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--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--                              P R J . E X T                               --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--          Copyright (C) 2000-2011, 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.          --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

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--  Subprograms to set, get and cache external references, to be used as

--  External functions in project files.

with GNAT.Dynamic_HTables;

package Prj.Ext is

   -------------------------

   -- External References --

   -------------------------

   --  External references influence the way a project tree is processed (in

   --  particular they provide the values for the typed string variables that

   --  are then used in case constructions).

   --  External references are project-tree specific, so that when multiple

   --  trees are loaded in parallel we can have different scenarios (or even

   --  load the same tree twice and see different views of it).

   type External_References is private;

   No_External_Refs : constant External_References;

   procedure Initialize

     (Self      : out External_References;

      Copy_From : External_References := No_External_Refs);

   --  Initialize Self, and copy all values from Copy_From if needed.

   --  This has no effect if Self was already initialized.

   procedure Free (Self : in out External_References);

   --  Free memory used by Self

   type External_Source is

     (From_Command_Line,

      From_Environment,

      From_External_Attribute);

   --  Indicates where was the value of an external reference defined. They are

   --  prioritized in that order, so that a user can always use the command

   --  line to override a value coming from his environment, or an environment

   --  variable to override a value defined in an aggregate project through the

   --  "for External()..." attribute.

   procedure Add

     (Self          : External_References;

      External_Name : String;

      Value         : String;

      Source        : External_Source := External_Source'First);

   --  Add an external reference (or modify an existing one). No overriding is

   --  done if the Source's priority is less than the one used to previously

   --  set the value of the variable. The default for Source is such that

   --  overriding always occurs.

   function Value_Of

     (Self          : External_References;

      External_Name : Name_Id;

      With_Default  : Name_Id := No_Name)

      return          Name_Id;

   --  Get the value of an external reference, and cache it for future uses

   function Check

     (Self        : External_References;

      Declaration : String) return Boolean;

   --  Check that an external declaration <external>=<value> is correct.

   --  If it is correct, the external reference is Added.

   procedure Reset (Self : External_References);

   --  Clear the internal data structure that stores the external references

   --  and free any allocated memory.

private

   --  Use a Static_HTable, rather than a Simple_HTable

   --  The issue is that we need to be able to copy the contents of the table

   --  (in Initialize), but this isn't doable for Simple_HTable for which

   --  iterators do not return the key.

   type Name_To_Name;

   type Name_To_Name_Ptr is access all Name_To_Name;

   type Name_To_Name is record

      Key    : Name_Id;

      Value  : Name_Id;

      Source : External_Source;

      Next   : Name_To_Name_Ptr;

   end record;

   procedure Set_Next (E : Name_To_Name_Ptr; Next : Name_To_Name_Ptr);

   function  Next     (E : Name_To_Name_Ptr) return Name_To_Name_Ptr;

   function  Get_Key  (E : Name_To_Name_Ptr) return Name_Id;

   package Name_To_Name_HTable is new GNAT.Dynamic_HTables.Static_HTable

     (Header_Num => Header_Num,

      Element    => Name_To_Name,

      Elmt_Ptr   => Name_To_Name_Ptr,

      Null_Ptr   => null,

      Set_Next   => Set_Next,

      Next       => Next,

      Key        => Name_Id,

      Get_Key    => Get_Key,

      Hash       => Hash,

      Equal      => "=");

   --  General type for htables associating name_id to name_id. This is in

   --  particular used to store the values of external references.

   type Instance_Access is access all Name_To_Name_HTable.Instance;

   type External_References is record

      Refs : Instance_Access;

      --  External references are stored in this hash table (and manipulated

      --  through subprogrames in prj-ext.ads). External references are

      --  project-tree specific so that one can load the same tree twice but

      --  have two views of it, for instance.

   end record;

   No_External_Refs : constant External_References := (Refs => null);

end Prj.Ext;