Full support of LSL

[WIP][Spec] Full support of the Lightweight Solution Load

Problem

NuGet client in VS is not fully functional in LSL mode. Currently only restore operation is supported. The main problem is NuGetProject and other components are not aware of LSL mode as all information from VS are retrieved via EnvDTE or CPS API.

Solution

NuGet VS client needs to support LSL mode without breaking it.

Development activity is tracked in NuGet/Home#5058.

List of NuGet operations per NuGet package management project model

Operation	packages.config	project.json	PackageRef	.NET Core
Restore	Supported	Supported	Supported	N/A
Manage packages (solution)	Supported	Supported	Supported	N/A
Manage packages (project)	Loads on right-click	Loads on right-click	Loads on right-click	N/A
Install package (PM)	Loads project	Supported	Loads project	N/A
Uninstall package (PM)	Loads project	Supported	Loads project	N/A
Update package (PM)	Loads project	Supported	Loads project	N/A
Execute init.ps1 (PMC)	Supported	Supported	Supported	N/A
Add-BindingRedirect	Loads project	Loads project	Loads project	N/A
Find-Package	N/A	N/A	N/A	N/A
Get-Package	Supported	Supported	Supported	N/A
Get-Project	Loads project	Loads project	Loads project	N/A
Install-Package	Loads project	Supported	Loads project	N/A
Open-PackagePage	N/A	N/A	N/A	N/A
Sync-Package	Supported	Supported	Loads project	N/A
Tab expansion (PMC)	Supported	Supported	Supported	N/A
Uninstall-Package	Loads project	Supported	Loads project	N/A
Update-Package	Loads project	Supported	Loads project	N/A
IVsPackageInstallerServices	Supported	Supported	Supported	N/A

Shared Infrastructure

A project adapter will be introduced to abstract away communication with EnvDTE and CPS API where needed. The adapter implementation will be able to detect LSL mode and switch between data sources and APIs. It will force load project if no equivalent data is available in LSL DB.

Project services will be introduced where project system specific implementation is needed thus the project adapter alone won't fit.

packages.config

In LSL mode it facilitates PackagesConfigReader to retrieve package references. Works correctly in LSL mode for majority of read-only operations. For install, uninstall, update operations will force load project as it needs to update assembly references in the project.

project.json

Utilizes JsonPackageSpecReader to get a PackageSpec for the project.

PackageRef

Relies on IDeferredProjectWorkspaceService to get all necessary project data.

.NET Core (Roslyn project system)

Does not support LSL. No action needed.