[DocC Live Preview] Cache on-disk snapshots opened in sourcekitd

[matthewbastien]

Removed SwiftLanguageService.withSnapshotFromDiskOpenedInSourcekitd() in favor of a new SymbolGraphCache actor that will cache all snapshots opened for the duration of a textDocument/doccDocumentation request. This will prevent the syntax tree from being parsed multiple times for the same document in a single request.

Follow up to #2216

[matthewbastien]

@swift-ci please test

[matthewbastien]

@swift-ci please test

[matthewbastien]

@swift-ci please test windows

[ahoppen]

Launching a task here means that the documents could be closed in parallel while another request is handled, which would be very hard to debug if this ends up creating some kind of data races in sourcekitd. I think I’d prefer a pattern where you have something like the following and then explicitly close the documents at end of the cache’s lifetime.

func withSymbolGraphCache<T>(_ body: (SymbolGraphCache) async throws -> T) async throws -> T

I recently wrote the following for another project, which might be helpful for such a with* implementation (or generally something that I think might be useful to have in SwiftExtensions).

/// Run `body` and always ensure that `cleanup` gets run, independently of whether `body` threw an error or returned a
/// value.
package func run<T>(
  _ body: () async throws -> T,
  cleanup: () async -> ()
) async throws -> T {
  do {
    let result = try await body()
    await cleanup()
    return result
  } catch {
    await cleanup()
    throw error
  }
}

[ahoppen]

I think we’re never re-using an open document, are we? I don’t even think that we ever register open documents.

[ahoppen]

Would something like OnDiskDocumentManager be a more appropriate name because this type neither really caches values (it manages document lifetimes), nor does it really cache symbol graphs but it keeps track of sourcekitd documents.