LSPBinder.h

//===--- LSPBinder.h - Tables of LSP handlers --------------------*- C++-*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_LSPBINDER_H
#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_LSPBINDER_H

#include "Protocol.h"
#include "support/Function.h"
#include "support/Logger.h"
#include "llvm/ADT/FunctionExtras.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Support/JSON.h"

namespace clang {
namespace clangd {

/// LSPBinder collects a table of functions that handle LSP calls.
///
/// It translates a handler method's signature, e.g.
///    void codeComplete(CompletionParams, Callback<CompletionList>)
/// into a wrapper with a generic signature:
///    void(json::Value, Callback<json::Value>)
/// The wrapper takes care of parsing/serializing responses.
///
/// Incoming calls can be methods, notifications, or commands - all are similar.
///
/// FIXME: this should also take responsibility for wrapping *outgoing* calls,
/// replacing the typed ClangdLSPServer::call<> etc.
class LSPBinder {
public:
  using JSON = llvm::json::Value;

  struct RawHandlers {
    template <typename HandlerT>
    using HandlerMap = llvm::StringMap<llvm::unique_function<HandlerT>>;

    HandlerMap<void(JSON)> NotificationHandlers;
    HandlerMap<void(JSON, Callback<JSON>)> MethodHandlers;
    HandlerMap<void(JSON, Callback<JSON>)> CommandHandlers;
  };
  class RawOutgoing {
  public:
    virtual ~RawOutgoing() = default;
    virtual void callMethod(llvm::StringRef Method, JSON Params,
                            Callback<JSON> Reply) = 0;
    virtual void notify(llvm::StringRef Method, JSON Params) = 0;
  };

  LSPBinder(RawHandlers &Raw, RawOutgoing &Out) : Raw(Raw), Out(Out) {}

  /// Bind a handler for an LSP method.
  /// e.g. Bind.method("peek", this, &ThisModule::peek);
  /// Handler should be e.g. void peek(const PeekParams&, Callback<PeekResult>);
  /// PeekParams must be JSON-parseable and PeekResult must be serializable.
  template <typename Param, typename Result, typename ThisT>
  void method(llvm::StringLiteral Method, ThisT *This,
              void (ThisT::*Handler)(const Param &, Callback<Result>));

  /// Bind a handler for an LSP notification.
  /// e.g. Bind.notification("poke", this, &ThisModule::poke);
  /// Handler should be e.g. void poke(const PokeParams&);
  /// PokeParams must be JSON-parseable.
  template <typename Param, typename ThisT>
  void notification(llvm::StringLiteral Method, ThisT *This,
                    void (ThisT::*Handler)(const Param &));

  /// Bind a handler for an LSP command.
  /// e.g. Bind.command("load", this, &ThisModule::load);
  /// Handler should be e.g. void load(const LoadParams&, Callback<LoadResult>);
  /// LoadParams must be JSON-parseable and LoadResult must be serializable.
  template <typename Param, typename Result, typename ThisT>
  void command(llvm::StringLiteral Command, ThisT *This,
               void (ThisT::*Handler)(const Param &, Callback<Result>));

  template <typename P, typename R>
  using OutgoingMethod = llvm::unique_function<void(const P &, Callback<R>)>;
  /// UntypedOutgoingMethod is convertible to OutgoingMethod<P, R>.
  class UntypedOutgoingMethod;
  /// Bind a function object to be used for outgoing method calls.
  /// e.g. OutgoingMethod<EParams, EResult> Edit = Bind.outgoingMethod("edit");
  /// EParams must be JSON-serializable, EResult must be parseable.
  UntypedOutgoingMethod outgoingMethod(llvm::StringLiteral Method);

  template <typename P>
  using OutgoingNotification = llvm::unique_function<void(const P &)>;
  /// UntypedOutgoingNotification is convertible to OutgoingNotification<T>.
  class UntypedOutgoingNotification;
  /// Bind a function object to be used for outgoing notifications.
  /// e.g. OutgoingNotification<LogParams> Log = Bind.outgoingMethod("log");
  /// LogParams must be JSON-serializable.
  UntypedOutgoingNotification outgoingNotification(llvm::StringLiteral Method);

private:
  // FIXME: remove usage from ClangdLSPServer and make this private.
  template <typename T>
  static llvm::Expected<T> parse(const llvm::json::Value &Raw,
                                 llvm::StringRef PayloadName,
                                 llvm::StringRef PayloadKind);

  RawHandlers &Raw;
  RawOutgoing &Out;
};

template <typename T>
llvm::Expected<T> LSPBinder::parse(const llvm::json::Value &Raw,
                                   llvm::StringRef PayloadName,
                                   llvm::StringRef PayloadKind) {
  T Result;
  llvm::json::Path::Root Root;
  if (!fromJSON(Raw, Result, Root)) {
    elog("Failed to decode {0} {1}: {2}", PayloadName, PayloadKind,
         Root.getError());
    // Dump the relevant parts of the broken message.
    std::string Context;
    llvm::raw_string_ostream OS(Context);
    Root.printErrorContext(Raw, OS);
    vlog("{0}", OS.str());
    // Report the error (e.g. to the client).
    return llvm::make_error<LSPError>(
        llvm::formatv("failed to decode {0} {1}: {2}", PayloadName, PayloadKind,
                      fmt_consume(Root.getError())),
        ErrorCode::InvalidParams);
  }
  return std::move(Result);
}

template <typename Param, typename Result, typename ThisT>
void LSPBinder::method(llvm::StringLiteral Method, ThisT *This,
                       void (ThisT::*Handler)(const Param &,
                                              Callback<Result>)) {
  Raw.MethodHandlers[Method] = [Method, Handler, This](JSON RawParams,
                                                       Callback<JSON> Reply) {
    auto P = LSPBinder::parse<Param>(RawParams, Method, "request");
    if (!P)
      return Reply(P.takeError());
    (This->*Handler)(*P, std::move(Reply));
  };
}

template <typename Param, typename ThisT>
void LSPBinder::notification(llvm::StringLiteral Method, ThisT *This,
                             void (ThisT::*Handler)(const Param &)) {
  Raw.NotificationHandlers[Method] = [Method, Handler, This](JSON RawParams) {
    llvm::Expected<Param> P =
        LSPBinder::parse<Param>(RawParams, Method, "request");
    if (!P)
      return llvm::consumeError(P.takeError());
    (This->*Handler)(*P);
  };
}

template <typename Param, typename Result, typename ThisT>
void LSPBinder::command(llvm::StringLiteral Method, ThisT *This,
                        void (ThisT::*Handler)(const Param &,
                                               Callback<Result>)) {
  Raw.CommandHandlers[Method] = [Method, Handler, This](JSON RawParams,
                                                        Callback<JSON> Reply) {
    auto P = LSPBinder::parse<Param>(RawParams, Method, "command");
    if (!P)
      return Reply(P.takeError());
    (This->*Handler)(*P, std::move(Reply));
  };
}

class LSPBinder::UntypedOutgoingNotification {
  llvm::StringLiteral Method;
  RawOutgoing *Out;
  UntypedOutgoingNotification(llvm::StringLiteral Method, RawOutgoing *Out)
      : Method(Method), Out(Out) {}
  friend UntypedOutgoingNotification
      LSPBinder::outgoingNotification(llvm::StringLiteral);

public:
  template <typename Request> operator OutgoingNotification<Request>() && {
    return
        [Method(Method), Out(Out)](Request R) { Out->notify(Method, JSON(R)); };
  }
};

inline LSPBinder::UntypedOutgoingNotification
LSPBinder::outgoingNotification(llvm::StringLiteral Method) {
  return UntypedOutgoingNotification(Method, &Out);
}

class LSPBinder::UntypedOutgoingMethod {
  llvm::StringLiteral Method;
  RawOutgoing *Out;
  UntypedOutgoingMethod(llvm::StringLiteral Method, RawOutgoing *Out)
      : Method(Method), Out(Out) {}
  friend UntypedOutgoingMethod LSPBinder::outgoingMethod(llvm::StringLiteral);

public:
  template <typename Request, typename Response>
  operator OutgoingMethod<Request, Response>() && {
    return [Method(Method), Out(Out)](Request R, Callback<Response> Reply) {
      Out->callMethod(
          Method, JSON(R),
          // FIXME: why keep ctx alive but not restore it for the callback?
          [Reply(std::move(Reply)), Ctx(Context::current().clone()),
           Method](llvm::Expected<JSON> RawRsp) mutable {
            if (!RawRsp)
              return Reply(RawRsp.takeError());
            Reply(LSPBinder::parse<Response>(std::move(*RawRsp), Method,
                                             "reply"));
          });
    };
  }
};

inline LSPBinder::UntypedOutgoingMethod
LSPBinder::outgoingMethod(llvm::StringLiteral Method) {
  return UntypedOutgoingMethod(Method, &Out);
}

} // namespace clangd
} // namespace clang

#endif