Referenced RCL project is built even though there are no recent changes to it

[kichalla]

Repro:

• Create a RP web application
• Add a RCL project to the solution | reference this RCL project from the RP application
• Build RP application
• Update the RCL project's Page1.cshtml's title to something else
• Build RP application (this is expected)
• Build RP application again (you see that the RCL project is being built again even though there aren't any changes)

Build output (in sequence...check the title for more info):
https://gist.github.com/kichalla/6a099b89d4aad043a3971f3b43b4f157
https://gist.github.com/kichalla/a9e9a5eb952f7adde54e568ef79b57c1
https://gist.github.com/kichalla/d0f4337bad4137934362566cd436888b

When I enabled Info level logging, I see the following output:

1>FastUpToDate: Latest write timestamp on input is 5/1/2018 11:18:25 AM on 'C:\Users\kichalla\source\repos\WebApplication28\RCL\Areas\MyFeature\Pages\Page1.cshtml'. (RCL)
1>FastUpToDate: Earliest write timestamp on output is 5/1/2018 11:16:45 AM on 'C:\Users\kichalla\source\repos\WebApplication28\RCL\bin\Debug\netstandard2.0\RCL.dll'. (RCL)
1>FastUpToDate: Output is newer than input, not up to date. (RCL)
1>FastUpToDate: Project is not up to date. (RCL)
1>------ Build started: Project: RCL, Configuration: Debug Any CPU ------
1>You are working with a preview version of the .NET Core SDK. You can define the SDK version via a global.json file in the current project. More at https://go.microsoft.com/fwlink/?linkid=869452
1>RCL -> C:\Users\kichalla\source\repos\WebApplication28\RCL\bin\Debug\netstandard2.0\RCL.dll
1>RCL -> C:\Users\kichalla\source\repos\WebApplication28\RCL\bin\Debug\netstandard2.0\RCL.Views.dll
2>FastUpToDate: Latest write timestamp on input is 5/1/2018 11:16:45 AM on 'C:\Users\kichalla\source\repos\WebApplication28\RCL\bin\Debug\netstandard2.0\RCL.dll'. (WebApplication28)
2>FastUpToDate: Earliest write timestamp on output is 5/1/2018 11:16:52 AM on 'C:\Users\kichalla\source\repos\WebApplication28\WebApplication28\bin\Debug\netcoreapp2.1\WebApplication28.dll'. (WebApplication28)
2>FastUpToDate: Latest write timestamp on input marker is 5/1/2018 11:18:30 AM on 'C:\Users\kichalla\source\repos\WebApplication28\RCL\obj\Debug\netstandard2.0\RCL.csproj.CopyComplete'. (WebApplication28)
2>FastUpToDate: Write timestamp on output marker is 5/1/2018 11:16:57 AM on 'C:\Users\kichalla\source\repos\WebApplication28\WebApplication28\obj\Debug\netcoreapp2.1\WebApplication28.csproj.CopyComplete'. (WebApplication28)
2>FastUpToDate: Input marker is newer than output marker, not up to date. (WebApplication28)
2>FastUpToDate: Project is not up to date. (WebApplication28)
2>------ Build started: Project: WebApplication28, Configuration: Debug Any CPU ------
2>WebApplication28 -> C:\Users\kichalla\source\repos\WebApplication28\WebApplication28\bin\Debug\netcoreapp2.1\WebApplication28.dll
2>WebApplication28 -> C:\Users\kichalla\source\repos\WebApplication28\WebApplication28\bin\Debug\netcoreapp2.1\WebApplication28.Views.dll
========== Build: 2 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========

Notice the following block...can it say 'Latest write timestamp' on both these lines? and also it should be input is newer than output?
1>FastUpToDate: Latest write timestamp on input is 5/1/2018 11:18:25 AM on 'C:\Users\kichalla\source\repos\WebApplication28\RCL\Areas\MyFeature\Pages\Page1.cshtml'. (RCL)
1>FastUpToDate: Earliest write timestamp on output is 5/1/2018 11:16:45 AM on 'C:\Users\kichalla\source\repos\WebApplication28\RCL\bin\Debug\netstandard2.0\RCL.dll'. (RCL)
1>FastUpToDate: Output is newer than input, not up to date. (RCL)
1>FastUpToDate: Project is not up to date. (RCL)

cc @pranavkm

[pranavkm]

To note, we're still doing an incremental noop build in MSBuild, it's just that we miss doing a FastUpToDate build where basically VS does not launch MSBuild. Possible fix might include touching the outputs of the class library.

[mkArtakMSFT]

@pranavkm, is the fix for this super cheap?

[pranavkm]

@pranavkm, is the fix for this super cheap?

The fix is likely cheap, but I'm concerned about testing this. I'd feel hesitant to consider this for 2.1.0-rtm.