Clarification on the MSBuild property RestorePackagesConfig

[Bartleby2718]

Goal

I want to be able to (restore and) build both SDK-style and non-SDK C# projects using a single MSBuild command.

Thought Process

1. MSBuild.exe MySolution.sln ... -restore works for SDK-style projects that use PackageReferences, but I also want to support non-SDK-style projects that use packages.config.
2. Based on https://learn.microsoft.com/en-us/nuget/consume-packages/package-restore, it seems like -p:RestorePackagesConfig=true is all I need. I confirmed that this works for non-SDK-style projects that use packages.config.

Questions

1. Does MSBuild.exe MySolution.sln ... -restore -p:RestorePackagesConfig=true also work for SDK-style projects that use PackageReferences? It worked for one such solution, but I'm not sure if I got lucky or this is the intended behavior. FWIW https://stackoverflow.com/a/73575473 says it works.
2. Not important if the answer is yes to the first question, but if possible, I want to move RestorePackagesConfig to a file. Therefore, I created Directory.Build.props next to the solution file:

<Project>
    <PropertyGroup>
      <RestorePackagesConfig>true</RestorePackagesConfig>
    </PropertyGroup>
</Project>

However, a bunch of <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">s are still mad at me because the package restore isn't being done. (This target is mentioned in #3320, but I feel like this target is doing its job in this case.) For some reason, I get

Determining projects to restore...
All projects are up-to-date for restore.

even though the projects are not.

Notes

• In Default Project2ProjectTimeOut value #12554 and Nuget restore doesn't restore all packages from project.assets.json #12982, @zivkan does "strongly recommend you stop using nuget.exe, and use msbuild -t:restore -p:RestorePackagesConfig=true instead" but it's unclear whether it'll work for SDK-style projects that use PackagReferences.

[zivkan]

1. yes, msbuild works on SDK style projects. I think of Visual Studio as a GUI on top of MSBuild, so in most (but unfortunately not all) cases, if it works in VS, it'll probably work on the CLI with msbuild.

2. msbuild restore of packages.config doesn't work on a per-project setting. It needs to be passed into Nuget's RestoreTask. This is why I specified the -p:RestorePackagesConfig=true on the command line, which personally I recommend in CI scripts as well, but that's just my personal preference. But in theory copying that Directory.Build.props example to Directory.Solution.props will work: https://learn.microsoft.com/en-us/visualstudio/msbuild/customize-solution-build?view=vs-2022

[Bartleby2718]

Thanks @zivkan for the response! A couple more questions:

1. I didn't find anything about RestorePackagesConfig in dotnet/msbuild, but I did see a few occurrences of RestorePackagesConfig in NuGet/NuGet.Client. When RestorePackagesConfig is set, can you tell from the code whether MSBuild restores packages only from packages.config or also packages.config? I think that'll give me extra confidence.
2. Huh, I had tried both Directory.Build.props and before.MySolution.sln.targets and thought neither worked. (I didn't know about Directory.Solution.props.) Now I see that Directory.Solution.props and before.MySolution.sln.targets work, which matches what you said, and Directory.Build.props doesn't. At least I have a working solution, so this is great!

[zivkan]

It restores both packages.config and PackageReference. Here's the code that does the pacakges.config restore, and immediately after that block is the PackageReference block. There's no else statement, or early return statement.