dotnet new generates incorrect project in case of - (dash) symbols in project name

[xtmq]

First of all the Stackoverflow question:
https://stackoverflow.com/questions/62676355/error-in-uno-platform-auto-generated-file-and-program-cs-only-on-mac/64200149#64200149

Steps to reproduce

1. Create a new project via dotnet new:

dotnet new -i Uno.ProjectTemplates.Dotnet
dotnet new unoapp -o App-CrossPlatform

2. Try to compile and observe errors in .g.cs files:

Error CS0826: No best type found for implicitly-typed array (CS0826)
Error CS1503: Argument 2: cannot convert from '?[]' to 'string[]' (CS1503)

Explanation

dotnet new expands project with the next files in that case (with dash - symbol):

App-CrossPlatform\App-CrossPlatform.Shared\App-CrossPlatform.Shared.shproj
App-CrossPlatform\App-CrossPlatform.Shared\App-CrossPlatform.Shared.projitems

But there are imports in other projects (with underscore _ symbol)

<Import Project="..\App_CrossPlatform.Shared\App_CrossPlatform.Shared.projitems" Label="Shared" Condition="Exists('..\App_CrossPlatform.Shared\App_CrossPlatform.Shared.projitems')" />

So MsBuild can not resolve imports and find projitems files.

[jeromelaban]

Thanks for the report. Unfortunately, at this point, this seems like a limitation of the template engine: dotnet/templating#1920.

If the templating engine adds the ability to choose the proper expansion to handle those cases, we'll adjust to use it. If you want to create such a project, you can use the Visual Studio 2019 templates.

[dean-toolhound]

Happens even in Visual Studio using the template if your solution name has a space in it. Get the same error as mentioned in the Stack Overflow issue.

[MartinZikmund]

Invalid characters in project name are now automatically prevented and user is informed when unsupported characters are used.