gcc/cp/friend.c

   1 /* Help friends in C++.
   2    Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
   3    Free Software Foundation, Inc.
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2, or (at your option)
  10 any later version.
  11
  12 GCC is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING.  If not, write to
  19 the Free Software Foundation, 59 Temple Place - Suite 330,
  20 Boston, MA 02111-1307, USA.  */
  21
  22 #include "config.h"
  23 #include "system.h"
  24 #include "coretypes.h"
  25 #include "tm.h"
  26 #include "tree.h"
  27 #include "rtl.h"
  28 #include "expr.h"
  29 #include "cp-tree.h"
  30 #include "flags.h"
  31 #include "output.h"
  32 #include "toplev.h"
  33
  34 /* Friend data structures are described in cp-tree.h.  */
  35
  36 /* Returns nonzero if SUPPLICANT is a friend of TYPE.  */
  37
  38 int
  39 is_friend (tree type, tree supplicant)
  40 {
  41   int declp;
  42   tree list;
  43   tree context;
  44
  45   if (supplicant == NULL_TREE || type == NULL_TREE)
  46     return 0;
  47
  48   declp = DECL_P (supplicant);
  49
  50   if (declp)
  51     /* It's a function decl.  */
  52     {
  53       tree list = DECL_FRIENDLIST (TYPE_MAIN_DECL (type));
  54       tree name = DECL_NAME (supplicant);
  55
  56       for (; list ; list = TREE_CHAIN (list))
  57         {
  58           if (name == FRIEND_NAME (list))
  59             {
  60               tree friends = FRIEND_DECLS (list);
  61               for (; friends ; friends = TREE_CHAIN (friends))
  62                 {
  63                   tree friend = TREE_VALUE (friends);
  64
  65                   if (friend == NULL_TREE)
  66                     continue;
  67
  68                   if (supplicant == friend)
  69                     return 1;
  70
  71                   if (is_specialization_of_friend (supplicant, friend))
  72                     return 1;
  73                 }
  74               break;
  75             }
  76         }
  77     }
  78   else
  79     /* It's a type.  */
  80     {
  81       /* Nested classes are implicitly friends of their enclosing types, as
  82          per core issue 45 (this is a change from the standard).  */
  83       for (context = supplicant;
  84            context && TYPE_P (context);
  85            context = TYPE_CONTEXT (context))
  86         if (type == context)
  87           return 1;
  88
  89       list = CLASSTYPE_FRIEND_CLASSES (TREE_TYPE (TYPE_MAIN_DECL (type)));
  90       for (; list ; list = TREE_CHAIN (list))
  91         {
  92           tree t = TREE_VALUE (list);
  93
  94           if (TREE_CODE (t) == TEMPLATE_DECL ?
  95               is_specialization_of_friend (TYPE_MAIN_DECL (supplicant), t) :
  96               same_type_p (supplicant, t))
  97             return 1;
  98         }
  99     }
 100
 101   if (declp && DECL_FUNCTION_MEMBER_P (supplicant))
 102     context = DECL_CONTEXT (supplicant);
 103   else if (! declp)
 104     /* Local classes have the same access as the enclosing function.  */
 105     context = decl_function_context (TYPE_MAIN_DECL (supplicant));
 106   else
 107     context = NULL_TREE;
 108
 109   /* A namespace is not friend to anybody.  */
 110   if (context && TREE_CODE (context) == NAMESPACE_DECL)
 111     context = NULL_TREE;
 112
 113   if (context)
 114     return is_friend (type, context);
 115
 116   return 0;
 117 }
 118
 119 /* Add a new friend to the friends of the aggregate type TYPE.
 120    DECL is the FUNCTION_DECL of the friend being added.
 121
 122    If COMPLAIN is true, warning about duplicate friend is issued.
 123    We want to have this diagnostics during parsing but not
 124    when a template is being instantiated.  */
 125
 126 void
 127 add_friend (tree type, tree decl, bool complain)
 128 {
 129   tree typedecl;
 130   tree list;
 131   tree name;
 132   tree ctx;
 133
 134   if (decl == error_mark_node)
 135     return;
 136
 137   typedecl = TYPE_MAIN_DECL (type);
 138   list = DECL_FRIENDLIST (typedecl);
 139   name = DECL_NAME (decl);
 140   type = TREE_TYPE (typedecl);
 141
 142   while (list)
 143     {
 144       if (name == FRIEND_NAME (list))
 145         {
 146           tree friends = FRIEND_DECLS (list);
 147           for (; friends ; friends = TREE_CHAIN (friends))
 148             {
 149               if (decl == TREE_VALUE (friends))
 150                 {
 151                   if (complain)
 152                     warning ("%qD is already a friend of class %qT",
 153                              decl, type);
 154                   return;
 155                 }
 156             }
 157
 158           maybe_add_class_template_decl_list (type, decl, /*friend_p=*/1);
 159
 160           TREE_VALUE (list) = tree_cons (NULL_TREE, decl,
 161                                          TREE_VALUE (list));
 162           return;
 163         }
 164       list = TREE_CHAIN (list);
 165     }
 166
 167   ctx = DECL_CONTEXT (decl);
 168   if (ctx && CLASS_TYPE_P (ctx) && !uses_template_parms (ctx))
 169     perform_or_defer_access_check (TYPE_BINFO (ctx), decl);
 170
 171   maybe_add_class_template_decl_list (type, decl, /*friend_p=*/1);
 172
 173   DECL_FRIENDLIST (typedecl)
 174     = tree_cons (DECL_NAME (decl), build_tree_list (NULL_TREE, decl),
 175                  DECL_FRIENDLIST (typedecl));
 176   if (!uses_template_parms (type))
 177     DECL_BEFRIENDING_CLASSES (decl)
 178       = tree_cons (NULL_TREE, type,
 179                    DECL_BEFRIENDING_CLASSES (decl));
 180 }
 181
 182 /* Make FRIEND_TYPE a friend class to TYPE.  If FRIEND_TYPE has already
 183    been defined, we make all of its member functions friends of
 184    TYPE.  If not, we make it a pending friend, which can later be added
 185    when its definition is seen.  If a type is defined, then its TYPE_DECL's
 186    DECL_UNDEFINED_FRIENDS contains a (possibly empty) list of friend
 187    classes that are not defined.  If a type has not yet been defined,
 188    then the DECL_WAITING_FRIENDS contains a list of types
 189    waiting to make it their friend.  Note that these two can both
 190    be in use at the same time!
 191
 192    If COMPLAIN is true, warning about duplicate friend is issued.
 193    We want to have this diagnostics during parsing but not
 194    when a template is being instantiated.  */
 195
 196 void
 197 make_friend_class (tree type, tree friend_type, bool complain)
 198 {
 199   tree classes;
 200
 201   /* CLASS_TEMPLATE_DEPTH counts the number of template headers for
 202      the enclosing class.  FRIEND_DEPTH counts the number of template
 203      headers used for this friend declaration.  TEMPLATE_MEMBER_P,
 204      defined inside the `if' block for TYPENAME_TYPE case, is true if
 205      a template header in FRIEND_DEPTH is intended for DECLARATOR.
 206      For example, the code
 207
 208        template <class T> struct A {
 209          template <class U> struct B {
 210            template <class V> template <class W>
 211              friend class C<V>::D;
 212          };
 213        };
 214
 215      will eventually give the following results
 216
 217      1. CLASS_TEMPLATE_DEPTH equals 2 (for `T' and `U').
 218      2. FRIEND_DEPTH equals 2 (for `V' and `W').
 219      3. TEMPLATE_MEMBER_P is true (for `W').
 220
 221      The friend is a template friend iff FRIEND_DEPTH is nonzero.  */
 222
 223   int class_template_depth = template_class_depth (type);
 224   int friend_depth = processing_template_decl - class_template_depth;
 225
 226   if (! IS_AGGR_TYPE (friend_type))
 227     {
 228       error ("invalid type %qT declared %<friend%>", friend_type);
 229       return;
 230     }
 231
 232   if (friend_depth)
 233     /* If the TYPE is a template then it makes sense for it to be
 234        friends with itself; this means that each instantiation is
 235        friends with all other instantiations.  */
 236     {
 237       if (CLASS_TYPE_P (friend_type)
 238           && CLASSTYPE_TEMPLATE_SPECIALIZATION (friend_type)
 239           && uses_template_parms (friend_type))
 240         {
 241           /* [temp.friend]
 242              Friend declarations shall not declare partial
 243              specializations.  */
 244           error ("partial specialization %qT declared %<friend%>",
 245                  friend_type);
 246           return;
 247         }
 248     }
 249   else if (same_type_p (type, friend_type))
 250     {
 251       if (complain)
 252         pedwarn ("class %qT is implicitly friends with itself",
 253                  type);
 254       return;
 255     }
 256
 257   /* [temp.friend]
 258
 259      A friend of a class or class template can be a function or
 260      class template, a specialization of a function template or
 261      class template, or an ordinary (nontemplate) function or
 262      class.  */
 263   if (!friend_depth)
 264     ;/* ok */
 265   else if (TREE_CODE (friend_type) == TYPENAME_TYPE)
 266     {
 267       if (TREE_CODE (TYPENAME_TYPE_FULLNAME (friend_type))
 268           == TEMPLATE_ID_EXPR)
 269         {
 270           /* template <class U> friend class T::X<U>; */
 271           /* [temp.friend]
 272              Friend declarations shall not declare partial
 273              specializations.  */
 274           error ("partial specialization %qT declared %<friend%>",
 275                  friend_type);
 276           return;
 277         }
 278       else
 279         {
 280           /* We will figure this out later.  */
 281           bool template_member_p = false;
 282
 283           tree ctype = TYPE_CONTEXT (friend_type);
 284           tree name = TYPE_IDENTIFIER (friend_type);
 285           tree decl;
 286
 287           if (!uses_template_parms_level (ctype, class_template_depth
 288                                                  + friend_depth))
 289             template_member_p = true;
 290
 291           if (class_template_depth)
 292             {
 293               /* We rely on tsubst_friend_class to check the
 294                  validity of the declaration later.  */
 295               if (template_member_p)
 296                 friend_type
 297                   = make_unbound_class_template (ctype,
 298                                                  name,
 299                                                  current_template_parms,
 300                                                  tf_error);
 301               else
 302                 friend_type
 303                   = make_typename_type (ctype, name, class_type, tf_error);
 304             }
 305           else
 306             {
 307               decl = lookup_member (ctype, name, 0, true);
 308               if (!decl)
 309                 {
 310                   error ("%qT is not a member of %qT", name, ctype);
 311                   return;
 312                 }
 313               if (template_member_p && !DECL_CLASS_TEMPLATE_P (decl))
 314                 {
 315                   error ("%qT is not a member class template of %qT",
 316                          name, ctype);
 317                   cp_error_at ("%qD declared here", decl);
 318                   return;
 319                 }
 320               if (!template_member_p && (TREE_CODE (decl) != TYPE_DECL
 321                                          || !CLASS_TYPE_P (TREE_TYPE (decl))))
 322                 {
 323                   error ("%qT is not a nested class of %qT",
 324                          name, ctype);
 325                   cp_error_at ("%qD declared here", decl);
 326                   return;
 327                 }
 328
 329               friend_type = CLASSTYPE_TI_TEMPLATE (TREE_TYPE (decl));
 330             }
 331         }
 332     }
 333   else if (TREE_CODE (friend_type) == TEMPLATE_TYPE_PARM)
 334     {
 335       /* template <class T> friend class T; */
 336       error ("template parameter type %qT declared %<friend%>", friend_type);
 337       return;
 338     }
 339   else if (!CLASSTYPE_TEMPLATE_INFO (friend_type))
 340     {
 341       /* template <class T> friend class A; where A is not a template */
 342       error ("%q#T is not a template", friend_type);
 343       return;
 344     }
 345   else
 346     /* template <class T> friend class A; where A is a template */
 347     friend_type = CLASSTYPE_TI_TEMPLATE (friend_type);
 348
 349   if (friend_type == error_mark_node)
 350     return;
 351
 352   /* See if it is already a friend.  */
 353   for (classes = CLASSTYPE_FRIEND_CLASSES (type);
 354        classes;
 355        classes = TREE_CHAIN (classes))
 356     {
 357       tree probe = TREE_VALUE (classes);
 358
 359       if (TREE_CODE (friend_type) == TEMPLATE_DECL)
 360         {
 361           if (friend_type == probe)
 362             {
 363               if (complain)
 364                 warning ("%qD is already a friend of %qT", probe, type);
 365               break;
 366             }
 367         }
 368       else if (TREE_CODE (probe) != TEMPLATE_DECL)
 369         {
 370           if (same_type_p (probe, friend_type))
 371             {
 372               if (complain)
 373                 warning ("%qT is already a friend of %qT", probe, type);
 374               break;
 375             }
 376         }
 377     }
 378
 379   if (!classes)
 380     {
 381       maybe_add_class_template_decl_list (type, friend_type, /*friend_p=*/1);
 382
 383       CLASSTYPE_FRIEND_CLASSES (type)
 384         = tree_cons (NULL_TREE, friend_type, CLASSTYPE_FRIEND_CLASSES (type));
 385       if (TREE_CODE (friend_type) == TEMPLATE_DECL)
 386         friend_type = TREE_TYPE (friend_type);
 387       if (!uses_template_parms (type))
 388         CLASSTYPE_BEFRIENDING_CLASSES (friend_type)
 389           = tree_cons (NULL_TREE, type,
 390                        CLASSTYPE_BEFRIENDING_CLASSES (friend_type));
 391     }
 392 }
 393
 394 /* Main friend processor.
 395
 396    CTYPE is the class this friend belongs to.
 397
 398    DECLARATOR is the name of the friend.
 399
 400    DECL is the FUNCTION_DECL that the friend is.
 401
 402    FLAGS is just used for `grokclassfn'.
 403
 404    QUALS say what special qualifies should apply to the object
 405    pointed to by `this'.  */
 406
 407 tree
 408 do_friend (tree ctype, tree declarator, tree decl,
 409            tree attrlist, enum overload_flags flags,
 410            cp_cv_quals quals,
 411            int funcdef_flag)
 412 {
 413   /* Every decl that gets here is a friend of something.  */
 414   DECL_FRIEND_P (decl) = 1;
 415
 416   if (TREE_CODE (declarator) == TEMPLATE_ID_EXPR)
 417     {
 418       declarator = TREE_OPERAND (declarator, 0);
 419       if (is_overloaded_fn (declarator))
 420         declarator = DECL_NAME (get_first_fn (declarator));
 421     }
 422
 423   gcc_assert (TREE_CODE (decl) == FUNCTION_DECL);
 424
 425   if (ctype)
 426     {
 427       /* CLASS_TEMPLATE_DEPTH counts the number of template headers for
 428          the enclosing class.  FRIEND_DEPTH counts the number of template
 429          headers used for this friend declaration.  TEMPLATE_MEMBER_P is
 430          true if a template header in FRIEND_DEPTH is intended for
 431          DECLARATOR.  For example, the code
 432
 433            template <class T> struct A {
 434              template <class U> struct B {
 435                template <class V> template <class W>
 436                  friend void C<V>::f(W);
 437              };
 438            };
 439
 440          will eventually give the following results
 441
 442          1. CLASS_TEMPLATE_DEPTH equals 2 (for `T' and `U').
 443          2. FRIEND_DEPTH equals 2 (for `V' and `W').
 444          3. TEMPLATE_MEMBER_P is true (for `W').  */
 445
 446       int class_template_depth = template_class_depth (current_class_type);
 447       int friend_depth = processing_template_decl - class_template_depth;
 448       /* We will figure this out later.  */
 449       bool template_member_p = false;
 450
 451       tree cname = TYPE_NAME (ctype);
 452       if (TREE_CODE (cname) == TYPE_DECL)
 453         cname = DECL_NAME (cname);
 454
 455       /* A method friend.  */
 456       if (flags == NO_SPECIAL && declarator == cname)
 457         DECL_CONSTRUCTOR_P (decl) = 1;
 458
 459       /* This will set up DECL_ARGUMENTS for us.  */
 460       grokclassfn (ctype, decl, flags, quals);
 461
 462       if (friend_depth)
 463         {
 464           if (!uses_template_parms_level (ctype, class_template_depth
 465                                                  + friend_depth))
 466             template_member_p = true;
 467         }
 468
 469       /* A nested class may declare a member of an enclosing class
 470          to be a friend, so we do lookup here even if CTYPE is in
 471          the process of being defined.  */
 472       if (class_template_depth
 473           || COMPLETE_TYPE_P (ctype)
 474           || TYPE_BEING_DEFINED (ctype))
 475         {
 476           if (DECL_TEMPLATE_INFO (decl))
 477             /* DECL is a template specialization.  No need to
 478                build a new TEMPLATE_DECL.  */
 479             ;
 480           else if (class_template_depth)
 481             /* We rely on tsubst_friend_function to check the
 482                validity of the declaration later.  */
 483             decl = push_template_decl_real (decl, /*is_friend=*/1);
 484           else
 485             decl = check_classfn (ctype, decl,
 486                                   template_member_p
 487                                   ? current_template_parms
 488                                   : NULL_TREE);
 489
 490           if (template_member_p && decl && TREE_CODE (decl) == FUNCTION_DECL)
 491             decl = DECL_TI_TEMPLATE (decl);
 492
 493           if (decl)
 494             add_friend (current_class_type, decl, /*complain=*/true);
 495         }
 496       else
 497         error ("member %qD declared as friend before type %qT defined",
 498                   decl, ctype);
 499     }
 500   /* A global friend.
 501      @@ or possibly a friend from a base class ?!?  */
 502   else if (TREE_CODE (decl) == FUNCTION_DECL)
 503     {
 504       int is_friend_template = PROCESSING_REAL_TEMPLATE_DECL_P ();
 505
 506       /* Friends must all go through the overload machinery,
 507          even though they may not technically be overloaded.
 508
 509          Note that because classes all wind up being top-level
 510          in their scope, their friend wind up in top-level scope as well.  */
 511       if (funcdef_flag)
 512         SET_DECL_FRIEND_CONTEXT (decl, current_class_type);
 513
 514       if (! DECL_USE_TEMPLATE (decl))
 515         {
 516           /* We must check whether the decl refers to template
 517              arguments before push_template_decl_real adds a
 518              reference to the containing template class.  */
 519           int warn = (warn_nontemplate_friend
 520                       && ! funcdef_flag && ! is_friend_template
 521                       && current_template_parms
 522                       && uses_template_parms (decl));
 523
 524           if (is_friend_template
 525               || template_class_depth (current_class_type) != 0)
 526             /* We can't call pushdecl for a template class, since in
 527                general, such a declaration depends on template
 528                parameters.  Instead, we call pushdecl when the class
 529                is instantiated.  */
 530             decl = push_template_decl_real (decl, /*is_friend=*/1);
 531           else if (current_function_decl)
 532             /* This must be a local class, so pushdecl will be ok, and
 533                insert an unqualified friend into the local scope
 534                (rather than the containing namespace scope, which the
 535                next choice will do).  */
 536             decl = pushdecl (decl);
 537           else
 538             {
 539               /* We can't use pushdecl, as we might be in a template
 540                  class specialization, and pushdecl will insert an
 541                  unqualified friend decl into the template parameter
 542                  scope, rather than the namespace containing it.  */
 543               tree ns = decl_namespace_context (decl);
 544
 545               push_nested_namespace (ns);
 546               decl = pushdecl_namespace_level (decl);
 547               pop_nested_namespace (ns);
 548             }
 549
 550           if (warn)
 551             {
 552               static int explained;
 553               warning ("friend declaration %q#D declares a non-template "
 554                        "function", decl);
 555               if (! explained)
 556                 {
 557                   warning ("(if this is not what you intended, make sure "
 558                            "the function template has already been declared "
 559                            "and add <> after the function name here) "
 560                            "-Wno-non-template-friend disables this warning");
 561                   explained = 1;
 562                 }
 563             }
 564         }
 565
 566       if (decl == error_mark_node)
 567         return error_mark_node;
 568
 569       add_friend (current_class_type,
 570                   is_friend_template ? DECL_TI_TEMPLATE (decl) : decl,
 571                   /*complain=*/true);
 572       DECL_FRIEND_P (decl) = 1;
 573     }
 574
 575   /* Unfortunately, we have to handle attributes here.  Normally we would
 576      handle them in start_decl_1, but since this is a friend decl start_decl_1
 577      never gets to see it.  */
 578
 579   /* Set attributes here so if duplicate decl, will have proper attributes.  */
 580   cplus_decl_attributes (&decl, attrlist, 0);
 581
 582   return decl;
 583 }