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 --                                                                          --
  10 --          Copyright (C) 1992-2001 Free Software Foundation, Inc.          --
  11 --                                                                          --
  12 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  13 -- terms of the  GNU General Public License as published  by the Free Soft- --
  14 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  15 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  16 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  17 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  18 -- for  more details.  You should have  received  a copy of the GNU General --
  19 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  20 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  21 -- MA 02111-1307, USA.                                                      --
  22 --                                                                          --
  23 -- GNAT was originally developed  by the GNAT team at  New York University. --
  24 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  25 --                                                                          --
  26 ------------------------------------------------------------------------------
  27
  28 --  This unit contains the routines used to handle type determination,
  29 --  including the routine used to support overload resolution.
  30
  31 with Alloc;
  32 with Table;
  33 with Types; use Types;
  34
  35 package Sem_Type is
  36
  37    ---------------------------------------------
  38    -- Data Structures for Overload Resolution --
  39    ---------------------------------------------
  40
  41    --  To determine the unique meaning of an identifier, overload resolution
  42    --  may have to be performed if the visibility rules alone identify more
  43    --  than one possible entity as the denotation of a given identifier. When
  44    --  the visibility rules find such a potential ambiguity, the set of
  45    --  possible interpretations must be attached to the identifier, and
  46    --  overload resolution must be performed over the innermost enclosing
  47    --  complete context. At the end of the resolution,  either a single
  48    --  interpretation is found for all identifiers in the context, or else a
  49    --  type error (invalid type or ambiguous reference) must be signalled.
  50
  51    --  The set of interpretations of a given name is stored in a data structure
  52    --  that is separate from the syntax tree, because it corresponds to
  53    --  transient information.  The interpretations themselves are stored in
  54    --  table All_Interp. A mapping from tree nodes to sets of interpretations
  55    --  called Interp_Map, is maintained by the overload resolution routines.
  56    --  Both these structures are initialized at the beginning of every complete
  57    --  context.
  58
  59    --  Corresponding to the set of interpretation for a given overloadable
  60    --  identifier, there is a set of possible types corresponding to the types
  61    --  that the overloaded call may return. We keep a 1-to-1 correspondence
  62    --  between interpretations and types: for user-defined subprograms the
  63    --  type is the declared return type. For operators, the type is determined
  64    --  by the type of the arguments. If the arguments themselves are
  65    --  overloaded, we enter the operator name in the names table for each
  66    --  possible result type. In most cases, arguments are not overloaded and
  67    --  only one interpretation is present anyway.
  68
  69    type Interp is record
  70       Nam : Entity_Id;
  71       Typ : Entity_Id;
  72    end record;
  73
  74    No_Interp : constant Interp := (Empty, Empty);
  75
  76    package All_Interp is new Table.Table (
  77      Table_Component_Type => Interp,
  78      Table_Index_Type     => Int,
  79      Table_Low_Bound      => 0,
  80      Table_Initial        => Alloc.All_Interp_Initial,
  81      Table_Increment      => Alloc.All_Interp_Increment,
  82      Table_Name           => "All_Interp");
  83
  84    --  The following data structures establish a mapping between nodes and
  85    --  their interpretations. Eventually the Interp_Index corresponding to
  86    --  the first interpretation of a node may be stored directly in the
  87    --  corresponding node.
  88
  89    subtype Interp_Index is Int;
  90
  91    type Interp_Ref is record
  92       Node  : Node_Id;
  93       Index : Interp_Index;
  94    end record;
  95
  96    package Interp_Map is new Table.Table (
  97      Table_Component_Type => Interp_Ref,
  98      Table_Index_Type     => Int,
  99      Table_Low_Bound      => 0,
 100      Table_Initial        => Alloc.Interp_Map_Initial,
 101      Table_Increment      => Alloc.Interp_Map_Increment,
 102      Table_Name           => "Interp_Map");
 103
 104    --  For now Interp_Map is searched sequentially
 105
 106    ----------------------
 107    --  Error Reporting --
 108    ----------------------
 109
 110    --  A common error is the use of an operator in infix notation on arguments
 111    --  of a type that is not directly visible. Rather than diagnosing a type
 112    --  mismatch, it is better to indicate that the type can be made use-visible
 113    --  with the appropriate use clause. The global variable Candidate_Type is
 114    --  set in Add_One_Interp whenever an interpretation might be legal for an
 115    --  operator if the type were directly visible. This variable is used in
 116    --  sem_ch4 when no legal interpretation is found.
 117
 118    Candidate_Type : Entity_Id;
 119
 120    -----------------
 121    -- Subprograms --
 122    -----------------
 123
 124    procedure Init_Interp_Tables;
 125    --  Invoked by gnatf when processing multiple files.
 126
 127    procedure Collect_Interps (N : Node_Id);
 128    --  Invoked when the name N has more than one visible interpretation.
 129    --  This is the high level routine which accumulates the possible
 130    --  interpretations of the node. The first meaning and type of N have
 131    --  already been stored in N. If the name is an expanded name, the homonyms
 132    --  are only those that belong to the same scope.
 133
 134    procedure New_Interps (N : Node_Id);
 135    --  Initialize collection of interpretations for the given node, which is
 136    --  either an overloaded entity, or an operation whose arguments have
 137    --  multiple intepretations. Interpretations can be added to only one
 138    --  node at a time.
 139
 140    procedure Add_One_Interp
 141      (N         : Node_Id;
 142       E         : Entity_Id;
 143       T         : Entity_Id;
 144       Opnd_Type : Entity_Id := Empty);
 145    --  Add (E, T) to the list of interpretations of the node being resolved.
 146    --  For calls and operators, i.e. for nodes that have a name field,
 147    --  E is an overloadable entity, and T is its type. For constructs such
 148    --  as indexed expressions, the caller sets E equal to T, because the
 149    --  overloading comes from other fields, and the node itself has no name
 150    --  to resolve. Add_One_Interp includes the semantic processing to deal
 151    --  with adding entries that hide one another etc.
 152
 153    --  For operators, the legality of the operation depends on the visibility
 154    --  of T and its scope. If the operator is an equality or comparison, T is
 155    --  always Boolean, and we use Opnd_Type, which is a candidate type for one
 156    --  of the operands of N, to check visibility.
 157
 158    procedure End_Interp_List;
 159    --  End the list of interpretations of current node.
 160
 161    procedure Get_First_Interp
 162      (N  : Node_Id;
 163       I  : out Interp_Index;
 164       It : out Interp);
 165    --  Initialize iteration over set of interpretations for Node N. The first
 166    --  interpretation is placed in It, and I is initialized for subsequent
 167    --  calls to Get_Next_Interp.
 168
 169    procedure Get_Next_Interp (I : in out Interp_Index; It : out Interp);
 170    --  Iteration step over set of interpretations. Using the value in I, which
 171    --  was set by a previous call to Get_First_Interp or Get_Next_Interp, the
 172    --  next interpretation is placed in It, and I is updated for the next call.
 173    --  The end of the list of interpretations is signalled by It.Nam = Empty.
 174
 175    procedure Remove_Interp (I : in out Interp_Index);
 176    --  Remove an interpretation that his hidden by another, or that does not
 177    --  match the context. The value of I on input was set by a call to either
 178    --  Get_First_Interp or Get_Next_Interp and references the interpretation
 179    --  to be removed. The only allowed use of the exit value of I is as input
 180    --  to a subsequent call to Get_Next_Interp, which yields the interpretation
 181    --  following the removed one.
 182
 183    procedure Save_Interps (Old_N : Node_Id; New_N : Node_Id);
 184    --  If an overloaded node is rewritten during semantic analysis, its
 185    --  possible interpretations must be linked to the copy. This procedure
 186    --  transfers the overload information from Old_N, the old node, to
 187    --  New_N, its new copy. It has no effect in the non-overloaded case.
 188
 189    function Covers (T1, T2 : Entity_Id) return Boolean;
 190    --  This is the basic type compatibility routine. T1 is the expexted
 191    --  type, imposed by context, and T2 is the actual type. The processing
 192    --  reflects both the definition of type coverage and the rules
 193    --  for operand matching.
 194
 195    function Disambiguate
 196      (N      : Node_Id;
 197       I1, I2 : Interp_Index;
 198       Typ    : Entity_Id)
 199       return   Interp;
 200    --  If more than one interpretation  of a name in a call is legal, apply
 201    --  preference rules (universal types first) and operator visibility in
 202    --  order to remove ambiguity. I1 and I2 are the first two interpretations
 203    --  that are compatible with the context, but there may be others.
 204
 205    function Entity_Matches_Spec (Old_S,  New_S : Entity_Id) return Boolean;
 206    --  To resolve subprogram renaming and default formal subprograms in generic
 207    --  definitions. Old_S is a possible interpretation of the entity being
 208    --  renamed, New_S has an explicit signature. If Old_S is a subprogram, as
 209    --  opposed to an operator, type and mode conformance are required.
 210
 211    function Find_Unique_Type (L : Node_Id; R : Node_Id) return Entity_Id;
 212    --  Used in second pass of resolution,  for equality and comparison nodes.
 213    --  L is the left operand, whose type is known to be correct, and R is
 214    --  the right operand,  which has one interpretation compatible with that
 215    --  of L. Return the type intersection of the two.
 216
 217    function Has_Compatible_Type
 218      (N    : Node_Id;
 219       Typ  : Entity_Id)
 220       return Boolean;
 221    --  Verify that some interpretation of the node N has a type compatible
 222    --  with Typ. If N is not overloaded, then its unique type must be
 223    --  compatible with Typ. Otherwise iterate through the interpretations
 224    --  of N looking for a compatible one.
 225
 226    function Hides_Op (F : Entity_Id; Op : Entity_Id) return Boolean;
 227    --  A user-defined function hides a predefined operator if it is
 228    --  matches the signature of the operator, and is declared in an
 229    --  open scope, or in the scope of the result type.
 230
 231    function Intersect_Types (L, R : Node_Id) return Entity_Id;
 232    --  Find the common interpretation to two analyzed nodes. If one of the
 233    --  interpretations is universal, choose the non-universal one. If either
 234    --  node is overloaded, find single common interpretation.
 235
 236    function Is_Subtype_Of (T1 : Entity_Id; T2 : Entity_Id) return Boolean;
 237    --  Checks whether T1 is any subtype of T2 directly or indirectly. Applies
 238    --  only to scalar subtypes ???
 239
 240    function Is_Ancestor (T1, T2 : Entity_Id) return Boolean;
 241    --  T1 is a tagged type (not class-wide). Verify that it is one of the
 242    --  ancestors of type T2 (which may or not be class-wide)
 243
 244    function Operator_Matches_Spec (Op,  New_S : Entity_Id) return Boolean;
 245    --  Used to resolve subprograms renaming operators, and calls to user
 246    --  defined operators. Determines whether a given operator Op, matches
 247    --  a specification, New_S.
 248
 249    function Valid_Comparison_Arg (T : Entity_Id) return Boolean;
 250    --  A valid argument to an ordering operator must be a discrete type, a
 251    --  real type, or a one dimensional array with a discrete component type.
 252
 253    function Valid_Boolean_Arg (T : Entity_Id) return Boolean;
 254    --  A valid argument of a boolean operator is either some boolean type,
 255    --  or a one-dimensional array of boolean type.
 256
 257    procedure Write_Overloads (N : Node_Id);
 258    --  Debugging procedure to output info on possibly overloaded entities
 259    --  for specified node.
 260
 261 end Sem_Type;