API Proposal: Allow creating custom Workspace classes

[grokys]

Background and Motivation

The Workspace API is currently essentially closed to extension. The AdhocWorkspace and MSBuildWorkspace classes are sealed and while one can derive from Workspace itself, trying to implement a basic Workspace by copying the code for AdhocWorkspace won't work because said class uses internal APIs.

Given that there are a number of Workspace implementations in the Roslyn codebase itself, I'm sure that you can appreciate that being able to implement/extend Workspace is valuable. Looking though old issues, it looks like Workspace was originally intended to be extensible.

Proposed API

Either remove sealed from AdhocWorkspace (and maybe MSBuildWorkspace?) or provide a new abstract AbstractCustomWorkspace class which implements the parts which require internal APIs.

Alternative Designs

It's entirely possible that I'm missing something here and that this is already possible. An alternative solution would be to document/provide a sample of how to implement a custom workspace on top of Workspace with existing APIs.

Risks

More API surface for the Roslyn team to maintain ;)

[CyrusNajmabadi]

Extending Workspace itself should be possible. If that doesn't work, let us know what API is blocking you.

[grokys]

let us know what API is blocking you.

I did link to one internal API in the original description, but these are the internal APIs used in AdhocWorkspace:

• TextDocument.GetTextSynchronously
• TextDocument.GetTextVersionSynchronously

These seem to be needed in order to get the SourceText in OpenDocument, in order to create a SourceTextContainer to pass to OnDocumentOpened: GetTextAsync can't be used as OpenDocument is not async.

Unless there's an alternative API I should be using?