Reduce code duplication across core assemblies

[marek-safar]

Sharing implementation via code duplication does not benefit size sensitive workloads and it would be great if it could be reduced from the current levels.

As an example, we can use https://github.com/dotnet/runtime/blob/master/src/libraries/Common/src/System/Text/ValueStringBuilder.cs which is compiled into 10 different assemblies while also being included inside System.Private.CoreLib assembly.

We could start with cleaning up duplicate code for cases which are compiled into System.Private.CoreLib as that assembly can be considered to be the common base for everything.

[eerhardt]

What are the options here?

• Making the shared code "public" so other libraries can use it
• InternalsVisibleTo

Are there other options?

There are also "layering" concerns in that 2 assemblies that want to share some code, but they don't want to depend on each other - would the shared code then need to go into a "lower" assembly?

[marek-safar]

Making the shared code "public" so other libraries can use it

There is already prior art at https://github.com/dotnet/runtime/blob/master/src/libraries/Common/src/System/Collections/Generic/ReferenceEqualityComparer.cs#L19

2 assemblies that want to share some code, but they don't want to depend on each other

That's why I picked SPC only for now

Are there other options??

• Make most "core" assemblies facade assemblies and have massive SPC
• Move the common code to shared library or libraries (any code will exist at most twice in SPC and common assembly/assemblies)

[eerhardt]

As an example, we can use https://github.com/dotnet/runtime/blob/master/src/libraries/Common/src/System/Text/ValueStringBuilder.cs which is compiled into 10 different assemblies while also being included inside System.Private.CoreLib assembly.

Making the shared code "public" so other libraries can use it

Linking #25587 (comment) for why ValueStringBuilder hasn't been been an approved public API to date.