Is there an equivalent of $(BuildingInsideVisualStudio) which will detect NuGet? - msbuild

Question

In MSBuild there is a variable $(BuildingInsideVisualStudio) which can be used to detect whether build is running inside Visual Studio, so I can do conditions like this:
<PropertyGroup Condition="'$(BuildingInsideVisualStudio)' != 'true'">
<GeneratePackageOnBuild>true</GeneratePackageOnBuild>
</PropertyGroup>
Is there anything similar for NuGet? I want different conditions to run if the project is being used inside package manager.

Answer 1

Your comment to the question makes it sound like your goal is to keep a packages versions consistent across different conditions in a single project, but it's also a common case that you want to keep it consistent across projects in a solution or repo.
I'm going to suggest a different solution. Create a Directory.Build.props in your repo root that looks something like this:
<Project>
<PropertyGroup>
<NewtonsoftJsonVersion>12.0.1</NewtonsoftJsonVersion>
<xunitVersion>2.4.1</xunitVersion>
</PropertyGroup>
</Project>
Now in your projects that need Newtonsoft.json, you change the PackageReference to <PackageReference Include="Newtonsoft.Json" Version="$(NewtonsoftJsonVersion)" />.
If you put your production code in src\ and test code in test\, then you can create a test\Directory.Build.props with the contents:
<Project>
<Import Project="$([MSBuild]::GetPathOfFileAbove('Directory.Build.props', '$(MSBuildThisFileDirectory)../'))" />
<PropertyGroup>
<PackageReference Include="xunit" Version="$(xunitVersion)" />
</PropertyGroup>
</Project>
Now all of your projects under test\ will get xunit automatically, and it's guaranteed to be the same version.
When you want to upgrade a package version, you can use the Package Manager UI to check for versions, but unfortunately not to upgrade the version. For that, you'll need to manually edit the repo root Directory.Build.props (so add it to your solution for quick access), but you can be confident that every reference to that package will use the same version. It is limited to projects using PackageReference, there's no solution currently for packages.config, but MSBuild conditions only for for PackageReference too.
You can see this pattern often in Microsoft repositories. Certainly NuGet (my team, yay!), and various .NET repos like cli and sdk do it, although in manually imported props files, rather than Directory.Build.props, though the concept is the same.

Answer 2

There is no direct solution for the case. NuGet is just download manager, it loads sources. MSBuild is a build system, it builds sources. They don't exchange any information between.
I would suggest you to move an another way. You can add a props file into your nuget packaging project with
<?xml version="1.0" encoding="utf-8" ?>
<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003" ToolsVersion="4.0">
<ItemGroup>
<PackageUsedFromNuget>true</PackageUsedFromNuget>
</ItemGroup>
</Project>