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+------------------------------------------------------------------------------
+-- --
+-- GNAT COMPILER COMPONENTS --
+-- --
+-- S E M _ A T T R --
+-- --
+-- S p e c --
+-- --
+-- Copyright (C) 1992-2009, 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 3, 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. --
+-- --
+-- You should have received a copy of the GNU General Public License along --
+-- with this program; see file COPYING3. If not see --
+-- <http://www.gnu.org/licenses/>. --
+-- --
+-- GNAT was originally developed by the GNAT team at New York University. --
+-- Extensive contributions were provided by Ada Core Technologies Inc. --
+-- --
+------------------------------------------------------------------------------
+
+-- Attribute handling is isolated in a separate package to ease the addition
+-- of implementation defined attributes. Logically this processing belongs
+-- in chapter 4. See Sem_Ch4 for a description of the relation of the
+-- Analyze and Resolve routines for expression components.
+
+-- This spec also documents all GNAT implementation defined pragmas
+
+with Exp_Tss; use Exp_Tss;
+with Namet; use Namet;
+with Snames; use Snames;
+with Types; use Types;
+
+package Sem_Attr is
+
+ -----------------------------------------
+ -- Implementation Dependent Attributes --
+ -----------------------------------------
+
+ -- This section describes the implementation dependent attributes
+ -- provided in GNAT, as well as constructing an array of flags
+ -- indicating which attributes these are.
+
+ Attribute_Impl_Def : Attribute_Class_Array := Attribute_Class_Array'(
+
+ ------------------
+ -- Abort_Signal --
+ ------------------
+
+ Attribute_Abort_Signal => True,
+ -- Standard'Abort_Signal (Standard is the only allowed prefix) provides
+ -- the entity for the special exception used to signal task abort or
+ -- asynchronous transfer of control. Normally this attribute should only
+ -- be used in the tasking runtime (it is highly peculiar, and completely
+ -- outside the normal semantics of Ada, for a user program to intercept
+ -- the abort exception).
+
+ ------------------
+ -- Address_Size --
+ ------------------
+
+ Attribute_Address_Size => True,
+ -- Standard'Address_Size (Standard is the only allowed prefix) is
+ -- a static constant giving the number of bits in an Address. It
+ -- is used primarily for constructing the definition of Memory_Size
+ -- in package Standard, but may be freely used in user programs.
+ -- This is a static attribute.
+
+ ---------------
+ -- Asm_Input --
+ ---------------
+
+ Attribute_Asm_Input => True,
+ -- Used only in conjunction with the Asm subprograms in package
+ -- Machine_Code to construct machine instructions. See documentation
+ -- in package Machine_Code in file s-maccod.ads.
+
+ ----------------
+ -- Asm_Output --
+ ----------------
+
+ Attribute_Asm_Output => True,
+ -- Used only in conjunction with the Asm subprograms in package
+ -- Machine_Code to construct machine instructions. See documentation
+ -- in package Machine_Code in file s-maccod.ads.
+
+ ---------------
+ -- AST_Entry --
+ ---------------
+
+ Attribute_AST_Entry => True,
+ -- E'Ast_Entry, where E is a task entry, yields a value of the
+ -- predefined type System.DEC.AST_Handler, that enables the given
+ -- entry to be called when an AST occurs. If the name to which the
+ -- attribute applies has not been specified with the pragma AST_Entry,
+ -- the attribute returns the value No_Ast_Handler, and no AST occurs.
+ -- If the entry is for a task that is not callable (T'Callable False),
+ -- the exception program error is raised. If an AST occurs for an
+ -- entry of a task that is terminated, the program is erroneous.
+ --
+ -- The attribute AST_Entry is supported only in OpenVMS versions
+ -- of GNAT. It will be rejected as illegal in other GNAT versions.
+
+ ---------
+ -- Bit --
+ ---------
+
+ Attribute_Bit => True,
+ -- Obj'Bit, where Obj is any object, yields the bit offset within the
+ -- storage unit (byte) that contains the first bit of storage allocated
+ -- for the object. The attribute value is of type Universal_Integer,
+ -- and is always a non-negative number not exceeding the value of
+ -- System.Storage_Unit.
+ --
+ -- For an object that is a variable or a constant allocated in a
+ -- register, the value is zero. (The use of this attribute does not
+ -- force the allocation of a variable to memory).
+ --
+ -- For an object that is a formal parameter, this attribute applies to
+ -- either the matching actual parameter or to a copy of the matching
+ -- actual parameter.
+ --
+ -- For an access object the value is zero. Note that Obj.all'Bit is
+ -- subject to an Access_Check for the designated object. Similarly
+ -- for a record component X.C'Bit is subject to a discriminant check
+ -- and X(I).Bit and X(I1..I2)'Bit are subject to index checks.
+ --
+ -- This attribute is designed to be compatible with the DEC Ada
+ -- definition and implementation of the Bit attribute.
+
+ ------------------
+ -- Code_Address --
+ ------------------
+
+ Attribute_Code_Address => True,
+ -- The reference subp'Code_Address, where subp is a subprogram entity,
+ -- gives the address of the first generated instruction for the sub-
+ -- program. This is often, but not always the same as the 'Address
+ -- value, which is the address to be used in a call. The differences
+ -- occur in the case of a nested procedure (where Address yields the
+ -- address of the trampoline code used to load the static link), and on
+ -- some systems which use procedure descriptors (in which case Address
+ -- yields the address of the descriptor).
+
+ -----------------------
+ -- Default_Bit_Order --
+ -----------------------
+
+ Attribute_Default_Bit_Order => True,
+ -- Standard'Default_Bit_Order (Standard is the only permissible prefix),
+ -- provides the value System.Default_Bit_Order as a Pos value (0 for
+ -- High_Order_First, 1 for Low_Order_First). This is used to construct
+ -- the definition of Default_Bit_Order in package System. This is a
+ -- static attribute.
+
+ ---------------
+ -- Elab_Body --
+ ---------------
+
+ Attribute_Elab_Body => True,
+ -- This attribute can only be applied to a program unit name. It returns
+ -- the entity for the corresponding elaboration procedure for elabor-
+ -- ating the body of the referenced unit. This is used in the main
+ -- generated elaboration procedure by the binder, and is not normally
+ -- used in any other context, but there may be specialized situations in
+ -- which it is useful to be able to call this elaboration procedure from
+ -- Ada code, e.g. if it is necessary to do selective reelaboration to
+ -- fix some error.
+
+ ---------------
+ -- Elab_Spec --
+ ---------------
+
+ Attribute_Elab_Spec => True,
+ -- This attribute can only be applied to a program unit name. It
+ -- returns the entity for the corresponding elaboration procedure
+ -- for elaborating the spec of the referenced unit. This is used
+ -- in the main generated elaboration procedure by the binder, and
+ -- is not normally used in any other context, but there may be
+ -- specialized situations in which it is useful to be able to
+ -- call this elaboration procedure from Ada code, e.g. if it
+ -- is necessary to do selective reelaboration to fix some error.
+
+ ----------------
+ -- Elaborated --
+ ----------------
+
+ Attribute_Elaborated => True,
+ -- Lunit'Elaborated, where Lunit is a library unit, yields a boolean
+ -- value indicating whether or not the body of the designated library
+ -- unit has been elaborated yet.
+
+ --------------
+ -- Enum_Rep --
+ --------------
+
+ Attribute_Enum_Rep => True,
+ -- For every enumeration subtype S, S'Enum_Rep denotes a function
+ -- with the following specification:
+ --
+ -- function S'Enum_Rep (Arg : S'Base) return universal_integer;
+ --
+ -- The function returns the representation value for the given
+ -- enumeration value. This will be equal to the 'Pos value in the
+ -- absence of an enumeration representation clause. This is a static
+ -- attribute (i.e. the result is static if the argument is static).
+
+ --------------
+ -- Enum_Val --
+ --------------
+
+ Attribute_Enum_Val => True,
+ -- For every enumeration subtype S, S'Enum_Val denotes a function
+ -- with the following specification:
+ --
+ -- function S'Enum_Val (Arg : universal_integer) return S'Base;
+ --
+ -- This function performs the inverse transformation to Enum_Rep. Given
+ -- a representation value for the type, it returns the corresponding
+ -- enumeration value. Constraint_Error is raised if no value of the
+ -- enumeration type corresponds to the given integer value.
+
+ -----------------
+ -- Fixed_Value --
+ -----------------
+
+ Attribute_Fixed_Value => True,
+ -- For every fixed-point type S, S'Fixed_Value denotes a function
+ -- with the following specification:
+ --
+ -- function S'Fixed_Value (Arg : universal_integer) return S;
+ --
+ -- The value returned is the fixed-point value V such that
+ --
+ -- V = Arg * S'Small
+ --
+ -- The effect is thus equivalent to first converting the argument to
+ -- the integer type used to represent S, and then doing an unchecked
+ -- conversion to the fixed-point type. This attribute is primarily
+ -- intended for use in implementation of the input-output functions for
+ -- fixed-point values.
+
+ -----------------------
+ -- Has_Discriminants --
+ -----------------------
+
+ Attribute_Has_Discriminants => True,
+ -- Gtyp'Has_Discriminants, where Gtyp is a generic formal type, yields
+ -- a Boolean value indicating whether or not the actual instantiation
+ -- type has discriminants.
+
+ ---------
+ -- Img --
+ ---------
+
+ Attribute_Img => True,
+ -- The 'Img function is defined for any prefix, P, that denotes an
+ -- object of scalar type T. P'Img is equivalent to T'Image (P). This
+ -- is convenient for debugging. For example:
+ --
+ -- Put_Line ("X = " & X'Img);
+ --
+ -- has the same meaning as the more verbose:
+ --
+ -- Put_Line ("X = " & Temperature_Type'Image (X));
+ --
+ -- where Temperature_Type is the subtype of the object X.
+
+ -------------------
+ -- Integer_Value --
+ -------------------
+
+ Attribute_Integer_Value => True,
+ -- For every integer type S, S'Integer_Value denotes a function
+ -- with the following specification:
+ --
+ -- function S'Integer_Value (Arg : universal_fixed) return S;
+ --
+ -- The value returned is the integer value V, such that
+ --
+ -- Arg = V * fixed-type'Small
+ --
+ -- The effect is thus equivalent to first doing an unchecked convert
+ -- from the fixed-point type to its corresponding implementation type,
+ -- and then converting the result to the target integer type. This
+ -- attribute is primarily intended for use in implementation of the
+ -- standard input-output functions for fixed-point values.
+
+ Attribute_Invalid_Value => True,
+ -- For every scalar type, S'Invalid_Value designates an undefined value
+ -- of the type. If possible this value is an invalid value, and in fact
+ -- is identical to the value that would be set if Initialize_Scalars
+ -- mode were in effect (including the behavior of its value on
+ -- environment variables or binder switches). The intended use is
+ -- to set a value where initialization is required (e.g. as a result of
+ -- the coding standards in use), but logically no initialization is
+ -- needed, and the value should never be accessed.
+
+ ------------------
+ -- Machine_Size --
+ ------------------
+
+ Attribute_Machine_Size => True,
+ -- This attribute is identical to the Object_Size attribute. It is
+ -- provided for compatibility with the DEC attribute of this name.
+
+ -----------------------
+ -- Maximum_Alignment --
+ -----------------------
+
+ Attribute_Maximum_Alignment => True,
+ -- Standard'Maximum_Alignment (Standard is the only permissible prefix)
+ -- provides the maximum useful alignment value for the target. This
+ -- is a static value that can be used to specify the alignment for an
+ -- object, guaranteeing that it is properly aligned in all cases. The
+ -- time this is useful is when an external object is imported and its
+ -- alignment requirements are unknown. This is a static attribute.
+
+ --------------------
+ -- Mechanism_Code --
+ --------------------
+
+ Attribute_Mechanism_Code => True,
+ -- function'Mechanism_Code yields an integer code for the mechanism
+ -- used for the result of function, and subprogram'Mechanism_Code (n)
+ -- yields the mechanism used for formal parameter number n (a static
+ -- integer value, 1 = first parameter). The code returned is:
+ --
+ -- 1 = by copy (value)
+ -- 2 = by reference
+ -- 3 = by descriptor (default descriptor type)
+ -- 4 = by descriptor (UBS unaligned bit string)
+ -- 5 = by descriptor (UBSB aligned bit string with arbitrary bounds)
+ -- 6 = by descriptor (UBA unaligned bit array)
+ -- 7 = by descriptor (S string, also scalar access type parameter)
+ -- 8 = by descriptor (SB string with arbitrary bounds)
+ -- 9 = by descriptor (A contiguous array)
+ -- 10 = by descriptor (NCA non-contiguous array)
+
+ --------------------
+ -- Null_Parameter --
+ --------------------
+
+ Attribute_Null_Parameter => True,
+ -- A reference T'Null_Parameter denotes an (imaginary) object of type or
+ -- subtype T allocated at (machine) address zero. The attribute is
+ -- allowed only as the default expression of a formal parameter, or as
+ -- an actual expression of a subprogram call. In either case, the
+ -- subprogram must be imported.
+ --
+ -- The identity of the object is represented by the address zero in the
+ -- argument list, independent of the passing mechanism (explicit or
+ -- default).
+ --
+ -- The reason that this capability is needed is that for a record or
+ -- other composite object passed by reference, there is no other way of
+ -- specifying that a zero address should be passed.
+
+ -----------------
+ -- Object_Size --
+ -----------------
+
+ Attribute_Object_Size => True,
+ -- Type'Object_Size is the same as Type'Size for all types except
+ -- fixed-point types and discrete types. For fixed-point types and
+ -- discrete types, this attribute gives the size used for default
+ -- allocation of objects and components of the size. See section in
+ -- Einfo ("Handling of type'Size values") for further details.
+
+ -------------------------
+ -- Passed_By_Reference --
+ -------------------------
+
+ Attribute_Passed_By_Reference => True,
+ -- T'Passed_By_Reference for any subtype T returns a boolean value that
+ -- is true if the type is normally passed by reference and false if the
+ -- type is normally passed by copy in calls. For scalar types, the
+ -- result is always False and is static. For non-scalar types, the
+ -- result is non-static (since it is computed by Gigi).
+
+ ------------------
+ -- Range_Length --
+ ------------------
+
+ Attribute_Range_Length => True,
+ -- T'Range_Length for any discrete type T yields the number of values
+ -- represented by the subtype (zero for a null range). The result is
+ -- static for static subtypes. Note that Range_Length applied to the
+ -- index subtype of a one dimensional array always gives the same result
+ -- as Range applied to the array itself. The result is of type universal
+ -- integer.
+
+ ------------------
+ -- Storage_Unit --
+ ------------------
+
+ Attribute_Storage_Unit => True,
+ -- Standard'Storage_Unit (Standard is the only permissible prefix)
+ -- provides the value System.Storage_Unit, and is intended primarily
+ -- for constructing this definition in package System (see note above
+ -- in Default_Bit_Order description). The is a static attribute.
+
+ ---------------
+ -- Stub_Type --
+ ---------------
+
+ Attribute_Stub_Type => True,
+ -- The GNAT implementation of remote access-to-classwide types is
+ -- organised as described in AARM E.4(20.t): a value of an RACW type
+ -- (designating a remote object) is represented as a normal access
+ -- value, pointing to a "stub" object which in turn contains the
+ -- necessary information to contact the designated remote object. A
+ -- call on any dispatching operation of such a stub object does the
+ -- remote call, if necessary, using the information in the stub object
+ -- to locate the target partition, etc.
+ --
+ -- For a prefix T that denotes a remote access-to-classwide type,
+ -- T'Stub_Type denotes the type of the corresponding stub objects.
+ --
+ -- By construction, the layout of T'Stub_Type is identical to that of
+ -- System.Partition_Interface.RACW_Stub_Type (see implementation notes
+ -- in body of Exp_Dist).
+
+ -----------------
+ -- Target_Name --
+ -----------------
+
+ Attribute_Target_Name => True,
+ -- Standard'Target_Name yields the string identifying the target for the
+ -- compilation, taken from Sdefault.Target_Name.
+
+ ----------------
+ -- To_Address --
+ ----------------
+
+ Attribute_To_Address => True,
+ -- System'To_Address (Address is the only permissible prefix) is a
+ -- function that takes any integer value, and converts it into an
+ -- address value. The semantics is to first convert the integer value to
+ -- type Integer_Address according to normal conversion rules, and then
+ -- to convert this to an address using the same semantics as the
+ -- System.Storage_Elements.To_Address function. The important difference
+ -- is that this is a static attribute so it can be used in
+ -- initializations in preelaborate packages.
+
+ ----------------
+ -- Type_Class --
+ ----------------
+
+ Attribute_Type_Class => True,
+ -- T'Type_Class for any type or subtype T yields the value of the type
+ -- class for the full type of T. If T is a generic formal type, then the
+ -- value is the value for the corresponding actual subtype. The value of
+ -- this attribute is of type System.Aux_DEC.Type_Class, which has the
+ -- following definition:
+ --
+ -- type Type_Class is
+ -- (Type_Class_Enumeration,
+ -- Type_Class_Integer,
+ -- Type_Class_Fixed_Point,
+ -- Type_Class_Floating_Point,
+ -- Type_Class_Array,
+ -- Type_Class_Record,
+ -- Type_Class_Access,
+ -- Type_Class_Task,
+ -- Type_Class_Address);
+ --
+ -- Protected types yield the value Type_Class_Task, which thus applies
+ -- to all concurrent types. This attribute is designed to be compatible
+ -- with the DEC Ada attribute of the same name.
+ --
+ -- Note: if pragma Extend_System is used to merge the definitions of
+ -- Aux_DEC into System, then the type Type_Class can be referenced
+ -- as an entity within System, as can its enumeration literals.
+
+ -----------------
+ -- UET_Address --
+ -----------------
+
+ Attribute_UET_Address => True,
+ -- Unit'UET_Address, where Unit is a program unit, yields the address
+ -- of the unit exception table for the specified unit. This is only
+ -- used in the internal implementation of exception handling. See the
+ -- implementation of unit Ada.Exceptions for details on its use.
+
+ ------------------------------
+ -- Universal_Literal_String --
+ ------------------------------
+
+ Attribute_Universal_Literal_String => True,
+ -- The prefix of 'Universal_Literal_String must be a named number. The
+ -- static result is the string consisting of the characters of the
+ -- number as defined in the original source. This allows the user
+ -- program to access the actual text of named numbers without
+ -- intermediate conversions and without the need to enclose the strings
+ -- in quotes (which would preclude their use as numbers). This is used
+ -- internally for the construction of values of the floating-point
+ -- attributes from the file ttypef.ads, but may also be used by user
+ -- programs.
+
+ -------------------------
+ -- Unrestricted_Access --
+ -------------------------
+
+ Attribute_Unrestricted_Access => True,
+ -- The Unrestricted_Access attribute is similar to Access except that
+ -- all accessibility and aliased view checks are omitted. This is very
+ -- much a user-beware attribute. Basically its status is very similar
+ -- to Address, for which it is a desirable replacement where the value
+ -- desired is an access type. In other words, its effect is identical
+ -- to first taking 'Address and then doing an unchecked conversion to
+ -- a desired access type. Note that in GNAT, but not necessarily in
+ -- other implementations, the use of static chains for inner level
+ -- subprograms means that Unrestricted_Access applied to a subprogram
+ -- yields a value that can be called as long as the subprogram is in
+ -- scope (normal Ada 95 accessibility rules restrict this usage).
+
+ ---------------
+ -- VADS_Size --
+ ---------------
+
+ Attribute_VADS_Size => True,
+ -- Typ'VADS_Size yields the Size value typically yielded by some Ada 83
+ -- compilers. The differences between VADS_Size and Size is that for
+ -- scalar types for which no Size has been specified, VADS_Size yields
+ -- the Object_Size rather than the Value_Size. For example, while
+ -- Natural'Size is typically 31, the value of Natural'VADS_Size is 32.
+ -- For all other types, Size and VADS_Size yield the same value.
+
+ ----------------
+ -- Value_Size --
+ ----------------
+
+ Attribute_Value_Size => True,
+ -- Type'Value_Size is the number of bits required to represent value of
+ -- the given subtype. It is the same as Type'Size, but, unlike Size, may
+ -- be set for non-first subtypes. See section in Einfo ("Handling of
+ -- type'Size values") for further details.
+
+ ---------------
+ -- Word_Size --
+ ---------------
+
+ Attribute_Word_Size => True,
+ -- Standard'Word_Size (Standard is the only permissible prefix)
+ -- provides the value System.Word_Size, and is intended primarily
+ -- for constructing this definition in package System (see note above
+ -- in Default_Bit_Order description). This is a static attribute.
+
+ others => False);
+
+ -----------------
+ -- Subprograms --
+ -----------------
+
+ procedure Analyze_Attribute (N : Node_Id);
+ -- Performs bottom up semantic analysis of an attribute. Note that the
+ -- parser has already checked that type returning attributes appear only
+ -- in appropriate contexts (i.e. in subtype marks, or as prefixes for
+ -- other attributes).
+
+ function Name_Implies_Lvalue_Prefix (Nam : Name_Id) return Boolean;
+ -- Determine whether the name of an attribute reference categorizes its
+ -- prefix as an lvalue. The following attributes fall under this bracket
+ -- by directly or indirectly modifying their prefixes.
+ -- Access
+ -- Address
+ -- Input
+ -- Read
+ -- Unchecked_Access
+ -- Unrestricted_Access
+
+ procedure Resolve_Attribute (N : Node_Id; Typ : Entity_Id);
+ -- Performs type resolution of attribute. If the attribute yields a
+ -- universal value, mark its type as that of the context. On the other
+ -- hand, if the context itself is universal (as in T'Val (T'Pos (X)), mark
+ -- the type as being the largest type of that class that can be used at
+ -- run-time. This is correct since either the value gets folded (in which
+ -- case it doesn't matter what type of the class we give if, since the
+ -- folding uses universal arithmetic anyway) or it doesn't get folded (in
+ -- which case it is going to be dealt with at runtime, and the largest type
+ -- is right).
+
+ function Stream_Attribute_Available
+ (Typ : Entity_Id;
+ Nam : TSS_Name_Type;
+ Partial_View : Entity_Id := Empty) return Boolean;
+ -- For a limited type Typ, return True iff the given attribute is
+ -- available. For Ada 05, availability is defined by 13.13.2(36/1). For Ada
+ -- 95, an attribute is considered to be available if it has been specified
+ -- using an attribute definition clause for the type, or for its full view,
+ -- or for an ancestor of either. Parameter Partial_View is used only
+ -- internally, when checking for an attribute definition clause that is not
+ -- visible (Ada 95 only).
+
+end Sem_Attr;