1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--                             S E M _ D I S P                              --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--          Copyright (C) 1992-2015, 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 routines involved in tagged types and dynamic
27--  dispatching.
28
29with Types; use Types;
30package Sem_Disp is
31
32   procedure Check_Controlling_Formals (Typ : Entity_Id; Subp : Entity_Id);
33   --  Check that all controlling parameters of Subp are of type Typ, that
34   --  defaults for controlling parameters are tag-indeterminate, and that the
35   --  nominal subtype of the parameters and result statically match the first
36   --  subtype of the controlling type. Issues appropriate error messages if
37   --  any of these requirements is not met.
38
39   procedure Check_Dispatching_Call (N : Node_Id);
40   --  Check if the call N is a dispatching call. The subprogram is known to be
41   --  a dispatching operation. The call is dispatching if all the controlling
42   --  actuals are dynamically tagged. This procedure is called after overload
43   --  resolution, so the call is known to be unambiguous.
44
45   procedure Check_Dispatching_Operation (Subp, Old_Subp : Entity_Id);
46   --  Add Subp to the list of primitive operations of the corresponding type
47   --  if it has a parameter of this type and is defined at a proper place for
48   --  primitive operations (new primitives are only defined in package spec,
49   --  overridden operation can be defined in any scope). If Old_Subp is not
50   --  Empty we are in the overriding case. If the tagged type associated with
51   --  Subp is a concurrent type (case that occurs when the type is declared
52   --  in a generic because the analysis of generics disables generation of the
53   --  corresponding record) then this routine does not add Subp to the list of
54   --  primitive operations but leaves Subp decorated as dispatching operation
55   --  to enable checks associated with the Object.Operation notation.
56
57   procedure Check_Operation_From_Incomplete_Type
58     (Subp : Entity_Id;
59      Typ  : Entity_Id);
60   --  If a primitive operation was defined for the incomplete view of the
61   --  type, and the full type declaration is a derived type definition,
62   --  the operation may override an inherited one.
63   --  Need more description here, what are the parameters, and what does
64   --  this call actually do???
65
66   procedure Check_Operation_From_Private_View (Subp, Old_Subp : Entity_Id);
67   --  Add Old_Subp to the list of primitive operations of the corresponding
68   --  tagged type if it is the full view of a private tagged type. The Alias
69   --  of Old_Subp is adjusted to point to the inherited procedure of the
70   --  full view because it is always this one which has to be called.
71   --  What is Subp used for???
72
73   function Covers_Some_Interface (Prim : Entity_Id) return Boolean;
74   --  Returns true if Prim covers some interface primitive of its associated
75   --  tagged type. The tagged type of Prim must be frozen when this function
76   --  is invoked.
77
78   function Find_Controlling_Arg (N : Node_Id) return Node_Id;
79   --  Returns the actual controlling argument if N is dynamically tagged, and
80   --  Empty if it is not dynamically tagged.
81
82   function Find_Dispatching_Type (Subp : Entity_Id) return Entity_Id;
83   --  Check whether the subprogram Subp is dispatching, and find the tagged
84   --  type of the controlling argument or arguments. Returns Empty if Subp
85   --  is not a dispatching operation.
86
87   function Find_Primitive_Covering_Interface
88     (Tagged_Type : Entity_Id;
89      Iface_Prim  : Entity_Id) return Entity_Id;
90   --  Search the homonym chain for the primitive of Tagged_Type that covers
91   --  Iface_Prim. The homonym chain traversal is required to catch primitives
92   --  associated with the partial view of private types when processing the
93   --  corresponding full view. If the entity is not found, then search for it
94   --  in the list of primitives of Tagged_Type. This latter search is needed
95   --  when the interface primitive is covered by a private subprogram. If the
96   --  primitive has not been covered yet then return the entity that will be
97   --  overridden when the primitive is covered (that is, return the entity
98   --  whose alias attribute references the interface primitive). If none of
99   --  these entities is found then return Empty.
100
101   type Subprogram_List is array (Nat range <>) of Entity_Id;
102   --  Type returned by Inherited_Subprograms function
103
104   function Inherited_Subprograms
105     (S               : Entity_Id;
106      No_Interfaces   : Boolean := False;
107      Interfaces_Only : Boolean := False;
108      One_Only        : Boolean := False) return Subprogram_List;
109   --  Given the spec of a subprogram, this function gathers any inherited
110   --  subprograms from direct inheritance or via interfaces. The result is an
111   --  array of Entity_Ids of the specs of inherited subprograms. Returns a
112   --  null array if passed an Empty spec id. Note that the returned array
113   --  only includes subprograms and generic subprograms (and excludes any
114   --  other inherited entities, in particular enumeration literals). If
115   --  No_Interfaces is True, only return inherited subprograms not coming
116   --  from an interface. If Interfaces_Only is True, only return inherited
117   --  subprograms from interfaces. Otherwise, subprograms inherited directly
118   --  come first, starting with the closest ancestors, and are followed by
119   --  subprograms inherited from interfaces. At most one of No_Interfaces
120   --  and Interfaces_Only should be True.
121   --
122   --  If One_Only is set, the search is discontinued as soon as one entry
123   --  is found. In this case the resulting array is either null or contains
124   --  exactly one element.
125
126   function Is_Dynamically_Tagged (N : Node_Id) return Boolean;
127   --  Used to determine whether a call is dispatching, i.e. if it is
128   --  an expression of a class_Wide type, or a call to a function with
129   --  controlling result where at least one operand is dynamically tagged.
130   --  Also used to determine whether an entity has a class-wide type, or a
131   --  function call that dispatches on the result. Used to verify that all the
132   --  dependent expressions in a conditional expression are equally tagged.
133
134   function Is_Null_Interface_Primitive (E : Entity_Id) return Boolean;
135   --  Returns True if E is a null procedure that is an interface primitive
136
137   function Is_Overriding_Subprogram (E : Entity_Id) return Boolean;
138   --  Returns True if E is an overriding subprogram
139
140   function Is_Tag_Indeterminate (N : Node_Id) return Boolean;
141   --  Returns true if the expression N is tag-indeterminate. An expression
142   --  is tag-indeterminate if it is a call that dispatches on result, and all
143   --  controlling operands are also indeterminate. Such a function call may
144   --  inherit a tag from an enclosing call.
145
146   procedure Override_Dispatching_Operation
147     (Tagged_Type : Entity_Id;
148      Prev_Op     : Entity_Id;
149      New_Op      : Entity_Id;
150      Is_Wrapper  : Boolean := False);
151   --  Replace an implicit dispatching operation of the type Tagged_Type
152   --  with an explicit one. Prev_Op is an inherited primitive operation which
153   --  is overridden by the explicit declaration of New_Op. Is_Wrapper is
154   --  True when New_Op is an internally generated wrapper of a controlling
155   --  function. The caller checks that Tagged_Type is indeed a tagged type.
156
157   procedure Propagate_Tag (Control : Node_Id; Actual : Node_Id);
158   --  If a function call is tag-indeterminate, its controlling argument is
159   --  found in the context: either an enclosing call, or the left-hand side
160   --  of the enclosing assignment statement. The tag must be propagated
161   --  recursively to the tag-indeterminate actuals of the call.
162   --  Need clear description of the parameters Control and Actual, especially
163   --  since the comments above refer to actuals in the plural ???
164
165end Sem_Disp;
166