Add a more thorough counterpart to dotnet clean

[lukeschlather]

Per dotnet/docs#12304, dotnet clean by design does not delete everything generated by dotnet build. This can result in dotnet build producing dirty published files.

It would be nice to have a more thorough command, which could be called dotnet purge which deletes all the contents of the bin and obj directories for the project.

[Mgamerz]

This feature would be useful and would also help workaround #3886 which, for me at least, is due to items in the obj folder being incorrectly used in some instances.

[asears]

Removing obj folder to deal with stale files was only way to get around the 'RuntimeIdentifiers' warning after upgrade.

This feature will help with modernization of projects using https://github.com/hvanbakel/CsprojToVs2017.

Also see:
dotnet/project-system#3164

There is some expectation that cleaning projects removes the artifacts generated during the restore & build process.

[Nerklers]

I just stumbled over this and i'll leave a comment just to state my interest, that this feature would be very appreciated.

[resnyanskiy]

Related issue - #377
P.S. Seems like it's not an issue for now - dotnet publish removes unnecessary files from output directory.

[lukeschlather]

The publish folder is typically a subdirectory of bin, so a side-effect would be wiping the publish directory but that's only one of many issues - dotnet purge would delete everything in the bin and obj directories, which is necessary for a variety of reasons. I think this comment is pretty applicable #377 (comment)

It doesn't make sense for dotnet build to clean up everything, and it also makes sense for dotnet clean to be conservative, but the proposed purge command would destroy everything that can reasonably be assumed to be an output of dotnet build.