//===--- ClangdLSPServer.cpp - LSP server ------------------------*- 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
//
//===----------------------------------------------------------------------===//

#include "ClangdLSPServer.h"
#include "ClangdServer.h"
#include "CodeComplete.h"
#include "Diagnostics.h"
#include "DraftStore.h"
#include "GlobalCompilationDatabase.h"
#include "Protocol.h"
#include "SemanticHighlighting.h"
#include "SourceCode.h"
#include "TUScheduler.h"
#include "URI.h"
#include "refactor/Tweak.h"
#include "support/Context.h"
#include "support/MemoryTree.h"
#include "support/Trace.h"
#include "clang/Basic/Version.h"
#include "clang/Tooling/Core/Replacement.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/FormatVariadic.h"
#include "llvm/Support/JSON.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/SHA1.h"
#include "llvm/Support/ScopedPrinter.h"
#include "llvm/Support/raw_ostream.h"
#include <chrono>
#include <cstddef>
#include <cstdint>
#include <functional>
#include <memory>
#include <mutex>
#include <string>
#include <vector>

namespace clang {
namespace clangd {
namespace {

// Tracks end-to-end latency of high level lsp calls. Measurements are in
// seconds.
constexpr trace::Metric LSPLatency("lsp_latency", trace::Metric::Distribution,
                                   "method_name");

// LSP defines file versions as numbers that increase.
// ClangdServer treats them as opaque and therefore uses strings instead.
std::string encodeVersion(int64_t LSPVersion) {
  return llvm::to_string(LSPVersion);
}
llvm::Optional<int64_t> decodeVersion(llvm::StringRef Encoded) {
  int64_t Result;
  if (llvm::to_integer(Encoded, Result, 10))
    return Result;
  if (!Encoded.empty()) // Empty can be e.g. diagnostics on close.
    elog("unexpected non-numeric version {0}", Encoded);
  return llvm::None;
}

/// Transforms a tweak into a code action that would apply it if executed.
/// EXPECTS: T.prepare() was called and returned true.
CodeAction toCodeAction(const ClangdServer::TweakRef &T, const URIForFile &File,
                        Range Selection) {
  CodeAction CA;
  CA.title = T.Title;
  CA.kind = T.Kind.str();
  // This tweak may have an expensive second stage, we only run it if the user
  // actually chooses it in the UI. We reply with a command that would run the
  // corresponding tweak.
  // FIXME: for some tweaks, computing the edits is cheap and we could send them
  //        directly.
  CA.command.emplace();
  CA.command->title = T.Title;
  CA.command->command = std::string(Command::CLANGD_APPLY_TWEAK);
  CA.command->tweakArgs.emplace();
  CA.command->tweakArgs->file = File;
  CA.command->tweakArgs->tweakID = T.ID;
  CA.command->tweakArgs->selection = Selection;
  return CA;
}

void adjustSymbolKinds(llvm::MutableArrayRef<DocumentSymbol> Syms,
                       SymbolKindBitset Kinds) {
  for (auto &S : Syms) {
    S.kind = adjustKindToCapability(S.kind, Kinds);
    adjustSymbolKinds(S.children, Kinds);
  }
}

SymbolKindBitset defaultSymbolKinds() {
  SymbolKindBitset Defaults;
  for (size_t I = SymbolKindMin; I <= static_cast<size_t>(SymbolKind::Array);
       ++I)
    Defaults.set(I);
  return Defaults;
}

CompletionItemKindBitset defaultCompletionItemKinds() {
  CompletionItemKindBitset Defaults;
  for (size_t I = CompletionItemKindMin;
       I <= static_cast<size_t>(CompletionItemKind::Reference); ++I)
    Defaults.set(I);
  return Defaults;
}

// Build a lookup table (HighlightingKind => {TextMate Scopes}), which is sent
// to the LSP client.
std::vector<std::vector<std::string>> buildHighlightScopeLookupTable() {
  std::vector<std::vector<std::string>> LookupTable;
  // HighlightingKind is using as the index.
  for (int KindValue = 0; KindValue <= (int)HighlightingKind::LastKind;
       ++KindValue)
    LookupTable.push_back(
        {std::string(toTextMateScope((HighlightingKind)(KindValue)))});
  return LookupTable;
}

// Makes sure edits in \p FE are applicable to latest file contents reported by
// editor. If not generates an error message containing information about files
// that needs to be saved.
llvm::Error validateEdits(const DraftStore &DraftMgr, const FileEdits &FE) {
  size_t InvalidFileCount = 0;
  llvm::StringRef LastInvalidFile;
  for (const auto &It : FE) {
    if (auto Draft = DraftMgr.getDraft(It.first())) {
      // If the file is open in user's editor, make sure the version we
      // saw and current version are compatible as this is the text that
      // will be replaced by editors.
      if (!It.second.canApplyTo(Draft->Contents)) {
        ++InvalidFileCount;
        LastInvalidFile = It.first();
      }
    }
  }
  if (!InvalidFileCount)
    return llvm::Error::success();
  if (InvalidFileCount == 1)
    return error("File must be saved first: {0}", LastInvalidFile);
  return error("Files must be saved first: {0} (and {1} others)",
               LastInvalidFile, InvalidFileCount - 1);
}
} // namespace

// MessageHandler dispatches incoming LSP messages.
// It handles cross-cutting concerns:
//  - serializes/deserializes protocol objects to JSON
//  - logging of inbound messages
//  - cancellation handling
//  - basic call tracing
// MessageHandler ensures that initialize() is called before any other handler.
class ClangdLSPServer::MessageHandler : public Transport::MessageHandler {
public:
  MessageHandler(ClangdLSPServer &Server) : Server(Server) {}

  bool onNotify(llvm::StringRef Method, llvm::json::Value Params) override {
    WithContext HandlerContext(handlerContext());
    log("<-- {0}", Method);
    if (Method == "exit")
      return false;
    if (!Server.Server) {
      elog("Notification {0} before initialization", Method);
    } else if (Method == "$/cancelRequest") {
      onCancel(std::move(Params));
    } else if (auto Handler = Notifications.lookup(Method)) {
      Handler(std::move(Params));
      Server.maybeExportMemoryProfile();
    } else {
      log("unhandled notification {0}", Method);
    }
    return true;
  }

  bool onCall(llvm::StringRef Method, llvm::json::Value Params,
              llvm::json::Value ID) override {
    WithContext HandlerContext(handlerContext());
    // Calls can be canceled by the client. Add cancellation context.
    WithContext WithCancel(cancelableRequestContext(ID));
    trace::Span Tracer(Method, LSPLatency);
    SPAN_ATTACH(Tracer, "Params", Params);
    ReplyOnce Reply(ID, Method, &Server, Tracer.Args);
    log("<-- {0}({1})", Method, ID);
    if (!Server.Server && Method != "initialize") {
      elog("Call {0} before initialization.", Method);
      Reply(llvm::make_error<LSPError>("server not initialized",
                                       ErrorCode::ServerNotInitialized));
    } else if (auto Handler = Calls.lookup(Method))
      Handler(std::move(Params), std::move(Reply));
    else
      Reply(llvm::make_error<LSPError>("method not found",
                                       ErrorCode::MethodNotFound));
    return true;
  }

  bool onReply(llvm::json::Value ID,
               llvm::Expected<llvm::json::Value> Result) override {
    WithContext HandlerContext(handlerContext());

    Callback<llvm::json::Value> ReplyHandler = nullptr;
    if (auto IntID = ID.getAsInteger()) {
      std::lock_guard<std::mutex> Mutex(CallMutex);
      // Find a corresponding callback for the request ID;
      for (size_t Index = 0; Index < ReplyCallbacks.size(); ++Index) {
        if (ReplyCallbacks[Index].first == *IntID) {
          ReplyHandler = std::move(ReplyCallbacks[Index].second);
          ReplyCallbacks.erase(ReplyCallbacks.begin() +
                               Index); // remove the entry
          break;
        }
      }
    }

    if (!ReplyHandler) {
      // No callback being found, use a default log callback.
      ReplyHandler = [&ID](llvm::Expected<llvm::json::Value> Result) {
        elog("received a reply with ID {0}, but there was no such call", ID);
        if (!Result)
          llvm::consumeError(Result.takeError());
      };
    }

    // Log and run the reply handler.
    if (Result) {
      log("<-- reply({0})", ID);
      ReplyHandler(std::move(Result));
    } else {
      auto Err = Result.takeError();
      log("<-- reply({0}) error: {1}", ID, Err);
      ReplyHandler(std::move(Err));
    }
    return true;
  }

  // Bind an LSP method name to a call.
  template <typename Param, typename Result>
  void bind(const char *Method,
            void (ClangdLSPServer::*Handler)(const Param &, Callback<Result>)) {
    Calls[Method] = [Method, Handler, this](llvm::json::Value RawParams,
                                            ReplyOnce Reply) {
      auto P = parse<Param>(RawParams, Method, "request");
      if (!P)
        return Reply(P.takeError());
      (Server.*Handler)(*P, std::move(Reply));
    };
  }

  // Bind a reply callback to a request. The callback will be invoked when
  // clangd receives the reply from the LSP client.
  // Return a call id of the request.
  llvm::json::Value bindReply(Callback<llvm::json::Value> Reply) {
    llvm::Optional<std::pair<int, Callback<llvm::json::Value>>> OldestCB;
    int ID;
    {
      std::lock_guard<std::mutex> Mutex(CallMutex);
      ID = NextCallID++;
      ReplyCallbacks.emplace_back(ID, std::move(Reply));

      // If the queue overflows, we assume that the client didn't reply the
      // oldest request, and run the corresponding callback which replies an
      // error to the client.
      if (ReplyCallbacks.size() > MaxReplayCallbacks) {
        elog("more than {0} outstanding LSP calls, forgetting about {1}",
             MaxReplayCallbacks, ReplyCallbacks.front().first);
        OldestCB = std::move(ReplyCallbacks.front());
        ReplyCallbacks.pop_front();
      }
    }
    if (OldestCB)
      OldestCB->second(
          error("failed to receive a client reply for request ({0})",
                OldestCB->first));
    return ID;
  }

  // Bind an LSP method name to a notification.
  template <typename Param>
  void bind(const char *Method,
            void (ClangdLSPServer::*Handler)(const Param &)) {
    Notifications[Method] = [Method, Handler,
                             this](llvm::json::Value RawParams) {
      llvm::Expected<Param> P = parse<Param>(RawParams, Method, "request");
      if (!P)
        return llvm::consumeError(P.takeError());
      trace::Span Tracer(Method, LSPLatency);
      SPAN_ATTACH(Tracer, "Params", RawParams);
      (Server.*Handler)(*P);
    };
  }

private:
  // Function object to reply to an LSP call.
  // Each instance must be called exactly once, otherwise:
  //  - the bug is logged, and (in debug mode) an assert will fire
  //  - if there was no reply, an error reply is sent
  //  - if there were multiple replies, only the first is sent
  class ReplyOnce {
    std::atomic<bool> Replied = {false};
    std::chrono::steady_clock::time_point Start;
    llvm::json::Value ID;
    std::string Method;
    ClangdLSPServer *Server; // Null when moved-from.
    llvm::json::Object *TraceArgs;

  public:
    ReplyOnce(const llvm::json::Value &ID, llvm::StringRef Method,
              ClangdLSPServer *Server, llvm::json::Object *TraceArgs)
        : Start(std::chrono::steady_clock::now()), ID(ID), Method(Method),
          Server(Server), TraceArgs(TraceArgs) {
      assert(Server);
    }
    ReplyOnce(ReplyOnce &&Other)
        : Replied(Other.Replied.load()), Start(Other.Start),
          ID(std::move(Other.ID)), Method(std::move(Other.Method)),
          Server(Other.Server), TraceArgs(Other.TraceArgs) {
      Other.Server = nullptr;
    }
    ReplyOnce &operator=(ReplyOnce &&) = delete;
    ReplyOnce(const ReplyOnce &) = delete;
    ReplyOnce &operator=(const ReplyOnce &) = delete;

    ~ReplyOnce() {
      // There's one legitimate reason to never reply to a request: clangd's
      // request handler send a call to the client (e.g. applyEdit) and the
      // client never replied. In this case, the ReplyOnce is owned by
      // ClangdLSPServer's reply callback table and is destroyed along with the
      // server. We don't attempt to send a reply in this case, there's little
      // to be gained from doing so.
      if (Server && !Server->IsBeingDestroyed && !Replied) {
        elog("No reply to message {0}({1})", Method, ID);
        assert(false && "must reply to all calls!");
        (*this)(llvm::make_error<LSPError>("server failed to reply",
                                           ErrorCode::InternalError));
      }
    }

    void operator()(llvm::Expected<llvm::json::Value> Reply) {
      assert(Server && "moved-from!");
      if (Replied.exchange(true)) {
        elog("Replied twice to message {0}({1})", Method, ID);
        assert(false && "must reply to each call only once!");
        return;
      }
      auto Duration = std::chrono::steady_clock::now() - Start;
      if (Reply) {
        log("--> reply:{0}({1}) {2:ms}", Method, ID, Duration);
        if (TraceArgs)
          (*TraceArgs)["Reply"] = *Reply;
        std::lock_guard<std::mutex> Lock(Server->TranspWriter);
        Server->Transp.reply(std::move(ID), std::move(Reply));
      } else {
        llvm::Error Err = Reply.takeError();
        log("--> reply:{0}({1}) {2:ms}, error: {3}", Method, ID, Duration, Err);
        if (TraceArgs)
          (*TraceArgs)["Error"] = llvm::to_string(Err);
        std::lock_guard<std::mutex> Lock(Server->TranspWriter);
        Server->Transp.reply(std::move(ID), std::move(Err));
      }
    }
  };

  llvm::StringMap<std::function<void(llvm::json::Value)>> Notifications;
  llvm::StringMap<std::function<void(llvm::json::Value, ReplyOnce)>> Calls;

  // Method calls may be cancelled by ID, so keep track of their state.
  // This needs a mutex: handlers may finish on a different thread, and that's
  // when we clean up entries in the map.
  mutable std::mutex RequestCancelersMutex;
  llvm::StringMap<std::pair<Canceler, /*Cookie*/ unsigned>> RequestCancelers;
  unsigned NextRequestCookie = 0; // To disambiguate reused IDs, see below.
  void onCancel(const llvm::json::Value &Params) {
    const llvm::json::Value *ID = nullptr;
    if (auto *O = Params.getAsObject())
      ID = O->get("id");
    if (!ID) {
      elog("Bad cancellation request: {0}", Params);
      return;
    }
    auto StrID = llvm::to_string(*ID);
    std::lock_guard<std::mutex> Lock(RequestCancelersMutex);
    auto It = RequestCancelers.find(StrID);
    if (It != RequestCancelers.end())
      It->second.first(); // Invoke the canceler.
  }

  Context handlerContext() const {
    return Context::current().derive(
        kCurrentOffsetEncoding,
        Server.Opts.Encoding.getValueOr(OffsetEncoding::UTF16));
  }

  // We run cancelable requests in a context that does two things:
  //  - allows cancellation using RequestCancelers[ID]
  //  - cleans up the entry in RequestCancelers when it's no longer needed
  // If a client reuses an ID, the last wins and the first cannot be canceled.
  Context cancelableRequestContext(const llvm::json::Value &ID) {
    auto Task = cancelableTask(
        /*Reason=*/static_cast<int>(ErrorCode::RequestCancelled));
    auto StrID = llvm::to_string(ID);  // JSON-serialize ID for map key.
    auto Cookie = NextRequestCookie++; // No lock, only called on main thread.
    {
      std::lock_guard<std::mutex> Lock(RequestCancelersMutex);
      RequestCancelers[StrID] = {std::move(Task.second), Cookie};
    }
    // When the request ends, we can clean up the entry we just added.
    // The cookie lets us check that it hasn't been overwritten due to ID
    // reuse.
    return Task.first.derive(llvm::make_scope_exit([this, StrID, Cookie] {
      std::lock_guard<std::mutex> Lock(RequestCancelersMutex);
      auto It = RequestCancelers.find(StrID);
      if (It != RequestCancelers.end() && It->second.second == Cookie)
        RequestCancelers.erase(It);
    }));
  }

  // The maximum number of callbacks held in clangd.
  //
  // We bound the maximum size to the pending map to prevent memory leakage
  // for cases where LSP clients don't reply for the request.
  // This has to go after RequestCancellers and RequestCancellersMutex since it
  // can contain a callback that has a cancelable context.
  static constexpr int MaxReplayCallbacks = 100;
  mutable std::mutex CallMutex;
  int NextCallID = 0; /* GUARDED_BY(CallMutex) */
  std::deque<std::pair</*RequestID*/ int,
                       /*ReplyHandler*/ Callback<llvm::json::Value>>>
      ReplyCallbacks; /* GUARDED_BY(CallMutex) */

  ClangdLSPServer &Server;
};
constexpr int ClangdLSPServer::MessageHandler::MaxReplayCallbacks;

// call(), notify(), and reply() wrap the Transport, adding logging and locking.
void ClangdLSPServer::callRaw(StringRef Method, llvm::json::Value Params,
                              Callback<llvm::json::Value> CB) {
  auto ID = MsgHandler->bindReply(std::move(CB));
  log("--> {0}({1})", Method, ID);
  std::lock_guard<std::mutex> Lock(TranspWriter);
  Transp.call(Method, std::move(Params), ID);
}

void ClangdLSPServer::notify(llvm::StringRef Method, llvm::json::Value Params) {
  log("--> {0}", Method);
  std::lock_guard<std::mutex> Lock(TranspWriter);
  Transp.notify(Method, std::move(Params));
}

static std::vector<llvm::StringRef> semanticTokenTypes() {
  std::vector<llvm::StringRef> Types;
  for (unsigned I = 0; I <= static_cast<unsigned>(HighlightingKind::LastKind);
       ++I)
    Types.push_back(toSemanticTokenType(static_cast<HighlightingKind>(I)));
  return Types;
}

void ClangdLSPServer::onInitialize(const InitializeParams &Params,
                                   Callback<llvm::json::Value> Reply) {
  // Determine character encoding first as it affects constructed ClangdServer.
  if (Params.capabilities.offsetEncoding && !Opts.Encoding) {
    Opts.Encoding = OffsetEncoding::UTF16; // fallback
    for (OffsetEncoding Supported : *Params.capabilities.offsetEncoding)
      if (Supported != OffsetEncoding::UnsupportedEncoding) {
        Opts.Encoding = Supported;
        break;
      }
  }

  Opts.TheiaSemanticHighlighting =
      Params.capabilities.TheiaSemanticHighlighting;
  if (Params.capabilities.TheiaSemanticHighlighting &&
      Params.capabilities.SemanticTokens) {
    log("Client supports legacy semanticHighlights notification and standard "
        "semanticTokens request, choosing the latter (no notifications).");
    Opts.TheiaSemanticHighlighting = false;
  }

  if (Params.rootUri && *Params.rootUri)
    Opts.WorkspaceRoot = std::string(Params.rootUri->file());
  else if (Params.rootPath && !Params.rootPath->empty())
    Opts.WorkspaceRoot = *Params.rootPath;
  if (Server)
    return Reply(llvm::make_error<LSPError>("server already initialized",
                                            ErrorCode::InvalidRequest));
  if (const auto &Dir = Params.initializationOptions.compilationDatabasePath)
    Opts.CompileCommandsDir = Dir;
  if (Opts.UseDirBasedCDB) {
    BaseCDB = std::make_unique<DirectoryBasedGlobalCompilationDatabase>(
        Opts.CompileCommandsDir);
    BaseCDB = getQueryDriverDatabase(llvm::makeArrayRef(Opts.QueryDriverGlobs),
                                     std::move(BaseCDB));
  }
  auto Mangler = CommandMangler::detect();
  if (Opts.ResourceDir)
    Mangler.ResourceDir = *Opts.ResourceDir;
  CDB.emplace(BaseCDB.get(), Params.initializationOptions.fallbackFlags,
              tooling::ArgumentsAdjuster(std::move(Mangler)));
  {
    // Switch caller's context with LSPServer's background context. Since we
    // rather want to propagate information from LSPServer's context into the
    // Server, CDB, etc.
    WithContext MainContext(BackgroundContext.clone());
    llvm::Optional<WithContextValue> WithOffsetEncoding;
    if (Opts.Encoding)
      WithOffsetEncoding.emplace(kCurrentOffsetEncoding, *Opts.Encoding);
    Server.emplace(*CDB, TFS, Opts,
                   static_cast<ClangdServer::Callbacks *>(this));
  }
  applyConfiguration(Params.initializationOptions.ConfigSettings);

  Opts.CodeComplete.EnableSnippets = Params.capabilities.CompletionSnippets;
  Opts.CodeComplete.IncludeFixIts = Params.capabilities.CompletionFixes;
  if (!Opts.CodeComplete.BundleOverloads.hasValue())
    Opts.CodeComplete.BundleOverloads = Params.capabilities.HasSignatureHelp;
  Opts.CodeComplete.DocumentationFormat =
      Params.capabilities.CompletionDocumentationFormat;
  DiagOpts.EmbedFixesInDiagnostics = Params.capabilities.DiagnosticFixes;
  DiagOpts.SendDiagnosticCategory = Params.capabilities.DiagnosticCategory;
  DiagOpts.EmitRelatedLocations =
      Params.capabilities.DiagnosticRelatedInformation;
  if (Params.capabilities.WorkspaceSymbolKinds)
    SupportedSymbolKinds |= *Params.capabilities.WorkspaceSymbolKinds;
  if (Params.capabilities.CompletionItemKinds)
    SupportedCompletionItemKinds |= *Params.capabilities.CompletionItemKinds;
  SupportsCodeAction = Params.capabilities.CodeActionStructure;
  SupportsHierarchicalDocumentSymbol =
      Params.capabilities.HierarchicalDocumentSymbol;
  SupportFileStatus = Params.initializationOptions.FileStatus;
  HoverContentFormat = Params.capabilities.HoverContentFormat;
  SupportsOffsetsInSignatureHelp = Params.capabilities.OffsetsInSignatureHelp;
  if (Params.capabilities.WorkDoneProgress)
    BackgroundIndexProgressState = BackgroundIndexProgress::Empty;
  BackgroundIndexSkipCreate = Params.capabilities.ImplicitProgressCreation;

  // Per LSP, renameProvider can be either boolean or RenameOptions.
  // RenameOptions will be specified if the client states it supports prepare.
  llvm::json::Value RenameProvider =
      llvm::json::Object{{"prepareProvider", true}};
  if (!Params.capabilities.RenamePrepareSupport) // Only boolean allowed per LSP
    RenameProvider = true;

  // Per LSP, codeActionProvide can be either boolean or CodeActionOptions.
  // CodeActionOptions is only valid if the client supports action literal
  // via textDocument.codeAction.codeActionLiteralSupport.
  llvm::json::Value CodeActionProvider = true;
  if (Params.capabilities.CodeActionStructure)
    CodeActionProvider = llvm::json::Object{
        {"codeActionKinds",
         {CodeAction::QUICKFIX_KIND, CodeAction::REFACTOR_KIND,
          CodeAction::INFO_KIND}}};

  llvm::json::Object Result{
      {{"serverInfo",
        llvm::json::Object{{"name", "clangd"},
                           {"version", getClangToolFullVersion("clangd")}}},
       {"capabilities",
        llvm::json::Object{
            {"textDocumentSync",
             llvm::json::Object{
                 {"openClose", true},
                 {"change", (int)TextDocumentSyncKind::Incremental},
                 {"save", true},
             }},
            {"documentFormattingProvider", true},
            {"documentRangeFormattingProvider", true},
            {"documentOnTypeFormattingProvider",
             llvm::json::Object{
                 {"firstTriggerCharacter", "\n"},
                 {"moreTriggerCharacter", {}},
             }},
            {"codeActionProvider", std::move(CodeActionProvider)},
            {"completionProvider",
             llvm::json::Object{
                 {"allCommitCharacters",
                  {" ", "\t", "(", ")", "[", "]", "{",  "}", "<",
                   ">", ":",  ";", ",", "+", "-", "/",  "*", "%",
                   "^", "&",  "#", "?", ".", "=", "\"", "'", "|"}},
                 {"resolveProvider", false},
                 // We do extra checks, e.g. that > is part of ->.
                 {"triggerCharacters", {".", "<", ">", ":", "\"", "/"}},
             }},
            {"semanticTokensProvider",
             llvm::json::Object{
                 {"full", llvm::json::Object{{"delta", true}}},
                 {"range", false},
                 {"legend",
                  llvm::json::Object{{"tokenTypes", semanticTokenTypes()},
                                     {"tokenModifiers", llvm::json::Array()}}},
             }},
            {"signatureHelpProvider",
             llvm::json::Object{
                 {"triggerCharacters", {"(", ","}},
             }},
            {"declarationProvider", true},
            {"definitionProvider", true},
            {"documentHighlightProvider", true},
            {"documentLinkProvider",
             llvm::json::Object{
                 {"resolveProvider", false},
             }},
            {"hoverProvider", true},
            {"renameProvider", std::move(RenameProvider)},
            {"selectionRangeProvider", true},
            {"documentSymbolProvider", true},
            {"workspaceSymbolProvider", true},
            {"referencesProvider", true},
            {"executeCommandProvider",
             llvm::json::Object{
                 {"commands",
                  {ExecuteCommandParams::CLANGD_APPLY_FIX_COMMAND,
                   ExecuteCommandParams::CLANGD_APPLY_TWEAK}},
             }},
            {"typeHierarchyProvider", true},
            {"memoryUsageProvider", true}, // clangd extension.
        }}}};
  if (Opts.Encoding)
    Result["offsetEncoding"] = *Opts.Encoding;
  if (Opts.TheiaSemanticHighlighting)
    Result.getObject("capabilities")
        ->insert(
            {"semanticHighlighting",
             llvm::json::Object{{"scopes", buildHighlightScopeLookupTable()}}});
  if (Opts.FoldingRanges)
    Result.getObject("capabilities")->insert({"foldingRangeProvider", true});
  Reply(std::move(Result));
}

void ClangdLSPServer::onInitialized(const InitializedParams &Params) {}

void ClangdLSPServer::onShutdown(const ShutdownParams &Params,
                                 Callback<std::nullptr_t> Reply) {
  // Do essentially nothing, just say we're ready to exit.
  ShutdownRequestReceived = true;
  Reply(nullptr);
}

// sync is a clangd extension: it blocks until all background work completes.
// It blocks the calling thread, so no messages are processed until it returns!
void ClangdLSPServer::onSync(const NoParams &Params,
                             Callback<std::nullptr_t> Reply) {
  if (Server->blockUntilIdleForTest(/*TimeoutSeconds=*/60))
    Reply(nullptr);
  else
    Reply(error("Not idle after a minute"));
}

void ClangdLSPServer::onDocumentDidOpen(
    const DidOpenTextDocumentParams &Params) {
  PathRef File = Params.textDocument.uri.file();

  const std::string &Contents = Params.textDocument.text;

  auto Version = DraftMgr.addDraft(File, Params.textDocument.version, Contents);
  Server->addDocument(File, Contents, encodeVersion(Version),
                      WantDiagnostics::Yes);
}

void ClangdLSPServer::onDocumentDidChange(
    const DidChangeTextDocumentParams &Params) {
  auto WantDiags = WantDiagnostics::Auto;
  if (Params.wantDiagnostics.hasValue())
    WantDiags = Params.wantDiagnostics.getValue() ? WantDiagnostics::Yes
                                                  : WantDiagnostics::No;

  PathRef File = Params.textDocument.uri.file();
  llvm::Expected<DraftStore::Draft> Draft = DraftMgr.updateDraft(
      File, Params.textDocument.version, Params.contentChanges);
  if (!Draft) {
    // If this fails, we are most likely going to be not in sync anymore with
    // the client.  It is better to remove the draft and let further operations
    // fail rather than giving wrong results.
    DraftMgr.removeDraft(File);
    Server->removeDocument(File);
    elog("Failed to update {0}: {1}", File, Draft.takeError());
    return;
  }

  Server->addDocument(File, Draft->Contents, encodeVersion(Draft->Version),
                      WantDiags, Params.forceRebuild);
}

void ClangdLSPServer::onDocumentDidSave(
    const DidSaveTextDocumentParams &Params) {
  reparseOpenFilesIfNeeded([](llvm::StringRef) { return true; });
}

void ClangdLSPServer::onFileEvent(const DidChangeWatchedFilesParams &Params) {
  // We could also reparse all open files here. However:
  //  - this could be frequent, and revalidating all the preambles isn't free
  //  - this is useful e.g. when switching git branches, but we're likely to see
  //    fresh headers but still have the old-branch main-file content
  Server->onFileEvent(Params);
}

void ClangdLSPServer::onCommand(const ExecuteCommandParams &Params,
                                Callback<llvm::json::Value> Reply) {
  auto ApplyEdit = [this](WorkspaceEdit WE, std::string SuccessMessage,
                          decltype(Reply) Reply) {
    ApplyWorkspaceEditParams Edit;
    Edit.edit = std::move(WE);
    call<ApplyWorkspaceEditResponse>(
        "workspace/applyEdit", std::move(Edit),
        [Reply = std::move(Reply), SuccessMessage = std::move(SuccessMessage)](
            llvm::Expected<ApplyWorkspaceEditResponse> Response) mutable {
          if (!Response)
            return Reply(Response.takeError());
          if (!Response->applied) {
            std::string Reason = Response->failureReason
                                     ? *Response->failureReason
                                     : "unknown reason";
            return Reply(error("edits were not applied: {0}", Reason));
          }
          return Reply(SuccessMessage);
        });
  };

  if (Params.command == ExecuteCommandParams::CLANGD_APPLY_FIX_COMMAND &&
      Params.workspaceEdit) {
    // The flow for "apply-fix" :
    // 1. We publish a diagnostic, including fixits
    // 2. The user clicks on the diagnostic, the editor asks us for code actions
    // 3. We send code actions, with the fixit embedded as context
    // 4. The user selects the fixit, the editor asks us to apply it
    // 5. We unwrap the changes and send them back to the editor
    // 6. The editor applies the changes (applyEdit), and sends us a reply
    // 7. We unwrap the reply and send a reply to the editor.
    ApplyEdit(*Params.workspaceEdit, "Fix applied.", std::move(Reply));
  } else if (Params.command == ExecuteCommandParams::CLANGD_APPLY_TWEAK &&
             Params.tweakArgs) {
    auto Code = DraftMgr.getDraft(Params.tweakArgs->file.file());
    if (!Code)
      return Reply(error("trying to apply a code action for a non-added file"));

    auto Action = [this, ApplyEdit, Reply = std::move(Reply),
                   File = Params.tweakArgs->file, Code = std::move(*Code)](
                      llvm::Expected<Tweak::Effect> R) mutable {
      if (!R)
        return Reply(R.takeError());

      assert(R->ShowMessage ||
             (!R->ApplyEdits.empty() && "tweak has no effect"));

      if (R->ShowMessage) {
        ShowMessageParams Msg;
        Msg.message = *R->ShowMessage;
        Msg.type = MessageType::Info;
        notify("window/showMessage", Msg);
      }
      // When no edit is specified, make sure we Reply().
      if (R->ApplyEdits.empty())
        return Reply("Tweak applied.");

      if (auto Err = validateEdits(DraftMgr, R->ApplyEdits))
        return Reply(std::move(Err));

      WorkspaceEdit WE;
      WE.changes.emplace();
      for (const auto &It : R->ApplyEdits) {
        (*WE.changes)[URI::createFile(It.first()).toString()] =
            It.second.asTextEdits();
      }
      // ApplyEdit will take care of calling Reply().
      return ApplyEdit(std::move(WE), "Tweak applied.", std::move(Reply));
    };
    Server->applyTweak(Params.tweakArgs->file.file(),
                       Params.tweakArgs->selection, Params.tweakArgs->tweakID,
                       std::move(Action));
  } else {
    // We should not get here because ExecuteCommandParams would not have
    // parsed in the first place and this handler should not be called. But if
    // more commands are added, this will be here has a safe guard.
    Reply(llvm::make_error<LSPError>(
        llvm::formatv("Unsupported command \"{0}\".", Params.command).str(),
        ErrorCode::InvalidParams));
  }
}

void ClangdLSPServer::onWorkspaceSymbol(
    const WorkspaceSymbolParams &Params,
    Callback<std::vector<SymbolInformation>> Reply) {
  Server->workspaceSymbols(
      Params.query, Opts.CodeComplete.Limit,
      [Reply = std::move(Reply),
       this](llvm::Expected<std::vector<SymbolInformation>> Items) mutable {
        if (!Items)
          return Reply(Items.takeError());
        for (auto &Sym : *Items)
          Sym.kind = adjustKindToCapability(Sym.kind, SupportedSymbolKinds);

        Reply(std::move(*Items));
      });
}

void ClangdLSPServer::onPrepareRename(const TextDocumentPositionParams &Params,
                                      Callback<llvm::Optional<Range>> Reply) {
  Server->prepareRename(
      Params.textDocument.uri.file(), Params.position, /*NewName*/ llvm::None,
      Opts.Rename,
      [Reply = std::move(Reply)](llvm::Expected<RenameResult> Result) mutable {
        if (!Result)
          return Reply(Result.takeError());
        return Reply(std::move(Result->Target));
      });
}

void ClangdLSPServer::onRename(const RenameParams &Params,
                               Callback<WorkspaceEdit> Reply) {
  Path File = std::string(Params.textDocument.uri.file());
  if (!DraftMgr.getDraft(File))
    return Reply(llvm::make_error<LSPError>(
        "onRename called for non-added file", ErrorCode::InvalidParams));
  Server->rename(
      File, Params.position, Params.newName, Opts.Rename,
      [File, Params, Reply = std::move(Reply),
       this](llvm::Expected<RenameResult> R) mutable {
        if (!R)
          return Reply(R.takeError());
        if (auto Err = validateEdits(DraftMgr, R->GlobalChanges))
          return Reply(std::move(Err));
        WorkspaceEdit Result;
        Result.changes.emplace();
        for (const auto &Rep : R->GlobalChanges) {
          (*Result.changes)[URI::createFile(Rep.first()).toString()] =
              Rep.second.asTextEdits();
        }
        Reply(Result);
      });
}

void ClangdLSPServer::onDocumentDidClose(
    const DidCloseTextDocumentParams &Params) {
  PathRef File = Params.textDocument.uri.file();
  DraftMgr.removeDraft(File);
  Server->removeDocument(File);

  {
    std::lock_guard<std::mutex> Lock(FixItsMutex);
    FixItsMap.erase(File);
  }
  {
    std::lock_guard<std::mutex> HLock(HighlightingsMutex);
    FileToHighlightings.erase(File);
  }
  {
    std::lock_guard<std::mutex> HLock(SemanticTokensMutex);
    LastSemanticTokens.erase(File);
  }
  // clangd will not send updates for this file anymore, so we empty out the
  // list of diagnostics shown on the client (e.g. in the "Problems" pane of
  // VSCode). Note that this cannot race with actual diagnostics responses
  // because removeDocument() guarantees no diagnostic callbacks will be
  // executed after it returns.
  PublishDiagnosticsParams Notification;
  Notification.uri = URIForFile::canonicalize(File, /*TUPath=*/File);
  publishDiagnostics(Notification);
}

void ClangdLSPServer::onDocumentOnTypeFormatting(
    const DocumentOnTypeFormattingParams &Params,
    Callback<std::vector<TextEdit>> Reply) {
  auto File = Params.textDocument.uri.file();
  auto Code = DraftMgr.getDraft(File);
  if (!Code)
    return Reply(llvm::make_error<LSPError>(
        "onDocumentOnTypeFormatting called for non-added file",
        ErrorCode::InvalidParams));

  Server->formatOnType(File, Code->Contents, Params.position, Params.ch,
                       std::move(Reply));
}

void ClangdLSPServer::onDocumentRangeFormatting(
    const DocumentRangeFormattingParams &Params,
    Callback<std::vector<TextEdit>> Reply) {
  auto File = Params.textDocument.uri.file();
  auto Code = DraftMgr.getDraft(File);
  if (!Code)
    return Reply(llvm::make_error<LSPError>(
        "onDocumentRangeFormatting called for non-added file",
        ErrorCode::InvalidParams));

  Server->formatRange(
      File, Code->Contents, Params.range,
      [Code = Code->Contents, Reply = std::move(Reply)](
          llvm::Expected<tooling::Replacements> Result) mutable {
        if (Result)
          Reply(replacementsToEdits(Code, Result.get()));
        else
          Reply(Result.takeError());
      });
}

void ClangdLSPServer::onDocumentFormatting(
    const DocumentFormattingParams &Params,
    Callback<std::vector<TextEdit>> Reply) {
  auto File = Params.textDocument.uri.file();
  auto Code = DraftMgr.getDraft(File);
  if (!Code)
    return Reply(llvm::make_error<LSPError>(
        "onDocumentFormatting called for non-added file",
        ErrorCode::InvalidParams));

  Server->formatFile(File, Code->Contents,
                     [Code = Code->Contents, Reply = std::move(Reply)](
                         llvm::Expected<tooling::Replacements> Result) mutable {
                       if (Result)
                         Reply(replacementsToEdits(Code, Result.get()));
                       else
                         Reply(Result.takeError());
                     });
}

/// The functions constructs a flattened view of the DocumentSymbol hierarchy.
/// Used by the clients that do not support the hierarchical view.
static std::vector<SymbolInformation>
flattenSymbolHierarchy(llvm::ArrayRef<DocumentSymbol> Symbols,
                       const URIForFile &FileURI) {
  std::vector<SymbolInformation> Results;
  std::function<void(const DocumentSymbol &, llvm::StringRef)> Process =
      [&](const DocumentSymbol &S, llvm::Optional<llvm::StringRef> ParentName) {
        SymbolInformation SI;
        SI.containerName = std::string(ParentName ? "" : *ParentName);
        SI.name = S.name;
        SI.kind = S.kind;
        SI.location.range = S.range;
        SI.location.uri = FileURI;

        Results.push_back(std::move(SI));
        std::string FullName =
            !ParentName ? S.name : (ParentName->str() + "::" + S.name);
        for (auto &C : S.children)
          Process(C, /*ParentName=*/FullName);
      };
  for (auto &S : Symbols)
    Process(S, /*ParentName=*/"");
  return Results;
}

void ClangdLSPServer::onDocumentSymbol(const DocumentSymbolParams &Params,
                                       Callback<llvm::json::Value> Reply) {
  URIForFile FileURI = Params.textDocument.uri;
  Server->documentSymbols(
      Params.textDocument.uri.file(),
      [this, FileURI, Reply = std::move(Reply)](
          llvm::Expected<std::vector<DocumentSymbol>> Items) mutable {
        if (!Items)
          return Reply(Items.takeError());
        adjustSymbolKinds(*Items, SupportedSymbolKinds);
        if (SupportsHierarchicalDocumentSymbol)
          return Reply(std::move(*Items));
        else
          return Reply(flattenSymbolHierarchy(*Items, FileURI));
      });
}

void ClangdLSPServer::onFoldingRange(
    const FoldingRangeParams &Params,
    Callback<std::vector<FoldingRange>> Reply) {
  Server->foldingRanges(Params.textDocument.uri.file(), std::move(Reply));
}

static llvm::Optional<Command> asCommand(const CodeAction &Action) {
  Command Cmd;
  if (Action.command && Action.edit)
    return None; // Not representable. (We never emit these anyway).
  if (Action.command) {
    Cmd = *Action.command;
  } else if (Action.edit) {
    Cmd.command = std::string(Command::CLANGD_APPLY_FIX_COMMAND);
    Cmd.workspaceEdit = *Action.edit;
  } else {
    return None;
  }
  Cmd.title = Action.title;
  if (Action.kind && *Action.kind == CodeAction::QUICKFIX_KIND)
    Cmd.title = "Apply fix: " + Cmd.title;
  return Cmd;
}

void ClangdLSPServer::onCodeAction(const CodeActionParams &Params,
                                   Callback<llvm::json::Value> Reply) {
  URIForFile File = Params.textDocument.uri;
  auto Code = DraftMgr.getDraft(File.file());
  if (!Code)
    return Reply(llvm::make_error<LSPError>(
        "onCodeAction called for non-added file", ErrorCode::InvalidParams));

  // Checks whether a particular CodeActionKind is included in the response.
  auto KindAllowed = [Only(Params.context.only)](llvm::StringRef Kind) {
    if (Only.empty())
      return true;
    return llvm::any_of(Only, [&](llvm::StringRef Base) {
      return Kind.consume_front(Base) && (Kind.empty() || Kind.startswith("."));
    });
  };

  // We provide a code action for Fixes on the specified diagnostics.
  std::vector<CodeAction> FixIts;
  if (KindAllowed(CodeAction::QUICKFIX_KIND)) {
    for (const Diagnostic &D : Params.context.diagnostics) {
      for (auto &F : getFixes(File.file(), D)) {
        FixIts.push_back(toCodeAction(F, Params.textDocument.uri));
        FixIts.back().diagnostics = {D};
      }
    }
  }

  // Now enumerate the semantic code actions.
  auto ConsumeActions =
      [Reply = std::move(Reply), File, Code = std::move(*Code),
       Selection = Params.range, FixIts = std::move(FixIts), this](
          llvm::Expected<std::vector<ClangdServer::TweakRef>> Tweaks) mutable {
        if (!Tweaks)
          return Reply(Tweaks.takeError());

        std::vector<CodeAction> Actions = std::move(FixIts);
        Actions.reserve(Actions.size() + Tweaks->size());
        for (const auto &T : *Tweaks)
          Actions.push_back(toCodeAction(T, File, Selection));

        // If there's exactly one quick-fix, call it "preferred".
        // We never consider refactorings etc as preferred.
        CodeAction *OnlyFix = nullptr;
        for (auto &Action : Actions) {
          if (Action.kind && *Action.kind == CodeAction::QUICKFIX_KIND) {
            if (OnlyFix) {
              OnlyFix->isPreferred = false;
              break;
            }
            Action.isPreferred = true;
            OnlyFix = &Action;
          }
        }

        if (SupportsCodeAction)
          return Reply(llvm::json::Array(Actions));
        std::vector<Command> Commands;
        for (const auto &Action : Actions) {
          if (auto Command = asCommand(Action))
            Commands.push_back(std::move(*Command));
        }
        return Reply(llvm::json::Array(Commands));
      };
  Server->enumerateTweaks(
      File.file(), Params.range,
      [this, KindAllowed(std::move(KindAllowed))](const Tweak &T) {
        return Opts.TweakFilter(T) && KindAllowed(T.kind());
      },
      std::move(ConsumeActions));
}

void ClangdLSPServer::onCompletion(const CompletionParams &Params,
                                   Callback<CompletionList> Reply) {
  if (!shouldRunCompletion(Params)) {
    // Clients sometimes auto-trigger completions in undesired places (e.g.
    // 'a >^ '), we return empty results in those cases.
    vlog("ignored auto-triggered completion, preceding char did not match");
    return Reply(CompletionList());
  }
  Server->codeComplete(
      Params.textDocument.uri.file(), Params.position, Opts.CodeComplete,
      [Reply = std::move(Reply),
       this](llvm::Expected<CodeCompleteResult> List) mutable {
        if (!List)
          return Reply(List.takeError());
        CompletionList LSPList;
        LSPList.isIncomplete = List->HasMore;
        for (const auto &R : List->Completions) {
          CompletionItem C = R.render(Opts.CodeComplete);
          C.kind = adjustKindToCapability(C.kind, SupportedCompletionItemKinds);
          LSPList.items.push_back(std::move(C));
        }
        return Reply(std::move(LSPList));
      });
}

void ClangdLSPServer::onSignatureHelp(const TextDocumentPositionParams &Params,
                                      Callback<SignatureHelp> Reply) {
  Server->signatureHelp(Params.textDocument.uri.file(), Params.position,
                        [Reply = std::move(Reply), this](
                            llvm::Expected<SignatureHelp> Signature) mutable {
                          if (!Signature)
                            return Reply(Signature.takeError());
                          if (SupportsOffsetsInSignatureHelp)
                            return Reply(std::move(*Signature));
                          // Strip out the offsets from signature help for
                          // clients that only support string labels.
                          for (auto &SigInfo : Signature->signatures) {
                            for (auto &Param : SigInfo.parameters)
                              Param.labelOffsets.reset();
                          }
                          return Reply(std::move(*Signature));
                        });
}

// Go to definition has a toggle function: if def and decl are distinct, then
// the first press gives you the def, the second gives you the matching def.
// getToggle() returns the counterpart location that under the cursor.
//
// We return the toggled location alone (ignoring other symbols) to encourage
// editors to "bounce" quickly between locations, without showing a menu.
static Location *getToggle(const TextDocumentPositionParams &Point,
                           LocatedSymbol &Sym) {
  // Toggle only makes sense with two distinct locations.
  if (!Sym.Definition || *Sym.Definition == Sym.PreferredDeclaration)
    return nullptr;
  if (Sym.Definition->uri.file() == Point.textDocument.uri.file() &&
      Sym.Definition->range.contains(Point.position))
    return &Sym.PreferredDeclaration;
  if (Sym.PreferredDeclaration.uri.file() == Point.textDocument.uri.file() &&
      Sym.PreferredDeclaration.range.contains(Point.position))
    return &*Sym.Definition;
  return nullptr;
}

void ClangdLSPServer::onGoToDefinition(const TextDocumentPositionParams &Params,
                                       Callback<std::vector<Location>> Reply) {
  Server->locateSymbolAt(
      Params.textDocument.uri.file(), Params.position,
      [Params, Reply = std::move(Reply)](
          llvm::Expected<std::vector<LocatedSymbol>> Symbols) mutable {
        if (!Symbols)
          return Reply(Symbols.takeError());
        std::vector<Location> Defs;
        for (auto &S : *Symbols) {
          if (Location *Toggle = getToggle(Params, S))
            return Reply(std::vector<Location>{std::move(*Toggle)});
          Defs.push_back(S.Definition.getValueOr(S.PreferredDeclaration));
        }
        Reply(std::move(Defs));
      });
}

void ClangdLSPServer::onGoToDeclaration(
    const TextDocumentPositionParams &Params,
    Callback<std::vector<Location>> Reply) {
  Server->locateSymbolAt(
      Params.textDocument.uri.file(), Params.position,
      [Params, Reply = std::move(Reply)](
          llvm::Expected<std::vector<LocatedSymbol>> Symbols) mutable {
        if (!Symbols)
          return Reply(Symbols.takeError());
        std::vector<Location> Decls;
        for (auto &S : *Symbols) {
          if (Location *Toggle = getToggle(Params, S))
            return Reply(std::vector<Location>{std::move(*Toggle)});
          Decls.push_back(std::move(S.PreferredDeclaration));
        }
        Reply(std::move(Decls));
      });
}

void ClangdLSPServer::onSwitchSourceHeader(
    const TextDocumentIdentifier &Params,
    Callback<llvm::Optional<URIForFile>> Reply) {
  Server->switchSourceHeader(
      Params.uri.file(),
      [Reply = std::move(Reply),
       Params](llvm::Expected<llvm::Optional<clangd::Path>> Path) mutable {
        if (!Path)
          return Reply(Path.takeError());
        if (*Path)
          return Reply(URIForFile::canonicalize(**Path, Params.uri.file()));
        return Reply(llvm::None);
      });
}

void ClangdLSPServer::onDocumentHighlight(
    const TextDocumentPositionParams &Params,
    Callback<std::vector<DocumentHighlight>> Reply) {
  Server->findDocumentHighlights(Params.textDocument.uri.file(),
                                 Params.position, std::move(Reply));
}

void ClangdLSPServer::onHover(const TextDocumentPositionParams &Params,
                              Callback<llvm::Optional<Hover>> Reply) {
  Server->findHover(Params.textDocument.uri.file(), Params.position,
                    [Reply = std::move(Reply), this](
                        llvm::Expected<llvm::Optional<HoverInfo>> H) mutable {
                      if (!H)
                        return Reply(H.takeError());
                      if (!*H)
                        return Reply(llvm::None);

                      Hover R;
                      R.contents.kind = HoverContentFormat;
                      R.range = (*H)->SymRange;
                      switch (HoverContentFormat) {
                      case MarkupKind::PlainText:
                        R.contents.value = (*H)->present().asPlainText();
                        return Reply(std::move(R));
                      case MarkupKind::Markdown:
                        R.contents.value = (*H)->present().asMarkdown();
                        return Reply(std::move(R));
                      };
                      llvm_unreachable("unhandled MarkupKind");
                    });
}

void ClangdLSPServer::onTypeHierarchy(
    const TypeHierarchyParams &Params,
    Callback<Optional<TypeHierarchyItem>> Reply) {
  Server->typeHierarchy(Params.textDocument.uri.file(), Params.position,
                        Params.resolve, Params.direction, std::move(Reply));
}

void ClangdLSPServer::onResolveTypeHierarchy(
    const ResolveTypeHierarchyItemParams &Params,
    Callback<Optional<TypeHierarchyItem>> Reply) {
  Server->resolveTypeHierarchy(Params.item, Params.resolve, Params.direction,
                               std::move(Reply));
}

void ClangdLSPServer::applyConfiguration(
    const ConfigurationSettings &Settings) {
  // Per-file update to the compilation database.
  llvm::StringSet<> ModifiedFiles;
  for (auto &Entry : Settings.compilationDatabaseChanges) {
    PathRef File = Entry.first;
    auto Old = CDB->getCompileCommand(File);
    auto New =
        tooling::CompileCommand(std::move(Entry.second.workingDirectory), File,
                                std::move(Entry.second.compilationCommand),
                                /*Output=*/"");
    if (Old != New) {
      CDB->setCompileCommand(File, std::move(New));
      ModifiedFiles.insert(File);
    }
  }

  reparseOpenFilesIfNeeded(
      [&](llvm::StringRef File) { return ModifiedFiles.count(File) != 0; });
}

void ClangdLSPServer::publishTheiaSemanticHighlighting(
    const TheiaSemanticHighlightingParams &Params) {
  notify("textDocument/semanticHighlighting", Params);
}

void ClangdLSPServer::publishDiagnostics(
    const PublishDiagnosticsParams &Params) {
  notify("textDocument/publishDiagnostics", Params);
}

void ClangdLSPServer::maybeExportMemoryProfile() {
  if (!trace::enabled())
    return;
  // Profiling might be expensive, so we throttle it to happen once every 5
  // minutes.
  static constexpr auto ProfileInterval = std::chrono::minutes(5);
  auto Now = std::chrono::steady_clock::now();
  if (Now < NextProfileTime)
    return;

  static constexpr trace::Metric MemoryUsage(
      "memory_usage", trace::Metric::Value, "component_name");
  trace::Span Tracer("ProfileBrief");
  MemoryTree MT;
  profile(MT);
  record(MT, "clangd_lsp_server", MemoryUsage);
  NextProfileTime = Now + ProfileInterval;
}

// FIXME: This function needs to be properly tested.
void ClangdLSPServer::onChangeConfiguration(
    const DidChangeConfigurationParams &Params) {
  applyConfiguration(Params.settings);
}

void ClangdLSPServer::onReference(const ReferenceParams &Params,
                                  Callback<std::vector<Location>> Reply) {
  Server->findReferences(Params.textDocument.uri.file(), Params.position,
                         Opts.CodeComplete.Limit,
                         [Reply = std::move(Reply)](
                             llvm::Expected<ReferencesResult> Refs) mutable {
                           if (!Refs)
                             return Reply(Refs.takeError());
                           return Reply(std::move(Refs->References));
                         });
}

void ClangdLSPServer::onSymbolInfo(const TextDocumentPositionParams &Params,
                                   Callback<std::vector<SymbolDetails>> Reply) {
  Server->symbolInfo(Params.textDocument.uri.file(), Params.position,
                     std::move(Reply));
}

void ClangdLSPServer::onSelectionRange(
    const SelectionRangeParams &Params,
    Callback<std::vector<SelectionRange>> Reply) {
  Server->semanticRanges(
      Params.textDocument.uri.file(), Params.positions,
      [Reply = std::move(Reply)](
          llvm::Expected<std::vector<SelectionRange>> Ranges) mutable {
        if (!Ranges)
          return Reply(Ranges.takeError());
        return Reply(std::move(*Ranges));
      });
}

void ClangdLSPServer::onDocumentLink(
    const DocumentLinkParams &Params,
    Callback<std::vector<DocumentLink>> Reply) {

  // TODO(forster): This currently resolves all targets eagerly. This is slow,
  // because it blocks on the preamble/AST being built. We could respond to the
  // request faster by using string matching or the lexer to find the includes
  // and resolving the targets lazily.
  Server->documentLinks(
      Params.textDocument.uri.file(),
      [Reply = std::move(Reply)](
          llvm::Expected<std::vector<DocumentLink>> Links) mutable {
        if (!Links) {
          return Reply(Links.takeError());
        }
        return Reply(std::move(Links));
      });
}

// Increment a numeric string: "" -> 1 -> 2 -> ... -> 9 -> 10 -> 11 ...
static void increment(std::string &S) {
  for (char &C : llvm::reverse(S)) {
    if (C != '9') {
      ++C;
      return;
    }
    C = '0';
  }
  S.insert(S.begin(), '1');
}

void ClangdLSPServer::onSemanticTokens(const SemanticTokensParams &Params,
                                       Callback<SemanticTokens> CB) {
  Server->semanticHighlights(
      Params.textDocument.uri.file(),
      [this, File(Params.textDocument.uri.file().str()), CB(std::move(CB))](
          llvm::Expected<std::vector<HighlightingToken>> HT) mutable {
        if (!HT)
          return CB(HT.takeError());
        SemanticTokens Result;
        Result.tokens = toSemanticTokens(*HT);
        {
          std::lock_guard<std::mutex> Lock(SemanticTokensMutex);
          auto &Last = LastSemanticTokens[File];

          Last.tokens = Result.tokens;
          increment(Last.resultId);
          Result.resultId = Last.resultId;
        }
        CB(std::move(Result));
      });
}

void ClangdLSPServer::onSemanticTokensDelta(
    const SemanticTokensDeltaParams &Params,
    Callback<SemanticTokensOrDelta> CB) {
  Server->semanticHighlights(
      Params.textDocument.uri.file(),
      [this, PrevResultID(Params.previousResultId),
       File(Params.textDocument.uri.file().str()), CB(std::move(CB))](
          llvm::Expected<std::vector<HighlightingToken>> HT) mutable {
        if (!HT)
          return CB(HT.takeError());
        std::vector<SemanticToken> Toks = toSemanticTokens(*HT);

        SemanticTokensOrDelta Result;
        {
          std::lock_guard<std::mutex> Lock(SemanticTokensMutex);
          auto &Last = LastSemanticTokens[File];

          if (PrevResultID == Last.resultId) {
            Result.edits = diffTokens(Last.tokens, Toks);
          } else {
            vlog("semanticTokens/full/delta: wanted edits vs {0} but last "
                 "result had ID {1}. Returning full token list.",
                 PrevResultID, Last.resultId);
            Result.tokens = Toks;
          }

          Last.tokens = std::move(Toks);
          increment(Last.resultId);
          Result.resultId = Last.resultId;
        }

        CB(std::move(Result));
      });
}

void ClangdLSPServer::onMemoryUsage(const NoParams &,
                                    Callback<MemoryTree> Reply) {
  llvm::BumpPtrAllocator DetailAlloc;
  MemoryTree MT(&DetailAlloc);
  profile(MT);
  Reply(std::move(MT));
}

ClangdLSPServer::ClangdLSPServer(class Transport &Transp,
                                 const ThreadsafeFS &TFS,
                                 const ClangdLSPServer::Options &Opts)
    : BackgroundContext(Context::current().clone()), Transp(Transp),
      MsgHandler(new MessageHandler(*this)), TFS(TFS),
      SupportedSymbolKinds(defaultSymbolKinds()),
      SupportedCompletionItemKinds(defaultCompletionItemKinds()), Opts(Opts) {
  // clang-format off
  MsgHandler->bind("initialize", &ClangdLSPServer::onInitialize);
  MsgHandler->bind("initialized", &ClangdLSPServer::onInitialized);
  MsgHandler->bind("shutdown", &ClangdLSPServer::onShutdown);
  MsgHandler->bind("sync", &ClangdLSPServer::onSync);
  MsgHandler->bind("textDocument/rangeFormatting", &ClangdLSPServer::onDocumentRangeFormatting);
  MsgHandler->bind("textDocument/onTypeFormatting", &ClangdLSPServer::onDocumentOnTypeFormatting);
  MsgHandler->bind("textDocument/formatting", &ClangdLSPServer::onDocumentFormatting);
  MsgHandler->bind("textDocument/codeAction", &ClangdLSPServer::onCodeAction);
  MsgHandler->bind("textDocument/completion", &ClangdLSPServer::onCompletion);
  MsgHandler->bind("textDocument/signatureHelp", &ClangdLSPServer::onSignatureHelp);
  MsgHandler->bind("textDocument/definition", &ClangdLSPServer::onGoToDefinition);
  MsgHandler->bind("textDocument/declaration", &ClangdLSPServer::onGoToDeclaration);
  MsgHandler->bind("textDocument/references", &ClangdLSPServer::onReference);
  MsgHandler->bind("textDocument/switchSourceHeader", &ClangdLSPServer::onSwitchSourceHeader);
  MsgHandler->bind("textDocument/prepareRename", &ClangdLSPServer::onPrepareRename);
  MsgHandler->bind("textDocument/rename", &ClangdLSPServer::onRename);
  MsgHandler->bind("textDocument/hover", &ClangdLSPServer::onHover);
  MsgHandler->bind("textDocument/documentSymbol", &ClangdLSPServer::onDocumentSymbol);
  MsgHandler->bind("workspace/executeCommand", &ClangdLSPServer::onCommand);
  MsgHandler->bind("textDocument/documentHighlight", &ClangdLSPServer::onDocumentHighlight);
  MsgHandler->bind("workspace/symbol", &ClangdLSPServer::onWorkspaceSymbol);
  MsgHandler->bind("textDocument/didOpen", &ClangdLSPServer::onDocumentDidOpen);
  MsgHandler->bind("textDocument/didClose", &ClangdLSPServer::onDocumentDidClose);
  MsgHandler->bind("textDocument/didChange", &ClangdLSPServer::onDocumentDidChange);
  MsgHandler->bind("textDocument/didSave", &ClangdLSPServer::onDocumentDidSave);
  MsgHandler->bind("workspace/didChangeWatchedFiles", &ClangdLSPServer::onFileEvent);
  MsgHandler->bind("workspace/didChangeConfiguration", &ClangdLSPServer::onChangeConfiguration);
  MsgHandler->bind("textDocument/symbolInfo", &ClangdLSPServer::onSymbolInfo);
  MsgHandler->bind("textDocument/typeHierarchy", &ClangdLSPServer::onTypeHierarchy);
  MsgHandler->bind("typeHierarchy/resolve", &ClangdLSPServer::onResolveTypeHierarchy);
  MsgHandler->bind("textDocument/selectionRange", &ClangdLSPServer::onSelectionRange);
  MsgHandler->bind("textDocument/documentLink", &ClangdLSPServer::onDocumentLink);
  MsgHandler->bind("textDocument/semanticTokens/full", &ClangdLSPServer::onSemanticTokens);
  MsgHandler->bind("textDocument/semanticTokens/full/delta", &ClangdLSPServer::onSemanticTokensDelta);
  MsgHandler->bind("$/memoryUsage", &ClangdLSPServer::onMemoryUsage);
  if (Opts.FoldingRanges)
    MsgHandler->bind("textDocument/foldingRange", &ClangdLSPServer::onFoldingRange);
  // clang-format on

  // Delay first profile until we've finished warming up.
  NextProfileTime = std::chrono::steady_clock::now() + std::chrono::minutes(1);
}

ClangdLSPServer::~ClangdLSPServer() {
  IsBeingDestroyed = true;
  // Explicitly destroy ClangdServer first, blocking on threads it owns.
  // This ensures they don't access any other members.
  Server.reset();
}

bool ClangdLSPServer::run() {
  // Run the Language Server loop.
  bool CleanExit = true;
  if (auto Err = Transp.loop(*MsgHandler)) {
    elog("Transport error: {0}", std::move(Err));
    CleanExit = false;
  }

  return CleanExit && ShutdownRequestReceived;
}

void ClangdLSPServer::profile(MemoryTree &MT) const {
  if (Server)
    Server->profile(MT.child("clangd_server"));
}

std::vector<Fix> ClangdLSPServer::getFixes(llvm::StringRef File,
                                           const clangd::Diagnostic &D) {
  std::lock_guard<std::mutex> Lock(FixItsMutex);
  auto DiagToFixItsIter = FixItsMap.find(File);
  if (DiagToFixItsIter == FixItsMap.end())
    return {};

  const auto &DiagToFixItsMap = DiagToFixItsIter->second;
  auto FixItsIter = DiagToFixItsMap.find(D);
  if (FixItsIter == DiagToFixItsMap.end())
    return {};

  return FixItsIter->second;
}

// A completion request is sent when the user types '>' or ':', but we only
// want to trigger on '->' and '::'. We check the preceeding text to make
// sure it matches what we expected.
// Running the lexer here would be more robust (e.g. we can detect comments
// and avoid triggering completion there), but we choose to err on the side
// of simplicity here.
bool ClangdLSPServer::shouldRunCompletion(
    const CompletionParams &Params) const {
  if (Params.context.triggerKind != CompletionTriggerKind::TriggerCharacter)
    return true;
  auto Code = DraftMgr.getDraft(Params.textDocument.uri.file());
  if (!Code)
    return true; // completion code will log the error for untracked doc.
  auto Offset = positionToOffset(Code->Contents, Params.position,
                                 /*AllowColumnsBeyondLineLength=*/false);
  if (!Offset) {
    vlog("could not convert position '{0}' to offset for file '{1}'",
         Params.position, Params.textDocument.uri.file());
    return true;
  }
  return allowImplicitCompletion(Code->Contents, *Offset);
}

void ClangdLSPServer::onHighlightingsReady(
    PathRef File, llvm::StringRef Version,
    std::vector<HighlightingToken> Highlightings) {
  std::vector<HighlightingToken> Old;
  std::vector<HighlightingToken> HighlightingsCopy = Highlightings;
  {
    std::lock_guard<std::mutex> Lock(HighlightingsMutex);
    Old = std::move(FileToHighlightings[File]);
    FileToHighlightings[File] = std::move(HighlightingsCopy);
  }
  // LSP allows us to send incremental edits of highlightings. Also need to diff
  // to remove highlightings from tokens that should no longer have them.
  std::vector<LineHighlightings> Diffed = diffHighlightings(Highlightings, Old);
  TheiaSemanticHighlightingParams Notification;
  Notification.TextDocument.uri =
      URIForFile::canonicalize(File, /*TUPath=*/File);
  Notification.TextDocument.version = decodeVersion(Version);
  Notification.Lines = toTheiaSemanticHighlightingInformation(Diffed);
  publishTheiaSemanticHighlighting(Notification);
}

void ClangdLSPServer::onDiagnosticsReady(PathRef File, llvm::StringRef Version,
                                         std::vector<Diag> Diagnostics) {
  PublishDiagnosticsParams Notification;
  Notification.version = decodeVersion(Version);
  Notification.uri = URIForFile::canonicalize(File, /*TUPath=*/File);
  DiagnosticToReplacementMap LocalFixIts; // Temporary storage
  for (auto &Diag : Diagnostics) {
    toLSPDiags(Diag, Notification.uri, DiagOpts,
               [&](clangd::Diagnostic Diag, llvm::ArrayRef<Fix> Fixes) {
                 auto &FixItsForDiagnostic = LocalFixIts[Diag];
                 llvm::copy(Fixes, std::back_inserter(FixItsForDiagnostic));
                 Notification.diagnostics.push_back(std::move(Diag));
               });
  }

  // Cache FixIts
  {
    std::lock_guard<std::mutex> Lock(FixItsMutex);
    FixItsMap[File] = LocalFixIts;
  }

  // Send a notification to the LSP client.
  publishDiagnostics(Notification);
}

void ClangdLSPServer::onBackgroundIndexProgress(
    const BackgroundQueue::Stats &Stats) {
  static const char ProgressToken[] = "backgroundIndexProgress";
  std::lock_guard<std::mutex> Lock(BackgroundIndexProgressMutex);

  auto NotifyProgress = [this](const BackgroundQueue::Stats &Stats) {
    if (BackgroundIndexProgressState != BackgroundIndexProgress::Live) {
      WorkDoneProgressBegin Begin;
      Begin.percentage = true;
      Begin.title = "indexing";
      progress(ProgressToken, std::move(Begin));
      BackgroundIndexProgressState = BackgroundIndexProgress::Live;
    }

    if (Stats.Completed < Stats.Enqueued) {
      assert(Stats.Enqueued > Stats.LastIdle);
      WorkDoneProgressReport Report;
      Report.percentage = 100.0 * (Stats.Completed - Stats.LastIdle) /
                          (Stats.Enqueued - Stats.LastIdle);
      Report.message =
          llvm::formatv("{0}/{1}", Stats.Completed - Stats.LastIdle,
                        Stats.Enqueued - Stats.LastIdle);
      progress(ProgressToken, std::move(Report));
    } else {
      assert(Stats.Completed == Stats.Enqueued);
      progress(ProgressToken, WorkDoneProgressEnd());
      BackgroundIndexProgressState = BackgroundIndexProgress::Empty;
    }
  };

  switch (BackgroundIndexProgressState) {
  case BackgroundIndexProgress::Unsupported:
    return;
  case BackgroundIndexProgress::Creating:
    // Cache this update for when the progress bar is available.
    PendingBackgroundIndexProgress = Stats;
    return;
  case BackgroundIndexProgress::Empty: {
    if (BackgroundIndexSkipCreate) {
      NotifyProgress(Stats);
      break;
    }
    // Cache this update for when the progress bar is available.
    PendingBackgroundIndexProgress = Stats;
    BackgroundIndexProgressState = BackgroundIndexProgress::Creating;
    WorkDoneProgressCreateParams CreateRequest;
    CreateRequest.token = ProgressToken;
    call<std::nullptr_t>(
        "window/workDoneProgress/create", CreateRequest,
        [this, NotifyProgress](llvm::Expected<std::nullptr_t> E) {
          std::lock_guard<std::mutex> Lock(BackgroundIndexProgressMutex);
          if (E) {
            NotifyProgress(this->PendingBackgroundIndexProgress);
          } else {
            elog("Failed to create background index progress bar: {0}",
                 E.takeError());
            // give up forever rather than thrashing about
            BackgroundIndexProgressState = BackgroundIndexProgress::Unsupported;
          }
        });
    break;
  }
  case BackgroundIndexProgress::Live:
    NotifyProgress(Stats);
    break;
  }
}

void ClangdLSPServer::onFileUpdated(PathRef File, const TUStatus &Status) {
  if (!SupportFileStatus)
    return;
  // FIXME: we don't emit "BuildingFile" and `RunningAction`, as these
  // two statuses are running faster in practice, which leads the UI constantly
  // changing, and doesn't provide much value. We may want to emit status at a
  // reasonable time interval (e.g. 0.5s).
  if (Status.PreambleActivity == PreambleAction::Idle &&
      (Status.ASTActivity.K == ASTAction::Building ||
       Status.ASTActivity.K == ASTAction::RunningAction))
    return;
  notify("textDocument/clangd.fileStatus", Status.render(File));
}

void ClangdLSPServer::reparseOpenFilesIfNeeded(
    llvm::function_ref<bool(llvm::StringRef File)> Filter) {
  // Reparse only opened files that were modified.
  for (const Path &FilePath : DraftMgr.getActiveFiles())
    if (Filter(FilePath))
      if (auto Draft = DraftMgr.getDraft(FilePath)) // else disappeared in race?
        Server->addDocument(FilePath, std::move(Draft->Contents),
                            encodeVersion(Draft->Version),
                            WantDiagnostics::Auto);
}

} // namespace clangd
} // namespace clang