When possible, use Reference6 to read ProjectReference metadata such as ReferenceOutputAssembly

[nkolev92]

Bug

Fixes: NuGet/Home#11163

Regression? Last working version:

Description

This is an attempt to the fix the UI delay caused by the double walk of the references..

I setup a test repo with the following relevant projects.

1. CPlusPlus.vcxproj - CpsProjectSystemReferencesReader
2. LegacyMSbuildProj.msbuildproj VSCoreProjectSystemReferencesReader
3. LegacyPackagesConfig.csproj VSCoreProjectSystemReferencesReader
4. ServiceFabric.sfproj VSCoreProjectSystemReferencesReader
5. Stateless.csproj VsManagedLanguagesProjectSystemServices

The project references are as follows:

LegacyPackagesConfig.csproj
=> CPlusPlus.vcxproj
=> LegacyMSbuildProj.msbuildproj
=> Stateless.csproj
ServiceFabric.sfproj
=> Stateless.csproj
LegacyMSbuildProj.msbuildproj
=> Stateless.csproj

When walking each of the 3 above projects for ProjectReference, the following happens:

• All the LegacyPackagesConfig project references can be cast to Reference6.
• None of the ServiceFabric project references can be cast to Reference6, but can be cast to Reference3.
• None of the LegacyMSbuildProj project references can be cast to Reference6, but can be cast to Reference3.

The proposal is the following:

Currently the behavior is:

• walk the tree for projects that should be excluded.
• walk the tree for all projects and skip the ones that should be excluded.

The first part is the expensive part.

The proposal is:

• Walk the tree for all projects and if the projects can be cast to Reference6, then just use the metadata from there, otherwise use Reference3 and keep track of the fact that we couldn't get the metadata.
• If any of the above projects couldn't be cast to Reference6, walk the tree for the excluded projects the expensive way to avoid any functional regressions (which are frankly, pretty unlikely, but we can't break the experience.)

This should fix the UI delay for most project types.

@lifengl @davkean
Based on the above findings, we'd need CPS to implement Reference6 - https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1431168

PR Checklist

• PR has a meaningful title

• PR has a linked issue.

• Described changes

• Tests

  • Automated tests added
  • OR
  • Test exception - Existing behavior.
  • OR
  • N/A

• Documentation

  • Documentation PR or issue filled
  • OR
  • N/A

[nkolev92]

@NuGet/nuget-client

Can I please get a review here?

[kartheekp-ms]

Should we add metadataElements.Length == 0 condition also?

Another question that I have is, metadataElements argument value is not used except for null or empty checks. Do we need this parameter?

[nkolev92]

I think we can just remove metadataElements.