Project-system: Project System: Support for file patterns

[davkean]

_From @davkean on March 24, 2016 17:28_

UserVoice: https://visualstudio.uservoice.com/forums/121579-visual-studio-2015/suggestions/4512873-vs-ide-should-support-file-patterns-in-project-fil

While it's currently supported to use *.cs in a project system, we blow it away the minute you make any changes, such as adding new files, exclude files, or changing metadata. We should make this better.

_Copied from original issue: dotnet/roslyn#10066_

[BillHiebert]

We need to handle excluding folders and files.

[asbjornu]

It would be awesome if MSBuild could be configured to use .gitignore as its file exclusion filter.

[Mike-E-angelo]

FANTASTIC idea, @asbjornu ... and I am not just saying that because I have thought of that,too. :smile:

The problem of course is that you are now tightly-coupling with an external technology. However, that doesn't mean that you could design this solution in such a way so that you could use providers for ignored files, Git being one of them. GitResourceProvider sounds like a good name to start with. :sunglasses:

I will say that I am in the minority here and prefer the "opt-in" model of project files (listing all files and then being able to remove them from the project), but that doesn't mean I am opposed to the opt-out model (Git, project.json), as long as the user experience is the same.