Setting PreserveCompilationContext=false trims Microsoft.AspNetCore.App shared runtime in deps files

From @pranavkm on March 26, 2018 17:18

Steps to reproduce

1. Create an webapi \ mvc \ emptyweb application using preview1 (or preview2) Sdk
2. Build the project

The generated deps file will say that the application references both Microsoft.NETCore.App and Microsoft.AspNetCore.App:

"blah/1.0.0": {
    "dependencies": {
      "Microsoft.AspNetCore.App": "2.1.0-preview1-final",
      "Microsoft.NETCore.App": "2.1.0-preview1-26216-03"
    },
    "runtime": {
      "blah.dll": {}
    },
    "compile": {
      "blah.dll": {}
    }
},

1. Delete the bin directory. Edit the csproj <PreserveCompilationContext>false</PreserveCompilationContext>. Rebuild the project
2. The generated deps file will say that the app no longer references Microsoft.AspNetCore.App:

 "blah/1.0.0": {
   "dependencies": {
     "Microsoft.NETCore.App": "2.1.0-preview1-26216-03"
   },
   "runtime": {
     "blah.dll": {}
   }
 },

Environment data

.NET Command Line Tools (2.1.300-preview1-008174)

Product Information:
 Version:            2.1.300-preview1-008174
 Commit SHA-1 hash:  b8df89a54f

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.16299
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Users\Pranav\Downloads\dotnet-sdk-2.1.300-preview1-008174-win-x64\sdk\2.1.300-preview1-008174\

Microsoft .NET Core Shared Framework Host

  Version  : 2.1.0-preview1-26216-03
  Build    : f2c3216183d20416568a4bbf5bb7d153e826f153

More information:

The bulk of MVC’s controller discovery model is based on finding libraries that directly or transitively depend on any one of Mvc’s libraries. In 2.1.0-preview2, the Razor.Sdk only sets PreserveCompilationContext=true if the app has any files that require runtime compilation. For projects without views, such as webapi or empty web template, the produced deps file claims that the app does not reference Microsoft.AspNetCore.App -> Microsoft.AspNetCore.Mvc. Consequently no controllers are discovered.

Copied from original issue: dotnet/core-setup#3902

[pranavkm]

Stepping back, the primary driver for turning off PreserveCompilationContext is to avoid publishing the refs directory when an application does not require it (e.g. when you’re writing an application not using runtime compiled views). Right now, there’s a single switch that determines the structure of the deps file and the published refs directory. Could we possibly introduce a new switch that controls publishing the refs directory?

// Microsoft.NET.Sdk.Razor.targets
<!-- Use PreserveCompilationContext's value if it was explicitly set in the user's project -->
<PreserveCompilationReferences Condition="'$(PreserveCompilationContext)' != ''">$(PreserveCompilationContext)</PreserveCompilationReferences>

<!-- Initialize PreserveCompilationContext -->
<PreserveCompilationReferences Condition="'$(PreserveCompilationReferences )' == ''">true</PreserveCompilationReferences>

Targets in Microsoft.NET.Sdk that control publishing would be modified to rely on this new switch: https://github.com/dotnet/sdk/blob/6945e3694c918eea4c8c4fb6217e1485b179994b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.PreserveCompilationContext.targets#L45-L46 https://github.com/dotnet/sdk/blob/6945e3694c918eea4c8c4fb6217e1485b179994b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.PreserveCompilationContext.targets#L84-L85

It’s a breaking change for users relying on the refs directory in non-web scenarios, but I’m not sure if that’s a common scenario.

[nguerrera]

Going with https://github.com/dotnet/sdk/issues/2092#issuecomment-377050440, which is tracked by #2122.