Added support for excluding search paths via globbing patterns

[filipw]

This PR is intended to fix #896

It introduces a new omnisharp.json setting to control which paths OmniSharp should skip (paths can be explicit or use globbing patterns).
Globbing is provided via Microsoft.Extensions.FileSystemGlobbing which we conveniently already referenced 😄

By default the following set up is used:

{
  "fileOptions": {
    "excludeSearchPatterns": [
      "**/node_modules/**/*",
      "**/bin/**/*",
      "**/obj/**/*"
    ]
  }
}

So no files from bin, obj or node_modules are discovered, at any level.

The default setup can be overridden using a global or local omnisharp.json file.
For example:

{
  "fileOptions": {
    "excludeSearchPatterns": [
      "build/**/*",
      "**/TestFixtures/*.csproj"
    ]
  }
}

This should not find anything from a build folder relative to currently open OmniSharp and any csproj file directly inside TestFixtures.
The new service is used in place of the old SearchOption.AllDirectories scanning.

[david-driscoll]

Seems sensible to me, I had forgotten there was a globber from ms extensions.

[david-driscoll]

Should we also add search inclusions? (in the future perhaps?

Kinda feels like it would be sort of similar to how we used to be able to do things with project.json.

[DustinCampbell]

What about "**/.git/**/*"?

[filipw]

that's a good one 👍

[david-driscoll]

Going to merge tomorrow afternoon if there are no other objections

[filipw]

One thing that might improve the usability of this feature is perhaps we should split the exclusion patterns into 2 separate properties that you can override and customize.

The way inheritance rules in our hierarchical configuration work, is that you can override everything, but you completely negate the setup from the previous source.
What I mean is that at the moment if you want to to exclude i.e. /foo locally, you'd do this:

{
  "fileOptions": {
    "excludeSearchPatterns": [
      "foo/**/*"
    ]
  }
}

The problem is, this overrides the default setup and bin/obj/node_modules are no longer excluded anymore.
So to make it work in a way that the defaults are still observed, you'd have to technically carry over the defaults, like this:

{
  "fileOptions": {
    "excludeSearchPatterns": [
      "**/node_modules/**/*",
      "**/bin/**/*",
      "**/obj/**/*"
      "foo/**/*"
    ]
  }
}

This is not the greatest experience.
However, we could have 2 properties to control all this. Something like: userExcludeSearchPatterns and systemSearchPatterns. The default setup would be:

{
  "fileOptions": {
    "systemExcludeSearchPatterns": [
      "**/node_modules/**/*",
      "**/bin/**/*",
      "**/obj/**/*"
    ],
    "userExcludeSearchPatterns": []
  }
}

Then, you'd only override userExcludeSearchPatterns, and the systemExcludeSearchPatterns carry over automatically.

{
  "fileOptions": {
    "userExcludeSearchPatterns": [
      "foo/**/*"
    ]
  }
}

If this makes sense, I will push this change before we merge.

[david-driscoll]

@filipw I like the idea of having a system level setting, and a user setting. 🚲 🏠 should the user property by userExcludeSearchPatterns or excludeSearchPatterns.

I tend to favor excludeSearchPatterns because most users won't want to even know that systemExcludeSearchPatterns exists, however by setting it up in such a way it makes the system exclusions less discoverable. I'm good to either way.

[filipw]

OK thanks. So based on the convo, I added systemExcludeSearchPatterns and moved the "default" excludes there, and made the excludeSearchPatterns empty.

This way you can inject your own excludes into excludeSearchPatterns and still benefit from the systemExcludeSearchPatterns as at the end of the day, they get merged.
If anyone, for whatever reason, is eager to load projects from i.e. node_modules, systemExcludeSearchPatterns is also overridable.

[DustinCampbell]

@filipw: should we update the WIki page with this information? https://github.com/OmniSharp/omnisharp-roslyn/wiki/Configuration-Options

[filipw]

yes - you are right! I'll do that 📚