cs and Helpers/SourceGeneratorsMemberExtractor.cs. The pipeline declares the members that attributes produce in one never-emitted file, adds it to a private copy of the compilation, and BindingGenerator.Detect reads call sites from that copy. A compilation that uses none of the attributes gets no copy and reads call sites exactly as before.
• Mechanical: the extractors take CallSiteContext instead of GeneratorSyntaxContext; both expose Node and SemanticModel, and the bodies are unchanged.
• The rules mirror ReactiveUI.SourceGenerators 4.0.0. That package's maintainers confirmed 4.0.1 changes none of them. SourceGeneratorsDeclarationTests is what to update if a rule changes.
• RXUIBIND021 on older compilers: below Roslyn 4.13 there are no interceptors, so a call resolving to the stub is the whole answer. With generated overloads (no interceptors), a call whose types match another generated call but whose lambda does not still binds to the generated overload and is not reported.

Checklist

• I have read the Contribute guide
• The PR title follows Conventional Commits
• Tests cover this change, or the summary says why they do not
• New or changed public API has XML documentation