void SwiftLangSupport::findInterfaceDocument(StringRef ModuleName,
                                             ArrayRef<const char *> Args,
                       std::function<void(const InterfaceDocInfo &)> Receiver) {
  InterfaceDocInfo Info;

  CompilerInstance CI;
  // Display diagnostics to stderr.
  PrintingDiagnosticConsumer PrintDiags;
  CI.addDiagnosticConsumer(&PrintDiags);

  CompilerInvocation Invocation;
  std::string Error;
  if (getASTManager().initCompilerInvocation(Invocation, Args, CI.getDiags(),
                                             StringRef(), Error)) {
    Info.Error = Error;
    return Receiver(Info);
  }

  if (auto IFaceGenRef = IFaceGenContexts.find(ModuleName, Invocation))
    Info.ModuleInterfaceName = IFaceGenRef->getDocumentName();

  SmallString<128> Buf;
  SmallVector<std::pair<unsigned, unsigned>, 16> ArgOffs;
  auto addArgPair = [&](StringRef Arg, StringRef Val) {
    assert(!Arg.empty());
    if (Val.empty())
      return;
    unsigned ArgBegin = Buf.size();
    Buf += Arg;
    unsigned ArgEnd = Buf.size();
    unsigned ValBegin = Buf.size();
    Buf += Val;
    unsigned ValEnd = Buf.size();
    ArgOffs.push_back(std::make_pair(ArgBegin, ArgEnd));
    ArgOffs.push_back(std::make_pair(ValBegin, ValEnd));
  };
  auto addSingleArg = [&](StringRef Arg) {
    assert(!Arg.empty());
    unsigned ArgBegin = Buf.size();
    Buf += Arg;
    unsigned ArgEnd = Buf.size();
    ArgOffs.push_back(std::make_pair(ArgBegin, ArgEnd));
  };

  addArgPair("-target", Invocation.getTargetTriple());

  const auto &SPOpts = Invocation.getSearchPathOptions();
  addArgPair("-sdk", SPOpts.SDKPath);
  for (auto &Path : SPOpts.FrameworkSearchPaths)
    addArgPair("-F", Path);
  for (auto &Path : SPOpts.ImportSearchPaths)
    addArgPair("-I", Path);

  const auto &ClangOpts = Invocation.getClangImporterOptions();
  addArgPair("-module-cache-path", ClangOpts.ModuleCachePath);
  for (auto &ExtraArg : ClangOpts.ExtraArgs)
    addArgPair("-Xcc", ExtraArg);

  if (Invocation.getFrontendOptions().ImportUnderlyingModule)
    addSingleArg("-import-underlying-module");
  addArgPair("-import-objc-header",
             Invocation.getFrontendOptions().ImplicitObjCHeaderPath);

  SmallVector<StringRef, 16> NewArgs;
  for (auto Pair : ArgOffs) {
    NewArgs.push_back(StringRef(Buf.begin()+Pair.first, Pair.second-Pair.first));
  }
  Info.CompilerArgs = NewArgs;

  return Receiver(Info);
}