PublicAPIAnalyzer files should capture more information

[drewnoakes]

There are quite a few additional things we could capture in the files used by the public API analyzer. For example, changing any of these would be an API "break" that the analyzer currently doesn't capture:

• Making something [Obsolete] (PublicApiAnalyzer should add info about members made [Obsolete] #2663)
• Sealing a class or override
• Making a class static
• Changing a base type or removing an inherited interface (without changing members)
• Making a non-private field readonly (PublicApiAnalyzers should track readonly-ness #2935)
• Changing nullable reference type annotations
• Reordering fields on sequential or explicit layout structs
• [AttributeUsage] values on attributes

[drewnoakes]

Repos that give IVT access to their internal members should probably capture internal members in their API descriptions too.

[dougbu]

Changing a base type or removing an inherited interface (without changing members)

Had an offline conversation w/ @halter73 about this bullet. Unfortunately, the current generated files do not mention explicitly-implemented members of an interface at all. Tracking the implemented interfaces would avoid that problem.

Somewhat separately, removing an implicitly-implemented member and making it explicit or visa versa is a change (which is breaking only in the implicit to explicit direction) rather than a removal but, right now, it shows up as a complete removal.

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Repos that give IVT access to their internal members should probably capture internal members in their API descriptions too.

If this were implemented, I'd appreciate a way to turn it off completely. IVT is often used in a very narrow / localized fashion e.g. just with DynamicProxyGenAssembly2 (for Moq) and associated test assemblies.

[Youssef1313]

Missing class modifiers looks like a roslyn issue. The analyzer uses SymbolDisplayMemberOptions.IncludeModifiers, but roslyn doesn't handle it for INamedType.

https://github.com/dotnet/roslyn/blob/f23a18008b23d30ba7ce753ff9f562dc9b4785eb/src/Compilers/CSharp/Portable/SymbolDisplay/SymbolDisplayVisitor.Types.cs#L185