[clangd] Implement textDocument/codeLens

[Trass3r]

Summary

Co-authored-by: lightmelodies <[e-mail]>

[Trass3r]

"base" refs are only useful on class forward decls
but for some reasons this still shows up on dtor implementations

[Trass3r]

squashed

[Trass3r]

clang-tools-extra/clangd/CodeLens.cpp

87

they still show up on dtor implementations iirc

[Trass3r]

I just searched again and found https://reviews.llvm.org/D91930.
But seems like it never got updated with the latest code featured here. Though looks like the test got dropped.

[nridge]

Haven't had a chance to look at this yet. I do see that the earier implementation in D91930 was the subject of some design discussions about performance with @kadircet, adding him as an additional reviewer.

[Trass3r]

remove bases codelens for classes
fix lit test
exclude self from ref count

https://github.com/clangd/clangd/issues/442#issuecomment-1125056812

[Trass3r]

clang-tools-extra/clangd/CodeLens.cpp

93

As noted in the previous PR it may be of low value, I guess only if override is missing or if it actually hides several functions.

[Trass3r]

clang-tools-extra/clangd/tool/ClangdMain.cpp

348

I guess we should rather make it opt-in and gather some feedback.

[Trass3r]

One remaining issue is multiple lenses for template code like

template <int V>
int i = 0;

template int i<0>;
template int i<1>;
template int i<2>;

template <int V>
struct Foo {
    int foo(); // I see 3 codelenses here
};

template struct Foo<0>;
template struct Foo<1>;

int main()
{
    // return Foo<0>().foo() + Foo<1>().foo();
    // return i<0> + i<1> + i<2>;
}

[lightmelodies]

In D131295#3933381, @Trass3r wrote:

One remaining issue is multiple lenses for template code like

template <int V>
int i = 0;

template int i<0>;
template int i<1>;
template int i<2>;

template <int V>
struct Foo {
    int foo(); // I see 3 codelenses here
};

template struct Foo<0>;
template struct Foo<1>;

int main()
{
    // return Foo<0>().foo() + Foo<1>().foo();
    // return i<0> + i<1> + i<2>;
}

Well, multiple lenses occured due to https://github.com/lightmelodies/llvm-project/blob/codelens/clang-tools-extra/clangd/FindSymbols.cpp#L500
And can be fixed by https://github.com/lightmelodies/llvm-project/blob/codelens/clang-tools-extra/clangd/CodeLens.cpp#L69

[Trass3r]

Thanks, it seems to fix the base case, but I still see multiple lenses when I add

template <int V>
int Foo<V>::foo()
{
    return 0;
}

[lightmelodies]

In D131295#3935027, @Trass3r wrote:

Thanks, it seems to fix the base case, but I still see multiple lenses when I add

template <int V>
int Foo<V>::foo()
{
    return 0;
}

Interesting, I see the same issue with DocumentSymbols. Maybe because foo is explicit specialization (though outside Foo<1>) so both check are passed. However I can not find a way to detect such case right now.

[Trass3r]

Yeah quite complex: https://godbolt.org/z/8T5Pqadro

[lightmelodies]

In D131295#3935759, @Trass3r wrote:

Yeah quite complex: https://godbolt.org/z/8T5Pqadro

Not very hard with a track of visited decls. It should also reslove other duplicate codelens.
https://github.com/lightmelodies/llvm-project/blob/b7d664bff5fcafb5a0758b73cd0b77e64cacb03c/clang-tools-extra/clangd/CodeLens.cpp#L69

clang-tools-extra/clangd/CMakeLists.txt

 
 add_clang_library(clangDaemon
   AST.cpp
   ASTSignals.cpp
   ClangdLSPServer.cpp
   ClangdServer.cpp
   CodeComplete.cpp
   CodeCompletionStrings.cpp
+  CodeLens.cpp
   CollectMacros.cpp
   CompileCommands.cpp
   Compiler.cpp
   Config.cpp
   ConfigCompile.cpp
   ConfigProvider.cpp
   ConfigYAML.cpp
   Diagnostics.cpp

clang-tools-extra/clangd/ClangdLSPServer.h

private:
   /// hierarchy.
   void onMemoryUsage(const NoParams &, Callback<MemoryTree>);
   void onCommand(const ExecuteCommandParams &, Callback<llvm::json::Value>);
 
   /// Implement commands.
   void onCommandApplyEdit(const WorkspaceEdit &, Callback<llvm::json::Value>);
   void onCommandApplyTweak(const TweakArgs &, 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>
       ApplyWorkspaceEdit;
   LSPBinder::OutgoingNotification<ShowMessageParams> ShowMessage;
   LSPBinder::OutgoingNotification<PublishDiagnosticsParams> PublishDiagnostics;
   LSPBinder::OutgoingNotification<FileStatus> NotifyFileStatus;
   LSPBinder::OutgoingMethod<WorkDoneProgressCreateParams, std::nullptr_t>

clang-tools-extra/clangd/ClangdLSPServer.cpp

llvm::json::Object Result{
       {{"serverInfo",
         llvm::json::Object{
             {"name", "clangd"},
             {"version", llvm::formatv("{0} {1} {2}", versionString(),
                                       featureString(), platformString())}}},
        {"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.
   // This can start background indexing and in turn trigger LSP notifications.
   applyConfiguration(Params.initializationOptions.ConfigSettings);
 }
 
 void ClangdLSPServer::onInitialized(const InitializedParams &Params) {}

 void ClangdLSPServer::onMemoryUsage(const NoParams &,
                                     Callback<MemoryTree> Reply) {
   llvm::BumpPtrAllocator DetailAlloc;
   MemoryTree MT(&DetailAlloc);
   profile(MT);
   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<llvm::Optional<ASTNode>> CB) {
   Server->getAST(Params.textDocument.uri.file(), Params.range, std::move(CB));
 }
 
 ClangdLSPServer::ClangdLSPServer(Transport &Transp, const ThreadsafeFS &TFS,
                                  const ClangdLSPServer::Options &Opts)
     : ShouldProfile(/*Period=*/std::chrono::minutes(5),
void ClangdLSPServer::bindMethods(LSPBinder &Bind,
   Bind.method("textDocument/semanticTokens/full", this, &ClangdLSPServer::onSemanticTokens);
   Bind.method("textDocument/semanticTokens/full/delta", this, &ClangdLSPServer::onSemanticTokensDelta);
   Bind.method("clangd/inlayHints", this, &ClangdLSPServer::onClangdInlayHints);
   Bind.method("textDocument/inlayHint", this, &ClangdLSPServer::onInlayHint);
   Bind.method("$/memoryUsage", this, &ClangdLSPServer::onMemoryUsage);
   Bind.method("textDocument/foldingRange", this, &ClangdLSPServer::onFoldingRange);
   Bind.command(ApplyFixCommand, this, &ClangdLSPServer::onCommandApplyEdit);
   Bind.command(ApplyTweakCommand, this, &ClangdLSPServer::onCommandApplyTweak);
-
+  if (Opts.CodeLens) {
+    Bind.method("textDocument/codeLens",this, &ClangdLSPServer::onCodeLens);
+    Bind.method("codeLens/resolve",this, &ClangdLSPServer::onCodeLensResolve);
+  }
   ApplyWorkspaceEdit = Bind.outgoingMethod("workspace/applyEdit");
   PublishDiagnostics = Bind.outgoingNotification("textDocument/publishDiagnostics");
   ShowMessage = Bind.outgoingNotification("window/showMessage");
   NotifyFileStatus = Bind.outgoingNotification("textDocument/clangd.fileStatus");
   CreateWorkDoneProgress = Bind.outgoingMethod("window/workDoneProgress/create");
   BeginWorkDoneProgress = Bind.outgoingNotification("$/progress");
   ReportWorkDoneProgress = Bind.outgoingNotification("$/progress");
   EndWorkDoneProgress = Bind.outgoingNotification("$/progress");

clang-tools-extra/clangd/ClangdServer.h

struct Options {
 
     /// Clangd will execute compiler drivers matching one of these globs to
     /// fetch system include path.
     std::vector<std::string> QueryDriverGlobs;
 
     // 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;
 
     // If true, parse emplace-like functions in the preamble.
     bool PreambleParseForwardingFunctions = false;
 
     explicit operator TUScheduler::Options() const;
public:
 
   void semanticHighlights(PathRef File,
                           Callback<std::vector<HighlightingToken>>);
 
   /// Describe the AST subtree for a piece of code.
   void getAST(PathRef File, llvm::Optional<Range> R,
               Callback<llvm::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.
   /// As with other actions, the file must have been opened.
   void customAction(PathRef File, llvm::StringRef Name,
                     Callback<InputsAndAST> Action);
 
   /// Fetches diagnostics for current version of the \p File. This might fail if

clang-tools-extra/clangd/ClangdServer.cpp

 //===--- ClangdServer.cpp - Main clangd server code --------------*- 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 "ClangdServer.h"
 #include "CodeComplete.h"
+#include "CodeLens.h"
 #include "Config.h"
 #include "Diagnostics.h"
 #include "DumpAST.h"
 #include "FindSymbols.h"
 #include "Format.h"
 #include "HeaderSourceSwitch.h"
 #include "InlayHints.h"
 #include "ParsedAST.h"
auto Action =
         // FIXME: Use ServerCancelled error once it is settled in LSP-3.17.
         return CB(llvm::make_error<LSPError>("server is busy parsing includes",
                                              ErrorCode::InternalError));
       };
 
   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();
 }
 
 [[nodiscard]] bool
 ClangdServer::blockUntilIdleForTest(llvm::Optional<double> TimeoutSeconds) {
   // Order is important here: we don't want to block on A and then B,
   // if B might schedule work on A.

clang-tools-extra/clangd/CodeLens.h

+//===--- 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

clang-tools-extra/clangd/CodeLens.cpp

+//===--- 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 {
+llvm::Optional<Location> declToLocation(const Decl *D) {
+  ASTContext &Ctx = D->getASTContext();
+  auto &SM = Ctx.getSourceManager();
+  SourceLocation NameLoc = nameLocation(*D, Ctx.getSourceManager());
+  auto FilePath =
+      getCanonicalPath(SM.getFileEntryForID(SM.getFileID(NameLoc)), SM);
+  auto TUPath = getCanonicalPath(SM.getFileEntryForID(SM.getMainFileID()), SM);
+  if (!FilePath || !TUPath)
+    return llvm::None; // 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 (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, None, 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 = std::to_string(Count) + " base(s)";
+    Cmd.argument = std::move(Super);
+    Results.emplace_back(CodeLens{Range, std::move(Cmd), None});
+  }
+
+  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 = std::to_string(Count) + " derived";
+    Cmd.argument = std::move(Sub);
+    Results.emplace_back(CodeLens{Range, std::move(Cmd), None});
+  }
+
+  // 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 Refs = findReferences(AST, Pos, Limit, Index).References;
+    Arg.locations.reserve(Refs.size());
+    for (auto &Ref : Refs) {
+      Arg.locations.emplace_back(std::move(Ref.Loc));
+    }
+    Cmd.title = std::to_string(Refs.size() - 1) + " ref(s)";
+    Cmd.argument = std::move(Arg);
+    return CodeLens{Params.range, std::move(Cmd), None};
+  }
+  return error("failed to resolve codelens");
+}
+} // namespace clangd
+} // namespace clang

clang-tools-extra/clangd/Protocol.h

struct Location {
   friend bool operator!=(const Location &LHS, const Location &RHS) {
     return !(LHS == RHS);
   }
 
   friend bool operator<(const Location &LHS, const Location &RHS) {
     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 &);
 
 struct TextEdit {
   /// The range of the text document to be manipulated. To insert
   /// text into a document create a range where start === end.
   Range range;
 
struct CodeAction {
   std::string title;
 
   /// The kind of the code action.
   /// Used to filter code actions.
   llvm::Optional<std::string> kind;
   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.
   llvm::Optional<std::vector<Diagnostic>> diagnostics;
 
   /// Marks this as a preferred action. Preferred actions are used by the
   /// `auto fix` command and can be targeted by keybindings.
   /// A quick fix should be marked preferred if it properly addresses the
   /// underlying error. A refactoring should be marked preferred if it is the
struct ASTNode {
   /// May be missing for implicit nodes, or those created by macro expansion.
   llvm::Optional<Range> range;
   /// Nodes nested within this one, such as the operands of a BinaryOperator.
   std::vector<ASTNode> children;
 };
 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.
+  llvm::Optional<Command> command;
+  // CodeLens resolve data.
+  llvm::Optional<CodeLensResolveData> data;
+};
+bool fromJSON(const llvm::json::Value &, CodeLens &, llvm::json::Path);
+llvm::json::Value toJSON(const CodeLens &);
 } // namespace clangd
 } // namespace clang
 
 namespace llvm {
 template <> struct format_provider<clang::clangd::Position> {
   static void format(const clang::clangd::Position &Pos, raw_ostream &OS,
                      StringRef Style) {
     assert(Style.empty() && "style modifiers for this type are not supported");
     OS << Pos;
   }
 };
 } // namespace llvm
 
 // NOLINTEND(readability-identifier-naming)
 
 #endif

clang-tools-extra/clangd/Protocol.cpp

return llvm::json::Object{
       {"end", P.end},
   };
 }
 
 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},
       {"range", P.range},
   };
 }
 
 llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const Location &L) {
llvm::json::Value toJSON(const Command &C) {
   if (!C.argument.getAsNull())
     Cmd["arguments"] = llvm::json::Array{C.argument};
   return std::move(Cmd);
 }
 
 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}};
   if (CA.kind)
     CodeAction["kind"] = *CA.kind;
   if (CA.diagnostics)
     CodeAction["diagnostics"] = llvm::json::Array(*CA.diagnostics);
   if (CA.isPreferred)
if (!ID) {
     P.report("malformed symbolid");
     return false;
   }
   S = *ID;
   return true;
 }
 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

clang-tools-extra/clangd/test/initialize-params.test

 # RUN: clangd -lit-test < %s | FileCheck -strict-whitespace %s
 # Test initialize request parameters with rootUri
 {"jsonrpc":"2.0","id":0,"method":"initialize","params":{"processId":123,"rootUri":"test:///workspace","capabilities":{},"trace":"off"}}
 #      CHECK:  "id": 0,
 # CHECK-NEXT:  "jsonrpc": "2.0",
 # CHECK-NEXT:  "result": {
 # CHECK-NEXT:    "capabilities": {
 # CHECK-NEXT:      "astProvider": true,
 # 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:      },
 # CHECK-NEXT:      "completionProvider": {
 # CHECK-NEXT:        "resolveProvider": false,
 # CHECK-NEXT:        "triggerCharacters": [
 # CHECK-NEXT:          ".",
 # CHECK-NEXT:          "<",

clang-tools-extra/clangd/tool/ClangdMain.cpp

 list<std::string> TweakList{
     "tweaks",
     cat(Features),
     desc("Specify a list of Tweaks to enable (only for clangd developers)."),
     Hidden,
     CommaSeparated,
 };
 
+opt<bool> EnableCodeLens{
+    "code-lens", cat(Features), desc("Enable preview of CodeLens feature"),
+    init(true),  Hidden,
+};
+
 opt<unsigned> WorkerThreadsCount{
     "j",
     cat(Misc),
     desc("Number of async workers used by clangd. Background index also "
          "uses this many workers."),
     init(getDefaultAsyncThreadsCount()),
 };
 
if (StaticIdx) {
     IdxStack.emplace_back(
         std::make_unique<MergedIndex>(PAI.get(), IdxStack.back().get()));
     Opts.StaticIndex = IdxStack.back().get();
   } else {
     Opts.StaticIndex = PAI.get();
   }
   Opts.AsyncThreadsCount = WorkerThreadsCount;
   Opts.MemoryCleanup = getMemoryCleanupFunction();
+  Opts.CodeLens = EnableCodeLens;
 
   Opts.CodeComplete.IncludeIneligibleResults = IncludeIneligibleResults;
   Opts.CodeComplete.Limit = LimitResults;
   if (CompletionStyle.getNumOccurrences())
     Opts.CodeComplete.BundleOverloads = CompletionStyle != Detailed;
   Opts.CodeComplete.ShowOrigins = ShowOrigins;
   Opts.CodeComplete.InsertIncludes = HeaderInsertion;
   if (!HeaderInsertionDecorators) {