gcc/ada/sem_type.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                             S E M _ T Y P E                              --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2004 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 2,  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 COPYING.  If not, write --
  19 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  20 -- MA 02111-1307, USA.                                                      --
  21 --                                                                          --
  22 -- GNAT was originally developed  by the GNAT team at  New York University. --
  23 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  24 --                                                                          --
  25 ------------------------------------------------------------------------------
  26
  27 --  This unit contains the routines used to handle type determination,
  28 --  including the routine used to support overload resolution.
  29
  30 with Types; use Types;
  31
  32 package Sem_Type is
  33
  34    ---------------------------------------------
  35    -- Data Structures for Overload Resolution --
  36    ---------------------------------------------
  37
  38    --  To determine the unique meaning of an identifier, overload resolution
  39    --  may have to be performed if the visibility rules alone identify more
  40    --  than one possible entity as the denotation of a given identifier. When
  41    --  the visibility rules find such a potential ambiguity, the set of
  42    --  possible interpretations must be attached to the identifier, and
  43    --  overload resolution must be performed over the innermost enclosing
  44    --  complete context. At the end of the resolution,  either a single
  45    --  interpretation is found for all identifiers in the context, or else a
  46    --  type error (invalid type or ambiguous reference) must be signalled.
  47
  48    --  The set of interpretations of a given name is stored in a data structure
  49    --  that is separate from the syntax tree, because it corresponds to
  50    --  transient information.  The interpretations themselves are stored in
  51    --  table All_Interp. A mapping from tree nodes to sets of interpretations
  52    --  called Interp_Map, is maintained by the overload resolution routines.
  53    --  Both these structures are initialized at the beginning of every complete
  54    --  context.
  55
  56    --  Corresponding to the set of interpretation for a given overloadable
  57    --  identifier, there is a set of possible types corresponding to the types
  58    --  that the overloaded call may return. We keep a 1-to-1 correspondence
  59    --  between interpretations and types: for user-defined subprograms the
  60    --  type is the declared return type. For operators, the type is determined
  61    --  by the type of the arguments. If the arguments themselves are
  62    --  overloaded, we enter the operator name in the names table for each
  63    --  possible result type. In most cases, arguments are not overloaded and
  64    --  only one interpretation is present anyway.
  65
  66    type Interp is record
  67       Nam : Entity_Id;
  68       Typ : Entity_Id;
  69    end record;
  70
  71    No_Interp : constant Interp := (Empty, Empty);
  72
  73    subtype Interp_Index is Int;
  74
  75    ---------------------
  76    -- Error Reporting --
  77    ---------------------
  78
  79    --  A common error is the use of an operator in infix notation on arguments
  80    --  of a type that is not directly visible. Rather than diagnosing a type
  81    --  mismatch, it is better to indicate that the type can be made use-visible
  82    --  with the appropriate use clause. The global variable Candidate_Type is
  83    --  set in Add_One_Interp whenever an interpretation might be legal for an
  84    --  operator if the type were directly visible. This variable is used in
  85    --  sem_ch4 when no legal interpretation is found.
  86
  87    Candidate_Type : Entity_Id;
  88
  89    -----------------
  90    -- Subprograms --
  91    -----------------
  92
  93    procedure Init_Interp_Tables;
  94    --  Invoked by gnatf when processing multiple files.
  95
  96    procedure Collect_Interps (N : Node_Id);
  97    --  Invoked when the name N has more than one visible interpretation.
  98    --  This is the high level routine which accumulates the possible
  99    --  interpretations of the node. The first meaning and type of N have
 100    --  already been stored in N. If the name is an expanded name, the homonyms
 101    --  are only those that belong to the same scope.
 102
 103    function Is_Invisible_Operator
 104      (N    : Node_Id;
 105       T    : Entity_Id)
 106       return Boolean;
 107    --  Check whether a predefined operation with universal operands appears
 108    --  in a context in which the operators of the expected type are not
 109    --  visible.
 110
 111    procedure List_Interps (Nam : Node_Id; Err : Node_Id);
 112    --  List candidate interpretations of an overloaded name. Used for
 113    --  various error reports.
 114
 115    procedure Add_One_Interp
 116      (N         : Node_Id;
 117       E         : Entity_Id;
 118       T         : Entity_Id;
 119       Opnd_Type : Entity_Id := Empty);
 120    --  Add (E, T) to the list of interpretations of the node being resolved.
 121    --  For calls and operators, i.e. for nodes that have a name field,
 122    --  E is an overloadable entity, and T is its type. For constructs such
 123    --  as indexed expressions, the caller sets E equal to T, because the
 124    --  overloading comes from other fields, and the node itself has no name
 125    --  to resolve. Add_One_Interp includes the semantic processing to deal
 126    --  with adding entries that hide one another etc.
 127
 128    --  For operators, the legality of the operation depends on the visibility
 129    --  of T and its scope. If the operator is an equality or comparison, T is
 130    --  always Boolean, and we use Opnd_Type, which is a candidate type for one
 131    --  of the operands of N, to check visibility.
 132
 133    procedure End_Interp_List;
 134    --  End the list of interpretations of current node.
 135
 136    procedure Get_First_Interp
 137      (N  : Node_Id;
 138       I  : out Interp_Index;
 139       It : out Interp);
 140    --  Initialize iteration over set of interpretations for Node N. The first
 141    --  interpretation is placed in It, and I is initialized for subsequent
 142    --  calls to Get_Next_Interp.
 143
 144    procedure Get_Next_Interp (I : in out Interp_Index; It : out Interp);
 145    --  Iteration step over set of interpretations. Using the value in I, which
 146    --  was set by a previous call to Get_First_Interp or Get_Next_Interp, the
 147    --  next interpretation is placed in It, and I is updated for the next call.
 148    --  The end of the list of interpretations is signalled by It.Nam = Empty.
 149
 150    procedure Remove_Interp (I : in out Interp_Index);
 151    --  Remove an interpretation that his hidden by another, or that does not
 152    --  match the context. The value of I on input was set by a call to either
 153    --  Get_First_Interp or Get_Next_Interp and references the interpretation
 154    --  to be removed. The only allowed use of the exit value of I is as input
 155    --  to a subsequent call to Get_Next_Interp, which yields the interpretation
 156    --  following the removed one.
 157
 158    procedure Save_Interps (Old_N : Node_Id; New_N : Node_Id);
 159    --  If an overloaded node is rewritten during semantic analysis, its
 160    --  possible interpretations must be linked to the copy. This procedure
 161    --  transfers the overload information from Old_N, the old node, to
 162    --  New_N, its new copy. It has no effect in the non-overloaded case.
 163
 164    function Covers (T1, T2 : Entity_Id) return Boolean;
 165    --  This is the basic type compatibility routine. T1 is the expected
 166    --  type, imposed by context, and T2 is the actual type. The processing
 167    --  reflects both the definition of type coverage and the rules
 168    --  for operand matching.
 169
 170    function Disambiguate
 171      (N      : Node_Id;
 172       I1, I2 : Interp_Index;
 173       Typ    : Entity_Id)
 174       return   Interp;
 175    --  If more than one interpretation  of a name in a call is legal, apply
 176    --  preference rules (universal types first) and operator visibility in
 177    --  order to remove ambiguity. I1 and I2 are the first two interpretations
 178    --  that are compatible with the context, but there may be others.
 179
 180    function Entity_Matches_Spec (Old_S,  New_S : Entity_Id) return Boolean;
 181    --  To resolve subprogram renaming and default formal subprograms in generic
 182    --  definitions. Old_S is a possible interpretation of the entity being
 183    --  renamed, New_S has an explicit signature. If Old_S is a subprogram, as
 184    --  opposed to an operator, type and mode conformance are required.
 185
 186    function Find_Unique_Type (L : Node_Id; R : Node_Id) return Entity_Id;
 187    --  Used in second pass of resolution,  for equality and comparison nodes.
 188    --  L is the left operand, whose type is known to be correct, and R is
 189    --  the right operand,  which has one interpretation compatible with that
 190    --  of L. Return the type intersection of the two.
 191
 192    function Has_Compatible_Type
 193      (N    : Node_Id;
 194       Typ  : Entity_Id)
 195       return Boolean;
 196    --  Verify that some interpretation of the node N has a type compatible
 197    --  with Typ. If N is not overloaded, then its unique type must be
 198    --  compatible with Typ. Otherwise iterate through the interpretations
 199    --  of N looking for a compatible one.
 200
 201    function Hides_Op (F : Entity_Id; Op : Entity_Id) return Boolean;
 202    --  A user-defined function hides a predefined operator if it is
 203    --  matches the signature of the operator, and is declared in an
 204    --  open scope, or in the scope of the result type.
 205
 206    function Intersect_Types (L, R : Node_Id) return Entity_Id;
 207    --  Find the common interpretation to two analyzed nodes. If one of the
 208    --  interpretations is universal, choose the non-universal one. If either
 209    --  node is overloaded, find single common interpretation.
 210
 211    function Is_Subtype_Of (T1 : Entity_Id; T2 : Entity_Id) return Boolean;
 212    --  Checks whether T1 is any subtype of T2 directly or indirectly. Applies
 213    --  only to scalar subtypes ???
 214
 215    function Is_Ancestor (T1, T2 : Entity_Id) return Boolean;
 216    --  T1 is a tagged type (not class-wide). Verify that it is one of the
 217    --  ancestors of type T2 (which may or not be class-wide)
 218
 219    function Operator_Matches_Spec (Op,  New_S : Entity_Id) return Boolean;
 220    --  Used to resolve subprograms renaming operators, and calls to user
 221    --  defined operators. Determines whether a given operator Op, matches
 222    --  a specification, New_S.
 223
 224    function Valid_Comparison_Arg (T : Entity_Id) return Boolean;
 225    --  A valid argument to an ordering operator must be a discrete type, a
 226    --  real type, or a one dimensional array with a discrete component type.
 227
 228    function Valid_Boolean_Arg (T : Entity_Id) return Boolean;
 229    --  A valid argument of a boolean operator is either some boolean type,
 230    --  or a one-dimensional array of boolean type.
 231
 232    procedure Write_Interp_Ref (Map_Ptr : Int);
 233    --  Debugging procedure to display entry in Interp_Map. Would not be
 234    --  needed if it were possible to debug instantiations of Table.
 235
 236    procedure Write_Overloads (N : Node_Id);
 237    --  Debugging procedure to output info on possibly overloaded entities
 238    --  for specified node.
 239
 240 end Sem_Type;