adding-api-guidelines.md

Recommended reading to better understand this document: .NET Standard | Project-Guidelines | Package-Projects

Add APIs

• Add APIs
  • Determine what library
  • Determine target framework
  • Determine library version
  • Making the changes in repo
  • Documentation
  • FAQ

Determine what library

• Propose a library for exposing it as part of the API review process.
• Keep in mind the API might be exposed in a reference assembly that doesn't match the identity of the implementation. There are many reasons for this but the primary reason is to abstract the runtime assembly identities across different platforms while sharing a common API surface and allowing us to refactor the implementation without compat concerns in future releases.

Determine target framework

netstandard or netcoreapp is the target framework version currently under development.

• If the library is part of netstandard
  • Your target framework should be netstandard
  • If it is a new API only available on .NET Core then it will be added to netcoreapp
• If the library is not part of netstandard
  • If package dependencies are changed then your target framework should be the minimum target framework that supports all your package dependencies.
  • If your package depends directly on runtime changes or library changes that ship with the runtime (i.e. System.Private.CoreLib) then your target framework should be netstandard.
  • When targeting netstandardX your new API must be supported by all target frameworks that map to that netstandard version (see mapping table). If not bump the version to the minimum netstandard version that supports this API on all frameworks that map to that netstandard version.

Determine library version

• If targeting netstandard
  • Ensure minor version of the assembly is bumped since last stable package release
• If targeting netcoreapp
  • No assembly version bump necessary

Making the changes in repo

If changing the library version

• The AssemblyVersion property isn't always in <Library>\Directory.Build.props file unless we want to override the default for some reason. For more information on how the original version is calculated, see Arcade documentation.
• If the AssemblyVersion property exists (for example, Microsoft.CSharp\Directory.Build.props), you can change it.
• If the AssemblyVersion property doesn't exist (for example, System.Runtime\Directory.Build.props), you can add it.

If changing the target group

• Update both the Configurations property in the library's csproj file and the BuildConfigurations property in the library's Configurations.props file.

Update pkg

• If changing the target framework
  • Update SupportedFramework metadata on the ref ProjectReference to declare the set of concrete platforms you expect your library to support. (see Specific platform mappings). Generally will be a combination of netcoreapp2.x, netfx46x, and/or $(AllXamarinFrameworks).
• If assembly or package version is updated the package index needs to be updated by running dotnet msbuild <Library>/pkg/<Library>.pkgproj /t:UpdatePackageIndex

Update tests

• Set TargetGroup which will generally match the TargetGroup in the src library build configuration. (ex: System.Runtime\tests\Configurations.props)
• Add new test code following conventions for new files to that are specific to the new target framework.
• To run just the new test configuration run dotnet msbuild <Library>.csproj /t:RebuildAndTest /p:TargetGroup=<TargetGroup>

Documentation

New public APIs must be documented with triple-slash comments on top of them. Visual Studio automatically generates the structure for you when you type ///.

If your new API or the APIs it calls throw any exceptions, those need to be manually documented by adding the <exception></exception> elements.

After your change is merged, we will eventually port them to the dotnet-api-docs repo, where we will review them for language and proper style (For more information, see the API writing guidelines).

Once the dotnet-api-docs change is merged, your comments will start showing up in the official API documentation at http://docs.microsoft.com/, and later they'll appear in IntelliSense in Visual Studio and Visual Studio Code. Once the documentation is official, any subsequent updates to it must be made directly in https://github.com/dotnet/dotnet-api-docs/. It's fine to make updates to the triple slash comments later, they just won't automatically flow into the official docs.

FAQ

Is your API part of netstandard?

Use apisof.net to identify the support matrix of a specific API.

What is the difference between being part of netstandard and building against netstandard?

Things that are part of netstandard can only change when we release a new version of a platform that supports the higher version of netstandard. Whereas things that build against netstandard and ship in independent packages can be changed without an update to the platform that it is running on. That gives more flexibility to add API to things that build against netstandard because it does not require a platform update to consume.

How do I consume APIs from another package that aren't yet published?

If you are adding APIs across multiple packages at the same time. You can temporarily add a direct ProjectReference from the ref\csproj to the ref\csproj, src\csproj to the ref\csproj, and/or tests\csproj to pkg\pkgproj. Once a new set of packages have been published these ProjectReferences should be removed.

What to do if you are moving types down into a lower contract?

If you are moving types down you need to version both contracts at the same time and temporarily use project references across the projects. You also need to be sure to leave type-forwards in the places where you removed types in order to maintain back-compat.