------------------------------------------------------------------------------
--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
--                                                                          --
--                               I T Y P E S                                --
--                                                                          --
--                                 S p e c                                  --
--                                                                          --
--          Copyright (C) 1992-2005, 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- --
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-- Boston, MA 02110-1301, USA.                                              --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc.      --
--                                                                          --
------------------------------------------------------------------------------

--  This package contains declarations for handling of implicit types

with Einfo;    use Einfo;
with Sem_Util; use Sem_Util;
with Types;    use Types;

package Itypes is

   --------------------
   -- Implicit Types --
   --------------------

   --  Implicit types are types and subtypes created by the semantic phase
   --  or the expander to reflect the underlying semantics. These could be
   --  generated by building trees for corresponding declarations and then
   --  analyzing these trees, but there are three reasons for not doing this:

   --    1. The declarations would require more tree nodes

   --    2. In some cases, the elaboration of these types is associated
   --       with internal nodes in the tree.

   --    3. For some types, notably class wide types, there is no Ada
   --       declaration that would correspond to the desired entity.

   --  So instead, implicit types are constructed by simply creating an
   --  appropriate entity with the help of routines in this package. These
   --  entities are fully decorated, as described in Einfo (just as though
   --  they had been created by the normal analysis procedure).

   --  The type declaration declaring an Itype must be analyzed with checks
   --  off because this declaration has not been inserted in the tree (if it
   --  has been then it is not an itype), and hence checks that would be
   --  generated during the analysis cannot be inserted in the tree. At any
   --  rate, itype analysis should always be done with checks off, otherwise
   --  duplicate checks will most likely be emitted.

   --  Unlike types declared explicitly, implicit types are defined on first
   --  use, which means that Gigi detects the use of such types, and defines
   --  them at the point of the first use automatically.

   --  Although Itypes are not explicitly declared, they are associated with
   --  a specific node in the tree (roughly the node that caused them to be
   --  created), via the Associated_Node_For_Itype field. This association is
   --  used particularly by New_Copy_Tree, which uses it to determine whether
   --  or not to copy a referenced Itype. If the associated node is part of
   --  the tree to be copied by New_Copy_Tree, then (since the idea of the
   --  call to New_Copy_Tree is to create a complete duplicate of a tree,
   --  as though it had appeared separately in the source), the Itype in
   --  question is duplicated as part of the New_Copy_Tree processing.

   -----------------
   -- Subprograms --
   -----------------

   function Create_Itype
     (Ekind        : Entity_Kind;
      Related_Nod  : Node_Id;
      Related_Id   : Entity_Id := Empty;
      Suffix       : Character := ' ';
      Suffix_Index : Nat       := 0;
      Scope_Id     : Entity_Id := Current_Scope) return Entity_Id;
   --  Used to create a new Itype.
   --
   --   Related_Nod is the node for which this Itype was created.  It is
   --   set as the Associated_Node_For_Itype of the new itype.  The Sloc of
   --   the new Itype is that of this node.
   --
   --   Related_Id is present only if the implicit type name may be referenced
   --   as a public symbol, and thus needs a unique external name. The name
   --   is created by a call to:
   --
   --     New_External_Name (Chars (Related_Id), Suffix, Suffix_Index, 'T')
   --
   --   If the implicit type does not need an external name, then the
   --   Related_Id parameter is omitted (and hence Empty). In this case
   --   Suffix and Suffix_Index are ignored and the implicit type name is
   --   created by a call to New_Internal_Name ('T').
   --
   --   Note that in all cases, the name starts with "T". This is used
   --   to identify implicit types in the error message handling circuits.
   --
   --  The Scope_Id parameter specifies the scope of the created type, and
   --  is normally the Current_Scope as shown, but can be set otherwise.

   ---------------------------------
   -- Create_Null_Excluding_Itype --
   ---------------------------------

   function Create_Null_Excluding_Itype
      (T           : Entity_Id;
       Related_Nod : Node_Id;
       Scope_Id    : Entity_Id := Current_Scope) return Entity_Id;
   --  Ada 2005 (AI-231): T is an access type and this subprogram creates and
   --  returns an internal access-subtype declaration of T that has the null
   --  exclusion attribute set to True.
   --
   --  Usage of null-excluding itypes
   --  ------------------------------
   --
   --      type T1 is access ...
   --      type T2 is not null T1;
   --
   --      type Rec is record
   --         Comp : not null T1;
   --      end record;
   --
   --      type Arr is array (...) of not null T1;
   --
   --  Instead of associating the not-null attribute with the defining ids of
   --  these declarations, we generate an internal subtype declaration of T1
   --  that has the null exclusion attribute set to true.

end Itypes;