[PATCH] D38464: [clangd] less boilerplate in RPC dispatch

[Ilya Biryukov via Phabricator via cfe-commits]

ilya-biryukov accepted this revision.
ilya-biryukov added a comment.
This revision is now accepted and ready to land.

LGTM.
Note there's a new LSP method handler added upstream (`textDocument/signatureHelp`), we should add it to this change before submitting.



================
Comment at: clangd/ClangdLSPServer.h:47
   // Implement ProtocolCallbacks.
-  void onInitialize(StringRef ID, InitializeParams IP,
-                    JSONOutput &Out) override;
-  void onShutdown(JSONOutput &Out) override;
-  void onDocumentDidOpen(DidOpenTextDocumentParams Params,
-                         JSONOutput &Out) override;
-  void onDocumentDidChange(DidChangeTextDocumentParams Params,
-                           JSONOutput &Out) override;
-  void onDocumentDidClose(DidCloseTextDocumentParams Params,
-                          JSONOutput &Out) override;
-  void onDocumentOnTypeFormatting(DocumentOnTypeFormattingParams Params,
-                                  StringRef ID, JSONOutput &Out) override;
-  void onDocumentRangeFormatting(DocumentRangeFormattingParams Params,
-                                 StringRef ID, JSONOutput &Out) override;
-  void onDocumentFormatting(DocumentFormattingParams Params, StringRef ID,
-                            JSONOutput &Out) override;
-  void onCodeAction(CodeActionParams Params, StringRef ID,
-                    JSONOutput &Out) override;
-  void onCompletion(TextDocumentPositionParams Params, StringRef ID,
-                    JSONOutput &Out) override;
-  void onGoToDefinition(TextDocumentPositionParams Params, StringRef ID,
-                        JSONOutput &Out) override;
-  void onSwitchSourceHeader(TextDocumentIdentifier Params, StringRef ID,
-                            JSONOutput &Out) override;
+  void onInitialize(Ctx &C, InitializeParams &Params) override;
+  void onShutdown(Ctx &C, NoParams &Params) override;
----------------
sammccall wrote:
> ilya-biryukov wrote:
> > ilya-biryukov wrote:
> > > Maybe there's a way to have a typed return value instead of `Ctx`?
> > > This would give an interface that's harder to misuse: one can't forget to call `reply` or call it twice.
> > > 
> > > Here's on design that comes to mind.
> > > Notification handlers could have `void` return, normal requests can return `Optional<Result>` or `Optional<std::string>` (with result json).
> > > `Optional` is be used to indicate whether error occurred while processing the request.
> > > 
> > After putting more thought into it, `Ctx`-based API seems to have an advantage: it will allow us to easily implement async responses.
> > E.g., we can run code completion on a background thread and continue processing other requests. When completion is ready, we will simply call `Ctx.reply` to return results to the language client.
> > 
> > To make that possible, can we allow moving `RequestContext` and pass it by-value instead of by-ref?
> Yeah I thought about returning a value... it certainly reads more nicely, but I don't think we're ready to do a good job in this patch:
>  - return value should be an object ready to be serialized (rather than a JSON string) - I don't want to bring that in scope here, but it might affect the details of the API
>  - there's several cases we know about (return object, no reply, error reply) and some we're not sure about (async as you mention - any multiple responses)? I think this needs some design, and I don't yet know the project well enough to drive it.
> 
> I've switched to passing Ctx by value as you suggest (though it's certainly cheap enough to copy, too).
Yeah, copy is also fine there performance-wise. 

I do think move-only interface fits slightly better. We can check a whole bunch of invariants if `Ctx` is move-only (i.e., that request wasn't dropped without response or `reply` was not called twice).


================
Comment at: clangd/ClangdLSPServer.h:48
+  void onInitialize(Ctx &C, InitializeParams &Params) override;
+  void onShutdown(Ctx &C, NoParams &Params) override;
+  void onDocumentDidOpen(Ctx &C, DidOpenTextDocumentParams &Params) override;
----------------
sammccall wrote:
> ilya-biryukov wrote:
> > Maybe there's a way to get rid of `NoParams`?
> > E.g. by adding a overload to `HandlerRegisterer`?
> Even if there was, I think I prefer the regularity (changed this to ShutdownParams - oops!).
> 
> Otherwise the signature's dependent on some combination of {current LSP, whether we actually implement the options, whether we've defined any extensions}. It's harder to remember, means changing lots of places when these factors change, and complicates the generic code.
> 
> Maybe I've just spent too long around Stubby, though - WDYT?
All those are good points. We also have only one method that does not have params currently, so it's probably not even worth additional complexity in the implementation.


https://reviews.llvm.org/D38464