path: root/gcc/ada/sem_aux.adb

------------------------------------------------------------------------------
--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
--                                                                          --
--                              S E M _ A U X                               --
--                                                                          --
--                                 B o d y                                  --
--                                                                          --
--          Copyright (C) 1992-2010, Free Software Foundation, Inc.         --
--                                                                          --
-- GNAT is free software;  you can  redistribute it  and/or modify it under --
-- terms of the  GNU General Public License as published  by the Free Soft- --
-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
-- for  more details.  You should have  received  a copy of the GNU General --
-- Public License  distributed with GNAT; see file COPYING3.  If not, go to --
-- http://www.gnu.org/licenses for a complete copy of the license.          --
--                                                                          --
-- As a special exception,  if other files  instantiate  generics from this --
-- unit, or you link  this unit with other files  to produce an executable, --
-- this  unit  does not  by itself cause  the resulting  executable  to  be --
-- covered  by the  GNU  General  Public  License.  This exception does not --
-- however invalidate  any other reasons why  the executable file  might be --
-- covered by the  GNU Public License.                                      --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc.      --
--                                                                          --
------------------------------------------------------------------------------

with Atree;  use Atree;
with Einfo;  use Einfo;
with Namet;  use Namet;
with Sinfo;  use Sinfo;
with Snames; use Snames;
with Stand;  use Stand;

package body Sem_Aux is

   ----------------------
   -- Ancestor_Subtype --
   ----------------------

   function Ancestor_Subtype (Typ : Entity_Id) return Entity_Id is
   begin
      --  If this is first subtype, or is a base type, then there is no
      --  ancestor subtype, so we return Empty to indicate this fact.

      if Is_First_Subtype (Typ) or else Is_Base_Type (Typ) then
         return Empty;
      end if;

      declare
         D : constant Node_Id := Declaration_Node (Typ);

      begin
         --  If we have a subtype declaration, get the ancestor subtype

         if Nkind (D) = N_Subtype_Declaration then
            if Nkind (Subtype_Indication (D)) = N_Subtype_Indication then
               return Entity (Subtype_Mark (Subtype_Indication (D)));
            else
               return Entity (Subtype_Indication (D));
            end if;

         --  If not, then no subtype indication is available

         else
            return Empty;
         end if;
      end;
   end Ancestor_Subtype;

   --------------------
   -- Available_View --
   --------------------

   function Available_View (Typ : Entity_Id) return Entity_Id is
   begin
      if Is_Incomplete_Type (Typ)
        and then Present (Non_Limited_View (Typ))
      then
         --  The non-limited view may itself be an incomplete type, in which
         --  case get its full view.

         return Get_Full_View (Non_Limited_View (Typ));

      elsif Is_Class_Wide_Type (Typ)
        and then Is_Incomplete_Type (Etype (Typ))
        and then Present (Non_Limited_View (Etype (Typ)))
      then
         return Class_Wide_Type (Non_Limited_View (Etype (Typ)));

      else
         return Typ;
      end if;
   end Available_View;

   --------------------
   -- Constant_Value --
   --------------------

   function Constant_Value (Ent : Entity_Id) return Node_Id is
      D      : constant Node_Id := Declaration_Node (Ent);
      Full_D : Node_Id;

   begin
      --  If we have no declaration node, then return no constant value. Not
      --  clear how this can happen, but it does sometimes and this is the
      --  safest approach.

      if No (D) then
         return Empty;

      --  Normal case where a declaration node is present

      elsif Nkind (D) = N_Object_Renaming_Declaration then
         return Renamed_Object (Ent);

      --  If this is a component declaration whose entity is a constant, it is
      --  a prival within a protected function (and so has no constant value).

      elsif Nkind (D) = N_Component_Declaration then
         return Empty;

      --  If there is an expression, return it

      elsif Present (Expression (D)) then
         return (Expression (D));

      --  For a constant, see if we have a full view

      elsif Ekind (Ent) = E_Constant
        and then Present (Full_View (Ent))
      then
         Full_D := Parent (Full_View (Ent));

         --  The full view may have been rewritten as an object renaming

         if Nkind (Full_D) = N_Object_Renaming_Declaration then
            return Name (Full_D);
         else
            return Expression (Full_D);
         end if;

      --  Otherwise we have no expression to return

      else
         return Empty;
      end if;
   end Constant_Value;

   -----------------------------
   -- Enclosing_Dynamic_Scope --
   -----------------------------

   function Enclosing_Dynamic_Scope (Ent : Entity_Id) return Entity_Id is
      S : Entity_Id;

   begin
      --  The following test is an error defense against some syntax errors
      --  that can leave scopes very messed up.

      if Ent = Standard_Standard then
         return Ent;
      end if;

      --  Normal case, search enclosing scopes

      --  Note: the test for Present (S) should not be required, it defends
      --  against an ill-formed tree.

      S := Scope (Ent);
      loop
         --  If we somehow got an empty value for Scope, the tree must be
         --  malformed. Rather than blow up we return Standard in this case.

         if No (S) then
            return Standard_Standard;

         --  Quit if we get to standard or a dynamic scope

         elsif S = Standard_Standard
           or else Is_Dynamic_Scope (S)
         then
            return S;

         --  Otherwise keep climbing

         else
            S := Scope (S);
         end if;
      end loop;
   end Enclosing_Dynamic_Scope;

   ------------------------
   -- First_Discriminant --
   ------------------------

   function First_Discriminant (Typ : Entity_Id) return Entity_Id is
      Ent : Entity_Id;

   begin
      pragma Assert
        (Has_Discriminants (Typ) or else Has_Unknown_Discriminants (Typ));

      Ent := First_Entity (Typ);

      --  The discriminants are not necessarily contiguous, because access
      --  discriminants will generate itypes. They are not the first entities
      --  either, because tag and controller record must be ahead of them.

      if Chars (Ent) = Name_uTag then
         Ent := Next_Entity (Ent);
      end if;

      if Chars (Ent) = Name_uController then
         Ent := Next_Entity (Ent);
      end if;

      --  Skip all hidden stored discriminants if any

      while Present (Ent) loop
         exit when Ekind (Ent) = E_Discriminant
           and then not Is_Completely_Hidden (Ent);

         Ent := Next_Entity (Ent);
      end loop;

      pragma Assert (Ekind (Ent) = E_Discriminant);

      return Ent;
   end First_Discriminant;

   -------------------------------
   -- First_Stored_Discriminant --
   -------------------------------

   function First_Stored_Discriminant (Typ : Entity_Id) return Entity_Id is
      Ent : Entity_Id;

      function Has_Completely_Hidden_Discriminant
        (Typ : Entity_Id) return Boolean;
      --  Scans the Discriminants to see whether any are Completely_Hidden
      --  (the mechanism for describing non-specified stored discriminants)

      ----------------------------------------
      -- Has_Completely_Hidden_Discriminant --
      ----------------------------------------

      function Has_Completely_Hidden_Discriminant
        (Typ : Entity_Id) return Boolean
      is
         Ent : Entity_Id;

      begin
         pragma Assert (Ekind (Typ) = E_Discriminant);

         Ent := Typ;
         while Present (Ent) and then Ekind (Ent) = E_Discriminant loop
            if Is_Completely_Hidden (Ent) then
               return True;
            end if;

            Ent := Next_Entity (Ent);
         end loop;

         return False;
      end Has_Completely_Hidden_Discriminant;

   --  Start of processing for First_Stored_Discriminant

   begin
      pragma Assert
        (Has_Discriminants (Typ)
          or else Has_Unknown_Discriminants (Typ));

      Ent := First_Entity (Typ);

      if Chars (Ent) = Name_uTag then
         Ent := Next_Entity (Ent);
      end if;

      if Chars (Ent) = Name_uController then
         Ent := Next_Entity (Ent);
      end if;

      if Has_Completely_Hidden_Discriminant (Ent) then

         while Present (Ent) loop
            exit when Is_Completely_Hidden (Ent);
            Ent := Next_Entity (Ent);
         end loop;

      end if;

      pragma Assert (Ekind (Ent) = E_Discriminant);

      return Ent;
   end First_Stored_Discriminant;

   -------------------
   -- First_Subtype --
   -------------------

   function First_Subtype (Typ : Entity_Id) return Entity_Id is
      B   : constant Entity_Id := Base_Type (Typ);
      F   : constant Node_Id   := Freeze_Node (B);
      Ent : Entity_Id;

   begin
      --  If the base type has no freeze node, it is a type in Standard, and
      --  always acts as its own first subtype, except where it is one of the
      --  predefined integer types. If the type is formal, it is also a first
      --  subtype, and its base type has no freeze node. On the other hand, a
      --  subtype of a generic formal is not its own first subtype. Its base
      --  type, if anonymous, is attached to the formal type decl. from which
      --  the first subtype is obtained.

      if No (F) then
         if B = Base_Type (Standard_Integer) then
            return Standard_Integer;

         elsif B = Base_Type (Standard_Long_Integer) then
            return Standard_Long_Integer;

         elsif B = Base_Type (Standard_Short_Short_Integer) then
            return Standard_Short_Short_Integer;

         elsif B = Base_Type (Standard_Short_Integer) then
            return Standard_Short_Integer;

         elsif B = Base_Type (Standard_Long_Long_Integer) then
            return Standard_Long_Long_Integer;

         elsif Is_Generic_Type (Typ) then
            if Present (Parent (B)) then
               return Defining_Identifier (Parent (B));
            else
               return Defining_Identifier (Associated_Node_For_Itype (B));
            end if;

         else
            return B;
         end if;

      --  Otherwise we check the freeze node, if it has a First_Subtype_Link
      --  then we use that link, otherwise (happens with some Itypes), we use
      --  the base type itself.

      else
         Ent := First_Subtype_Link (F);

         if Present (Ent) then
            return Ent;
         else
            return B;
         end if;
      end if;
   end First_Subtype;

   -------------------------
   -- First_Tag_Component --
   -------------------------

   function First_Tag_Component (Typ : Entity_Id) return Entity_Id is
      Comp : Entity_Id;
      Ctyp : Entity_Id;

   begin
      Ctyp := Typ;
      pragma Assert (Is_Tagged_Type (Ctyp));

      if Is_Class_Wide_Type (Ctyp) then
         Ctyp := Root_Type (Ctyp);
      end if;

      if Is_Private_Type (Ctyp) then
         Ctyp := Underlying_Type (Ctyp);

         --  If the underlying type is missing then the source program has
         --  errors and there is nothing else to do (the full-type declaration
         --  associated with the private type declaration is missing).

         if No (Ctyp) then
            return Empty;
         end if;
      end if;

      Comp := First_Entity (Ctyp);
      while Present (Comp) loop
         if Is_Tag (Comp) then
            return Comp;
         end if;

         Comp := Next_Entity (Comp);
      end loop;

      --  No tag component found

      return Empty;
   end First_Tag_Component;

   ----------------
   -- Initialize --
   ----------------

   procedure Initialize is
   begin
      Obsolescent_Warnings.Init;
   end Initialize;

   ---------------------
   -- Is_By_Copy_Type --
   ---------------------

   function Is_By_Copy_Type (Ent : Entity_Id) return Boolean is
   begin
      --  If Id is a private type whose full declaration has not been seen,
      --  we assume for now that it is not a By_Copy type. Clearly this
      --  attribute should not be used before the type is frozen, but it is
      --  needed to build the associated record of a protected type. Another
      --  place where some lookahead for a full view is needed ???

      return
        Is_Elementary_Type (Ent)
          or else (Is_Private_Type (Ent)
                     and then Present (Underlying_Type (Ent))
                     and then Is_Elementary_Type (Underlying_Type (Ent)));
   end Is_By_Copy_Type;

   --------------------------
   -- Is_By_Reference_Type --
   --------------------------

   function Is_By_Reference_Type (Ent : Entity_Id) return Boolean is
      Btype : constant Entity_Id := Base_Type (Ent);

   begin
      if Error_Posted (Ent)
        or else Error_Posted (Btype)
      then
         return False;

      elsif Is_Private_Type (Btype) then
         declare
            Utyp : constant Entity_Id := Underlying_Type (Btype);
         begin
            if No (Utyp) then
               return False;
            else
               return Is_By_Reference_Type (Utyp);
            end if;
         end;

      elsif Is_Incomplete_Type (Btype) then
         declare
            Ftyp : constant Entity_Id := Full_View (Btype);
         begin
            if No (Ftyp) then
               return False;
            else
               return Is_By_Reference_Type (Ftyp);
            end if;
         end;

      elsif Is_Concurrent_Type (Btype) then
         return True;

      elsif Is_Record_Type (Btype) then
         if Is_Limited_Record (Btype)
           or else Is_Tagged_Type (Btype)
           or else Is_Volatile (Btype)
         then
            return True;

         else
            declare
               C : Entity_Id;

            begin
               C := First_Component (Btype);
               while Present (C) loop
                  if Is_By_Reference_Type (Etype (C))
                    or else Is_Volatile (Etype (C))
                  then
                     return True;
                  end if;

                  C := Next_Component (C);
               end loop;
            end;

            return False;
         end if;

      elsif Is_Array_Type (Btype) then
         return
           Is_Volatile (Btype)
             or else Is_By_Reference_Type (Component_Type (Btype))
             or else Is_Volatile (Component_Type (Btype))
             or else Has_Volatile_Components (Btype);

      else
         return False;
      end if;
   end Is_By_Reference_Type;

   ---------------------
   -- Is_Derived_Type --
   ---------------------

   function Is_Derived_Type (Ent : E) return B is
      Par : Node_Id;

   begin
      if Is_Type (Ent)
        and then Base_Type (Ent) /= Root_Type (Ent)
        and then not Is_Class_Wide_Type (Ent)
      then
         if not Is_Numeric_Type (Root_Type (Ent)) then
            return True;

         else
            Par := Parent (First_Subtype (Ent));

            return Present (Par)
              and then Nkind (Par) = N_Full_Type_Declaration
              and then Nkind (Type_Definition (Par)) =
                         N_Derived_Type_Definition;
         end if;

      else
         return False;
      end if;
   end Is_Derived_Type;

   -----------------------
   -- Is_Generic_Formal --
   -----------------------

   function Is_Generic_Formal (E : Entity_Id) return Boolean is
      Kind : Node_Kind;
   begin
      if No (E) then
         return False;
      else
         Kind := Nkind (Parent (E));
         return
           Nkind_In (Kind, N_Formal_Object_Declaration,
                           N_Formal_Package_Declaration,
                           N_Formal_Type_Declaration)
             or else Is_Formal_Subprogram (E);
      end if;
   end Is_Generic_Formal;

   ---------------------------
   -- Is_Indefinite_Subtype --
   ---------------------------

   function Is_Indefinite_Subtype (Ent : Entity_Id) return Boolean is
      K : constant Entity_Kind := Ekind (Ent);

   begin
      if Is_Constrained (Ent) then
         return False;

      elsif K in Array_Kind
        or else K in Class_Wide_Kind
        or else Has_Unknown_Discriminants (Ent)
      then
         return True;

      --  Known discriminants: indefinite if there are no default values

      elsif K in Record_Kind
        or else Is_Incomplete_Or_Private_Type (Ent)
        or else Is_Concurrent_Type (Ent)
      then
         return (Has_Discriminants (Ent)
           and then
             No (Discriminant_Default_Value (First_Discriminant (Ent))));

      else
         return False;
      end if;
   end Is_Indefinite_Subtype;

   -------------------------------
   -- Is_Immutably_Limited_Type --
   -------------------------------

   function Is_Immutably_Limited_Type (Ent : Entity_Id) return Boolean is
      Btype : constant Entity_Id := Base_Type (Ent);

   begin
      if Is_Limited_Record (Btype) then
         return True;

      elsif Ekind (Btype) = E_Limited_Private_Type
        and then Nkind (Parent (Btype)) = N_Formal_Type_Declaration
      then
         return not In_Package_Body (Scope ((Btype)));
      end if;

      if Is_Private_Type (Btype) then

         --  AI05-0063: A type derived from a limited private formal type is
         --  not immutably limited in a generic body.

         if Is_Derived_Type (Btype)
           and then Is_Generic_Type (Etype (Btype))
         then
            if not Is_Limited_Type (Etype (Btype)) then
               return False;

            --  A descendant of a limited formal type is not immutably limited
            --  in the generic body, or in the body of a generic child.

            elsif Ekind (Scope (Etype (Btype))) = E_Generic_Package then
               return not In_Package_Body (Scope (Btype));

            else
               return False;
            end if;

         else
            declare
               Utyp : constant Entity_Id := Underlying_Type (Btype);
            begin
               if No (Utyp) then
                  return False;
               else
                  return Is_Immutably_Limited_Type (Utyp);
               end if;
            end;
         end if;

      elsif Is_Concurrent_Type (Btype) then
         return True;

      elsif Is_Record_Type (Btype) then

         --  Note that we return True for all limited interfaces, even though
         --  (unsynchronized) limited interfaces can have descendants that are
         --  nonlimited, because this is a predicate on the type itself, and
         --  things like functions with limited interface results need to be
         --  handled as build in place even though they might return objects
         --  of a type that is not inherently limited.

         if Is_Class_Wide_Type (Btype) then
            return Is_Immutably_Limited_Type (Root_Type (Btype));

         else
            declare
               C : Entity_Id;

            begin
               C := First_Component (Btype);
               while Present (C) loop

                  --  Don't consider components with interface types (which can
                  --  only occur in the case of a _parent component anyway).
                  --  They don't have any components, plus it would cause this
                  --  function to return true for nonlimited types derived from
                  --  limited interfaces.

                  if not Is_Interface (Etype (C))
                    and then Is_Immutably_Limited_Type (Etype (C))
                  then
                     return True;
                  end if;

                  C := Next_Component (C);
               end loop;
            end;

            return False;
         end if;

      elsif Is_Array_Type (Btype) then
         return Is_Immutably_Limited_Type (Component_Type (Btype));

      else
         return False;
      end if;
   end Is_Immutably_Limited_Type;

   ---------------------
   -- Is_Limited_Type --
   ---------------------

   function Is_Limited_Type (Ent : Entity_Id) return Boolean is
      Btype : constant E := Base_Type (Ent);
      Rtype : constant E := Root_Type (Btype);

   begin
      if not Is_Type (Ent) then
         return False;

      elsif Ekind (Btype) = E_Limited_Private_Type
        or else Is_Limited_Composite (Btype)
      then
         return True;

      elsif Is_Concurrent_Type (Btype) then
         return True;

         --  The Is_Limited_Record flag normally indicates that the type is
         --  limited. The exception is that a type does not inherit limitedness
         --  from its interface ancestor. So the type may be derived from a
         --  limited interface, but is not limited.

      elsif Is_Limited_Record (Ent)
        and then not Is_Interface (Ent)
      then
         return True;

      --  Otherwise we will look around to see if there is some other reason
      --  for it to be limited, except that if an error was posted on the
      --  entity, then just assume it is non-limited, because it can cause
      --  trouble to recurse into a murky erroneous entity!

      elsif Error_Posted (Ent) then
         return False;

      elsif Is_Record_Type (Btype) then

         if Is_Limited_Interface (Ent) then
            return True;

         --  AI-419: limitedness is not inherited from a limited interface

         elsif Is_Limited_Record (Rtype) then
            return not Is_Interface (Rtype)
              or else Is_Protected_Interface (Rtype)
              or else Is_Synchronized_Interface (Rtype)
              or else Is_Task_Interface (Rtype);

         elsif Is_Class_Wide_Type (Btype) then
            return Is_Limited_Type (Rtype);

         else
            declare
               C : E;

            begin
               C := First_Component (Btype);
               while Present (C) loop
                  if Is_Limited_Type (Etype (C)) then
                     return True;
                  end if;

                  C := Next_Component (C);
               end loop;
            end;

            return False;
         end if;

      elsif Is_Array_Type (Btype) then
         return Is_Limited_Type (Component_Type (Btype));

      else
         return False;
      end if;
   end Is_Limited_Type;

   ----------------------
   -- Nearest_Ancestor --
   ----------------------

   function Nearest_Ancestor (Typ : Entity_Id) return Entity_Id is
         D : constant Node_Id := Declaration_Node (Typ);

   begin
      --  If we have a subtype declaration, get the ancestor subtype

      if Nkind (D) = N_Subtype_Declaration then
         if Nkind (Subtype_Indication (D)) = N_Subtype_Indication then
            return Entity (Subtype_Mark (Subtype_Indication (D)));
         else
            return Entity (Subtype_Indication (D));
         end if;

      --  If derived type declaration, find who we are derived from

      elsif Nkind (D) = N_Full_Type_Declaration
        and then Nkind (Type_Definition (D)) = N_Derived_Type_Definition
      then
         declare
            DTD : constant Entity_Id := Type_Definition (D);
            SI  : constant Entity_Id := Subtype_Indication (DTD);
         begin
            if Is_Entity_Name (SI) then
               return Entity (SI);
            else
               return Entity (Subtype_Mark (SI));
            end if;
         end;

      --  Otherwise, nothing useful to return, return Empty

      else
         return Empty;
      end if;
   end Nearest_Ancestor;

   ---------------------------
   -- Nearest_Dynamic_Scope --
   ---------------------------

   function Nearest_Dynamic_Scope (Ent : Entity_Id) return Entity_Id is
   begin
      if Is_Dynamic_Scope (Ent) then
         return Ent;
      else
         return Enclosing_Dynamic_Scope (Ent);
      end if;
   end Nearest_Dynamic_Scope;

   ------------------------
   -- Next_Tag_Component --
   ------------------------

   function Next_Tag_Component (Tag : Entity_Id) return Entity_Id is
      Comp : Entity_Id;

   begin
      pragma Assert (Is_Tag (Tag));

      --  Loop to look for next tag component

      Comp := Next_Entity (Tag);
      while Present (Comp) loop
         if Is_Tag (Comp) then
            pragma Assert (Chars (Comp) /= Name_uTag);
            return Comp;
         end if;

         Comp := Next_Entity (Comp);
      end loop;

      --  No tag component found

      return Empty;
   end Next_Tag_Component;

   --------------------------
   -- Number_Discriminants --
   --------------------------

   function Number_Discriminants (Typ : Entity_Id) return Pos is
      N     : Int;
      Discr : Entity_Id;

   begin
      N := 0;
      Discr := First_Discriminant (Typ);
      while Present (Discr) loop
         N := N + 1;
         Discr := Next_Discriminant (Discr);
      end loop;

      return N;
   end Number_Discriminants;

   ---------------
   -- Tree_Read --
   ---------------

   procedure Tree_Read is
   begin
      Obsolescent_Warnings.Tree_Read;
   end Tree_Read;

   ----------------
   -- Tree_Write --
   ----------------

   procedure Tree_Write is
   begin
      Obsolescent_Warnings.Tree_Write;
   end Tree_Write;

   --------------------
   -- Ultimate_Alias --
   --------------------

   function Ultimate_Alias (Prim : Entity_Id) return Entity_Id is
      E : Entity_Id := Prim;

   begin
      while Present (Alias (E)) loop
         pragma Assert (Alias (E) /= E);
         E := Alias (E);
      end loop;

      return E;
   end Ultimate_Alias;

end Sem_Aux;