The Extensions.sln contains invalid content

Describe the bug

1. Extensions.sln contains git merge conflict marker(<<<<<<<) on release/2.2 branch.
2. Extensions.sln contains removed projects(src\Shared\testassets\ThrowingLibrary\ThrowingLibrary.csproj) on master and release/2.2 branch.

To Reproduce

1. Clone this repo
2. Run build script

.\build.ps1

1. Run this code

dotnet clean

1. See error

on release/2.2 branch

Microsoft (R) Build Engine version 16.0.225-preview+g5ebeba52a1 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 1/29/2019 11:18:39 AM.
     0>D:\ReferenceSource\aspnet\Extensions\Extensions.sln(1619): Solution file error MSB5007: Error parsing the project configuration section in solution file. The entry "<<<<<<< HEAD" is invalid.

Build FAILED.

         D:\ReferenceSource\aspnet\Extensions\Extensions.sln(1619): Solution file error MSB5007: Error parsing the project configuration section in solution file. The entry "<<<<<<< HEAD" is invalid.

    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:00.06

on master branch

Microsoft (R) Build Engine version 16.0.225-preview+g5ebeba52a1 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 1/29/2019 11:23:43 AM.
     1>Project "D:\ReferenceSource\aspnet\Extensions\Extensions.sln" on node 1 (Clean target(s)).
     1>ValidateSolutionConfiguration:
         Building solution configuration "Debug|Any CPU".
     1>D:\ReferenceSource\aspnet\Extensions\Extensions.sln.metaproj : error MSB3202: The project file "D:\ReferenceSource\aspnet\Extensions\src\Shared\testassets\ThrowingLibrary\ThrowingLibrary.csproj" was not found. [D:\ReferenceSource\aspnet\Extensions\Extensions.sln]
     1>Project "D:\ReferenceSource\aspnet\Extensions\Extensions.sln" (1) is building "D:\ReferenceSource\aspnet\Extensions\src\JSInterop\Microsoft.JSInterop.JS\src\Microsoft.JSInterop.JS.csproj" (7) on node 2 (Clean target(s)).
     7>PreComputeCompileTypeScriptWithTSConfig:
         C:\Users\akunzai\.nuget\packages\microsoft.typescript.msbuild\2.9.2\build\\..\tools\tsc\tsc.exe --project "D:\ReferenceSource\aspnet\Extensions\src\JSInterop\Microsoft.JSInterop.JS\src\tsconfig.json" --listEmittedFiles
     7>Done Building Project "D:\ReferenceSource\aspnet\Extensions\src\JSInterop\Microsoft.JSInterop.JS\src\Microsoft.JSInterop.JS.csproj" (Clean target(s)).
     1>Project "D:\ReferenceSource\aspnet\Extensions\Extensions.sln" (1) is building "D:\ReferenceSource\aspnet\Extensions\src\Localization\Localization\test\Microsoft.Extensions.Localization.Tests.csproj" (14) on node 2 (Clean target(s)).
    14>Project "D:\ReferenceSource\aspnet\Extensions\src\Localization\Localization\test\Microsoft.Extensions.Localization.Tests.csproj" (14) is building "D:\ReferenceSource\aspnet\Extensions\src\Localization\Localization\test\Microsoft.Extensions.Localization.Tests.csproj" (14:3) on node 1 (Clean target(s)).
  14:3>Project "D:\ReferenceSource\aspnet\Extensions\src\Localization\Localization\test\Microsoft.Extensions.Localization.Tests.csproj" (14:3) is building "D:\ReferenceSource\aspnet\Extensions\src\Logging\Logging.Testing\src\Microsoft.Extensions.Logging.Testing.csproj" (17:5) on node 3 (Clean target(s)).
  17:5>Project "D:\ReferenceSource\aspnet\Extensions\src\Logging\Logging.Testing\src\Microsoft.Extensions.Logging.Testing.csproj" (17:5) is building "D:\ReferenceSource\aspnet\Extensions\src\logging\Logging\src\Microsoft.Extensions.Logging.csproj" (26:9) on node 1 (Clean target(s)).
    26>D:\ReferenceSource\aspnet\Extensions\eng\targets\ResolveReferences.targets(117,5): warning : Package references changed since the last release. This could be a breaking change. References removed: [D:\ReferenceSource\aspnet\Extensions\src\logging\Logging\src\Microsoft.Extensions.Logging.csproj]
D:\ReferenceSource\aspnet\Extensions\eng\targets\ResolveReferences.targets(117,5): warning :  - Microsoft.Extensions.DependencyInjection.Abstractions [D:\ReferenceSource\aspnet\Extensions\src\logging\Logging\src\Microsoft.Extensions.Logging.csproj]
    26>Done Building Project "D:\ReferenceSource\aspnet\Extensions\src\logging\Logging\src\Microsoft.Extensions.Logging.csproj" (Clean target(s)).
    17>Done Building Project "D:\ReferenceSource\aspnet\Extensions\src\Logging\Logging.Testing\src\Microsoft.Extensions.Logging.Testing.csproj" (Clean target(s)).
    14>Done Building Project "D:\ReferenceSource\aspnet\Extensions\src\Localization\Localization\test\Microsoft.Extensions.Localization.Tests.csproj" (Clean target(s)).
    14>Done Building Project "D:\ReferenceSource\aspnet\Extensions\src\Localization\Localization\test\Microsoft.Extensions.Localization.Tests.csproj" (Clean target(s)).
     1>Project "D:\ReferenceSource\aspnet\Extensions\Extensions.sln" (1) is building "D:\ReferenceSource\aspnet\Extensions\eng\tools\BaselineGenerator\BaselineGenerator.csproj" (116) on node 1 (Clean target(s)).
   116>_CheckForNETCoreSdkIsPreview:
       C:\Program Files\dotnet\sdk\3.0.100-preview-009812\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.RuntimeIdentifierInference.targets(142,5): message NETSDK1057: You are using a preview version of .NET Core. See: https://aka.ms/dotnet-core-preview [D:\ReferenceSource\aspnet\Extensions\eng\tools\BaselineGenerator\BaselineGenerator.csproj]
   116>C:\Program Files\dotnet\sdk\3.0.100-preview-009812\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(220,5): error NETSDK1047: Assets file 'D:\ReferenceSource\aspnet\Extensions\eng\tools\BaselineGenerator\obj\project.assets.json' doesn't have a target for '.NETCoreApp,Version=v2.1/win-x64'. Ensure that restore has run and that you have included 'netcoreapp2.1' in the TargetFrameworks for your project. You may also need to include 'win-x64' in your project's RuntimeIdentifiers. [D:\ReferenceSource\aspnet\Extensions\eng\tools\BaselineGenerator\BaselineGenerator.csproj]
   116>Done Building Project "D:\ReferenceSource\aspnet\Extensions\eng\tools\BaselineGenerator\BaselineGenerator.csproj" (Clean target(s)) -- FAILED.
     1>Done Building Project "D:\ReferenceSource\aspnet\Extensions\Extensions.sln" (Clean target(s)) -- FAILED.

Build FAILED.

       "D:\ReferenceSource\aspnet\Extensions\Extensions.sln" (Clean target) (1) ->
       "D:\ReferenceSource\aspnet\Extensions\src\Localization\Localization\test\Microsoft.Extensions.Localization.Tests.csproj" (Clean target) (14) ->
       "D:\ReferenceSource\aspnet\Extensions\src\Localization\Localization\test\Microsoft.Extensions.Localization.Tests.csproj" (Clean target) (14:3) ->
       "D:\ReferenceSource\aspnet\Extensions\src\Logging\Logging.Testing\src\Microsoft.Extensions.Logging.Testing.csproj" (Clean target) (17:5) ->
       "D:\ReferenceSource\aspnet\Extensions\src\logging\Logging\src\Microsoft.Extensions.Logging.csproj" (Clean target) (26:9) ->
       (ResolveCustomReferences target) ->
         D:\ReferenceSource\aspnet\Extensions\eng\targets\ResolveReferences.targets(117,5): warning : Package references changed since the last release. This could be a breaking change. References removed: [D:\ReferenceSource\aspnet\Extensions\src\logging\Logging\src\Microsoft.Extensions.Logging.csproj]
       D:\ReferenceSource\aspnet\Extensions\eng\targets\ResolveReferences.targets(117,5): warning :  - Microsoft.Extensions.DependencyInjection.Abstractions [D:\ReferenceSource\aspnet\Extensions\src\logging\Logging\src\Microsoft.Extensions.Logging.csproj]


       "D:\ReferenceSource\aspnet\Extensions\Extensions.sln" (Clean target) (1) ->
       (Clean target) ->
         D:\ReferenceSource\aspnet\Extensions\Extensions.sln.metaproj : error MSB3202: The project file "D:\ReferenceSource\aspnet\Extensions\src\Shared\testassets\ThrowingLibrary\ThrowingLibrary.csproj" was not found. [D:\ReferenceSource\aspnet\Extensions\Extensions.sln]


       "D:\ReferenceSource\aspnet\Extensions\Extensions.sln" (Clean target) (1) ->
       "D:\ReferenceSource\aspnet\Extensions\eng\tools\BaselineGenerator\BaselineGenerator.csproj" (Clean target) (116) ->
       (ResolvePackageAssets target) ->
         C:\Program Files\dotnet\sdk\3.0.100-preview-009812\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(220,5): error NETSDK1047: Assets file 'D:\ReferenceSource\aspnet\Extensions\eng\tools\BaselineGenerator\obj\project.assets.json' doesn't have a target for '.NETCoreApp,Version=v2.1/win-x64'. Ensure that restore has run and that you have included 'netcoreapp2.1' in the TargetFrameworks for your project. You may also need to include 'win-x64' in your project's RuntimeIdentifiers. [D:\ReferenceSource\aspnet\Extensions\eng\tools\BaselineGenerator\BaselineGenerator.csproj]

    1 Warning(s)
    2 Error(s)

Time Elapsed 00:00:17.32

Expected behavior

dotnet cleanup without any errors.

Additional context

$ dotnet --info
.NET Core SDK (reflecting any global.json):
 Version:   3.0.100-preview-009812
 Commit:    e3abf6e935

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.17763
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.0.100-preview-009812\

Host (useful for support):
  Version: 3.0.0-preview-27122-01
  Commit:  00c5c8bc40

.NET Core SDKs installed:
  2.1.600-preview-009472 [C:\Program Files\dotnet\sdk]
  2.2.102 [C:\Program Files\dotnet\sdk]
  3.0.100-preview-009812 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0-preview-18579-0056 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0-preview-27122-01 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.0-alpha-27128-4 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

[dougbu]

Thanks for the information @akunzai. I only removed the merge conflict. Reopening because I have more work to do.

[akunzai]

@dougbu Thank you!