Add a switch to control publishing files to the refs directory - PreserveCompilationReferences

[pranavkm]

Related issues - #2092, #2121

PreserveCompilationContext is used in two places today

1. To determine if compilation content goes in the deps file
2. If reference assemblies need to be copied to the bin\refs and publish\refs directories.

Prior to 2.1.0, the Web Sdk always set PreserveCompilationContext=true. This resulted in increased deployment sizes even when the app did not require these files due to design time compilation of views. In 2.1.0-preview2, we tried conditionally setting this value in the WebSdk based on the presence of Razor files. This broke Mvc's runtime capabilities which relies on being able to inspect the deps file to query dependencies. There's more information about it here - #2092 (comment).

What we care about, is the ability to suppress publishing the refs directory for most applications. In lieu of solving #2092, which seems like a much more involved issue, it would be easier if we could have a different switch (suggestion PreserveCompilationReferences) that is used to determine if the refs directory gets emitted. Here are the two places we'd use this switch in lieu of PreserveCompilationContext:

• sdk/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.PreserveCompilationContext.targets

  Lines 45 to 46 in 6945e36

  	<Target Name="ComputeRefAssembliesToPublish"
  	Condition="'$(PreserveCompilationContext)' == 'true'"

• sdk/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.PreserveCompilationContext.targets

  Lines 84 to 85 in 6945e36

  	<Target Name="_CopyReferenceOnlyAssembliesForBuild"
  	Condition="'$(PreserveCompilationContext)' == 'true'"

The Web.Sdk \ Razor.Sdk would be responsible for setting the default value of this property as also initializing it if the user explicitly specified PreserveCompilationContext in their project files.

[pranavkm]

cc @eerhardt \ @livarcocc \ @DamianEdwards \ @rynowak

We'd like to get this considered for 2.1.0 rc. Let me know if you'd like to set up an offline discussion for this.

[normj]

Any progress on this? For us we want to keep the publish package size small so we are always setting PreserveCompilationContext to false but this breaks some customer scenarios.

[lmolotii]

Guys, do we have any progress on this issue?

[nguerrera]

See https://github.com/dotnet/cli/issues/10502#issuecomment-452408306

We should do this now. cc @dsplaisted

[rynowak]

This would be super nice to have built-in. We do our own workaround for this in Razor, and it would be better if we could just set a property default value 👍