------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- S E M _ T Y P E -- -- -- -- S p e c -- -- -- -- -- -- Copyright (C) 1992-2001 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 unit contains the routines used to handle type determination, -- including the routine used to support overload resolution. with Alloc; with Table; with Types; use Types; package Sem_Type is --------------------------------------------- -- Data Structures for Overload Resolution -- --------------------------------------------- -- To determine the unique meaning of an identifier, overload resolution -- may have to be performed if the visibility rules alone identify more -- than one possible entity as the denotation of a given identifier. When -- the visibility rules find such a potential ambiguity, the set of -- possible interpretations must be attached to the identifier, and -- overload resolution must be performed over the innermost enclosing -- complete context. At the end of the resolution, either a single -- interpretation is found for all identifiers in the context, or else a -- type error (invalid type or ambiguous reference) must be signalled. -- The set of interpretations of a given name is stored in a data structure -- that is separate from the syntax tree, because it corresponds to -- transient information. The interpretations themselves are stored in -- table All_Interp. A mapping from tree nodes to sets of interpretations -- called Interp_Map, is maintained by the overload resolution routines. -- Both these structures are initialized at the beginning of every complete -- context. -- Corresponding to the set of interpretation for a given overloadable -- identifier, there is a set of possible types corresponding to the types -- that the overloaded call may return. We keep a 1-to-1 correspondence -- between interpretations and types: for user-defined subprograms the -- type is the declared return type. For operators, the type is determined -- by the type of the arguments. If the arguments themselves are -- overloaded, we enter the operator name in the names table for each -- possible result type. In most cases, arguments are not overloaded and -- only one interpretation is present anyway. type Interp is record Nam : Entity_Id; Typ : Entity_Id; end record; No_Interp : constant Interp := (Empty, Empty); package All_Interp is new Table.Table ( Table_Component_Type => Interp, Table_Index_Type => Int, Table_Low_Bound => 0, Table_Initial => Alloc.All_Interp_Initial, Table_Increment => Alloc.All_Interp_Increment, Table_Name => "All_Interp"); -- The following data structures establish a mapping between nodes and -- their interpretations. Eventually the Interp_Index corresponding to -- the first interpretation of a node may be stored directly in the -- corresponding node. subtype Interp_Index is Int; type Interp_Ref is record Node : Node_Id; Index : Interp_Index; end record; package Interp_Map is new Table.Table ( Table_Component_Type => Interp_Ref, Table_Index_Type => Int, Table_Low_Bound => 0, Table_Initial => Alloc.Interp_Map_Initial, Table_Increment => Alloc.Interp_Map_Increment, Table_Name => "Interp_Map"); -- For now Interp_Map is searched sequentially ---------------------- -- Error Reporting -- ---------------------- -- A common error is the use of an operator in infix notation on arguments -- of a type that is not directly visible. Rather than diagnosing a type -- mismatch, it is better to indicate that the type can be made use-visible -- with the appropriate use clause. The global variable Candidate_Type is -- set in Add_One_Interp whenever an interpretation might be legal for an -- operator if the type were directly visible. This variable is used in -- sem_ch4 when no legal interpretation is found. Candidate_Type : Entity_Id; ----------------- -- Subprograms -- ----------------- procedure Init_Interp_Tables; -- Invoked by gnatf when processing multiple files. procedure Collect_Interps (N : Node_Id); -- Invoked when the name N has more than one visible interpretation. -- This is the high level routine which accumulates the possible -- interpretations of the node. The first meaning and type of N have -- already been stored in N. If the name is an expanded name, the homonyms -- are only those that belong to the same scope. procedure New_Interps (N : Node_Id); -- Initialize collection of interpretations for the given node, which is -- either an overloaded entity, or an operation whose arguments have -- multiple intepretations. Interpretations can be added to only one -- node at a time. procedure Add_One_Interp (N : Node_Id; E : Entity_Id; T : Entity_Id; Opnd_Type : Entity_Id := Empty); -- Add (E, T) to the list of interpretations of the node being resolved. -- For calls and operators, i.e. for nodes that have a name field, -- E is an overloadable entity, and T is its type. For constructs such -- as indexed expressions, the caller sets E equal to T, because the -- overloading comes from other fields, and the node itself has no name -- to resolve. Add_One_Interp includes the semantic processing to deal -- with adding entries that hide one another etc. -- For operators, the legality of the operation depends on the visibility -- of T and its scope. If the operator is an equality or comparison, T is -- always Boolean, and we use Opnd_Type, which is a candidate type for one -- of the operands of N, to check visibility. procedure End_Interp_List; -- End the list of interpretations of current node. procedure Get_First_Interp (N : Node_Id; I : out Interp_Index; It : out Interp); -- Initialize iteration over set of interpretations for Node N. The first -- interpretation is placed in It, and I is initialized for subsequent -- calls to Get_Next_Interp. procedure Get_Next_Interp (I : in out Interp_Index; It : out Interp); -- Iteration step over set of interpretations. Using the value in I, which -- was set by a previous call to Get_First_Interp or Get_Next_Interp, the -- next interpretation is placed in It, and I is updated for the next call. -- The end of the list of interpretations is signalled by It.Nam = Empty. procedure Remove_Interp (I : in out Interp_Index); -- Remove an interpretation that his hidden by another, or that does not -- match the context. The value of I on input was set by a call to either -- Get_First_Interp or Get_Next_Interp and references the interpretation -- to be removed. The only allowed use of the exit value of I is as input -- to a subsequent call to Get_Next_Interp, which yields the interpretation -- following the removed one. procedure Save_Interps (Old_N : Node_Id; New_N : Node_Id); -- If an overloaded node is rewritten during semantic analysis, its -- possible interpretations must be linked to the copy. This procedure -- transfers the overload information from Old_N, the old node, to -- New_N, its new copy. It has no effect in the non-overloaded case. function Covers (T1, T2 : Entity_Id) return Boolean; -- This is the basic type compatibility routine. T1 is the expexted -- type, imposed by context, and T2 is the actual type. The processing -- reflects both the definition of type coverage and the rules -- for operand matching. function Disambiguate (N : Node_Id; I1, I2 : Interp_Index; Typ : Entity_Id) return Interp; -- If more than one interpretation of a name in a call is legal, apply -- preference rules (universal types first) and operator visibility in -- order to remove ambiguity. I1 and I2 are the first two interpretations -- that are compatible with the context, but there may be others. function Entity_Matches_Spec (Old_S, New_S : Entity_Id) return Boolean; -- To resolve subprogram renaming and default formal subprograms in generic -- definitions. Old_S is a possible interpretation of the entity being -- renamed, New_S has an explicit signature. If Old_S is a subprogram, as -- opposed to an operator, type and mode conformance are required. function Find_Unique_Type (L : Node_Id; R : Node_Id) return Entity_Id; -- Used in second pass of resolution, for equality and comparison nodes. -- L is the left operand, whose type is known to be correct, and R is -- the right operand, which has one interpretation compatible with that -- of L. Return the type intersection of the two. function Has_Compatible_Type (N : Node_Id; Typ : Entity_Id) return Boolean; -- Verify that some interpretation of the node N has a type compatible -- with Typ. If N is not overloaded, then its unique type must be -- compatible with Typ. Otherwise iterate through the interpretations -- of N looking for a compatible one. function Hides_Op (F : Entity_Id; Op : Entity_Id) return Boolean; -- A user-defined function hides a predefined operator if it is -- matches the signature of the operator, and is declared in an -- open scope, or in the scope of the result type. function Intersect_Types (L, R : Node_Id) return Entity_Id; -- Find the common interpretation to two analyzed nodes. If one of the -- interpretations is universal, choose the non-universal one. If either -- node is overloaded, find single common interpretation. function Is_Subtype_Of (T1 : Entity_Id; T2 : Entity_Id) return Boolean; -- Checks whether T1 is any subtype of T2 directly or indirectly. Applies -- only to scalar subtypes ??? function Is_Ancestor (T1, T2 : Entity_Id) return Boolean; -- T1 is a tagged type (not class-wide). Verify that it is one of the -- ancestors of type T2 (which may or not be class-wide) function Operator_Matches_Spec (Op, New_S : Entity_Id) return Boolean; -- Used to resolve subprograms renaming operators, and calls to user -- defined operators. Determines whether a given operator Op, matches -- a specification, New_S. function Valid_Comparison_Arg (T : Entity_Id) return Boolean; -- A valid argument to an ordering operator must be a discrete type, a -- real type, or a one dimensional array with a discrete component type. function Valid_Boolean_Arg (T : Entity_Id) return Boolean; -- A valid argument of a boolean operator is either some boolean type, -- or a one-dimensional array of boolean type. procedure Write_Overloads (N : Node_Id); -- Debugging procedure to output info on possibly overloaded entities -- for specified node. end Sem_Type;