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Exclude Project in sln from dotnet build

I have a roslyn analyzer project based on Microsoft's default template. I can easily build the analyzer in Visual Studio or with msbuild.
The problem is that the solution includes a vsix project that relies on the microsoft.vssdk.buildtools which are not supported by dotnet build.
This results in an error message when trying to build the solution in the command line with dotnet build: microsoft.vssdk.buildtools\17.4.2119\tools\VSSDK\Microsoft.VsSDK.targets(826,5): error : VSIX deployment is not supported with 'dotnet build'
The vsix is nice to have when developing with Visual Studio, but I do publish my analyzer via NuGet package instead of as vsix so I don't need the vsix on the CLI.
Is there a way to specify in the csproj that I don't want it to be built when it is invoked from dotnet build? I'd like to avoid having a separate sln file or a specific dotnet configuration that excludes the project if possible.

Two possible approaches include using a solution filter and changing the project to not build under certain conditions.
Use a Solution Filter
dotnet build will accept a solution filter file (.slnf).
To create the solution filter:
Open the solution in Visual Studio
Go to the solution explorer window
Right-click on the VSIX project, choose 'Unload Project'
Right-click on the solution, choose 'Save As Solution Filter'
When building with dotnet the .slnf will need to be used. Using the .sln file or the VSIX project file with dotnet will be an error.
Detecting when Invoked from dotnet build
There isn't a defined property or function in MSBuild that identifies the executable that is running the MSBuild engine.
However there is a MSBuildRuntimeType property.
Prior to MSBuild 15, MSBuildRuntimeType will be undefined. In MSBuild 15 and later MSBuildRuntimeType will have a value of Full, Core, or Mono. From the documentation MSBuildRuntimeType will have a value of Core when dotnet build is used. (Further the error message "VSIX deployment is not supported with 'dotnet build'" is only displayed when '$(MSBuildRuntimeType)' == 'Core'.)
There isn't an 'exit build' task so the project can't detect and then end. We need to detect before the project really starts. But wrapping a project within a project is clunky especially if you want to be able to work with the project and change properties from the Visual Studio IDE.
Targets can be redefined and an Import can have a condition. A file can be imported when MSBuildRuntimeType is Core and the file can redefine the 'Build' target.
Add to the VSIX project file:
<Import Project="noop.targets" Condition="'$(MSBuildRuntimeType)' == 'Core'" />
The noop.targets may contain the following:
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<Target Name="Build">
<Message Text="$(MSBuildProjectName) has been skipped." />
</Target>
</Project>
Hope this helps or at least provides some ideas.

docfx metadata step fails with error "Could not load SDK Resolver"

Whenever I try to build any documentation using docfx, I get the following error in the metadata build step that uses msbuild to analyze the xml comments in the code of the csprojs:
Warning:MetadataCommand.ExtractMetadataWorkspace failed with: [Failure] Msbuild failed when processing the file 'C:\temp\docfxtest\docfx_project\src\src.csproj' with message: Could not load SDK Resolver. A manifest file exists, but the path to the SDK Resolver DLL file could not be found. Manifest file path 'C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools\MSBuild\15.0\Bin\SdkResolvers\Microsoft.Build.NuGetSdkResolver\Microsoft.Build.NuGetSdkResolver.xml'. SDK resolver path: C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools\Common7\IDE\CommonExtensions\Microsoft\NuGet\Microsoft.Build.NuGetSdkResolver.dll C:\temp\docfxtest\docfx_project\src\src.csproj
It seems that msbuild cannot be correctly resolved by docfx. Any idea how I could fix this?
Im using docfx version 2.56.5.0 on Windows and I also have VS Enterprise 2019 (16.8.2) and VS Build Tools 2017 (15.9.29) installed:
UPDATE:
I have now uninstalled the VS 2017 build tools completely and repaired the VS 2019 installation using the installer. I now get a different error when I run docfx. It seems that it can't find msbuild at all anymore.
Warning:MetadataCommand.ExtractMetadataWorkspace failed with: [Failure] Msbuild failed when processing the file 'C:\temp\docfxtest\docfx_project\src\src.csproj' with message: The SDK 'Microsoft.NET.Sdk' specified could not be found. C:\temp\docfxtest\docfx_project\src\src.csproj
Running msbuild -t:restore,build also shows that it can't find msbuild
'msbuild' is not recognized as an internal or external command
The targets are isntalled:
And so is the .NET Core workload:

Your Build Tool for VS2017 might have some problems due to some issues. The most issue is this:
C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools\Common7\IDE\CommonExtensions\Microsoft\NuGet\Microsoft.Build.NuGetSdkResolver.dll
Either you lost the dll or the dll is damaged.
Update
1) First, you should check whether you have installed NuGet targets and build tasks workload and net core build tools workload. If not, please install it.
2) Second, please delete bin and obj folder of your project and then try again.
You should use msbuild -t:restore,build to build your project.
3) Third, try to Repair from vs_installer for your build tool. It will repair the related dll. And then delete bin and obj folder, use build tool to test your project again.
Important:
VS2017 does not support net core 3.1. You should note that. It supports <=net core 2.1.
So if you still want to use Build Tool of VS2017 for your net core project, you should try the the above three steps and then target your project to net core 2.1.
Besides, if you start msbuild by CMD, I think you should check your environment variable PATH and check whether you have configured the msbuild.exe from Build Tool of VS2017 on it. Instead, you could add C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Current\Bin\MSBuild.exe. This way is for VS2019.
=================================================
Update 1
The problem is that you have already installed a docfx tool by choco command line.
At the beginning, I always thought that you used docfx.console nuget package on your project and just invoke docfx.exe from C:\Users\xxx\.nuget\packages\docfx.console\2.56.5\tools\docfx.exe under command line.
Regardless of the installation of docfx.console package on your project, if you installed docfx tool by choco command and then just invoke docfx.exe on command line, it used the local docfx.exe under C:\ProgramData\chocolatey\lib\docfx\tools\docfx.exe rather than the nuget package.
So the issue is that your local docfx.exe has some errors due to some issues. You should reinstall the docfx.exe by choco command choco uninstall docfx; choco install docfx.
Actually, directly use docfx.console nuget package on your project might be easier. From this link.
It already contains the generation step of the documentation by docfx.exe(from C:\Users\xxx\.nuget\packages\docfx.console\2.56.5\tools\docfx.exe) and will execute it automatically rather than run docfx.exe again manually.

I have completely uninstalled docfx using chocolatey (choco uninstall docfx) removed every folder named docfxfrom c:\ProgramData\chocolatey\.chocolatey\ and then reinstalled it (choco install docfx). After that, everything worked fine again. The file c:\ProgramData\chocolatey\lib\docfx\tools\docfx.exe.config contains a lot of msbuild related configuration. Maybe something was messed up there.

.NET Core Build Fails, Can't find csc.dll file in MSBuild folder

Installed .NET Core 3.1 SDK from Microsoft.com/net/core
If I run
dotnet --version it says: 3.1.101
I run dotnet new console -o myApp and it successfully creates a console app in c:\myApp.
I change to the folder and try to run dotnet run or dotnet run myapp and I get the following error every time.
C:\Program Files\dotnet\sdk\3.1.101\Roslyn\Microsoft.CSharp.Core.targets(59,5): error MSB6004: The specified task executable location "C:\Program Files (x86)\MSBuild\14.0\Bin\csc.dll" is invalid. [C:\myApp\myApp.csproj] The build failed. Fix the build errors and run again.
I've checked the folder it mentions in the error message, and of course, there is no csc.dll file, just a csc.exe.
This is a clean project, with no modifications, immediately after running the installer (dotnet-sdk-3.1.101-win-x64.exe)
Not really sure where to go from here. How do I fix MSBuild to look for the .exe (or am I barking up the wrong tree?)

dotnet build xamarin project fails using console

When I try to build my .csproj file with dotnet it throws an error, but when I build project at Visual Studio 2019 it succeeds.
I need to build with dotnet because my Azure pipeline job uses it.
This is the error:
dotnet build MyProject.Mobile.Droid.csproj --configuration Release --force
MyProject.Mobile.Droid.csproj(584,3): error MSB4019: The imported project "C:\Program Files\dotnet\sdk\3.1.100\\Xamarin\Android\Xamarin.Android.CSharp.targets was not found. Confirm that the expression in the Import declaration "C:\Program Files\dotnet\sdk\3.1.100\\Xamarin\Android\Xamarin.Android.CSharp.targets" is correct, and the file exists on disk.
Build FAILED.
(Also as a screenshot.)
If I set the path parameter in my .csproj to this:
<MSBuildExtensionsPath>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild</MSBuildExtensionsPath>
Then the error changes:
The reference assemblies for MonoAndroid,Version=v1.0 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
Any suggestions on how to solve this?

You'll need to use msbuild (like msbuild MySolution.sln) to build a Xamarin project today.
You can build the individual netstandard2.x projects using dotnet build, however the Mono based platform projects (i.e. the Android and iOS projects) need to be built using msbuild.

Try setting the TargetFrameworkRootPath to where you have xamarin installed.
<TargetFrameworkRootPath>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\Common7\IDE\ReferenceAssemblies\Microsoft\Framework\</TargetFrameworkRootPath>
or on the command line
dotnet build -clp:ErrorsOnly -p:MSBuildExtensionsPath="C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/MSBuild"/ -p:TargetFrameworkRootPath="C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/Common7/IDE/ReferenceAssemblies/Microsoft/Framework/"

How to restore nuget private feed using MSBuild in Visual Studio

I'm configuring an existing project (dotnet core) to use private nuget repository.
I've setup my project with the structure as follows:
Project1
Project2
Project3
.sln
nuget.config
I'm able to restore my packages if i'm to run a "dotnet restore" commands but not while using Visual Studio's build (MSBuild).
I would like to be able to restore my package while using Visual Studio's MSBuild.(not using cli)
If possible, i'd like to avoid using msbuild's Exec task to run dotnet restore before build.
I've tried them in both Visual Studio 2017 and 2019

You will need to run the MSBuild Restore target before the actual target. MSBuild.exe provides a built-in way to execute this target, then flush all caches (needed to avoid incremental build issues due to freshly restored packages) and then perform the actual build with the the -r (long: -restore) argument:
e.g.:
msbuild -r -p:Configuration=Release the.sln