Version conflict with imported packages

[ryanbrandenburg]

In aspnet/MvcPrecompilation#49 we discovered that if you try to run a task which uses a conflicting version of packages like CoreFx then the task will crash with errors like System.IO.FileNotFoundException: Could not load file or assembly 'System.Collections.Immutable, Version=1.2.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The system cannot find the file specified.

@pranavkm has created a repro app here.

[paul1956]

This also happens with Visual Studio VSIX projects that use

    Public cache As New WeakReference(Of ImmutableDictionary(Of SyntaxTree, Boolean))(ImmutableDictionary(Of SyntaxTree, Boolean).Empty)

[paul1956]

@ryanbrandenburg did you find any workaround? It is always that exact error.

[pranavkm]

@paul1956 we did not dig in to this issue further. For precompilation, we went with an alternate route and spawned a new dotnet process (via Exec).

[rainersigwald]

Fixed by #4916