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perhaps a clone issue. it builds for me.
I tried cloning again, and got build issue again, so I tried to see what could be the possible causes.
I also tried to open up another solution, IdentityServer4.Core.sln, and I get the same error as for the sample project, so it seems I cannot build any solution from IdentityServer4...
When trying to do nuget restore: Error occurred while restoring NuGet packages: The local source 'D:\GitHub\IdentityServer\IdentityServer4\nuget' doesn't exist.



UPDATE: The issue was caused by NuGet localsource, I found the solution here: https://stackoverflow.com/questions/49446394/unable-to-find-nuget-local-source-error-occurred-while-restoring-nuget-packages
So I did the following, in case it occurs to someone else in the future:
Now the nuget packages are able to be restored and now the build works.
This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.
Most helpful comment
UPDATE: The issue was caused by NuGet localsource, I found the solution here: https://stackoverflow.com/questions/49446394/unable-to-find-nuget-local-source-error-occurred-while-restoring-nuget-packages
So I did the following, in case it occurs to someone else in the future:
Now the nuget packages are able to be restored and now the build works.