gcc/ada/sem_elab.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                             S E M _ E L A B                              --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1997-2017, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT; see file COPYING3.  If not, go to --
  19 -- http://www.gnu.org/licenses for a complete copy of the license.          --
  20 --                                                                          --
  21 -- GNAT was originally developed  by the GNAT team at  New York University. --
  22 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  23 --                                                                          --
  24 ------------------------------------------------------------------------------
  25
  26 --  This package contains the routines used to deal with issuing warnings
  27 --  for cases of calls that may require warnings about possible access
  28 --  before elaboration.
  29
  30 with Types; use Types;
  31
  32 package Sem_Elab is
  33
  34    -----------------------------
  35    -- Description of Approach --
  36    -----------------------------
  37
  38    --  Every non-static call that is encountered by Sem_Res results in a call
  39    --  to Check_Elab_Call, with N being the call node, and Outer set to its
  40    --  default value of True. In addition X'Access is treated like a call
  41    --  for the access-to-procedure case, and in SPARK mode only we also
  42    --  check variable references.
  43
  44    --  The goal of Check_Elab_Call is to determine whether or not the reference
  45    --  in question can generate an access before elaboration error (raising
  46    --  Program_Error) either by directly calling a subprogram whose body
  47    --  has not yet been elaborated, or indirectly, by calling a subprogram
  48    --  whose body has been elaborated, but which contains a call to such a
  49    --  subprogram.
  50
  51    --  In addition, in SPARK mode, we are checking for a variable reference in
  52    --  another package, which requires an explicit Elaborate_All pragma.
  53
  54    --  The only references that we need to look at the outer level are
  55    --  references that occur in elaboration code. There are two cases. The
  56    --  reference can be at the outer level of elaboration code, or it can
  57    --  be within another unit, e.g. the elaboration code of a subprogram.
  58
  59    --  In the case of an elaboration call at the outer level, we must trace
  60    --  all calls to outer level routines either within the current unit or to
  61    --  other units that are with'ed. For calls within the current unit, we can
  62    --  determine if the body has been elaborated or not, and if it has not,
  63    --  then a warning is generated.
  64
  65    --  Note that there are two subcases. If the original call directly calls a
  66    --  subprogram whose body has not been elaborated, then we know that an ABE
  67    --  will take place, and we replace the call by a raise of Program_Error.
  68    --  If the call is indirect, then we don't know that the PE will be raised,
  69    --  since the call might be guarded by a conditional. In this case we set
  70    --  Do_Elab_Check on the call so that a dynamic check is generated, and
  71    --  output a warning.
  72
  73    --  For calls to a subprogram in a with'ed unit or a 'Access or variable
  74    --  reference (SPARK mode case), we require that a pragma Elaborate_All
  75    --  or pragma Elaborate be present, or that the referenced unit have a
  76    --  pragma Preelaborate, pragma Pure, or pragma Elaborate_Body. If none
  77    --  of these conditions is met, then a warning is generated that a pragma
  78    --  Elaborate_All may be needed (error in the SPARK case), or an implicit
  79    --  pragma is generated.
  80
  81    --  For the case of an elaboration call at some inner level, we are
  82    --  interested in tracing only calls to subprograms at the same level,
  83    --  i.e. those that can be called during elaboration. Any calls to
  84    --  outer level routines cannot cause ABE's as a result of the original
  85    --  call (there might be an outer level call to the subprogram from
  86    --  outside that causes the ABE, but that gets analyzed separately).
  87
  88    --  Note that we never trace calls to inner level subprograms, since
  89    --  these cannot result in ABE's unless there is an elaboration problem
  90    --  at a lower level, which will be separately detected.
  91
  92    --  Note on pragma Elaborate. The checking here assumes that a pragma
  93    --  Elaborate on a with'ed unit guarantees that subprograms within the
  94    --  unit can be called without causing an ABE. This is not in fact the
  95    --  case since pragma Elaborate does not guarantee the transitive
  96    --  coverage guaranteed by Elaborate_All. However, we decide to trust
  97    --  the user in this case.
  98
  99    --------------------------------------
 100    -- Instantiation Elaboration Errors --
 101    --------------------------------------
 102
 103    --  A special case arises when an instantiation appears in a context
 104    --  that is known to be before the body is elaborated, e.g.
 105
 106    --       generic package x is ...
 107    --       ...
 108    --       package xx is new x;
 109    --       ...
 110    --       package body x is ...
 111
 112    --  In this situation it is certain that an elaboration error will
 113    --  occur, and an unconditional raise Program_Error statement is
 114    --  inserted before the instantiation, and a warning generated.
 115
 116    --  The problem is that in this case we have no place to put the
 117    --  body of the instantiation. We can't put it in the normal place,
 118    --  because it is too early, and will cause errors to occur as a
 119    --  result of referencing entities before they are declared.
 120
 121    --  Our approach in this case is simply to avoid creating the body
 122    --  of the instantiation in such a case. The instantiation spec is
 123    --  modified to include dummy bodies for all subprograms, so that
 124    --  the resulting code does not contain subprogram specs with no
 125    --  corresponding bodies.
 126
 127    procedure Check_Elab_Call
 128      (N            : Node_Id;
 129       Outer_Scope  : Entity_Id := Empty;
 130       In_Init_Proc : Boolean   := False);
 131    --  Check a call for possible elaboration problems. The node N is either an
 132    --  N_Function_Call or N_Procedure_Call_Statement node or an access
 133    --  attribute reference whose prefix is a subprogram.
 134    --
 135    --  If SPARK_Mode is On, then N can also be a variable reference, since
 136    --  SPARK requires the use of Elaborate_All for references to variables
 137    --  in other packages.
 138
 139    --  The Outer_Scope argument indicates whether this is an outer level
 140    --  call from Sem_Res (Outer_Scope set to Empty), or an internal recursive
 141    --  call (Outer_Scope set to entity of outermost call, see body). The flag
 142    --  In_Init_Proc should be set whenever the current context is a type
 143    --  init proc.
 144
 145    --  Note: this might better be called Check_Elab_Reference (to recognize
 146    --  the SPARK case), but we prefer to keep the original name, since this
 147    --  is primarily used for checking for calls that could generate an ABE).
 148
 149    procedure Check_Elab_Calls;
 150    --  Not all the processing for Check_Elab_Call can be done at the time
 151    --  of calls to Check_Elab_Call. This is because for internal calls, we
 152    --  need to wait to complete the check until all generic bodies have been
 153    --  instantiated. The Check_Elab_Calls procedure cleans up these waiting
 154    --  checks. It is called once after the completion of instantiation.
 155
 156    procedure Check_Elab_Assign (N : Node_Id);
 157    --  N is either the left side of an assignment, or a procedure argument for
 158    --  a mode OUT or IN OUT formal. This procedure checks for a possible case
 159    --  of access to an entity from elaboration code before the entity has been
 160    --  initialized, and issues appropriate warnings.
 161
 162    procedure Check_Elab_Instantiation
 163      (N           : Node_Id;
 164       Outer_Scope : Entity_Id := Empty);
 165    --  Check an instantiation for possible elaboration problems. N is an
 166    --  instantiation node (N_Package_Instantiation, N_Function_Instantiation,
 167    --  or N_Procedure_Instantiation), and Outer_Scope indicates if this is
 168    --  an outer level call from Sem_Ch12 (Outer_Scope set to Empty), or an
 169    --  internal recursive call (Outer_Scope set to scope of outermost call,
 170    --  see body for further details). The returned value is relevant only
 171    --  for an outer level call, and is set to False if an elaboration error
 172    --  is bound to occur on the instantiation, and True otherwise. This is
 173    --  used by the caller to signal that the body of the instance should
 174    --  not be generated (see detailed description in body).
 175
 176    procedure Check_Task_Activation (N : Node_Id);
 177    --  At the point at which tasks are activated in a package body, check
 178    --  that the bodies of the tasks are elaborated.
 179
 180 end Sem_Elab;