gcc/ada/aspects.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                              A S P E C T S                               --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 2010-2013, 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.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  This package defines the aspects that are recognized by GNAT in aspect
  33 --  specifications. It also contains the subprograms for storing/retrieving
  34 --  aspect specifications from the tree. The semantic processing for aspect
  35 --  specifications is found in Sem_Ch13.Analyze_Aspect_Specifications.
  36
  37 ------------------------
  38 -- Adding New Aspects --
  39 ------------------------
  40
  41 --  In general, each aspect should have a corresponding pragma, so that the
  42 --  newly developed functionality is available for Ada versions < Ada 2012.
  43 --  When both are defined, it is convenient to first transform the aspect into
  44 --  an equivalent pragma in Sem_Ch13.Analyze_Aspect_Specifications, and then
  45 --  analyze the pragma in Sem_Prag.Analyze_Pragma.
  46
  47 --  To add a new aspect, you need to do the following
  48
  49 --    1. Create a name in snames.ads-tmpl
  50
  51 --    2. Create a value in type Aspect_Id in this unit
  52
  53 --    3. Add a value for the aspect in the global arrays defined in this unit
  54
  55 --    4. Add code for the aspect in Sem_Ch13.Analyze_Aspect_Specifications.
  56 --       This may involve adding some nodes to the tree to perform additional
  57 --       treatments later.
  58
  59 --    5. If the semantic analysis of expressions/names in the aspect should not
  60 --       occur at the point the aspect is defined, add code in the adequate
  61 --       semantic analysis procedure for the aspect. For example, this is the
  62 --       case for aspects Pre and Post on subprograms, which are pre-analyzed
  63 --       at the end of the declaration list to which the subprogram belongs,
  64 --       and fully analyzed (possibly with expansion) during the semantic
  65 --       analysis of subprogram bodies.
  66
  67 with Namet;  use Namet;
  68 with Snames; use Snames;
  69 with Types;  use Types;
  70
  71 package Aspects is
  72
  73    --  Type defining recognized aspects
  74
  75    type Aspect_Id is
  76      (No_Aspect,                            -- Dummy entry for no aspect
  77       Aspect_Abstract_State,                -- GNAT
  78       Aspect_Address,
  79       Aspect_Alignment,
  80       Aspect_Attach_Handler,
  81       Aspect_Bit_Order,
  82       Aspect_Component_Size,
  83       Aspect_Constant_Indexing,
  84       Aspect_Contract_Cases,                -- GNAT
  85       Aspect_Convention,
  86       Aspect_CPU,
  87       Aspect_Default_Component_Value,
  88       Aspect_Default_Iterator,
  89       Aspect_Default_Value,
  90       Aspect_Depends,                       -- GNAT
  91       Aspect_Dimension,                     -- GNAT
  92       Aspect_Dimension_System,              -- GNAT
  93       Aspect_Dispatching_Domain,
  94       Aspect_Dynamic_Predicate,
  95       Aspect_External_Name,
  96       Aspect_External_Tag,
  97       Aspect_Global,                        -- GNAT
  98       Aspect_Implicit_Dereference,
  99       Aspect_Initial_Condition,             -- GNAT
 100       Aspect_Initializes,                   -- GNAT
 101       Aspect_Input,
 102       Aspect_Interrupt_Priority,
 103       Aspect_Invariant,                     -- GNAT
 104       Aspect_Iterator_Element,
 105       Aspect_Iterable,                      -- GNAT
 106       Aspect_Link_Name,
 107       Aspect_Linker_Section,                -- GNAT
 108       Aspect_Machine_Radix,
 109       Aspect_Object_Size,                   -- GNAT
 110       Aspect_Output,
 111       Aspect_Part_Of,                       -- GNAT
 112       Aspect_Post,
 113       Aspect_Postcondition,
 114       Aspect_Pre,
 115       Aspect_Precondition,
 116       Aspect_Predicate,                     -- GNAT
 117       Aspect_Priority,
 118       Aspect_Read,
 119       Aspect_Refined_Depends,               -- GNAT
 120       Aspect_Refined_Global,                -- GNAT
 121       Aspect_Refined_Post,                  -- GNAT
 122       Aspect_Refined_State,                 -- GNAT
 123       Aspect_Relative_Deadline,
 124       Aspect_Scalar_Storage_Order,          -- GNAT
 125       Aspect_Simple_Storage_Pool,           -- GNAT
 126       Aspect_Size,
 127       Aspect_Small,
 128       Aspect_SPARK_Mode,                    -- GNAT
 129       Aspect_Static_Predicate,
 130       Aspect_Storage_Pool,
 131       Aspect_Storage_Size,
 132       Aspect_Stream_Size,
 133       Aspect_Suppress,
 134       Aspect_Synchronization,
 135       Aspect_Test_Case,                     -- GNAT
 136       Aspect_Type_Invariant,
 137       Aspect_Unsuppress,
 138       Aspect_Value_Size,                    -- GNAT
 139       Aspect_Variable_Indexing,
 140       Aspect_Warnings,                      -- GNAT
 141       Aspect_Write,
 142
 143       --  The following aspects correspond to library unit pragmas
 144
 145       Aspect_All_Calls_Remote,
 146       Aspect_Elaborate_Body,
 147       Aspect_Preelaborate,
 148       Aspect_Pure,
 149       Aspect_Remote_Call_Interface,
 150       Aspect_Remote_Types,
 151       Aspect_Shared_Passive,
 152       Aspect_Universal_Data,                -- GNAT
 153
 154       --  Remaining aspects have a static boolean value that turns the aspect
 155       --  on or off. They all correspond to pragmas, but are only converted to
 156       --  the pragmas where the value is True. A value of False normally means
 157       --  that the aspect is ignored, except in the case of derived types where
 158       --  the aspect value is inherited from the parent, in which case, we do
 159       --  not allow False if we inherit a True value from the parent.
 160
 161       Aspect_Async_Readers,                 -- GNAT
 162       Aspect_Async_Writers,                 -- GNAT
 163       Aspect_Asynchronous,
 164       Aspect_Atomic,
 165       Aspect_Atomic_Components,
 166       Aspect_Discard_Names,
 167       Aspect_Effective_Reads,               -- GNAT
 168       Aspect_Effective_Writes,              -- GNAT
 169       Aspect_Export,
 170       Aspect_Favor_Top_Level,               -- GNAT
 171       Aspect_Independent,
 172       Aspect_Independent_Components,
 173       Aspect_Import,
 174       Aspect_Inline,
 175       Aspect_Inline_Always,                 -- GNAT
 176       Aspect_Interrupt_Handler,
 177       Aspect_No_Return,
 178       Aspect_Pack,
 179       Aspect_Persistent_BSS,                -- GNAT
 180       Aspect_Preelaborable_Initialization,
 181       Aspect_Pure_Function,                 -- GNAT
 182       Aspect_Remote_Access_Type,            -- GNAT
 183       Aspect_Shared,                        -- GNAT (equivalent to Atomic)
 184       Aspect_Simple_Storage_Pool_Type,      -- GNAT
 185       Aspect_Suppress_Debug_Info,           -- GNAT
 186       Aspect_Unchecked_Union,
 187       Aspect_Universal_Aliasing,            -- GNAT
 188       Aspect_Unmodified,                    -- GNAT
 189       Aspect_Unreferenced,                  -- GNAT
 190       Aspect_Unreferenced_Objects,          -- GNAT
 191       Aspect_Volatile,
 192       Aspect_Volatile_Components,
 193
 194       --  Aspects that have a static boolean value but don't correspond to
 195       --  pragmas
 196
 197       Aspect_Lock_Free);                    -- GNAT
 198
 199    subtype Aspect_Id_Exclude_No_Aspect is
 200      Aspect_Id range Aspect_Id'Succ (No_Aspect) .. Aspect_Id'Last;
 201    --  Aspect_Id's excluding No_Aspect
 202
 203    --  The following array indicates aspects that accept 'Class
 204
 205    Class_Aspect_OK : constant array (Aspect_Id) of Boolean :=
 206      (Aspect_Invariant      => True,
 207       Aspect_Pre            => True,
 208       Aspect_Predicate      => True,
 209       Aspect_Post           => True,
 210       Aspect_Type_Invariant => True,
 211       others                => False);
 212
 213    --  The following array identifies all implementation defined aspects
 214
 215    Implementation_Defined_Aspect : constant array (Aspect_Id) of Boolean :=
 216      (Aspect_Abstract_State           => True,
 217       Aspect_Async_Readers            => True,
 218       Aspect_Async_Writers            => True,
 219       Aspect_Contract_Cases           => True,
 220       Aspect_Depends                  => True,
 221       Aspect_Dimension                => True,
 222       Aspect_Dimension_System         => True,
 223       Aspect_Effective_Reads          => True,
 224       Aspect_Effective_Writes         => True,
 225       Aspect_Favor_Top_Level          => True,
 226       Aspect_Global                   => True,
 227       Aspect_Inline_Always            => True,
 228       Aspect_Invariant                => True,
 229       Aspect_Lock_Free                => True,
 230       Aspect_Object_Size              => True,
 231       Aspect_Persistent_BSS           => True,
 232       Aspect_Predicate                => True,
 233       Aspect_Pure_Function            => True,
 234       Aspect_Remote_Access_Type       => True,
 235       Aspect_Scalar_Storage_Order     => True,
 236       Aspect_Shared                   => True,
 237       Aspect_Simple_Storage_Pool      => True,
 238       Aspect_Simple_Storage_Pool_Type => True,
 239       Aspect_Suppress_Debug_Info      => True,
 240       Aspect_Test_Case                => True,
 241       Aspect_Universal_Aliasing       => True,
 242       Aspect_Universal_Data           => True,
 243       Aspect_Unmodified               => True,
 244       Aspect_Unreferenced             => True,
 245       Aspect_Unreferenced_Objects     => True,
 246       Aspect_Value_Size               => True,
 247       Aspect_Warnings                 => True,
 248       others                          => False);
 249
 250    --  The following array indicates aspects for which multiple occurrences of
 251    --  the same aspect attached to the same declaration are allowed.
 252
 253    No_Duplicates_Allowed : constant array (Aspect_Id) of Boolean :=
 254      (Aspect_Test_Case => False,
 255       others           => True);
 256
 257    --  The following subtype defines aspects corresponding to library unit
 258    --  pragmas, these can only validly appear as aspects for library units,
 259    --  and result in a corresponding pragma being inserted immediately after
 260    --  the occurrence of the aspect.
 261
 262    subtype Library_Unit_Aspects is
 263      Aspect_Id range Aspect_All_Calls_Remote .. Aspect_Universal_Data;
 264
 265    --  The following subtype defines aspects accepting an optional static
 266    --  boolean parameter indicating if the aspect should be active or
 267    --  cancelling. If the parameter is missing the effective value is True,
 268    --  enabling the aspect. If the parameter is present it must be a static
 269    --  expression of type Standard.Boolean. If the value is True, then the
 270    --  aspect is enabled. If it is False, the aspect is disabled.
 271
 272    subtype Boolean_Aspects is
 273      Aspect_Id range Aspect_Async_Readers .. Aspect_Id'Last;
 274
 275    subtype Pre_Post_Aspects is
 276      Aspect_Id range Aspect_Post .. Aspect_Precondition;
 277
 278    --  The following type is used for indicating allowed expression forms
 279
 280    type Aspect_Expression is
 281      (Expression,             -- Required expression
 282       Name,                   -- Required name
 283       Optional_Expression,    -- Optional boolean expression
 284       Optional_Name);         -- Optional name
 285
 286    --  The following array indicates what argument type is required
 287
 288    Aspect_Argument : constant array (Aspect_Id) of Aspect_Expression :=
 289      (No_Aspect                      => Optional_Expression,
 290       Aspect_Abstract_State          => Expression,
 291       Aspect_Address                 => Expression,
 292       Aspect_Alignment               => Expression,
 293       Aspect_Attach_Handler          => Expression,
 294       Aspect_Bit_Order               => Expression,
 295       Aspect_Component_Size          => Expression,
 296       Aspect_Constant_Indexing       => Name,
 297       Aspect_Contract_Cases          => Expression,
 298       Aspect_Convention              => Name,
 299       Aspect_CPU                     => Expression,
 300       Aspect_Default_Component_Value => Expression,
 301       Aspect_Default_Iterator        => Name,
 302       Aspect_Default_Value           => Expression,
 303       Aspect_Depends                 => Expression,
 304       Aspect_Dimension               => Expression,
 305       Aspect_Dimension_System        => Expression,
 306       Aspect_Dispatching_Domain      => Expression,
 307       Aspect_Dynamic_Predicate       => Expression,
 308       Aspect_External_Name           => Expression,
 309       Aspect_External_Tag            => Expression,
 310       Aspect_Global                  => Expression,
 311       Aspect_Implicit_Dereference    => Name,
 312       Aspect_Initial_Condition       => Expression,
 313       Aspect_Initializes             => Expression,
 314       Aspect_Input                   => Name,
 315       Aspect_Interrupt_Priority      => Expression,
 316       Aspect_Invariant               => Expression,
 317       Aspect_Iterable                => Expression,
 318       Aspect_Iterator_Element        => Name,
 319       Aspect_Link_Name               => Expression,
 320       Aspect_Linker_Section          => Expression,
 321       Aspect_Machine_Radix           => Expression,
 322       Aspect_Object_Size             => Expression,
 323       Aspect_Output                  => Name,
 324       Aspect_Part_Of                 => Expression,
 325       Aspect_Post                    => Expression,
 326       Aspect_Postcondition           => Expression,
 327       Aspect_Pre                     => Expression,
 328       Aspect_Precondition            => Expression,
 329       Aspect_Predicate               => Expression,
 330       Aspect_Priority                => Expression,
 331       Aspect_Read                    => Name,
 332       Aspect_Refined_Depends         => Expression,
 333       Aspect_Refined_Global          => Expression,
 334       Aspect_Refined_Post            => Expression,
 335       Aspect_Refined_State           => Expression,
 336       Aspect_Relative_Deadline       => Expression,
 337       Aspect_Scalar_Storage_Order    => Expression,
 338       Aspect_Simple_Storage_Pool     => Name,
 339       Aspect_Size                    => Expression,
 340       Aspect_Small                   => Expression,
 341       Aspect_SPARK_Mode              => Optional_Name,
 342       Aspect_Static_Predicate        => Expression,
 343       Aspect_Storage_Pool            => Name,
 344       Aspect_Storage_Size            => Expression,
 345       Aspect_Stream_Size             => Expression,
 346       Aspect_Suppress                => Name,
 347       Aspect_Synchronization         => Name,
 348       Aspect_Test_Case               => Expression,
 349       Aspect_Type_Invariant          => Expression,
 350       Aspect_Unsuppress              => Name,
 351       Aspect_Value_Size              => Expression,
 352       Aspect_Variable_Indexing       => Name,
 353       Aspect_Warnings                => Name,
 354       Aspect_Write                   => Name,
 355
 356       Boolean_Aspects                => Optional_Expression,
 357       Library_Unit_Aspects           => Optional_Expression);
 358
 359    -----------------------------------------
 360    -- Table Linking Names and Aspect_Id's --
 361    -----------------------------------------
 362
 363    --  Table linking aspect names and id's
 364
 365    Aspect_Names : constant array (Aspect_Id) of Name_Id :=
 366      (No_Aspect                           => No_Name,
 367       Aspect_Abstract_State               => Name_Abstract_State,
 368       Aspect_Address                      => Name_Address,
 369       Aspect_Alignment                    => Name_Alignment,
 370       Aspect_All_Calls_Remote             => Name_All_Calls_Remote,
 371       Aspect_Async_Readers                => Name_Async_Readers,
 372       Aspect_Async_Writers                => Name_Async_Writers,
 373       Aspect_Asynchronous                 => Name_Asynchronous,
 374       Aspect_Atomic                       => Name_Atomic,
 375       Aspect_Atomic_Components            => Name_Atomic_Components,
 376       Aspect_Attach_Handler               => Name_Attach_Handler,
 377       Aspect_Bit_Order                    => Name_Bit_Order,
 378       Aspect_Component_Size               => Name_Component_Size,
 379       Aspect_Constant_Indexing            => Name_Constant_Indexing,
 380       Aspect_Contract_Cases               => Name_Contract_Cases,
 381       Aspect_Convention                   => Name_Convention,
 382       Aspect_CPU                          => Name_CPU,
 383       Aspect_Default_Iterator             => Name_Default_Iterator,
 384       Aspect_Default_Value                => Name_Default_Value,
 385       Aspect_Default_Component_Value      => Name_Default_Component_Value,
 386       Aspect_Depends                      => Name_Depends,
 387       Aspect_Dimension                    => Name_Dimension,
 388       Aspect_Dimension_System             => Name_Dimension_System,
 389       Aspect_Discard_Names                => Name_Discard_Names,
 390       Aspect_Dispatching_Domain           => Name_Dispatching_Domain,
 391       Aspect_Dynamic_Predicate            => Name_Dynamic_Predicate,
 392       Aspect_Effective_Reads              => Name_Effective_Reads,
 393       Aspect_Effective_Writes             => Name_Effective_Writes,
 394       Aspect_Elaborate_Body               => Name_Elaborate_Body,
 395       Aspect_External_Name                => Name_External_Name,
 396       Aspect_External_Tag                 => Name_External_Tag,
 397       Aspect_Export                       => Name_Export,
 398       Aspect_Favor_Top_Level              => Name_Favor_Top_Level,
 399       Aspect_Global                       => Name_Global,
 400       Aspect_Implicit_Dereference         => Name_Implicit_Dereference,
 401       Aspect_Import                       => Name_Import,
 402       Aspect_Independent                  => Name_Independent,
 403       Aspect_Independent_Components       => Name_Independent_Components,
 404       Aspect_Inline                       => Name_Inline,
 405       Aspect_Inline_Always                => Name_Inline_Always,
 406       Aspect_Initial_Condition            => Name_Initial_Condition,
 407       Aspect_Initializes                  => Name_Initializes,
 408       Aspect_Input                        => Name_Input,
 409       Aspect_Interrupt_Handler            => Name_Interrupt_Handler,
 410       Aspect_Interrupt_Priority           => Name_Interrupt_Priority,
 411       Aspect_Invariant                    => Name_Invariant,
 412       Aspect_Iterator_Element             => Name_Iterator_Element,
 413       Aspect_Iterable                     => Name_Iterable,
 414       Aspect_Link_Name                    => Name_Link_Name,
 415       Aspect_Linker_Section               => Name_Linker_Section,
 416       Aspect_Lock_Free                    => Name_Lock_Free,
 417       Aspect_Machine_Radix                => Name_Machine_Radix,
 418       Aspect_No_Return                    => Name_No_Return,
 419       Aspect_Object_Size                  => Name_Object_Size,
 420       Aspect_Output                       => Name_Output,
 421       Aspect_Pack                         => Name_Pack,
 422       Aspect_Part_Of                      => Name_Part_Of,
 423       Aspect_Persistent_BSS               => Name_Persistent_BSS,
 424       Aspect_Post                         => Name_Post,
 425       Aspect_Postcondition                => Name_Postcondition,
 426       Aspect_Pre                          => Name_Pre,
 427       Aspect_Precondition                 => Name_Precondition,
 428       Aspect_Predicate                    => Name_Predicate,
 429       Aspect_Preelaborable_Initialization => Name_Preelaborable_Initialization,
 430       Aspect_Preelaborate                 => Name_Preelaborate,
 431       Aspect_Priority                     => Name_Priority,
 432       Aspect_Pure                         => Name_Pure,
 433       Aspect_Pure_Function                => Name_Pure_Function,
 434       Aspect_Read                         => Name_Read,
 435       Aspect_Refined_Depends              => Name_Refined_Depends,
 436       Aspect_Refined_Global               => Name_Refined_Global,
 437       Aspect_Refined_Post                 => Name_Refined_Post,
 438       Aspect_Refined_State                => Name_Refined_State,
 439       Aspect_Relative_Deadline            => Name_Relative_Deadline,
 440       Aspect_Remote_Access_Type           => Name_Remote_Access_Type,
 441       Aspect_Remote_Call_Interface        => Name_Remote_Call_Interface,
 442       Aspect_Remote_Types                 => Name_Remote_Types,
 443       Aspect_Scalar_Storage_Order         => Name_Scalar_Storage_Order,
 444       Aspect_Shared                       => Name_Shared,
 445       Aspect_Shared_Passive               => Name_Shared_Passive,
 446       Aspect_Simple_Storage_Pool          => Name_Simple_Storage_Pool,
 447       Aspect_Simple_Storage_Pool_Type     => Name_Simple_Storage_Pool_Type,
 448       Aspect_Size                         => Name_Size,
 449       Aspect_Small                        => Name_Small,
 450       Aspect_SPARK_Mode                   => Name_SPARK_Mode,
 451       Aspect_Static_Predicate             => Name_Static_Predicate,
 452       Aspect_Storage_Pool                 => Name_Storage_Pool,
 453       Aspect_Storage_Size                 => Name_Storage_Size,
 454       Aspect_Stream_Size                  => Name_Stream_Size,
 455       Aspect_Suppress                     => Name_Suppress,
 456       Aspect_Suppress_Debug_Info          => Name_Suppress_Debug_Info,
 457       Aspect_Synchronization              => Name_Synchronization,
 458       Aspect_Test_Case                    => Name_Test_Case,
 459       Aspect_Type_Invariant               => Name_Type_Invariant,
 460       Aspect_Unchecked_Union              => Name_Unchecked_Union,
 461       Aspect_Universal_Aliasing           => Name_Universal_Aliasing,
 462       Aspect_Universal_Data               => Name_Universal_Data,
 463       Aspect_Unmodified                   => Name_Unmodified,
 464       Aspect_Unreferenced                 => Name_Unreferenced,
 465       Aspect_Unreferenced_Objects         => Name_Unreferenced_Objects,
 466       Aspect_Unsuppress                   => Name_Unsuppress,
 467       Aspect_Value_Size                   => Name_Value_Size,
 468       Aspect_Variable_Indexing            => Name_Variable_Indexing,
 469       Aspect_Volatile                     => Name_Volatile,
 470       Aspect_Volatile_Components          => Name_Volatile_Components,
 471       Aspect_Warnings                     => Name_Warnings,
 472       Aspect_Write                        => Name_Write);
 473
 474    function Get_Aspect_Id (Name : Name_Id) return Aspect_Id;
 475    pragma Inline (Get_Aspect_Id);
 476    --  Given a name Nam, returns the corresponding aspect id value. If the name
 477    --  does not match any aspect, then No_Aspect is returned as the result.
 478
 479    function Get_Aspect_Id (Aspect : Node_Id) return Aspect_Id;
 480    pragma Inline (Get_Aspect_Id);
 481    --  Given an aspect specification, return the corresponding aspect_id value.
 482    --  If the name does not match any aspect, return No_Aspect.
 483
 484    ------------------------------------
 485    -- Delaying Evaluation of Aspects --
 486    ------------------------------------
 487
 488    --  The RM requires that all language defined aspects taking an expression
 489    --  delay evaluation of the expression till the freeze point of the entity
 490    --  to which the aspect applies. This allows forward references, and is of
 491    --  use for example in connection with preconditions and postconditions
 492    --  where the requirement of making all references in contracts to local
 493    --  functions be backwards references would be onerous.
 494
 495    --  For consistency, even attributes like Size are delayed, so we can do:
 496
 497    --    type A is range 1 .. 10
 498    --      with Size => Not_Defined_Yet;
 499    --    ..
 500    --    Not_Defined_Yet : constant := 64;
 501
 502    --  Resulting in A having a size of 64, which gets set when A is frozen.
 503    --  Furthermore, we can have a situation like
 504
 505    --    type A is range 1 .. 10
 506    --      with Size => Not_Defined_Yet;
 507    --    ..
 508    --    type B is new A;
 509    --    ..
 510    --    Not_Defined_Yet : constant := 64;
 511
 512    --  where the Size of A is considered to have been previously specified at
 513    --  the point of derivation, even though the actual value of the size is
 514    --  not known yet, and in this example B inherits the size value of 64.
 515
 516    --  Our normal implementation model (prior to Ada 2012) was simply to copy
 517    --  inheritable attributes at the point of derivation. Then any subsequent
 518    --  representation items apply either to the parent type, not affecting the
 519    --  derived type, or to the derived type, not affecting the parent type.
 520
 521    --  To deal with the delayed aspect case, we use two flags. The first is
 522    --  set on the parent type if it has delayed representation aspects. This
 523    --  flag Has_Delayed_Rep_Aspects indicates that if we derive from this type
 524    --  we have to worry about making sure we inherit any delayed aspects. The
 525    --  second flag is set on a derived type: May_Have_Inherited_Rep_Aspects
 526    --  is set if the parent type has Has_Delayed_Rep_Aspects set.
 527
 528    --  When we freeze a derived type, if the May_Have_Inherited_Rep_Aspects
 529    --  flag is set, then we call Freeze.Inherit_Delayed_Rep_Aspects when
 530    --  the derived type is frozen, which deals with the necessary copying of
 531    --  information from the parent type, which must be frozen at that point
 532    --  (since freezing the derived type first freezes the parent type).
 533
 534    --  The following shows which aspects are delayed. There are three cases:
 535
 536    type Delay_Type is
 537      (Always_Delay,
 538       --  This aspect is not a representation aspect that can be inherited and
 539       --  is always delayed, as required by the language definition.
 540
 541       Never_Delay,
 542       --  There are two cases. There are language defined aspects like
 543       --  Convention where the "expression" is simply an uninterpreted
 544       --  identifier, and there is no issue of evaluating it and thus no
 545       --  issue of delaying the evaluation. The second case is implementation
 546       --  defined aspects where we have decided that we don't want to allow
 547       --  delays (and for our own aspects we can do what we like).
 548
 549       Rep_Aspect);
 550       --  These are the cases of representation aspects that are in general
 551       --  delayed, and where there is a potential issue of derived types that
 552       --  inherit delayed representation values.
 553
 554    --  Note: even if this table indicates that an aspect is delayed, we never
 555    --  delay Boolean aspects that have a missing expression (taken as True),
 556    --  or expressions for delayed rep items that consist of an integer literal
 557    --  (most cases of Size etc. in practice), since in these cases we know we
 558    --  can get the value of the expression without delay. Note that we still
 559    --  need to delay Boolean aspects that are specifically set to True:
 560
 561    --     type R is array (0 .. 31) of Boolean
 562    --       with Pack => True;
 563    --     True : constant Boolean := False;
 564
 565    --  This is nonsense, but we need to make it work and result in R not
 566    --  being packed, and if we have something like:
 567
 568    --     type R is array (0 .. 31) of Boolean
 569    --       with Pack => True;
 570    --     RR : R;
 571    --     True : constant Boolean := False;
 572
 573    --  This is illegal because the visibility of True changes after the freeze
 574    --  point, which is not allowed, and we need the delay mechanism to properly
 575    --  diagnose this error.
 576
 577    Aspect_Delay : constant array (Aspect_Id) of Delay_Type :=
 578      (No_Aspect                           => Always_Delay,
 579       Aspect_Address                      => Always_Delay,
 580       Aspect_All_Calls_Remote             => Always_Delay,
 581       Aspect_Async_Readers                => Always_Delay,
 582       Aspect_Async_Writers                => Always_Delay,
 583       Aspect_Asynchronous                 => Always_Delay,
 584       Aspect_Attach_Handler               => Always_Delay,
 585       Aspect_Constant_Indexing            => Always_Delay,
 586       Aspect_Contract_Cases               => Always_Delay,
 587       Aspect_CPU                          => Always_Delay,
 588       Aspect_Default_Iterator             => Always_Delay,
 589       Aspect_Default_Value                => Always_Delay,
 590       Aspect_Default_Component_Value      => Always_Delay,
 591       Aspect_Depends                      => Always_Delay,
 592       Aspect_Discard_Names                => Always_Delay,
 593       Aspect_Dispatching_Domain           => Always_Delay,
 594       Aspect_Dynamic_Predicate            => Always_Delay,
 595       Aspect_Effective_Reads              => Always_Delay,
 596       Aspect_Effective_Writes             => Always_Delay,
 597       Aspect_Elaborate_Body               => Always_Delay,
 598       Aspect_External_Name                => Always_Delay,
 599       Aspect_External_Tag                 => Always_Delay,
 600       Aspect_Export                       => Always_Delay,
 601       Aspect_Favor_Top_Level              => Always_Delay,
 602       Aspect_Global                       => Always_Delay,
 603       Aspect_Implicit_Dereference         => Always_Delay,
 604       Aspect_Import                       => Always_Delay,
 605       Aspect_Independent                  => Always_Delay,
 606       Aspect_Independent_Components       => Always_Delay,
 607       Aspect_Inline                       => Always_Delay,
 608       Aspect_Inline_Always                => Always_Delay,
 609       Aspect_Initial_Condition            => Always_Delay,
 610       Aspect_Initializes                  => Always_Delay,
 611       Aspect_Input                        => Always_Delay,
 612       Aspect_Interrupt_Handler            => Always_Delay,
 613       Aspect_Interrupt_Priority           => Always_Delay,
 614       Aspect_Invariant                    => Always_Delay,
 615       Aspect_Iterable                     => Always_Delay,
 616       Aspect_Iterator_Element             => Always_Delay,
 617       Aspect_Link_Name                    => Always_Delay,
 618       Aspect_Linker_Section               => Always_Delay,
 619       Aspect_Lock_Free                    => Always_Delay,
 620       Aspect_No_Return                    => Always_Delay,
 621       Aspect_Output                       => Always_Delay,
 622       Aspect_Persistent_BSS               => Always_Delay,
 623       Aspect_Post                         => Always_Delay,
 624       Aspect_Postcondition                => Always_Delay,
 625       Aspect_Pre                          => Always_Delay,
 626       Aspect_Precondition                 => Always_Delay,
 627       Aspect_Predicate                    => Always_Delay,
 628       Aspect_Preelaborable_Initialization => Always_Delay,
 629       Aspect_Preelaborate                 => Always_Delay,
 630       Aspect_Priority                     => Always_Delay,
 631       Aspect_Pure                         => Always_Delay,
 632       Aspect_Pure_Function                => Always_Delay,
 633       Aspect_Read                         => Always_Delay,
 634       Aspect_Refined_Depends              => Always_Delay,
 635       Aspect_Refined_Global               => Always_Delay,
 636       Aspect_Refined_State                => Always_Delay,
 637       Aspect_Relative_Deadline            => Always_Delay,
 638       Aspect_Remote_Access_Type           => Always_Delay,
 639       Aspect_Remote_Call_Interface        => Always_Delay,
 640       Aspect_Remote_Types                 => Always_Delay,
 641       Aspect_Shared                       => Always_Delay,
 642       Aspect_Shared_Passive               => Always_Delay,
 643       Aspect_Simple_Storage_Pool          => Always_Delay,
 644       Aspect_Simple_Storage_Pool_Type     => Always_Delay,
 645       Aspect_Static_Predicate             => Always_Delay,
 646       Aspect_Storage_Pool                 => Always_Delay,
 647       Aspect_Stream_Size                  => Always_Delay,
 648       Aspect_Suppress                     => Always_Delay,
 649       Aspect_Suppress_Debug_Info          => Always_Delay,
 650       Aspect_Type_Invariant               => Always_Delay,
 651       Aspect_Unchecked_Union              => Always_Delay,
 652       Aspect_Universal_Aliasing           => Always_Delay,
 653       Aspect_Universal_Data               => Always_Delay,
 654       Aspect_Unmodified                   => Always_Delay,
 655       Aspect_Unreferenced                 => Always_Delay,
 656       Aspect_Unreferenced_Objects         => Always_Delay,
 657       Aspect_Unsuppress                   => Always_Delay,
 658       Aspect_Variable_Indexing            => Always_Delay,
 659       Aspect_Write                        => Always_Delay,
 660
 661       Aspect_Abstract_State               => Never_Delay,
 662       Aspect_Convention                   => Never_Delay,
 663       Aspect_Dimension                    => Never_Delay,
 664       Aspect_Dimension_System             => Never_Delay,
 665       Aspect_Part_Of                      => Never_Delay,
 666       Aspect_Refined_Post                 => Never_Delay,
 667       Aspect_SPARK_Mode                   => Never_Delay,
 668       Aspect_Synchronization              => Never_Delay,
 669       Aspect_Test_Case                    => Never_Delay,
 670       Aspect_Warnings                     => Never_Delay,
 671
 672       Aspect_Alignment                    => Rep_Aspect,
 673       Aspect_Atomic                       => Rep_Aspect,
 674       Aspect_Atomic_Components            => Rep_Aspect,
 675       Aspect_Bit_Order                    => Rep_Aspect,
 676       Aspect_Component_Size               => Rep_Aspect,
 677       Aspect_Machine_Radix                => Rep_Aspect,
 678       Aspect_Object_Size                  => Rep_Aspect,
 679       Aspect_Pack                         => Rep_Aspect,
 680       Aspect_Scalar_Storage_Order         => Rep_Aspect,
 681       Aspect_Size                         => Rep_Aspect,
 682       Aspect_Small                        => Rep_Aspect,
 683       Aspect_Storage_Size                 => Rep_Aspect,
 684       Aspect_Value_Size                   => Rep_Aspect,
 685       Aspect_Volatile                     => Rep_Aspect,
 686       Aspect_Volatile_Components          => Rep_Aspect);
 687
 688    ------------------------------------------------
 689    -- Handling of Aspect Specifications on Stubs --
 690    ------------------------------------------------
 691
 692    --  Aspects that appear on the following stub nodes
 693
 694    --    N_Package_Body_Stub
 695    --    N_Protected_Body_Stub
 696    --    N_Subprogram_Body_Stub
 697    --    N_Task_Body_Stub
 698
 699    --  are treated as if they apply to the corresponding proper body. Their
 700    --  analysis is postponed until the analysis of the proper body takes place
 701    --  (see Analyze_Proper_Body). The delay is required because the analysis
 702    --  may generate extra code which would be harder to relocate to the body.
 703    --  If the proper body is present, the aspect specifications are relocated
 704    --  to the corresponding body node:
 705
 706    --    N_Package_Body
 707    --    N_Protected_Body
 708    --    N_Subprogram_Body
 709    --    N_Task_Body
 710
 711    --  The subsequent analysis takes care of the aspect-to-pragma conversions
 712    --  and verification of pragma legality. In the case where the proper body
 713    --  is not available, the aspect specifications are analyzed on the spot
 714    --  (see Analyze_Proper_Body) to catch potential errors.
 715
 716    --  The following table lists all aspects that can apply to a subprogram
 717    --  body [stub]. For instance, the following example is legal:
 718
 719    --    package P with SPARK_Mode ...;
 720    --    package body P with SPARK_Mode is ...;
 721
 722    --  The table should be synchronized with Pragma_On_Body_Or_Stub_OK in unit
 723    --  Sem_Prag if the aspects below are implemented by a pragma.
 724
 725    Aspect_On_Body_Or_Stub_OK : constant array (Aspect_Id) of Boolean :=
 726      (Aspect_Refined_Depends              => True,
 727       Aspect_Refined_Global               => True,
 728       Aspect_Refined_Post                 => True,
 729       Aspect_SPARK_Mode                   => True,
 730       Aspect_Warnings                     => True,
 731       others                              => False);
 732
 733    ---------------------------------------------------
 734    -- Handling of Aspect Specifications in the Tree --
 735    ---------------------------------------------------
 736
 737    --  Several kinds of declaration node permit aspect specifications in Ada
 738    --  2012 mode. If there was room in all the corresponding declaration nodes,
 739    --  we could just have a field Aspect_Specifications pointing to a list of
 740    --  nodes for the aspects (N_Aspect_Specification nodes). But there isn't
 741    --  room, so we adopt a different approach.
 742
 743    --  The following subprograms provide access to a specialized interface
 744    --  implemented internally with a hash table in the body, that provides
 745    --  access to aspect specifications.
 746
 747    function Aspect_Specifications (N : Node_Id) return List_Id;
 748    --  Given a node N, returns the list of N_Aspect_Specification nodes that
 749    --  are attached to this declaration node. If the node is in the class of
 750    --  declaration nodes that permit aspect specifications, as defined by the
 751    --  predicate above, and if their Has_Aspects flag is set to True, then this
 752    --  will always be a non-empty list. If this flag is set to False, then
 753    --  No_List is returned. Normally, the only nodes that have Has_Aspects set
 754    --  True are the nodes for which Permits_Aspect_Specifications would return
 755    --  True (i.e. the declaration nodes defined in the RM as permitting the
 756    --  presence of Aspect_Specifications). However, it is possible for the
 757    --  flag Has_Aspects to be set on other nodes as a result of Rewrite and
 758    --  Replace calls, and this function may be used to retrieve the aspect
 759    --  specifications for the original rewritten node in such cases.
 760
 761    function Aspects_On_Body_Or_Stub_OK (N : Node_Id) return Boolean;
 762    --  N denotes a body [stub] with aspects. Determine whether all aspects of N
 763    --  are allowed to appear on a body [stub].
 764
 765    procedure Exchange_Aspects (N1 : Node_Id; N2 : Node_Id);
 766    --  Exchange the aspect specifications of two nodes. If either node lacks an
 767    --  aspect specification list, the routine has no effect. It is assumed that
 768    --  both nodes can support aspects.
 769
 770    function Find_Aspect (Id : Entity_Id; A : Aspect_Id) return Node_Id;
 771    --  Find the aspect specification of aspect A associated with entity I.
 772    --  Return Empty if Id does not have the requested aspect.
 773
 774    function Find_Value_Of_Aspect
 775      (Id : Entity_Id;
 776       A  : Aspect_Id) return Node_Id;
 777    --  Find the value of aspect A associated with entity Id. Return Empty if
 778    --  Id does not have the requested aspect.
 779
 780    function Has_Aspect (Id : Entity_Id; A : Aspect_Id) return Boolean;
 781    --  Determine whether entity Id has aspect A
 782
 783    procedure Move_Aspects (From : Node_Id; To : Node_Id);
 784    --  Relocate the aspect specifications of node From to node To. On entry it
 785    --  is assumed that To does not have aspect specifications. If From has no
 786    --  aspects, the routine has no effect.
 787
 788    procedure Move_Or_Merge_Aspects (From : Node_Id; To : Node_Id);
 789    --  Relocate the aspect specifications of node From to node To. If To has
 790    --  aspects, the aspects of From are added to the aspects of To. If From has
 791    --  no aspects, the routine has no effect. When From denotes a subprogram
 792    --  body stub that also acts as a spec, the only aspects relocated to node
 793    --  To are those from table Aspect_On_Body_Or_Stub_OK and preconditions.
 794
 795    function Permits_Aspect_Specifications (N : Node_Id) return Boolean;
 796    --  Returns True if the node N is a declaration node that permits aspect
 797    --  specifications in the grammar. It is possible for other nodes to have
 798    --  aspect specifications as a result of Rewrite or Replace calls.
 799
 800    procedure Remove_Aspects (N : Node_Id);
 801    --  Delete the aspect specifications associated with node N. If the node has
 802    --  no aspects, the routine has no effect.
 803
 804    function Same_Aspect (A1 : Aspect_Id; A2 : Aspect_Id) return Boolean;
 805    --  Returns True if A1 and A2 are (essentially) the same aspect. This is not
 806    --  a simple equality test because e.g. Post and Postcondition are the same.
 807    --  This is used for detecting duplicate aspects.
 808
 809    procedure Set_Aspect_Specifications (N : Node_Id; L : List_Id);
 810    --  The node N must be in the class of declaration nodes that permit aspect
 811    --  specifications and the Has_Aspects flag must be False on entry. L must
 812    --  be a non-empty list of N_Aspect_Specification nodes. This procedure sets
 813    --  the Has_Aspects flag to True, and makes an entry that can be retrieved
 814    --  by a subsequent Aspect_Specifications call. It is an error to call this
 815    --  procedure with a node that does not permit aspect specifications, or a
 816    --  node that has its Has_Aspects flag set True on entry, or with L being an
 817    --  empty list or No_List.
 818
 819    procedure Tree_Read;
 820    --  Reads contents of Aspect_Specifications hash table from the tree file
 821
 822    procedure Tree_Write;
 823    --  Writes contents of Aspect_Specifications hash table to the tree file
 824
 825 end Aspects;