GenerateDepsFile task failing with "System.ArgumentException: An item with the same key has already been added."

Steps to reproduce

Sorry, wasn’t able to make a nice little minimal repro for this one. In PowerShell:

1. git clone https://github.com/joelverhagen/NuGet.Client.git
2. cd NuGet.Client
3. git checkout jver/sdk-repro
4. cd src\NuGet.Core
5. Get-ChildItem .\*.csproj -Recurse | % { dotnet restore3 $_.FullName }
6. dotnet build3 NuGet.RuntimeModel\NuGet.RuntimeModel.csproj

Expected behavior

The build should succeed… or at least no fail with this error 😄. I’ve been working through a lot of failures so it’s possible there’s another waiting in line.

Actual behavior

Build fails.

The "GenerateDepsFile" task failed unexpectedly. 
System.ArgumentException: An item with the same key has already been added. Key: Newtonsoft.Json 
   at System.ThrowHelper.ThrowAddingDuplicateWithKeyArgumentException(Object key) 
   at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) 
   at System.Linq.Enumerable.ToDictionary
   at System.Linq.Enumerable.ToDictionary
   at Microsoft.NET.Build.Tasks.DependencyContextBuilder.Build(SingleProjectInfo mainProjectInfo, CompilationOptions compilationOptions, LockFile lockFile, NuGetFramework framework, String runtime) 
   at Microsoft.NET.Build.Tasks.GenerateDepsFile.ExecuteCore() 
   at Microsoft.NET.Build.Tasks.TaskBase.Execute() 
   at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute() 
   at Microsoft.Build.BackEnd.TaskBuilder.<ExecuteInstantiatedTask>d__25.MoveNext() 

Environment data

dotnet --info output:

.NET Command Line Tools (1.0.0-preview3-003842)

Product Information:
 Version:            1.0.0-preview3-003842
 Commit SHA-1 hash:  3ae14ab618

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.14393
 OS Platform: Windows
 RID:         win10-x64

[eerhardt]

Looks like I had a bad assumption when I wrote this code. 😞 Looking at the CLI code, it uses https://github.com/dotnet/cli/blob/rel/1.0.0/src/Microsoft.DotNet.ProjectModel/Graph/LockFileLookup.cs.

I’ll do the same in the sdk code - with one addition: it will handle case-insensitive package IDs.

[joelverhagen]

Confirmed with Microsoft.NET.Sdk/1.0.0-alpha-20161018-2.