Add ability to "jake link-vs" & "jake unlink-vs" which adds/removes symlink

[jbondc]

• Using an elevated command prompt or PS, allows to symlink current build of compiler & services used by Visual Studio. for Visual Studio, use latest tsc release #1110

Create symlinks
jake link-vs

Remove symlinks & restore original Visual Studio files
jake unlink-vs

Also improved 'jake diff' so it works from PowerShell + looks up WinMerge by defaut
jake diff

[DanielRosenwasser]

I'm not sure we want to include this; it seems a little presumptuous, and our general attitude for this sort of thing has been a hands-off/"use at your own risk" approach. I don't want our users to accidentally bork their language service.

[jbondc]

Seems reasonable, then again anyone who clones the repo can likely fix their language service.
I'd prefer if Visual Studio could use alternative paths for tsc.js or typescriptServices.js but this was the known & quickest solution.

[jbondc]

Added a 'community / risk disclaimer' to jake -T as attempt to make it more acceptable.

[DanielRosenwasser]

Hey @jbondc, we always appreciate contributions, and I think it's always great to exchange ideas about features like this, but what I meant by my original response is that this may be beyond the scope of what we aim to provide, even with the disclaimer.

I think that in the short term, we should document the workflow a little bit better, so that others can do this on their own. But what we should also do is find a way to make this process much safer and easier. @mhegazy should have some input on this, and might be able to better elaborate on that.

[mhegazy]

thanks @jbondc for your submission. I believe a better solution is to get the VS plugin to load the files from different location, possibly through a reg key. We also need to add an API version on the LS, which @DanielRosenwasser is planning on doing in the next few days, along with a check in the VS plugin for supported versions. this way you get to update your VS setup and get some feedback if something is not working.
Will try to get this in the next release (1.4) though i can not promise :)

[jbondc]

reg key + api version sound excellent.
Should I submit a standalone patch for 'jake diff'? %DIFF% doesn't work in PowerShell

[DanielRosenwasser]

It might be better to do a different PR for that if you do. For the record, I'd prefer it be kept simple (i.e. just grab the 'DIFF' environment variable, don't try to resolve WinMerge, don't try to do anything relating to checking if something is installed, and don't commit the .d.ts files for Node.

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