Default ProduceReferenceAssembly to true

Get better incremental build performance by opting in to reference assembly based builds by defaulting ProduceReferenceAssembly to true.

Since this is a behaviour change, it may be good to do it in 3.0 and for SDK projects only.

[dsplaisted]

In our sync-up, we decided to go ahead with enabling this by default for .NET 5.0 and higher.

[rainersigwald]

Ok, I did a small proof-of-concept that things are still broken.

MixedSolutionWithRefAssemblies.zip

This solution has:

• An SDK netstandard library that produces reference assemblies
• A net472 .exe
• A net472 unit test project

The unit test project tests library functionality by calling the app that calls the library.

1. Open up the solution in VS and run the test through the UI.

========== Build: 3 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========

1. It fails, because there’s an error in the library. It subtracts instead of adds.
2. Fix the error:

diff --git a/Lib/Class1.cs b/Lib/Class1.cs
index a33c4c0..76a1c90 100644
--- a/Lib/Class1.cs
+++ b/Lib/Class1.cs
@@ -6,7 +6,7 @@ namespace Lib
     {
         public static int Add(int a, int b)
         {
-            return a - b; // note deliberate error
+            return a + b;
         }
     }
 }

1. Run the test again.
2. The test still fails, because

========== Build: 1 succeeded, 0 failed, 2 up-to-date, 0 skipped ==========

That’s because the fast-up-to-date check in csproj doesn’t understand that it needs to tell MSBuild to build the app even though its direct input (the lib.dll reference assembly) hasn’t changed. CoreCompile will be skipped, but the build will copy the implementation assembly along, so that the updated implementation is available at runtime.