I just did something along these lines - works great for creating your datamodel in Typescript from your c# classes. I built it to generate a single AMD-module with an interface which mimics the basic data of your Models. Also supports Generics, and creates a class with Knockout properties, including a toJS() method and an update(data:Interface) method to update your class.

The whole thing is just a single T4 template. If anyone finds this and is interested: http://spabuilder.wordpress.com/2014/07/31/generating-typescript-from-c/

Also honors [KeyAttribute] and [Timespan] attributes for data models if you are using data annotations.

I've been messing around with generating js, and I'm finding Reflection to be a better tool for this. I'm basically pointing my generator at the bin folder of the project which the metadata comes from. There might be some difficulties with loading all the needed assemblies, and caveats with versions of assemblies in the bin folder, and versions of the same assemblies that your generator project references. But once you get over all of this, which I did with minimal difficulty, Reflection is a lot easier to use, and more reliable.

With Roslyn, you are basically just parsing c#. Roslyn does this very well, but I'm hesitant to switch to it from Reflection. With reflection, you get metadata more reliably.

Let's say you want the Prefix property of a RoutePrefixAttribute that decorates a controller class. If you're parsing c#, you may have: [RoutePrefix("stringliteral")] or [RoutePrefix(constantString)]. So, you have to worry about whether it's a literal or a constant expression, then find out how to get the value of a constant expression, worry about all the different ways in which you can pass parameters to an atatribute (for example, will this break your code: [RoutePrefix(Prefix="literal")]...

Once you're dealing with the actual runtime objects with reflection, everything is just easier. You have a nice RoutePrefixAttribute object, and you can go routePrefix.Prefix to get, reliably, the value of the prefix.

This is just one example of how doing things with Reflection is easier. It's the difference between gathering metadata from a set of c# objects in a type-safe way, and scraping data from c# code, albeit with a really nice scraping tool.

EDIT: Since writing this answer, I've bit the bullet and switched to Roslyn. It's fairly powerful once you get the hang of it, and I did find one big advantage: you can get a reference to the workspace from a visual studio plugin, and easily do all kinds of stuff within the plugin.

Doesn't the license only forbid you personally from distributing the binaries? It doesn't forbid you from adding a dependency from your NuGet package to the Rosyln CTP NuGet package. You personally cannot deliver the bits, but you can have NuGet pull in Roslyn automatically.

So just avoid checking Rosyln source or binaries into your version control.

The Roslyn website not clearly states that:

The current license is for evaluation and preview purposes only and does not allow redistribution of the Roslyn binaries. Sharing of sample projects built on the Roslyn APIs is permitted, but sample users must have either the Roslyn CTP or the Roslyn NuGet package installed in order to build and run.

I wouldn't use the current Roslyn CTP - simply because there will be new versions in 2014 and those will bring many breaking changes for sure. So you might end up with totally deprecated code.

(There recently was a blog post on this by a MS team member, but I'm afraid I currently don't have the link at hand.)

Edit
There's a good chance that Roslyn then will get a license that also permits for commercial use...

Update - July 2015

Roslyn is still in CTP, but their FAQ on GitHub is much more to the point:

For sample code or learning purposes, the recommended way to redistribute the Roslyn DLLs is with the Roslyn NuGet package: [url:Microsoft.CodeAnalysis|http://www.nuget.org/packages/Microsoft.CodeAnalysis].

So it appears that you still cannot redistribute the DLLs in finished products. The project will need to be open sourced and the solution will need a reference the NuGet package.

Original Answer (November 2012)

I don't believe you can distribute under open source.

6.DISTRIBUTABLE CODE. The software contains code that you are permitted to distribute in programs you develop if you comply with the terms below.

6.c Distribution Restrictions you may not modify or distribute the source code of any Distributable Code so that any part of it becomes subject to an Excluded License. An Excluded License is one that requires, as a condition of use, modification or distribution,

• the code be disclosed or distributed in source code form; or item
• others have the right to modify it.

At first it sounds like you could do it if you just include the Roslyn binaries, but the Distributable Code definition specifically says "The software contains code..." and I believe that is what everything after is referring to.

To your other question, Roslyn isn't fully finished and is still Beta. I don't know exactly if it is currently in a state that allows it to handle your needs. That's something you may just want to spend a couple of hours tinkering with. I wouldn't think it had more functionality than what .NET currently allows. You can see what they recently added in September here and what is currently not implemented here.

For my experience using T4 generations based on reflection, as TypeLite does, is somehow simpler but has some drawbacks, like once the project depends on the classes that have been generated, regenerating them with a breaking change (renamed a class) will lead to a non compiling project so running the template again will output a blanck file and the user will have an hard time making everything compile again.

So, having the same need, i started experimenting with Roslyn, and it seems very promising, but i have many doubts on how to use it properly...

You can take a look at what i'm doing and maybe help me here: https://github.com/TrabacchinLuigi/RoslynExporter