path: root/lsp-codelens.patch

diff --git a/clang-tools-extra/clangd/CMakeLists.txt b/clang-tools-extra/clangd/CMakeLists.txt
index c21d277d2ffc..f400b69d380b 100644
--- a/clang-tools-extra/clangd/CMakeLists.txt
+++ b/clang-tools-extra/clangd/CMakeLists.txt
@@ -68,6 +68,7 @@ add_clang_library(clangDaemon
   ClangdServer.cpp
   CodeComplete.cpp
   CodeCompletionStrings.cpp
+  CodeLens.cpp
   CollectMacros.cpp
   CompileCommands.cpp
   Compiler.cpp
diff --git a/clang-tools-extra/clangd/ClangdLSPServer.cpp b/clang-tools-extra/clangd/ClangdLSPServer.cpp
index 06573a575542..970511f8ad08 100644
--- a/clang-tools-extra/clangd/ClangdLSPServer.cpp
+++ b/clang-tools-extra/clangd/ClangdLSPServer.cpp
@@ -692,6 +692,11 @@ void ClangdLSPServer::onInitialize(const InitializeParams &Params,
        {"capabilities", std::move(ServerCaps)}}};
   if (Opts.Encoding)
     Result["offsetEncoding"] = *Opts.Encoding;
+  if (Opts.CodeLens)
+    Result.getObject("capabilities")
+        ->insert({"codeLensProvider", llvm::json::Object{
+                                          {"resolveProvider", true},
+                                      }});
   Reply(std::move(Result));
 
   // Apply settings after we're fully initialized.
@@ -1631,6 +1636,30 @@ void ClangdLSPServer::onMemoryUsage(const NoParams &,
   Reply(std::move(MT));
 }
 
+void ClangdLSPServer::onCodeLens(const CodeLensParams &Params,
+                                 Callback<std::vector<CodeLens>> Reply) {
+  URIForFile FileURI = Params.textDocument.uri;
+  Server->provideCodeLens(
+      FileURI.file(), Opts.ReferencesLimit,
+      [Reply = std::move(Reply)](
+          llvm::Expected<std::vector<CodeLens>> CodeLens) mutable {
+        if (!CodeLens)
+          return Reply(CodeLens.takeError());
+        return Reply(std::move(*CodeLens));
+      });
+}
+
+void ClangdLSPServer::onCodeLensResolve(const CodeLens &Params,
+                                        Callback<CodeLens> Reply) {
+  Server->resolveCodeLens(
+      Params, Opts.ReferencesLimit,
+      [Reply = std::move(Reply)](llvm::Expected<CodeLens> CodeLens) mutable {
+        if (!CodeLens)
+          return Reply(CodeLens.takeError());
+        return Reply(std::move(*CodeLens));
+      });
+}
+
 void ClangdLSPServer::onAST(const ASTParams &Params,
                             Callback<std::optional<ASTNode>> CB) {
   Server->getAST(Params.textDocument.uri.file(), Params.range, std::move(CB));
@@ -1708,6 +1737,10 @@ void ClangdLSPServer::bindMethods(LSPBinder &Bind,
   Bind.command(ApplyTweakCommand, this, &ClangdLSPServer::onCommandApplyTweak);
   Bind.command(ApplyRenameCommand, this, &ClangdLSPServer::onCommandApplyRename);
 
+  if (Opts.CodeLens) {
+    Bind.method("textDocument/codeLens",this, &ClangdLSPServer::onCodeLens);
+    Bind.method("codeLens/resolve",this, &ClangdLSPServer::onCodeLensResolve);
+  }
   ApplyWorkspaceEdit = Bind.outgoingMethod("workspace/applyEdit");
   PublishDiagnostics = Bind.outgoingNotification("textDocument/publishDiagnostics");
   if (Caps.InactiveRegions)
diff --git a/clang-tools-extra/clangd/ClangdLSPServer.h b/clang-tools-extra/clangd/ClangdLSPServer.h
index 0b8e4720f532..d76aef527ec4 100644
--- a/clang-tools-extra/clangd/ClangdLSPServer.h
+++ b/clang-tools-extra/clangd/ClangdLSPServer.h
@@ -179,6 +179,10 @@ private:
   void onCommandApplyTweak(const TweakArgs &, Callback<llvm::json::Value>);
   void onCommandApplyRename(const RenameParams &, Callback<llvm::json::Value>);
 
+  /// CodeLens
+  void onCodeLens(const CodeLensParams &, Callback<std::vector<CodeLens>>);
+  void onCodeLensResolve(const CodeLens &, Callback<CodeLens>);
+
   /// Outgoing LSP calls.
   LSPBinder::OutgoingMethod<ApplyWorkspaceEditParams,
                             ApplyWorkspaceEditResponse>
diff --git a/clang-tools-extra/clangd/ClangdServer.cpp b/clang-tools-extra/clangd/ClangdServer.cpp
index e910a80ba0ba..e97b6761383e 100644
--- a/clang-tools-extra/clangd/ClangdServer.cpp
+++ b/clang-tools-extra/clangd/ClangdServer.cpp
@@ -8,6 +8,7 @@
 
 #include "ClangdServer.h"
 #include "CodeComplete.h"
+#include "CodeLens.h"
 #include "Config.h"
 #include "Diagnostics.h"
 #include "DumpAST.h"
@@ -1106,6 +1107,31 @@ void ClangdServer::diagnostics(PathRef File, Callback<std::vector<Diag>> CB) {
   WorkScheduler->runWithAST("Diagnostics", File, std::move(Action));
 }
 
+void ClangdServer::provideCodeLens(PathRef File, uint32_t Limit,
+                                   Callback<std::vector<CodeLens>> CB) {
+  auto Action = [CB = std::move(CB), File = File.str(), Limit,
+                 this](llvm::Expected<InputsAndAST> InpAST) mutable {
+    if (!InpAST)
+      return CB(InpAST.takeError());
+    CB(clangd::getDocumentCodeLens(InpAST->AST, Index, Limit, File));
+  };
+  WorkScheduler->runWithAST("DocumentCodeLens", File, std::move(Action),
+                            TUScheduler::InvalidateOnUpdate);
+}
+
+void ClangdServer::resolveCodeLens(const CodeLens &Params, uint32_t Limit,
+                                   Callback<CodeLens> CB) {
+  auto File = Params.data->uri;
+  auto Action = [CB = std::move(CB), File, Params, Limit,
+                 this](llvm::Expected<InputsAndAST> InpAST) mutable {
+    if (!InpAST)
+      return CB(InpAST.takeError());
+    CB(clangd::resolveCodeLens(InpAST->AST, Params, Limit, Index, File));
+  };
+  WorkScheduler->runWithAST("ResolveCodeLens", File, std::move(Action),
+                            TUScheduler::InvalidateOnUpdate);
+}
+
 llvm::StringMap<TUScheduler::FileStats> ClangdServer::fileStats() const {
   return WorkScheduler->fileStats();
 }
diff --git a/clang-tools-extra/clangd/ClangdServer.h b/clang-tools-extra/clangd/ClangdServer.h
index a653cdb56b75..0c8aa845d0e1 100644
--- a/clang-tools-extra/clangd/ClangdServer.h
+++ b/clang-tools-extra/clangd/ClangdServer.h
@@ -174,6 +174,9 @@ public:
     // Whether the client supports folding only complete lines.
     bool LineFoldingOnly = false;
 
+    /// Enable preview of CodeLens feature.
+    bool CodeLens = false;
+
     FeatureModuleSet *FeatureModules = nullptr;
     /// If true, use the dirty buffer contents when building Preambles.
     bool UseDirtyHeaders = false;
@@ -422,6 +425,12 @@ public:
   void getAST(PathRef File, std::optional<Range> R,
               Callback<std::optional<ASTNode>> CB);
 
+  /// CodeLenses.
+  void provideCodeLens(PathRef File, uint32_t Limit,
+                       Callback<std::vector<CodeLens>> CB);
+  void resolveCodeLens(const CodeLens &Params, uint32_t Limit,
+                       Callback<CodeLens> CB);
+
   /// Runs an arbitrary action that has access to the AST of the specified file.
   /// The action will execute on one of ClangdServer's internal threads.
   /// The AST is only valid for the duration of the callback.
diff --git a/clang-tools-extra/clangd/CodeLens.cpp b/clang-tools-extra/clangd/CodeLens.cpp
new file mode 100644
index 000000000000..da927f0ac490
--- /dev/null
+++ b/clang-tools-extra/clangd/CodeLens.cpp
@@ -0,0 +1,195 @@
+//===--- CodeLens.cpp --------------------------------------------*- 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 "CodeLens.h"
+#include "AST.h"
+#include "FindSymbols.h"
+#include "XRefs.h"
+#include "support/Logger.h"
+
+namespace clang {
+namespace clangd {
+std::optional<Location> declToLocation(const Decl *D) {
+  ASTContext &Ctx = D->getASTContext();
+  auto &SM = Ctx.getSourceManager();
+  SourceLocation NameLoc = nameLocation(*D, Ctx.getSourceManager());
+  auto FileFieldRef = SM.getFileEntryRefForID(SM.getFileID(NameLoc));
+  if (!FileFieldRef)
+    return std::nullopt;
+  auto FilePath = getCanonicalPath(*FileFieldRef, SM.getFileManager());
+  auto TUFieldRef = SM.getFileEntryRefForID(SM.getFileID(NameLoc));
+  if (!TUFieldRef)
+    return std::nullopt;
+  auto TUPath = getCanonicalPath(*TUFieldRef, SM.getFileManager());
+  if (!FilePath || !TUPath)
+    return std::nullopt; // Not useful without a uri.
+
+  Position NameBegin = sourceLocToPosition(SM, NameLoc);
+  Position NameEnd = sourceLocToPosition(
+      SM, Lexer::getLocForEndOfToken(NameLoc, 0, SM, Ctx.getLangOpts()));
+  return Location{URIForFile::canonicalize(*FilePath, *TUPath),
+                  {NameBegin, NameEnd}};
+}
+
+std::vector<Location> lookupIndex(const SymbolIndex *Index, uint32_t Limit,
+                                  PathRef Path, Decl *D, RelationKind R) {
+  std::vector<Location> Results;
+  if (!Index)
+    return Results;
+  auto ID = getSymbolID(D);
+  if (!ID)
+    return Results;
+  RelationsRequest Req;
+  Req.Subjects.insert(ID);
+  Req.Limit = Limit;
+  Req.Predicate = R;
+  Index->relations(Req, [&](const SymbolID &Subject, const Symbol &Object) {
+    if (Object.SymInfo.Kind == clang::index::SymbolKind::Class ||
+        Object.SymInfo.Kind == clang::index::SymbolKind::Struct) {
+      if (auto Loc = indexToLSPLocation(Object.Definition, Path)) {
+        Results.emplace_back(std::move(*Loc));
+      }
+    } else if (auto Loc =
+                   indexToLSPLocation(Object.CanonicalDeclaration, Path)) {
+      Results.emplace_back(std::move(*Loc));
+    }
+  });
+  return Results;
+}
+
+void traverseDecl(ParsedAST &AST, const SymbolIndex *Index, uint32_t Limit,
+                  PathRef Path, Decl *D, std::vector<CodeLens> &Results) {
+  auto &SM = AST.getSourceManager();
+  // Skip symbols which do not originate from the main file.
+  if (!isInsideMainFile(D->getLocation(), SM))
+    return;
+  if (D->isImplicit() || !isa<NamedDecl>(D) || D->getLocation().isMacroID())
+    return;
+
+  if (auto *Templ = llvm::dyn_cast<TemplateDecl>(D)) {
+    if (auto *TD = Templ->getTemplatedDecl())
+      D = TD;
+  };
+  auto Location = D->getLocation();
+  Range Range = {
+      sourceLocToPosition(SM, Location),
+      sourceLocToPosition(
+          SM, Lexer::getLocForEndOfToken(Location, 0, SM, AST.getLangOpts()))};
+
+  // Namspaces are not indexed, so it's meaningless to provide codelens.
+  if (!isa<NamespaceDecl, NamespaceAliasDecl>(D)) {
+    CodeLensResolveData Data;
+    Data.uri = std::string(Path);
+    Results.emplace_back(CodeLens{Range, std::nullopt, Data});
+  }
+
+  // handle inheritance codelens directly
+  CodeLensArgument Sub, Super;
+  if (auto *CXXRD = dyn_cast<CXXRecordDecl>(D)) {
+    if (!CXXRD->isEffectivelyFinal()) {
+      Sub.locations = lookupIndex(Index, Limit, Path, D, RelationKind::BaseOf);
+    }
+  } else if (auto *CXXMD = dyn_cast<CXXMethodDecl>(D)) {
+    if (CXXMD->isVirtual()) {
+      Sub.locations =
+          lookupIndex(Index, Limit, Path, D, RelationKind::OverriddenBy);
+    }
+    for (const auto *P : CXXMD->overridden_methods()) {
+      if (auto Loc = declToLocation(P->getCanonicalDecl()))
+        Super.locations.emplace_back(*Loc);
+    }
+  }
+
+  if (auto Count = Super.locations.size()) {
+    Super.position = Range.start;
+    Super.uri = std::string(Path);
+    Command Cmd;
+    Cmd.command = std::string(CodeAction::SHOW_REFERENCES);
+    Cmd.title = llvm::utostr(Count) + " base(s)";
+    Cmd.argument = std::move(Super);
+    Results.emplace_back(CodeLens{Range, std::move(Cmd), std::nullopt});
+  }
+
+  if (auto Count = Sub.locations.size()) {
+    Sub.position = Range.start;
+    Sub.uri = std::string(Path);
+    Command Cmd;
+    Cmd.command = std::string(CodeAction::SHOW_REFERENCES);
+    Cmd.title = llvm::utostr(Count) + " derived";
+    Cmd.argument = std::move(Sub);
+    Results.emplace_back(CodeLens{Range, std::move(Cmd), std::nullopt});
+  }
+
+  // Skip symbols inside function body.
+  if (isa<FunctionDecl>(D)) {
+    return;
+  }
+
+  if (auto *Scope = dyn_cast<DeclContext>(D)) {
+    for (auto *C : Scope->decls())
+      traverseDecl(AST, Index, Limit, Path, C, Results);
+  }
+}
+
+llvm::Expected<std::vector<CodeLens>>
+getDocumentCodeLens(ParsedAST &AST, const SymbolIndex *Index, uint32_t Limit,
+                    PathRef Path) {
+  std::vector<CodeLens> Results;
+  Limit = Limit ? Limit : std::numeric_limits<uint32_t>::max();
+  for (auto &TopLevel : AST.getLocalTopLevelDecls())
+    traverseDecl(AST, Index, Limit, Path, TopLevel, Results);
+  return Results;
+}
+
+llvm::Expected<CodeLens> resolveCodeLens(ParsedAST &AST, const CodeLens &Params,
+                                         uint32_t Limit,
+                                         const SymbolIndex *Index,
+                                         PathRef Path) {
+  Command Cmd;
+  Cmd.command = std::string(CodeAction::SHOW_REFERENCES);
+  Position Pos = Params.range.start;
+  if (Params.data) {
+    CodeLensArgument Arg;
+    Arg.uri = std::string(Path);
+    Arg.position = Pos;
+    auto FindedRefs = findReferences(AST, Pos, Limit, Index);
+    auto Refs = FindedRefs.References;
+    Arg.locations.reserve(Refs.size());
+    bool ThisLocSkipped = false;
+    size_t NotUsedRefs = 0u;
+    for (auto &Ref : Refs) {
+      if (!ThisLocSkipped && Ref.Loc.range.contains(Pos)) {
+        ThisLocSkipped = true;
+        continue;
+      }
+      if ((Ref.Attributes &
+           (ReferencesResult::Declaration | ReferencesResult::Definition |
+            ReferencesResult::Override)) != 0)
+        NotUsedRefs++;
+
+      Arg.locations.emplace_back(std::move(Ref.Loc));
+    }
+    if (Arg.locations.empty())
+      Cmd.title = "Unused";
+    else {
+      auto NumRefs = llvm::utostr(Arg.locations.size());
+      if (FindedRefs.HasMore)
+        NumRefs += "+";
+      NumRefs += " ref(s)";
+      if (Arg.locations.size() == NotUsedRefs)
+        Cmd.title = "Unused " + NumRefs;
+      else
+        Cmd.title = NumRefs;
+    }
+    Cmd.argument = std::move(Arg);
+    return CodeLens{Params.range, std::move(Cmd), std::nullopt};
+  }
+  return error("failed to resolve codelens");
+}
+} // namespace clangd
+} // namespace clang
\ No newline at end of file
diff --git a/clang-tools-extra/clangd/CodeLens.h b/clang-tools-extra/clangd/CodeLens.h
new file mode 100644
index 000000000000..2dbfaf87baed
--- /dev/null
+++ b/clang-tools-extra/clangd/CodeLens.h
@@ -0,0 +1,27 @@
+//===--- CodeLens.h ----------------------------------------------*- 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_CODELENS_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_CODELENS_H
+
+#include "ParsedAST.h"
+#include "Protocol.h"
+
+namespace clang {
+namespace clangd {
+llvm::Expected<std::vector<CodeLens>>
+getDocumentCodeLens(ParsedAST &AST, const SymbolIndex *Index, uint32_t Limit,
+                    PathRef Path);
+
+llvm::Expected<CodeLens> resolveCodeLens(ParsedAST &AST, const CodeLens &Params,
+                                         uint32_t Limit,
+                                         const SymbolIndex *Index,
+                                         PathRef Path);
+} // namespace clangd
+} // namespace clang
+#endif
\ No newline at end of file
diff --git a/clang-tools-extra/clangd/Protocol.cpp b/clang-tools-extra/clangd/Protocol.cpp
index c08f80442eaa..471f467af5bd 100644
--- a/clang-tools-extra/clangd/Protocol.cpp
+++ b/clang-tools-extra/clangd/Protocol.cpp
@@ -151,6 +151,12 @@ llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const Range &R) {
   return OS << R.start << '-' << R.end;
 }
 
+bool fromJSON(const llvm::json::Value &Params, Location &L,
+              llvm::json::Path P) {
+  llvm::json::ObjectMapper O(Params, P);
+  return O && O.map("uri", L.uri) && O.map("range", L.range);
+}
+
 llvm::json::Value toJSON(const Location &P) {
   return llvm::json::Object{
       {"uri", P.uri},
@@ -869,6 +875,8 @@ llvm::json::Value toJSON(const Command &C) {
 const llvm::StringLiteral CodeAction::QUICKFIX_KIND = "quickfix";
 const llvm::StringLiteral CodeAction::REFACTOR_KIND = "refactor";
 const llvm::StringLiteral CodeAction::INFO_KIND = "info";
+const llvm::StringLiteral CodeAction::SHOW_REFERENCES =
+    "clangd.action.showReferences";
 
 llvm::json::Value toJSON(const CodeAction &CA) {
   auto CodeAction = llvm::json::Object{{"title", CA.title}};
@@ -1698,5 +1706,37 @@ bool fromJSON(const llvm::json::Value &E, SymbolID &S, llvm::json::Path P) {
 }
 llvm::json::Value toJSON(const SymbolID &S) { return S.str(); }
 
+bool fromJSON(const llvm::json::Value &Params, CodeLensResolveData &R,
+              llvm::json::Path P) {
+  llvm::json::ObjectMapper O(Params, P);
+  return O && O.map("uri", R.uri);
+}
+
+llvm::json::Value toJSON(const CodeLensResolveData &P) {
+  llvm::json::Object O{{"uri", P.uri}};
+  return std::move(O);
+}
+
+llvm::json::Value toJSON(const CodeLensArgument &P) {
+  llvm::json::Object O{
+      {"uri", P.uri}, {"position", P.position}, {"locations", P.locations}};
+  return std::move(O);
+}
+
+bool fromJSON(const llvm::json::Value &Params, CodeLens &R,
+              llvm::json::Path P) {
+  llvm::json::ObjectMapper O(Params, P);
+  return O && O.map("range", R.range) && O.map("data", R.data);
+}
+
+llvm::json::Value toJSON(const CodeLens &C) {
+  llvm::json::Object O{{"range", C.range}};
+  if (C.command)
+    O["command"] = *C.command;
+  if (C.data)
+    O["data"] = *C.data;
+  return std::move(O);
+}
+
 } // namespace clangd
 } // namespace clang
diff --git a/clang-tools-extra/clangd/Protocol.h b/clang-tools-extra/clangd/Protocol.h
index a0f8b04bc4ff..91e309d1cf70 100644
--- a/clang-tools-extra/clangd/Protocol.h
+++ b/clang-tools-extra/clangd/Protocol.h
@@ -225,6 +225,7 @@ struct Location {
     return std::tie(LHS.uri, LHS.range) < std::tie(RHS.uri, RHS.range);
   }
 };
+bool fromJSON(const llvm::json::Value &, Location &, llvm::json::Path);
 llvm::json::Value toJSON(const Location &);
 llvm::raw_ostream &operator<<(llvm::raw_ostream &, const Location &);
 
@@ -1070,6 +1071,9 @@ struct CodeAction {
   const static llvm::StringLiteral QUICKFIX_KIND;
   const static llvm::StringLiteral REFACTOR_KIND;
   const static llvm::StringLiteral INFO_KIND;
+  /// This action should be implemented by client,
+  /// because we can not call 'editor.action.showReferences' directly.
+  const static llvm::StringLiteral SHOW_REFERENCES;
 
   /// The diagnostics that this code action resolves.
   std::optional<std::vector<Diagnostic>> diagnostics;
@@ -2019,6 +2023,33 @@ struct ASTNode {
 llvm::json::Value toJSON(const ASTNode &);
 llvm::raw_ostream &operator<<(llvm::raw_ostream &, const ASTNode &);
 
+/// https://microsoft.github.io/language-server-protocol/specification#textDocument_codeLens
+struct CodeLensResolveData {
+  std::string uri;
+};
+bool fromJSON(const llvm::json::Value &, CodeLensResolveData &,
+              llvm::json::Path);
+llvm::json::Value toJSON(const CodeLensResolveData &A);
+
+struct CodeLensArgument {
+  std::string uri;
+  Position position;
+  std::vector<Location> locations;
+};
+llvm::json::Value toJSON(const CodeLensArgument &A);
+
+struct CodeLensParams : DocumentSymbolParams {};
+
+struct CodeLens {
+  // CodeLens range.
+  Range range;
+  // CodeLens command.
+  std::optional<Command> command;
+  // CodeLens resolve data.
+  std::optional<CodeLensResolveData> data;
+};
+bool fromJSON(const llvm::json::Value &, CodeLens &, llvm::json::Path);
+llvm::json::Value toJSON(const CodeLens &);
 } // namespace clangd
 } // namespace clang
 
diff --git a/clang-tools-extra/clangd/test/initialize-params.test b/clang-tools-extra/clangd/test/initialize-params.test
index 7c96eb9835b7..9571a9a2d966 100644
--- a/clang-tools-extra/clangd/test/initialize-params.test
+++ b/clang-tools-extra/clangd/test/initialize-params.test
@@ -9,6 +9,9 @@
 # CHECK-NEXT:      "callHierarchyProvider": true,
 # CHECK-NEXT:      "clangdInlayHintsProvider": true,
 # CHECK-NEXT:      "codeActionProvider": true,
+# CHECK-NEXT:      "codeLensProvider": {
+# CHECK-NEXT:        "resolveProvider": true
+# CHECK-NEXT:      },
 # CHECK-NEXT:      "compilationDatabase": {
 # CHECK-NEXT:        "automaticReload": true
 # CHECK-NEXT:      },
diff --git a/clang-tools-extra/clangd/tool/ClangdMain.cpp b/clang-tools-extra/clangd/tool/ClangdMain.cpp
index 3a5449ac8c79..07a33429bf84 100644
--- a/clang-tools-extra/clangd/tool/ClangdMain.cpp
+++ b/clang-tools-extra/clangd/tool/ClangdMain.cpp
@@ -344,6 +344,11 @@ list<std::string> TweakList{
     CommaSeparated,
 };
 
+opt<bool> EnableCodeLens{
+    "code-lens", cat(Features), desc("Enable preview of CodeLens feature"),
+    init(true),  Hidden,
+};
+
 opt<unsigned> WorkerThreadsCount{
     "j",
     cat(Misc),
@@ -904,6 +909,7 @@ clangd accepts flags on the commandline, and in the CLANGD_FLAGS environment var
   Opts.StaticIndex = PAI.get();
   Opts.AsyncThreadsCount = WorkerThreadsCount;
   Opts.MemoryCleanup = getMemoryCleanupFunction();
+  Opts.CodeLens = EnableCodeLens;
 
   Opts.CodeComplete.IncludeIneligibleResults = IncludeIneligibleResults;
   Opts.CodeComplete.Limit = LimitResults;