Add client-side support for macro expansions

[fwcd]

This implements basic client-side support for the sourcekit-lsp/macroExpansion request introduced in

• Add LSP extension request for retrieving macro expansions apple/sourcekit-lsp#892

The expansion is presented using an in-memory text document in a peeked editor:

To do

• Declare the request (sourcekit-lsp/macroExpansion)
• Add a VSCode command for performing the request (swift.expandMacro)
• Find a better presentation style than dumping the expansion into an info message popup

[adam-fowler]

The third todo in your list is going to be the stumbling block. I've looked into finding a better way to present macros a while back and didn't find an easy solution.

You mention rust-analyser in the related sourcekit-lsp PR. Do you know what they do to present macros?

[fwcd]

They spawn another (regular) editor containing the expansion:

[adam-fowler]

That's not really a great solution

[fwcd]

I agree, haven't dug in too deep what APIs VSCode exposes in this regard, but I think it would be really cool if we could use an "inline editor" for this, which incidentally would also approximate Xcode's macro expansion UI:

I think GitLens does or used to do something similar. We might still have to register a virtual document provider, but that should probably be doable.

Edit: This presentation style seems to be called "Peeked editors" and there's an open upstream issue on exposing an API for creating custom peek widgets:

• Custom peek widgets microsoft/vscode#3220

Since we only need to display, perhaps there is a still a way to present such an editor with the existing APIs. Another proposed API that might be of interest (which would require us to implement a custom view though):

• Api for editor insets microsoft/vscode#85682

[fwcd]

The peeked editor approach seems to work well and looks nice too (check the PR description for a screenshot).

[DougGregor]

The peeked editor approach seems to work well and looks nice too (check the PR description for a screenshot).

That looks great, thank you!

[adam-fowler]

It looks very nice. I didn't know about "editor.action.peekLocations"
In SourceKit-LSP you could add a CodeAction for macros to call the command you've setup here.

[adam-fowler]

We will need to manage the text document content providers slightly better. Currently you just keep creating them, without cleaning up the unused ones. Adding them to the workspaceContext subscriptions means they get removed when the workspace is closed, but not before then.