If you have the ProBuilder Editor Examples installed in your project, then select the Samples folder in Project View and delete it, a compiler error will appear in the console:

Microsoft (R) Visual C# Compiler version 2.9.1.65535 (9d34608e)
Copyright (C) Microsoft Corporation. All rights reserved.

error CS2001: Source file 'C:\Users\marctourle\Documents\New Unity Project (34)\Assets\Samples\ProBuilder\4.1.0\Editor Examples\CustomAction.cs' could not be found.
error CS2001: Source file 'C:\Users\marctourle\Documents\New Unity Project (34)\Assets\Samples\ProBuilder\4.1.0\Editor Examples\RenameNewObjects.cs' could not be found.
error CS2001: Source file 'C:\Users\marctourle\Documents\New Unity Project (34)\Assets\Samples\ProBuilder\4.1.0\Editor Examples\SetCustomUnwrapParams.cs' could not be found.
error CS2001: Source file 'C:\Users\marctourle\Documents\New Unity Project (34)\Assets\Samples\ProBuilder\4.1.0\Editor Examples\CreateShadowObject.cs' could not be found.
error CS2001: Source file 'C:\Users\marctourle\Documents\New Unity Project (34)\Assets\Samples\ProBuilder\4.1.0\Editor Examples\EditorCallbackViewer.cs' could not be found.
error CS2001: Source file 'C:\Users\marctourle\Documents\New Unity Project (34)\Assets\Samples\ProBuilder\4.1.0\Editor Examples\ClearUnusedAttributes.cs' could not be found.

1. Open Unity
2. Open the attached project
3. In the Project View, select the Samples folder
4. Delete the Samples folder

Expected Result:
The samples folder and all it's children are deleted without any warnings or errors in the console.

Actual Result:
A compiler error appears in the console.

Tested on Windows.

Occurs on package version 4.1.0 using 2019.3.0a10