ccls/src/messages/textDocument_signatureHelp.cc

// Copyright 2017-2018 ccls Authors
// SPDX-License-Identifier: Apache-2.0

#include "clang_complete.hh"
#include "message_handler.h"
#include "pipeline.hh"

#include <clang/Sema/Sema.h>

using namespace ccls;
using namespace clang;

namespace {
MethodType kMethodType = "textDocument/signatureHelp";

// Represents a parameter of a callable-signature. A parameter can
// have a label and a doc-comment.
struct lsParameterInformation {
  std::string label;
  // Not available in clang
  // std::optional<std::string> documentation;
};
MAKE_REFLECT_STRUCT(lsParameterInformation, label);

// Represents the signature of something callable. A signature
// can have a label, like a function-name, a doc-comment, and
// a set of parameters.
struct lsSignatureInformation {
  std::string label;
  std::optional<std::string> documentation;
  std::vector<lsParameterInformation> parameters;
};
MAKE_REFLECT_STRUCT(lsSignatureInformation, label, documentation, parameters);

// Signature help represents the signature of something
// callable. There can be multiple signature but only one
// active and only one active parameter.
struct lsSignatureHelp {
  std::vector<lsSignatureInformation> signatures;
  int activeSignature = 0;
  int activeParameter = 0;
};
MAKE_REFLECT_STRUCT(lsSignatureHelp, signatures, activeSignature,
                    activeParameter);

struct In_TextDocumentSignatureHelp : public RequestMessage {
  MethodType GetMethodType() const override { return kMethodType; }
  lsTextDocumentPositionParams params;
};
MAKE_REFLECT_STRUCT(In_TextDocumentSignatureHelp, id, params);
REGISTER_IN_MESSAGE(In_TextDocumentSignatureHelp);

std::string BuildOptional(const CodeCompletionString &CCS,
                          std::vector<lsParameterInformation> &ls_params) {
  std::string ret;
  for (const auto &Chunk : CCS) {
    switch (Chunk.Kind) {
    case CodeCompletionString::CK_Optional:
      ret += BuildOptional(*Chunk.Optional, ls_params);
      break;
    case CodeCompletionString::CK_Placeholder:
      // A string that acts as a placeholder for, e.g., a function call
      // argument.
      // Intentional fallthrough here.
    case CodeCompletionString::CK_CurrentParameter: {
      // A piece of text that describes the parameter that corresponds to
      // the code-completion location within a function call, message send,
      // macro invocation, etc.
      ret += Chunk.Text;
      ls_params.push_back(lsParameterInformation{Chunk.Text});
      break;
    }
    case CodeCompletionString::CK_VerticalSpace:
      break;
    default:
      ret += Chunk.Text;
      break;
    }
  }
  return ret;
}

class SignatureHelpConsumer : public CodeCompleteConsumer {
  std::shared_ptr<GlobalCodeCompletionAllocator> Alloc;
  CodeCompletionTUInfo CCTUInfo;
public:
  bool from_cache;
  lsSignatureHelp ls_sighelp;
  SignatureHelpConsumer(const clang::CodeCompleteOptions &CCOpts,
                        bool from_cache)
      : CodeCompleteConsumer(CCOpts, false),
        Alloc(std::make_shared<GlobalCodeCompletionAllocator>()),
        CCTUInfo(Alloc), from_cache(from_cache) {}
  void ProcessOverloadCandidates(Sema &S, unsigned CurrentArg,
                                 OverloadCandidate *Candidates,
                                 unsigned NumCandidates
#if LLVM_VERSION_MAJOR >= 8
                                 ,
                                 SourceLocation OpenParLoc
#endif
                                 ) override {
    ls_sighelp.activeParameter = (int)CurrentArg;
    for (unsigned i = 0; i < NumCandidates; i++) {
      OverloadCandidate Cand = Candidates[i];
      // We want to avoid showing instantiated signatures, because they may be
      // long in some cases (e.g. when 'T' is substituted with 'std::string', we
      // would get 'std::basic_string<char>').
      if (auto *Func = Cand.getFunction())
        if (auto *Pattern = Func->getTemplateInstantiationPattern())
          Cand = OverloadCandidate(Pattern);

      const auto *CCS =
          Cand.CreateSignatureString(CurrentArg, S, *Alloc, CCTUInfo, true);

      const char *ret_type = nullptr;
      lsSignatureInformation &ls_sig = ls_sighelp.signatures.emplace_back();
#if LLVM_VERSION_MAJOR >= 8
      const RawComment *RC = getCompletionComment(S.getASTContext(), Cand.getFunction());
      ls_sig.documentation = RC ? RC->getBriefText(S.getASTContext()) : "";
#endif
      for (const auto &Chunk : *CCS)
        switch (Chunk.Kind) {
        case CodeCompletionString::CK_ResultType:
          ret_type = Chunk.Text;
          break;
        case CodeCompletionString::CK_Placeholder:
        case CodeCompletionString::CK_CurrentParameter: {
          ls_sig.label += Chunk.Text;
          ls_sig.parameters.push_back(lsParameterInformation{Chunk.Text});
          break;
        }
        case CodeCompletionString::CK_Optional:
          ls_sig.label += BuildOptional(*Chunk.Optional, ls_sig.parameters);
          break;
        case CodeCompletionString::CK_VerticalSpace:
          break;
        default:
          ls_sig.label += Chunk.Text;
          break;
        }
      if (ret_type) {
        ls_sig.label += " -> ";
        ls_sig.label += ret_type;
      }
    }
    std::sort(
        ls_sighelp.signatures.begin(), ls_sighelp.signatures.end(),
        [](const lsSignatureInformation &l, const lsSignatureInformation &r) {
          if (l.parameters.size() != r.parameters.size())
            return l.parameters.size() < r.parameters.size();
          if (l.label.size() != r.label.size())
            return l.label.size() < r.label.size();
          return l.label < r.label;
        });
  }

  CodeCompletionAllocator &getAllocator() override { return *Alloc; }
  CodeCompletionTUInfo &getCodeCompletionTUInfo() override { return CCTUInfo; }
};

struct Handler_TextDocumentSignatureHelp
    : BaseMessageHandler<In_TextDocumentSignatureHelp> {
  MethodType GetMethodType() const override { return kMethodType; }

  void Run(In_TextDocumentSignatureHelp *request) override {
    static CompleteConsumerCache<lsSignatureHelp> cache;

    const auto &params = request->params;
    std::string path = params.textDocument.uri.GetPath();
    lsPosition begin_pos = params.position;
    if (WorkingFile *file = working_files->GetFileByFilename(path)) {
      std::string completion_text;
      lsPosition end_pos = params.position;
      begin_pos = file->FindStableCompletionSource(
        request->params.position, &completion_text, &end_pos);
    }

    CompletionManager::OnComplete callback =
        [id = request->id, path, begin_pos](CodeCompleteConsumer *OptConsumer) {
          if (!OptConsumer)
            return;
          auto *Consumer = static_cast<SignatureHelpConsumer *>(OptConsumer);
          pipeline::Reply(id, Consumer->ls_sighelp);
          if (!Consumer->from_cache) {
            cache.WithLock([&]() {
              cache.path = path;
              cache.position = begin_pos;
              cache.result = Consumer->ls_sighelp;
            });
          }
        };

    CodeCompleteOptions CCOpts;
    CCOpts.IncludeGlobals = false;
    CCOpts.IncludeMacros = false;
    CCOpts.IncludeBriefComments = false;
    if (cache.IsCacheValid(path, begin_pos)) {
      SignatureHelpConsumer Consumer(CCOpts, true);
      cache.WithLock([&]() { Consumer.ls_sighelp = cache.result; });
      callback(&Consumer);
    } else {
      clang_complete->completion_request_.PushBack(
          std::make_unique<CompletionManager::CompletionRequest>(
              request->id, params.textDocument, params.position,
              std::make_unique<SignatureHelpConsumer>(CCOpts, false), CCOpts,
              callback));
    }
  }
};
REGISTER_MESSAGE_HANDLER(Handler_TextDocumentSignatureHelp);
} // namespace