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-------------------------------------------------------------------------------
--- --
--- GNAT COMPILER COMPONENTS --
--- --
--- S E M _ E L A B --
--- --
--- S p e c --
--- --
--- $Revision: 1.1.16.1 $
--- --
--- Copyright (C) 1997-2001 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 2, 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 COPYING. If not, write --
--- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
--- MA 02111-1307, 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 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 transititive
- -- 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. N is either an
- -- N_Function_Call or N_Procedure_Call_Statement node, and Outer
- -- 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_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;
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