/// Collect the visible conversions of a base class.
///
/// \param Base a base class of the class we're considering
/// \param InVirtual whether this base class is a virtual base (or a base
///   of a virtual base)
/// \param Access the access along the inheritance path to this base
/// \param ParentHiddenTypes the conversions provided by the inheritors
///   of this base
/// \param Output the set to which to add conversions from non-virtual bases
/// \param VOutput the set to which to add conversions from virtual bases
/// \param HiddenVBaseCs the set of conversions which were hidden in a
///   virtual base along some inheritance path
static void CollectVisibleConversions(ASTContext &Context,
                                      CXXRecordDecl *Record,
                                      bool InVirtual,
                                      AccessSpecifier Access,
                  const llvm::SmallPtrSet<CanQualType, 8> &ParentHiddenTypes,
                                      UnresolvedSetImpl &Output,
                                      UnresolvedSetImpl &VOutput,
                           llvm::SmallPtrSet<NamedDecl*, 8> &HiddenVBaseCs) {
  // The set of types which have conversions in this class or its
  // subclasses.  As an optimization, we don't copy the derived set
  // unless it might change.
  const llvm::SmallPtrSet<CanQualType, 8> *HiddenTypes = &ParentHiddenTypes;
  llvm::SmallPtrSet<CanQualType, 8> HiddenTypesBuffer;

  // Collect the direct conversions and figure out which conversions
  // will be hidden in the subclasses.
  UnresolvedSetImpl &Cs = *Record->getConversionFunctions();
  if (!Cs.empty()) {
    HiddenTypesBuffer = ParentHiddenTypes;
    HiddenTypes = &HiddenTypesBuffer;

    for (UnresolvedSetIterator I = Cs.begin(), E = Cs.end(); I != E; ++I) {
      bool Hidden =
        !HiddenTypesBuffer.insert(GetConversionType(Context, I.getDecl()));

      // If this conversion is hidden and we're in a virtual base,
      // remember that it's hidden along some inheritance path.
      if (Hidden && InVirtual)
        HiddenVBaseCs.insert(cast<NamedDecl>(I.getDecl()->getCanonicalDecl()));

      // If this conversion isn't hidden, add it to the appropriate output.
      else if (!Hidden) {
        AccessSpecifier IAccess
          = CXXRecordDecl::MergeAccess(Access, I.getAccess());

        if (InVirtual)
          VOutput.addDecl(I.getDecl(), IAccess);
        else
          Output.addDecl(I.getDecl(), IAccess);
      }
    }
  }

  // Collect information recursively from any base classes.
  for (CXXRecordDecl::base_class_iterator
         I = Record->bases_begin(), E = Record->bases_end(); I != E; ++I) {
    const RecordType *RT = I->getType()->getAs<RecordType>();
    if (!RT) continue;

    AccessSpecifier BaseAccess
      = CXXRecordDecl::MergeAccess(Access, I->getAccessSpecifier());
    bool BaseInVirtual = InVirtual || I->isVirtual();

    CXXRecordDecl *Base = cast<CXXRecordDecl>(RT->getDecl());
    CollectVisibleConversions(Context, Base, BaseInVirtual, BaseAccess,
                              *HiddenTypes, Output, VOutput, HiddenVBaseCs);
  }
}

/// \brief Figure out if an expression could be turned into a call.
///
/// Use this when trying to recover from an error where the programmer may have
/// written just the name of a function instead of actually calling it.
///
/// \param E - The expression to examine.
/// \param ZeroArgCallReturnTy - If the expression can be turned into a call
///  with no arguments, this parameter is set to the type returned by such a
///  call; otherwise, it is set to an empty QualType.
/// \param NonTemplateOverloads - If the expression is an overloaded function
///  name, this parameter is populated with the decls of the various overloads.
bool Sema::isExprCallable(const Expr &E, QualType &ZeroArgCallReturnTy,
                          UnresolvedSetImpl &NonTemplateOverloads) {
  ZeroArgCallReturnTy = QualType();
  NonTemplateOverloads.clear();
  if (const OverloadExpr *Overloads = dyn_cast<OverloadExpr>(&E)) {
    for (OverloadExpr::decls_iterator it = Overloads->decls_begin(),
         DeclsEnd = Overloads->decls_end(); it != DeclsEnd; ++it) {
      // Our overload set may include TemplateDecls, which we'll ignore for our
      // present purpose.
      if (const FunctionDecl *OverloadDecl = dyn_cast<FunctionDecl>(*it)) {
        NonTemplateOverloads.addDecl(*it);
        if (OverloadDecl->getMinRequiredArguments() == 0)
          ZeroArgCallReturnTy = OverloadDecl->getResultType();
      }
    }
    return true;
  }

  if (const DeclRefExpr *DeclRef = dyn_cast<DeclRefExpr>(&E)) {
    if (const FunctionDecl *Fun = dyn_cast<FunctionDecl>(DeclRef->getDecl())) {
      if (Fun->getMinRequiredArguments() == 0)
        ZeroArgCallReturnTy = Fun->getResultType();
      return true;
    }
  }

  // We don't have an expression that's convenient to get a FunctionDecl from,
  // but we can at least check if the type is "function of 0 arguments".
  QualType ExprTy = E.getType();
  const FunctionType *FunTy = NULL;
  QualType PointeeTy = ExprTy->getPointeeType();
  if (!PointeeTy.isNull())
    FunTy = PointeeTy->getAs<FunctionType>();
  if (!FunTy)
    FunTy = ExprTy->getAs<FunctionType>();
  if (!FunTy && ExprTy == Context.BoundMemberTy) {
    // Look for the bound-member type.  If it's still overloaded, give up,
    // although we probably should have fallen into the OverloadExpr case above
    // if we actually have an overloaded bound member.
    QualType BoundMemberTy = Expr::findBoundMemberType(&E);
    if (!BoundMemberTy.isNull())
      FunTy = BoundMemberTy->castAs<FunctionType>();
  }

  if (const FunctionProtoType *FPT =
      dyn_cast_or_null<FunctionProtoType>(FunTy)) {
    if (FPT->getNumArgs() == 0)
      ZeroArgCallReturnTy = FunTy->getResultType();
    return true;
  }
  return false;
}

static void notePlausibleOverloads(Sema &S, SourceLocation Loc,
                                   const UnresolvedSetImpl &Overloads,
                                   bool (*IsPlausibleResult)(QualType)) {
  if (!IsPlausibleResult)
    return noteOverloads(S, Overloads, Loc);

  UnresolvedSet<2> PlausibleOverloads;
  for (OverloadExpr::decls_iterator It = Overloads.begin(),
         DeclsEnd = Overloads.end(); It != DeclsEnd; ++It) {
    const FunctionDecl *OverloadDecl = cast<FunctionDecl>(*It);
    QualType OverloadResultTy = OverloadDecl->getResultType();
    if (IsPlausibleResult(OverloadResultTy))
      PlausibleOverloads.addDecl(It.getDecl());
  }
  noteOverloads(S, PlausibleOverloads, Loc);
}

/// \brief Give notes for a set of overloads.
///
/// A companion to isExprCallable. In cases when the name that the programmer
/// wrote was an overloaded function, we may be able to make some guesses about
/// plausible overloads based on their return types; such guesses can be handed
/// off to this method to be emitted as notes.
///
/// \param Overloads - The overloads to note.
/// \param FinalNoteLoc - If we've suppressed printing some overloads due to
///  -fshow-overloads=best, this is the location to attach to the note about too
///  many candidates. Typically this will be the location of the original
///  ill-formed expression.
void Sema::NoteOverloads(const UnresolvedSetImpl &Overloads,
                         const SourceLocation FinalNoteLoc) {
  int ShownOverloads = 0;
  int SuppressedOverloads = 0;
  for (UnresolvedSetImpl::iterator It = Overloads.begin(),
       DeclsEnd = Overloads.end(); It != DeclsEnd; ++It) {
    // FIXME: Magic number for max shown overloads stolen from
    // OverloadCandidateSet::NoteCandidates.
    if (ShownOverloads >= 4 &&
        Diags.getShowOverloads() == DiagnosticsEngine::Ovl_Best) {
      ++SuppressedOverloads;
      continue;
    }
    Diag(cast<FunctionDecl>(*It)->getSourceRange().getBegin(),
         diag::note_member_ref_possible_intended_overload);
    ++ShownOverloads;
  }
  if (SuppressedOverloads)
    Diag(FinalNoteLoc, diag::note_ovl_too_many_candidates)
        << SuppressedOverloads;
}

/// \brief Give notes for a set of overloads.
///
/// A companion to isExprCallable. In cases when the name that the programmer
/// wrote was an overloaded function, we may be able to make some guesses about
/// plausible overloads based on their return types; such guesses can be handed
/// off to this method to be emitted as notes.
///
/// \param Overloads - The overloads to note.
/// \param FinalNoteLoc - If we've suppressed printing some overloads due to
///  -fshow-overloads=best, this is the location to attach to the note about too
///  many candidates. Typically this will be the location of the original
///  ill-formed expression.
static void noteOverloads(Sema &S, const UnresolvedSetImpl &Overloads,
                          const SourceLocation FinalNoteLoc) {
  int ShownOverloads = 0;
  int SuppressedOverloads = 0;
  for (UnresolvedSetImpl::iterator It = Overloads.begin(),
       DeclsEnd = Overloads.end(); It != DeclsEnd; ++It) {
    // FIXME: Magic number for max shown overloads stolen from
    // OverloadCandidateSet::NoteCandidates.
    if (ShownOverloads >= 4 && S.Diags.getShowOverloads() == Ovl_Best) {
      ++SuppressedOverloads;
      continue;
    }

    NamedDecl *Fn = (*It)->getUnderlyingDecl();
    S.Diag(Fn->getLocation(), diag::note_possible_target_of_call);
    ++ShownOverloads;
  }

  if (SuppressedOverloads)
    S.Diag(FinalNoteLoc, diag::note_ovl_too_many_candidates)
      << SuppressedOverloads;
}

/// \brief Figure out if an expression could be turned into a call.
///
/// Use this when trying to recover from an error where the programmer may have
/// written just the name of a function instead of actually calling it.
///
/// \param E - The expression to examine.
/// \param ZeroArgCallReturnTy - If the expression can be turned into a call
///  with no arguments, this parameter is set to the type returned by such a
///  call; otherwise, it is set to an empty QualType.
/// \param OverloadSet - If the expression is an overloaded function
///  name, this parameter is populated with the decls of the various overloads.
bool Sema::isExprCallable(const Expr &E, QualType &ZeroArgCallReturnTy,
                          UnresolvedSetImpl &OverloadSet) {
  ZeroArgCallReturnTy = QualType();
  OverloadSet.clear();

  if (E.getType() == Context.OverloadTy) {
    OverloadExpr::FindResult FR = OverloadExpr::find(const_cast<Expr*>(&E));
    const OverloadExpr *Overloads = FR.Expression;

    for (OverloadExpr::decls_iterator it = Overloads->decls_begin(),
         DeclsEnd = Overloads->decls_end(); it != DeclsEnd; ++it) {
      OverloadSet.addDecl(*it);

      // Check whether the function is a non-template which takes no
      // arguments.
      if (const FunctionDecl *OverloadDecl
            = dyn_cast<FunctionDecl>((*it)->getUnderlyingDecl())) {
        if (OverloadDecl->getMinRequiredArguments() == 0)
          ZeroArgCallReturnTy = OverloadDecl->getResultType();
      }
    }

    // Ignore overloads that are pointer-to-member constants.
    if (FR.HasFormOfMemberPointer)
      return false;

    return true;
  }

  if (const DeclRefExpr *DeclRef = dyn_cast<DeclRefExpr>(E.IgnoreParens())) {
    if (const FunctionDecl *Fun = dyn_cast<FunctionDecl>(DeclRef->getDecl())) {
      if (Fun->getMinRequiredArguments() == 0)
        ZeroArgCallReturnTy = Fun->getResultType();
      return true;
    }
  }

  // We don't have an expression that's convenient to get a FunctionDecl from,
  // but we can at least check if the type is "function of 0 arguments".
  QualType ExprTy = E.getType();
  const FunctionType *FunTy = NULL;
  QualType PointeeTy = ExprTy->getPointeeType();
  if (!PointeeTy.isNull())
    FunTy = PointeeTy->getAs<FunctionType>();
  if (!FunTy)
    FunTy = ExprTy->getAs<FunctionType>();
  if (!FunTy && ExprTy == Context.BoundMemberTy) {
    // Look for the bound-member type.  If it's still overloaded, give up,
    // although we probably should have fallen into the OverloadExpr case above
    // if we actually have an overloaded bound member.
    QualType BoundMemberTy = Expr::findBoundMemberType(&E);
    if (!BoundMemberTy.isNull())
      FunTy = BoundMemberTy->castAs<FunctionType>();
  }

  if (const FunctionProtoType *FPT =
      dyn_cast_or_null<FunctionProtoType>(FunTy)) {
    if (FPT->getNumArgs() == 0)
      ZeroArgCallReturnTy = FunTy->getResultType();
    return true;
  }
  return false;
}