[clangd] Implement textDocument/codeLens

[lightmelodies]

Summary

This commit adds support for https://microsoft.github.io/language-server-protocol/specification#textDocument_codeLens.
See also https://github.com/clangd/clangd/issues/442 and https://github.com/lightmelodies/vscode-clangd.

CodeLens is a popular feature in Visual Studio Code, which provides actionable contextual information interspersed when opening a file:

• Contextual: codelens is displayed as a decoration and contains information of nearby code, e.g. show how many usages of a function without invoking findReferences manually.
• Actionable: codelens has an associate command, so you can click it and tiggers some action.

Here is a simple gif to show how it works.

Implementation details:

• getDocumentCodeLens: This function implements the textDocument/codeLens API.
  • use documentSymbol to determine where codelens can occur.
  • For each symbol, add a reference codelens which displays the count of references. To avoid unnecessary lookup, only resolve data will be returned to the client in this step. The actual command will be filled by codeLens/resolve when the symbol getting into the viewport.
  • For class and virtual methods, use getTypeHierarchy and getMemberHierarchy to get hierarchy codelens which displays the count of base and derived. We resolve the command directly since the overhead is little in general and '0 derived' seems to be weird and useless.
• resolveCodeLens: This function implements the codeLens/resolve API. Just use findReferences to get the count of references according to the resolve data.
• onCodeLensCommand: This function extends the onCommand function to support codeLens command. It just returns the location of related symbols. VSCode use editor.action.showReferences to show them, so the whole action will work like invoking Peek References.

[njames93]

Please upload the diff with full context and fix the failing unit tests

[kadircet]

Thanks a lot for working on improving clangd!

Can you also give a high-level overview of what kind of functionality you are providing here? Looks like there's a lot going on here, and it would be nice to know what you are attempting to do, rather than inferring that from the code. It would also help future travellers, as they can just read the description rather than going through the whole patch.

[lightmelodies]

In D91930#2411338, @kadircet wrote:

Thanks a lot for working on improving clangd!

Can you also give a high-level overview of what kind of functionality you are providing here? Looks like there's a lot going on here, and it would be nice to know what you are attempting to do, rather than inferring that from the code. It would also help future travellers, as they can just read the description rather than going through the whole patch.

Thanks for your response. I have updated the summary and add some detailed explanation.

[kadircet]

Thanks for the explanations. I've also had some discussions with @sammccall about this and would like to summarize them.

There are two important things to keep in mind:

• Collection is performed for the whole document.
• Resolve requests cannot fail. (there's no null for the return type)

So this forces us to be really certain about existence of codelenses during collection time, while making sure latency is low enough for clangd to not feel sluggish, as this needs to be served after inactivity (i.e. not typing for a while).
Hence first of all we can't surface these lenses for all kinds of symbols, limiting the scope to top-level symbols as you do in this patch sounds like a sweet-spot.

But it is not enough on its own, for example we are still performing multiple index queries per symbol to figure out derived classes/methods, which doesn't scale well to big TUs, especially in presence of remote-index where each query can have considerable RTT.
So we need to ensure total number of index queries are kept to a minimum, possibly by batching all of the queries and performing them at once.
This requires significant changes to current implementation, but is really a must to ensure scalability of the feature. WDYT about evolving the patch in such a direction?

Another point around the usefulness of the lenses in this patch; The information we can deduce using only the AST doesn't seem to be useful.
Particularly:

• for bases, they are available next to the cursor and user can do go-to-definition on them.
• for overridden methods, most of the time there are 0 or 1, and again they keyword override is usually an indicator of that (moreover users can do go-to-def on that, but it is not as visible).

So it might be better to just drop them to not clutter the UI.

[lightmelodies]

I have also considered these problems, and here is some points of my view.
Latency
Consider llvm-project itself, textDocument/codeLens can be done in <500ms generally and <100ms if collect hierarchy is disabled in my notebook. Latency is significant in some rare case like Type.h which has too complex hierarchy relations. Meanwhile, vscode is smart to remember previous codelens's positions so the text rendering will not look too weird during long-time request. In fact, the biggest performance issue I find is that building AST when open a new file costs too much time, which makes textDocument/codeLens quite slow, as well as other action such as textDocument/documentSymbols. That's why I modified ClangdLSPServer.cpp to keep AST for recent closed files.

file	line count	cost	cost (without hierarchy)
ASTVector.h	411	4ms	1ms
APValue.h	693	16 ms	8ms
Decl.h	4599	213 ms	40 ms
Expr.h	6383	447 ms	61 ms
Type.h	7222	3765 ms	47 ms

Batch
That's definitely a problem with remote index since vscode can only do resolution per symbol. Maybe it will be better to resolve directly in textDocument/codeLens requests when deal with remote index. Just need add an option to allow users switch the strategy.

Useless Lens
Yes, we can see the base directly in class declaration. However c++ has forward declaration and type alias, in such case the base can not be seen directly. So someone may prefer to have these codelens. Typescript in vscode has options to allow users disable specific type of codelens. We can use similar strategy, e.g. -codelens=references,base,derived instead of -codelens=true.

I'm currently working on an implemention by traversing AST directly instead of using textDocument/documentSymbols, since symbols defined by macro are often reported a wrong range. It should save much time of findNamedDeclAt comparing to current implemention, and make it easier to add additional filters on symbols.

clang-tools-extra/clangd/ClangdLSPServer.h

   void onSemanticTokens(const SemanticTokensParams &, Callback<SemanticTokens>);
   void onSemanticTokensDelta(const SemanticTokensDeltaParams &,
                              Callback<SemanticTokensOrDelta>);
+  void onCodeLens(const CodeLensParams &, Callback<std::vector<CodeLens>>);
+  void onCodeLensResolve(const CodeLens &, Callback<CodeLens>);
   /// This is a clangd extension. Provides a json tree representing memory usage
   /// hierarchy.
   void onMemoryUsage(const NoParams &, Callback<MemoryTree>);

clang-tools-extra/clangd/ClangdLSPServer.cpp

              llvm::json::Object{
                  {"commands",
                   {ExecuteCommandParams::CLANGD_APPLY_FIX_COMMAND,
-                   ExecuteCommandParams::CLANGD_APPLY_TWEAK}},
+                   ExecuteCommandParams::CLANGD_APPLY_TWEAK,
+                   ExecuteCommandParams::CLANGD_SERVER_CODELENS}},
              }},
             {"typeHierarchyProvider", true},
             {"memoryUsageProvider", true}, // clangd extension.

              llvm::json::Object{{"scopes", buildHighlightScopeLookupTable()}}});
   if (Opts.FoldingRanges)
     Result.getObject("capabilities")->insert({"foldingRangeProvider", true});
+  if (Opts.CodeLens)
+    Result.getObject("capabilities")
+        ->insert({"codeLensProvider", llvm::json::Object{
+                                          {"resolveProvider", true},
+                                      }});
   Reply(std::move(Result));
 }
 

     Server->applyTweak(Params.tweakArgs->file.file(),
                        Params.tweakArgs->selection, Params.tweakArgs->tweakID,
                        std::move(Action));
+  } else if (Params.command == ExecuteCommandParams::CLANGD_SERVER_CODELENS &&
+             Params.codeLens) {
+    Server->onCodeLensCommand(*Params.codeLens, Opts.CodeComplete.Limit,
+                              std::move(Reply));
   } 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

     const DidCloseTextDocumentParams &Params) {
   PathRef File = Params.textDocument.uri.file();
   DraftMgr.removeDraft(File);
-  Server->removeDocument(File);
+  // Rebuilding AST wastes a lot of time, which makes codeLens unacceptably
+  // slow (100x in common). So keep AST of the opened file for a better user
+  // experience. Maybe we need to change the current LRU Cache implementation.
+  // See also https://github.com/clangd/clangd/issues/589.
+
+  // Server->removeDocument(File);
 
   {
     std::lock_guard<std::mutex> Lock(FixItsMutex);

       });
 }
 
+void ClangdLSPServer::onCodeLens(const CodeLensParams &Params,
+                                 Callback<std::vector<CodeLens>> Reply) {
+  URIForFile FileURI = Params.textDocument.uri;
+  Server->provideCodeLens(
+      FileURI.file(),
+      [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.CodeComplete.Limit,
+      [Reply = std::move(Reply)](llvm::Expected<CodeLens> CodeLens) mutable {
+        if (!CodeLens)
+          return Reply(CodeLens.takeError());
+        return Reply(std::move(*CodeLens));
+      });
+}
+
 void ClangdLSPServer::onMemoryUsage(const NoParams &,
                                     Callback<MemoryTree> Reply) {
   llvm::BumpPtrAllocator DetailAlloc;

   MsgHandler->bind("$/memoryUsage", &ClangdLSPServer::onMemoryUsage);
   if (Opts.FoldingRanges)
     MsgHandler->bind("textDocument/foldingRange", &ClangdLSPServer::onFoldingRange);
+  if (Opts.CodeLens) {
+    MsgHandler->bind("textDocument/codeLens", &ClangdLSPServer::onCodeLens);
+    MsgHandler->bind("codeLens/resolve", &ClangdLSPServer::onCodeLensResolve);
+  }
   // clang-format on
 
   // Delay first profile until we've finished warming up.

clang-tools-extra/clangd/ClangdServer.h

     /// thread, and callbacks are invoked before "async" functions return.
     unsigned AsyncThreadsCount = getDefaultAsyncThreadsCount();
 
-    /// AST caching policy. The default is to keep up to 3 ASTs in memory.
+    /// AST caching policy. The default is to keep up to 16 ASTs in memory.
     ASTRetentionPolicy RetentionPolicy;
 
     /// Cached preambles are potentially large. If false, store them on disk.

     /// Enable preview of FoldingRanges feature.
     bool FoldingRanges = false;
 
+    /// Enable preview of CodeLens feature.
+    bool CodeLens = false;
+
     explicit operator TUScheduler::Options() const;
   };
   // Sensible default options for use in tests.

   /// Apply the code tweak with a specified \p ID.
   void applyTweak(PathRef File, Range Sel, StringRef ID,
                   Callback<Tweak::Effect> CB);
+  /// Implement 'clangd.server.codeLens'
+  void onCodeLensCommand(const CodeLensResolveData &Params, uint32_t Limit,
+                         Callback<llvm::json::Value> CB);
 
   /// Called when an event occurs for a watched file in the workspace.
   void onFileEvent(const DidChangeWatchedFilesParams &Params);

 
   void semanticHighlights(PathRef File,
                           Callback<std::vector<HighlightingToken>>);
+  /// CodeLenses.
+  void provideCodeLens(PathRef File, Callback<std::vector<CodeLens>> CB);
+  void resolveCodeLens(const CodeLens &Params, uint32_t Limit,
+                       Callback<CodeLens> CB);
 
   /// Describe the AST subtree for a piece of code.
   void getAST(PathRef File, Range R, Callback<llvm::Optional<ASTNode>> CB);

clang-tools-extra/clangd/ClangdServer.cpp

   WorkScheduler.runWithAST("ApplyTweak", File, std::move(Action));
 }
 
+void ClangdServer::onCodeLensCommand(const CodeLensResolveData &Params,
+                                     uint32_t Limit,
+                                     Callback<llvm::json::Value> Reply) {
+  auto File = Params.location.uri.file();
+  auto Pos = Params.location.range.start;
+  switch (Params.type) {
+  case CodeLensType::Reference: {
+    auto Action =
+        [Reply = std::move(Reply)](Expected<ReferencesResult> Refs) mutable {
+          if (!Refs)
+            return Reply(Refs.takeError());
+          Reply(Refs->References);
+        };
+    findReferences(File, Pos, Limit, std::move(Action));
+    break;
+  }
+  case CodeLensType::TypeParent: {
+    auto Action = [File, Pos, Reply = std::move(Reply),
+                   this](Expected<InputsAndAST> InpAST) mutable {
+      std::vector<Location> Results;
+      auto Items = getTypeHierarchy(
+          InpAST->AST, Pos, 1, TypeHierarchyDirection::Parents, Index, File);
+      if (Items && Items->parents) {
+        for (auto Item : *Items->parents) {
+          Results.emplace_back(Location{Item.uri, Item.selectionRange});
+        }
+      }
+      Reply(std::move(Results));
+    };
+    WorkScheduler.runWithAST("CodeLensCommand", File, std::move(Action));
+    break;
+  }
+  case CodeLensType::TypeChildren: {
+    auto Action = [File, Pos, Reply = std::move(Reply),
+                   this](Expected<InputsAndAST> InpAST) mutable {
+      std::vector<Location> Results;
+      auto Items = getTypeHierarchy(
+          InpAST->AST, Pos, 1, TypeHierarchyDirection::Children, Index, File);
+      if (Items && Items->children) {
+        for (auto Item : *Items->children) {
+          Results.emplace_back(Location{Item.uri, Item.selectionRange});
+        }
+      }
+      Reply(std::move(Results));
+    };
+    WorkScheduler.runWithAST("CodeLensCommand", File, std::move(Action));
+    break;
+  }
+  case CodeLensType::MemberParent: {
+    auto Action = [File, Pos, Reply = std::move(Reply),
+                   this](Expected<InputsAndAST> InpAST) mutable {
+      std::vector<Location> Results;
+      auto Items = getMemberHierarchy(
+          InpAST->AST, Pos, 1, TypeHierarchyDirection::Parents, Index, File);
+      if (Items && Items->parents) {
+        for (auto Item : *Items->parents) {
+          Results.emplace_back(Location{Item.uri, Item.selectionRange});
+        }
+      }
+      Reply(std::move(Results));
+    };
+    WorkScheduler.runWithAST("CodeLensCommand", File, std::move(Action));
+    break;
+  }
+  case CodeLensType::MemberChildren: {
+    auto Action = [File, Pos, Reply = std::move(Reply),
+                   this](Expected<InputsAndAST> InpAST) mutable {
+      std::vector<Location> Results;
+      auto Items = getMemberHierarchy(
+          InpAST->AST, Pos, 1, TypeHierarchyDirection::Children, Index, File);
+      if (Items && Items->children) {
+        for (auto Item : *Items->children) {
+          Results.emplace_back(Location{Item.uri, Item.selectionRange});
+        }
+      }
+      Reply(std::move(Results));
+    };
+    WorkScheduler.runWithAST("CodeLensCommand", File, std::move(Action));
+    break;
+  }
+  }
+}
+
 void ClangdServer::locateSymbolAt(PathRef File, Position Pos,
                                   Callback<std::vector<LocatedSymbol>> CB) {
   auto Action = [Pos, CB = std::move(CB),

       };
   WorkScheduler.runWithAST("GetAST", File, std::move(Action));
 }
+void ClangdServer::provideCodeLens(PathRef File,
+                                   Callback<std::vector<CodeLens>> CB) {
+  auto Action = [CB = std::move(CB), File = File.str(),
+                 this](llvm::Expected<InputsAndAST> InpAST) mutable {
+    if (!InpAST)
+      return CB(InpAST.takeError());
+    CB(clangd::getDocumentCodeLens(InpAST->AST, Index, 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->location.uri.file();
+  auto Action = [CB = std::move(CB), File = File.str(), 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);
+}
 
 void ClangdServer::customAction(PathRef File, llvm::StringRef Name,
                                 Callback<InputsAndAST> Action) {

clang-tools-extra/clangd/Protocol.h

     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 &);
 

   /// Note: "documentChanges" is not currently used because currently there is
   /// no support for versioned edits.
 };
+bool operator==(const WorkspaceEdit &, const WorkspaceEdit &);
 bool fromJSON(const llvm::json::Value &, WorkspaceEdit &, llvm::json::Path);
 llvm::json::Value toJSON(const WorkspaceEdit &WE);
 

   /// ID of the tweak that should be executed. Corresponds to Tweak::id().
   std::string tweakID;
 };
+bool operator==(const TweakArgs &, const TweakArgs &);
 bool fromJSON(const llvm::json::Value &, TweakArgs &, llvm::json::Path);
 llvm::json::Value toJSON(const TweakArgs &A);
 
+enum class CodeLensType {
+  Reference = 1,
+  TypeParent = 2,
+  TypeChildren = 3,
+  MemberParent = 4,
+  MemberChildren = 5
+};
+bool fromJSON(const llvm::json::Value &, CodeLensType &, llvm::json::Path);
+
+struct CodeLensResolveData {
+  CodeLensType type;
+  Location location;
+};
+bool operator==(const CodeLensResolveData &, const CodeLensResolveData &);
+bool fromJSON(const llvm::json::Value &, CodeLensResolveData &,
+              llvm::json::Path);
+llvm::json::Value toJSON(const CodeLensResolveData &A);
+
 /// Exact commands are not specified in the protocol so we define the
 /// ones supported by Clangd here. The protocol specifies the command arguments
 /// to be "any[]" but to make this safer and more manageable, each command we

   // Command to apply the code action. Uses TweakArgs as argument.
   const static llvm::StringLiteral CLANGD_APPLY_TWEAK;
 
+  // Command to identify codeLens. Only used from server to client.
+  // Note it should be implemented in client by calling CLANGD_SERVER_CODELENS,
+  // so that client can handle codeLens result themselves, e.g. invoke
+  // 'editor.action.showReferences' in vscode
+  const static llvm::StringLiteral CLANGD_CLIENT_CODELENS;
+  // The actucal codeLens commands implemented by clangd sever.
+  const static llvm::StringLiteral CLANGD_SERVER_CODELENS;
   /// The command identifier, e.g. CLANGD_APPLY_FIX_COMMAND
   std::string command;
 
   // Arguments
   llvm::Optional<WorkspaceEdit> workspaceEdit;
   llvm::Optional<TweakArgs> tweakArgs;
+  llvm::Optional<CodeLensResolveData> codeLens;
 };
 bool fromJSON(const llvm::json::Value &, ExecuteCommandParams &,
               llvm::json::Path);

 struct Command : public ExecuteCommandParams {
   std::string title;
 };
+bool operator==(const Command &, const Command &);
 llvm::json::Value toJSON(const Command &C);
 
+/// https://microsoft.github.io/language-server-protocol/specification#textDocument_codeLens
+struct CodeLensParams : DocumentSymbolParams {};
+
+struct CodeLens {
+  // CodeLens range.
+  Range range;
+  // CodeLens command.
+  llvm::Optional<Command> command;
+  // CodeLens resolve data.
+  llvm::Optional<CodeLensResolveData> data;
+};
+bool operator==(const CodeLens &, const CodeLens &);
+bool fromJSON(const llvm::json::Value &, CodeLens &, llvm::json::Path);
+llvm::json::Value toJSON(const CodeLens &);
+
 /// A code action represents a change that can be performed in code, e.g. to fix
 /// a problem or to refactor code.
 ///

clang-tools-extra/clangd/Protocol.cpp

   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},

          O.map("range", R.range) && O.map("context", R.context);
 }
 
+bool operator==(const WorkspaceEdit &LHS, const WorkspaceEdit &RHS) {
+  return LHS.changes == RHS.changes;
+}
+
 bool fromJSON(const llvm::json::Value &Params, WorkspaceEdit &R,
               llvm::json::Path P) {
   llvm::json::ObjectMapper O(Params, P);
   return O && O.map("changes", R.changes);
 }
 
+bool fromJSON(const llvm::json::Value &Params, CodeLensType &R,
+              llvm::json::Path P) {
+  if (auto T = Params.getAsInteger()) {
+    if (*T < static_cast<int>(CodeLensType::Reference) ||
+        *T > static_cast<int>(CodeLensType::MemberChildren))
+      return false;
+    R = static_cast<CodeLensType>(*T);
+    return true;
+  }
+  return false;
+}
+
+bool operator==(const CodeLensResolveData &LHS,
+                const CodeLensResolveData &RHS) {
+  return LHS.location == RHS.location && LHS.type == RHS.type;
+}
+
+bool fromJSON(const llvm::json::Value &Params, CodeLensResolveData &R,
+              llvm::json::Path P) {
+  llvm::json::ObjectMapper O(Params, P);
+  return O && O.map("type", R.type) && O.map("location", R.location);
+}
+
+llvm::json::Value toJSON(const CodeLensResolveData &P) {
+  llvm::json::Object O{{"type", static_cast<int>(P.type)},
+                       {"location", P.location}};
+  return std::move(O);
+}
+
 const llvm::StringLiteral ExecuteCommandParams::CLANGD_APPLY_FIX_COMMAND =
     "clangd.applyFix";
 const llvm::StringLiteral ExecuteCommandParams::CLANGD_APPLY_TWEAK =
     "clangd.applyTweak";
+const llvm::StringLiteral ExecuteCommandParams::CLANGD_CLIENT_CODELENS =
+    "clangd.client.codeLens";
+const llvm::StringLiteral ExecuteCommandParams::CLANGD_SERVER_CODELENS =
+    "clangd.server.codeLens";
 
 bool fromJSON(const llvm::json::Value &Params, ExecuteCommandParams &R,
               llvm::json::Path P) {

   if (R.command == ExecuteCommandParams::CLANGD_APPLY_TWEAK)
     return Args && Args->size() == 1 &&
            fromJSON(Args->front(), R.tweakArgs, P.field("arguments").index(0));
+  if (R.command == ExecuteCommandParams::CLANGD_SERVER_CODELENS)
+    return Args && Args->size() == 1 &&
+           fromJSON(Args->front(), R.codeLens, P.field("arguments").index(0));
   return false; // Unrecognized command.
 }
 

   return O && O.map("query", R.query);
 }
 
+bool operator==(const Command &LHS, const Command &RHS) {
+  return LHS.title == RHS.title && LHS.command == RHS.command &&
+         LHS.codeLens == RHS.codeLens && LHS.tweakArgs == RHS.tweakArgs &&
+         LHS.workspaceEdit == RHS.workspaceEdit;
+}
+
 llvm::json::Value toJSON(const Command &C) {
   auto Cmd = llvm::json::Object{{"title", C.title}, {"command", C.command}};
   if (C.workspaceEdit)
     Cmd["arguments"] = {*C.workspaceEdit};
   if (C.tweakArgs)
     Cmd["arguments"] = {*C.tweakArgs};
+  if (C.codeLens)
+    Cmd["arguments"] = {*C.codeLens};
   return std::move(Cmd);
 }
 
+bool operator==(const CodeLens &LHS, const CodeLens &RHS) {
+  return LHS.command == RHS.command && LHS.data == RHS.data &&
+         LHS.range == RHS.range;
+}
+
+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);
+}
+
 const llvm::StringLiteral CodeAction::QUICKFIX_KIND = "quickfix";
 const llvm::StringLiteral CodeAction::REFACTOR_KIND = "refactor";
 const llvm::StringLiteral CodeAction::INFO_KIND = "info";

   return llvm::json::Object{{"changes", std::move(FileChanges)}};
 }
 
+bool operator==(const TweakArgs &LHS, const TweakArgs &RHS) {
+  return LHS.file == RHS.file && LHS.tweakID == RHS.tweakID &&
+         LHS.selection == RHS.selection;
+}
+
 bool fromJSON(const llvm::json::Value &Params, TweakArgs &A,
               llvm::json::Path P) {
   llvm::json::ObjectMapper O(Params, P);

clang-tools-extra/clangd/TUScheduler.h

 struct ASTRetentionPolicy {
   /// Maximum number of ASTs to be retained in memory when there are no pending
   /// requests for them.
-  unsigned MaxRetainedASTs = 3;
+  unsigned MaxRetainedASTs = 16;
 };
 
 /// Clangd may wait after an update to see if another one comes along.

clang-tools-extra/clangd/XRefs.h

     ParsedAST &AST, Position Pos, int Resolve, TypeHierarchyDirection Direction,
     const SymbolIndex *Index = nullptr, PathRef TUPath = PathRef{});
 
+llvm::Optional<TypeHierarchyItem>
+getMemberHierarchy(ParsedAST &AST, Position Pos, int ResolveLevels,
+                   TypeHierarchyDirection Direction,
+                   const SymbolIndex *Index = nullptr,
+                   PathRef TUPath = PathRef{});
+
 void resolveTypeHierarchy(TypeHierarchyItem &Item, int ResolveLevels,
                           TypeHierarchyDirection Direction,
                           const SymbolIndex *Index);

 /// Returns all decls that are referenced in the \p FD except local symbols.
 llvm::DenseSet<const Decl *> getNonLocalDeclRefs(ParsedAST &AST,
                                                  const FunctionDecl *FD);
+
+/// Get codelens
+llvm::Expected<std::vector<CodeLens>>
+getDocumentCodeLens(ParsedAST &AST, const SymbolIndex *Index, PathRef Path);
+
+llvm::Expected<CodeLens> resolveCodeLens(ParsedAST &AST, const CodeLens &Params,
+                                         uint32_t Limit,
+                                         const SymbolIndex *Index,
+                                         PathRef Path);
 } // namespace clangd
 } // namespace clang
 

clang-tools-extra/clangd/XRefs.cpp

                  TypeHierarchyDirection Direction, const SymbolIndex *Index,
                  PathRef TUPath) {
   const CXXRecordDecl *CXXRD = findRecordTypeAt(AST, Pos);
-  if (!CXXRD)
-    return llvm::None;
 
   bool WantParents = Direction == TypeHierarchyDirection::Parents ||
                      Direction == TypeHierarchyDirection::Both;

   // specialization parameters, while the children would involve classes
   // that derive from other specializations of the template.
   if (WantChildren) {
-    if (auto *CTSD = dyn_cast<ClassTemplateSpecializationDecl>(CXXRD))
+    if (auto *CTSD = dyn_cast_or_null<ClassTemplateSpecializationDecl>(CXXRD))
       CXXRD = CTSD->getTemplateInstantiationPattern();
   }
 
+  if (!CXXRD)
+    return llvm::None;
+
   Optional<TypeHierarchyItem> Result =
       declToTypeHierarchyItem(AST.getASTContext(), *CXXRD);
   if (!Result)

   }
 }
 
+static void fillSuperMethods(const CXXMethodDecl &CXXMD, ASTContext &ASTCtx,
+                             std::vector<TypeHierarchyItem> &SuperMethods) {
+  for (const CXXMethodDecl *ParentDecl : CXXMD.overridden_methods()) {
+    if (Optional<TypeHierarchyItem> ParentSym =
+            declToTypeHierarchyItem(ASTCtx, *ParentDecl)) {
+      ParentSym->parents.emplace();
+      fillSuperMethods(*ParentDecl, ASTCtx, *ParentSym->parents);
+      SuperMethods.emplace_back(std::move(*ParentSym));
+    }
+  }
+}
+
+static void fillSubMethods(const SymbolID &ID,
+                           std::vector<TypeHierarchyItem> &SubMethods,
+                           const SymbolIndex *Index, int Levels,
+                           PathRef TUPath) {
+  RelationsRequest Req;
+  Req.Subjects.insert(ID);
+  Req.Predicate = RelationKind::OverriddenBy;
+  Index->relations(Req, [&](const SymbolID &Subject, const Symbol &Object) {
+    if (Optional<TypeHierarchyItem> ChildSym =
+            symbolToTypeHierarchyItem(Object, Index, TUPath)) {
+      if (Levels > 1) {
+        ChildSym->children.emplace();
+        fillSubMethods(Object.ID, *ChildSym->children, Index, Levels - 1,
+                       TUPath);
+      }
+      SubMethods.emplace_back(std::move(*ChildSym));
+    }
+  });
+}
+
+const NamedDecl *findNamedDeclAt(ParsedAST &AST, Position Pos) {
+  auto DeclFromNode = [](const SelectionTree::Node *N) -> const NamedDecl * {
+    if (!N)
+      return nullptr;
+
+    // Note: explicitReferenceTargets() will search for both template
+    // instantiations and template patterns, and prefer the former if available
+    // (generally, one will be available for non-dependent specializations of a
+    // class template).
+    auto Decls = explicitReferenceTargets(N->ASTNode, DeclRelation::Underlying);
+    if (Decls.empty())
+      return nullptr;
+
+    return Decls[0];
+  };
+
+  const SourceManager &SM = AST.getSourceManager();
+  const NamedDecl *Result = nullptr;
+  auto Offset = positionToOffset(SM.getBufferData(SM.getMainFileID()), Pos);
+  if (!Offset) {
+    llvm::consumeError(Offset.takeError());
+    return Result;
+  }
+  SelectionTree::createEach(AST.getASTContext(), AST.getTokens(), *Offset,
+                            *Offset, [&](SelectionTree ST) {
+                              Result = DeclFromNode(ST.commonAncestor());
+                              return Result != nullptr;
+                            });
+  return Result;
+}
+
+llvm::Optional<TypeHierarchyItem>
+getMemberHierarchy(ParsedAST &AST, Position Pos, int ResolveLevels,
+                   TypeHierarchyDirection Direction, const SymbolIndex *Index,
+                   PathRef TUPath) {
+  auto CXXMD = dyn_cast_or_null<CXXMethodDecl>(findNamedDeclAt(AST, Pos));
+  if (!CXXMD || !CXXMD->isVirtual())
+    return llvm::None;
+
+  Optional<TypeHierarchyItem> Result =
+      declToTypeHierarchyItem(AST.getASTContext(), *CXXMD);
+
+  if (!Result)
+    return Result;
+
+  if (Direction == TypeHierarchyDirection::Parents ||
+      Direction == TypeHierarchyDirection::Both) {
+    Result->parents.emplace();
+    fillSuperMethods(*CXXMD, AST.getASTContext(), *Result->parents);
+  }
+
+  if ((Direction == TypeHierarchyDirection::Children ||
+       Direction == TypeHierarchyDirection::Both) &&
+      ResolveLevels > 0) {
+    Result->children.emplace();
+
+    if (Index) {
+      if (auto ID = getSymbolID(CXXMD))
+        fillSubMethods(ID, *Result->children, Index, ResolveLevels, TUPath);
+    }
+  }
+  return Result;
+}
+
 llvm::DenseSet<const Decl *> getNonLocalDeclRefs(ParsedAST &AST,
                                                  const FunctionDecl *FD) {
   if (!FD->hasBody())

   });
   return DeclRefs;
 }
+
+void collectCodeLens(ParsedAST &AST, const DocumentSymbol &Symbol,
+                     const SymbolIndex *Index, PathRef Path,
+                     std::vector<CodeLens> &Result) {
+  CodeLensResolveData Data;
+  Data.location =
+      Location{URIForFile::canonicalize(Path, Path), Symbol.selectionRange};
+  Data.type = CodeLensType::Reference;
+  Result.emplace_back(CodeLens{Symbol.selectionRange, None, Data});
+  // Collect codelens for hierarchy directly.
+  Position Pos = Symbol.selectionRange.start;
+  Command Cmd;
+  Cmd.command = std::string(ExecuteCommandParams::CLANGD_CLIENT_CODELENS);
+  switch (Symbol.kind) {
+  case SymbolKind::Class:
+  case SymbolKind::Struct:
+  case SymbolKind::Interface: {
+    auto CXXRD = dyn_cast_or_null<CXXRecordDecl>(findNamedDeclAt(AST, Pos));
+    if (CXXRD && CXXRD->hasDefinition() && CXXRD->getNumBases()) {
+      Data.type = CodeLensType::TypeParent;
+      Cmd.codeLens = Data;
+      Cmd.title = std::to_string(CXXRD->getNumBases()) + " base";
+      Result.emplace_back(CodeLens{Symbol.selectionRange, Cmd, None});
+    }
+    auto Items = getTypeHierarchy(AST, Pos, 1, TypeHierarchyDirection::Children,
+                                  Index, Path);
+    if (Items && Items->children && Items->children->size()) {
+      Data.type = CodeLensType::TypeChildren;
+      Cmd.codeLens = Data;
+      Cmd.title = std::to_string(Items->children->size()) + " derived";
+      Result.emplace_back(CodeLens{Symbol.selectionRange, Cmd, None});
+    }
+    break;
+  }
+  case SymbolKind::Method: {
+    auto CXXMD = dyn_cast_or_null<CXXMethodDecl>(
+        findNamedDeclAt(AST, Symbol.selectionRange.start));
+    if (CXXMD && CXXMD->isVirtual()) {
+      if (CXXMD->size_overridden_methods()) {
+        Data.type = CodeLensType::MemberParent;
+        Cmd.codeLens = Data;
+        Cmd.title = std::to_string(CXXMD->size_overridden_methods()) + " base";
+        Result.emplace_back(CodeLens{Symbol.selectionRange, Cmd, None});
+      }
+      auto Items = getMemberHierarchy(
+          AST, Pos, 1, TypeHierarchyDirection::Children, Index, Path);
+      if (Items && Items->children && Items->children->size()) {
+        Data.type = CodeLensType::MemberChildren;
+        Cmd.codeLens = Data;
+        Cmd.title = std::to_string(Items->children->size()) + " derived";
+        Result.emplace_back(CodeLens{Symbol.selectionRange, Cmd, None});
+      }
+    }
+    break;
+  }
+  default:
+    break;
+  }
+  for (auto &&Child : Symbol.children) {
+    collectCodeLens(AST, Child, Index, Path, Result);
+  }
+}
+
+llvm::Expected<std::vector<CodeLens>>
+getDocumentCodeLens(ParsedAST &AST, const SymbolIndex *Index, PathRef Path) {
+  auto DocumentSymbols = getDocumentSymbols(AST);
+  if (!DocumentSymbols)
+    return DocumentSymbols.takeError();
+  std::vector<CodeLens> Result;
+  for (const auto &Symbol : *DocumentSymbols) {
+    collectCodeLens(AST, Symbol, Index, Path, Result);
+  }
+  return Result;
+}
+
+llvm::Expected<CodeLens> resolveCodeLens(ParsedAST &AST, const CodeLens &Params,
+                                         uint32_t Limit,
+                                         const SymbolIndex *Index,
+                                         PathRef Path) {
+  CodeLensResolveData Data = *Params.data;
+  Command Cmd;
+  Cmd.command = std::string(ExecuteCommandParams::CLANGD_CLIENT_CODELENS);
+  Cmd.codeLens = Data;
+  Position Pos = Params.range.start;
+  if (Data.type == CodeLensType::Reference) {
+    auto Refs = findReferences(AST, Pos, Limit, Index).References;
+    Cmd.title = std::to_string(Refs.size()) + " refs";
+  }
+  return CodeLens{Params.range, Cmd, None};
+}
 } // namespace clangd
 } // namespace clang

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

 # CHECK-NEXT:      "executeCommandProvider": {
 # CHECK-NEXT:        "commands": [
 # CHECK-NEXT:          "clangd.applyFix",
-# CHECK-NEXT:          "clangd.applyTweak"
+# CHECK-NEXT:          "clangd.applyTweak",
+# CHECK-NEXT:          "clangd.server.codeLens"
 # CHECK-NEXT:        ]
 # CHECK-NEXT:      },
 # CHECK-NEXT:      "hoverProvider": true,

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

     Hidden,
 };
 
+opt<bool> EnableCodeLens{
+    "code-lens", cat(Features), desc("Enable preview of CodeLens feature"),
+    init(false), Hidden,
+};
+
 opt<unsigned> WorkerThreadsCount{
     "j",
     cat(Misc),

   Opts.BuildRecoveryAST = RecoveryAST;
   Opts.PreserveRecoveryASTType = RecoveryASTType;
   Opts.FoldingRanges = FoldingRanges;
+  Opts.CodeLens = EnableCodeLens;
 
   Opts.CodeComplete.IncludeIneligibleResults = IncludeIneligibleResults;
   Opts.CodeComplete.Limit = LimitResults;

clang-tools-extra/clangd/unittests/XRefsTests.cpp

                         URIForFile::canonicalize(testPath("bar.h"), "")})));
 }
 
+CodeLens lens(const URIForFile &URI, const CodeLensType &Type,
+              const Range &Range) {
+  return CodeLens{Range, None, CodeLensResolveData{Type, {URI, Range}}};
+}
+
+CodeLens lens(const URIForFile &URI, const std::string &Title,
+              const CodeLensType &Type, const Range &Range) {
+  Command Cmd;
+  Cmd.title = Title;
+  Cmd.command = std::string(ExecuteCommandParams::CLANGD_CLIENT_CODELENS);
+  Cmd.codeLens = CodeLensResolveData{Type, {URI, Range}};
+  return CodeLens{Range, Cmd, None};
+}
+
+TEST(CodeLensTest, Reference) {
+  Annotations Main(R"cpp(
+    class $X[[X]] {
+    };
+    int $main[[main]]() {
+      X x;
+    }
+  )cpp");
+  TestTU TU;
+  TU.Code = std::string(Main.code());
+  auto AST = TU.build();
+  auto Path = URIForFile::canonicalize(testPath(TU.Filename), testRoot());
+  if (auto CodeLens1 =
+          getDocumentCodeLens(AST, nullptr, testPath(TU.Filename))) {
+    EXPECT_THAT(
+        *CodeLens1,
+        ElementsAre(lens(Path, CodeLensType::Reference, Main.range("X")),
+                    lens(Path, CodeLensType::Reference, Main.range("main"))));
+    std::vector<CodeLens> CodeLens2;
+    for (auto &&CD : *CodeLens1) {
+      CodeLens2.emplace_back(
+          *resolveCodeLens(AST, CD, 0, nullptr, testPath(TU.Filename)));
+    }
+    EXPECT_THAT(
+        CodeLens2,
+        ElementsAre(
+            lens(Path, "2 refs", CodeLensType::Reference, Main.range("X")),
+            lens(Path, "1 refs", CodeLensType::Reference, Main.range("main"))));
+  }
+}
+
+TEST(CodeLensTest, Inheritance) {
+  Annotations Main(R"cpp(
+    class $X[[X]] {
+    public:
+      virtual void $m1[[method]]();
+    };
+
+    class $Y[[Y]] : public X {
+    public:
+      void $m2[[method]]() override;
+    };
+  )cpp");
+  TestTU TU;
+  TU.Code = std::string(Main.code());
+  auto AST = TU.build();
+  auto URI = URIForFile::canonicalize(testPath(TU.Filename), testRoot());
+  if (auto CodeLens =
+          getDocumentCodeLens(AST, TU.index().get(), testPath(TU.Filename))) {
+    EXPECT_THAT(
+        *CodeLens,
+        ElementsAre(
+            lens(URI, CodeLensType::Reference, Main.range("X")),
+            lens(URI, "1 derived", CodeLensType::TypeChildren, Main.range("X")),
+            lens(URI, CodeLensType::Reference, Main.range("m1")),
+            lens(URI, "1 derived", CodeLensType::MemberChildren,
+                 Main.range("m1")),
+            lens(URI, CodeLensType::Reference, Main.range("Y")),
+            lens(URI, "1 base", CodeLensType::TypeParent, Main.range("Y")),
+            lens(URI, CodeLensType::Reference, Main.range("m2")),
+            lens(URI, "1 base", CodeLensType::MemberParent, Main.range("m2"))));
+  }
+}
 } // namespace
 } // namespace clangd
 } // namespace clang