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--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--                             S E M _ E L A B                              --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--          Copyright (C) 1997-2008, 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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--  This package contains the routines used to deal with issuing warnings

--  for cases of calls that may require warnings about possible access

--  before elaboration.

with Types; use Types;

package Sem_Elab is

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

   -- Description of Approach --

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

   --  Every non-static call that is encountered by Sem_Res results in

   --  a call to Check_Elab_Call, with N being the call node, and Outer

   --  set to its default value of True.

   --  The goal of Check_Elab_Call is to determine whether or not the

   --  call in question can generate an access before elaboration

   --  error (raising Program_Error) either by directly calling a

   --  subprogram whose body has not yet been elaborated, or indirectly,

   --  by calling a subprogram whose body has been elaborated, but which

   --  contains a call to such a subprogram.

   --  The only calls that we need to look at at the outer level are

   --  calls that occur in elaboration code. There are two cases. The

   --  call can be at the outer level of elaboration code, or it can

   --  be within another unit, e.g. the elaboration code of a subprogram.

   --  In the case of an elaboration call at the outer level, we must

   --  trace all calls to outer level routines either within the current

   --  unit or to other units that are with'ed. For calls within the

   --  current unit, we can determine if the body has been elaborated

   --  or not, and if it has not, then a warning is generated.

   --  Note that there are two subcases. If the original call directly

   --  calls a subprogram whose body has not been elaborated, then we

   --  know that an ABE will take place, and we replace the call by

   --  a raise of Program_Error. If the call is indirect, then we don't

   --  know that the PE will be raised, since the call might be guarded

   --  by a conditional. In this case we set Do_Elab_Check on the call

   --  so that a dynamic check is generated, and output a warning.

   --  For calls to a subprogram in a with'ed unit, we require that

   --  a pragma Elaborate_All or pragma Elaborate be present, or that

   --  the referenced unit have a pragma Preelaborate, pragma Pure, or

   --  pragma Elaborate_Body. If none of these conditions is met, then

   --  a warning is generated that a pragma Elaborate_All may be needed.

   --  For the case of an elaboration call at some inner level, we are

   --  interested in tracing only calls to subprograms at the same level,

   --  i.e. those that can be called during elaboration. Any calls to

   --  outer level routines cannot cause ABE's as a result of the original

   --  call (there might be an outer level call to the subprogram from

   --  outside that causes the ABE, but that gets analyzed separately).

   --  Note that we never trace calls to inner level subprograms, since

   --  these cannot result in ABE's unless there is an elaboration problem

   --  at a lower level, which will be separately detected.

   --  Note on pragma Elaborate. The checking here assumes that a pragma

   --  Elaborate on a with'ed unit guarantees that subprograms within the

   --  unit can be called without causing an ABE. This is not in fact the

   --  case since pragma Elaborate does not guarantee the transitive

   --  coverage guaranteed by Elaborate_All. However, we leave this issue

   --  up to the binder, which has generates warnings if there are possible

   --  problems in the use of pragma Elaborate.

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

   -- Instantiation Elaboration Errors --

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

   --  A special case arises when an instantiation appears in a context

   --  that is known to be before the body is elaborated, e.g.

   --       generic package x is ...

   --       ...

   --       package xx is new x;

   --       ...

   --       package body x is ...

   --  In this situation it is certain that an elaboration error will

   --  occur, and an unconditional raise Program_Error statement is

   --  inserted before the instantiation, and a warning generated.

   --  The problem is that in this case we have no place to put the

   --  body of the instantiation. We can't put it in the normal place,

   --  because it is too early, and will cause errors to occur as a

   --  result of referencing entities before they are declared.

   --  Our approach in this case is simply to avoid creating the body

   --  of the instantiation in such a case. The instantiation spec is

   --  modified to include dummy bodies for all subprograms, so that

   --  the resulting code does not contain subprogram specs with no

   --  corresponding bodies.

   procedure Check_Elab_Call (N : Node_Id; Outer_Scope : Entity_Id := Empty);

   --  Check a call for possible elaboration problems. The node N is either

   --  an N_Function_Call or N_Procedure_Call_Statement node. The Outer_Scope

   --  argument indicates whether this is an outer level call from Sem_Res

   --  (Outer_Scope set to Empty), or an internal recursive call (Outer_Scope

   --  set to entity of outermost call, see body).

   procedure Check_Elab_Calls;

   --  Not all the processing for Check_Elab_Call can be done at the time

   --  of calls to Check_Elab_Call. This is because for internal calls, we

   --  need to wait to complete the check until all generic bodies have been

   --  instantiated. The Check_Elab_Calls procedure cleans up these waiting

   --  checks. It is called once after the completion of instantiation.

   procedure Check_Elab_Assign (N : Node_Id);

   --  N is either the left side of an assignment, or a procedure argument for

   --  a mode OUT or IN OUT formal. This procedure checks for a possible case

   --  of access to an entity from elaboration code before the entity has been

   --  initialized, and issues appropriate warnings.

   procedure Check_Elab_Instantiation

     (N           : Node_Id;

      Outer_Scope : Entity_Id := Empty);

   --  Check an instantiation for possible elaboration problems. N is an

   --  instantiation node (N_Package_Instantiation, N_Function_Instantiation,

   --  or N_Procedure_Instantiation), and Outer_Scope indicates if this is

   --  an outer level call from Sem_Ch12 (Outer_Scope set to Empty), or an

   --  internal recursive call (Outer_Scope set to scope of outermost call,

   --  see body for further details). The returned value is relevant only

   --  for an outer level call, and is set to False if an elaboration error

   --  is bound to occur on the instantiation, and True otherwise. This is

   --  used by the caller to signal that the body of the instance should

   --  not be generated (see detailed description in body).

   procedure Check_Task_Activation (N : Node_Id);

   --  at the point at which tasks are activated in a package body, check

   --  that the bodies of the tasks are elaborated.

end Sem_Elab;