better initial prompt

[nikomatsakis]

The initial prompt right now is pretty bare bones. I want to try providing it better and more context. I'm going to do some experimenting, I suspect we can do this in a fairly language-agnostic fashion but I have to explore what APIs vscode offers me.

[nikomatsakis]

From what I can tell, the only way to do what I want is to wrap the rust-analyzer language server (and presumably extension??). I had assumed it would be possible to ask vscode to do common operations (getDocumentSymbols) so that people could implement extensions that work across languages, but that doesn't seem to be true, at least based on what I see in the publicly documented API.

[nikomatsakis]

Examples of things I want to do:

• Given the line on which the error occurred, find the extent of the current function so we can supply it for context.
• Traverse the context of the error to find the public signature of functions that are being called, the definition of the types of the expressions, and so forth so we can include those in the context too.

[nikomatsakis]

OK, I've found that rust-analyzer returns a language client as part of its extension API. So by loading that I am able to get what I need, it seems, though so far it feels awfully clumsy (maybe I've not found the right vscode.d interface definitions).