gcc/cp/friend.c

   1 /* Help friends in C++.
   2    Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
   3    2007, 2008, 2010, 2011, 2012  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 3, 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 COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "tm.h"
  25 #include "tree.h"
  26 #include "cp-tree.h"
  27 #include "flags.h"
  28
  29 /* Friend data structures are described in cp-tree.h.  */
  30
  31 /* Returns nonzero if SUPPLICANT is a friend of TYPE.  */
  32
  33 int
  34 is_friend (tree type, tree supplicant)
  35 {
  36   int declp;
  37   tree list;
  38   tree context;
  39
  40   if (supplicant == NULL_TREE || type == NULL_TREE)
  41     return 0;
  42
  43   declp = DECL_P (supplicant);
  44
  45   if (declp)
  46     /* It's a function decl.  */
  47     {
  48       tree list = DECL_FRIENDLIST (TYPE_MAIN_DECL (type));
  49       tree name = DECL_NAME (supplicant);
  50
  51       for (; list ; list = TREE_CHAIN (list))
  52         {
  53           if (name == FRIEND_NAME (list))
  54             {
  55               tree friends = FRIEND_DECLS (list);
  56               for (; friends ; friends = TREE_CHAIN (friends))
  57                 {
  58                   tree this_friend = TREE_VALUE (friends);
  59
  60                   if (this_friend == NULL_TREE)
  61                     continue;
  62
  63                   if (supplicant == this_friend)
  64                     return 1;
  65
  66                   if (is_specialization_of_friend (supplicant, this_friend))
  67                     return 1;
  68                 }
  69               break;
  70             }
  71         }
  72     }
  73   else
  74     /* It's a type.  */
  75     {
  76       if (same_type_p (supplicant, type))
  77         return 1;
  78
  79       list = CLASSTYPE_FRIEND_CLASSES (TREE_TYPE (TYPE_MAIN_DECL (type)));
  80       for (; list ; list = TREE_CHAIN (list))
  81         {
  82           tree t = TREE_VALUE (list);
  83
  84           if (TREE_CODE (t) == TEMPLATE_DECL ?
  85               is_specialization_of_friend (TYPE_MAIN_DECL (supplicant), t) :
  86               same_type_p (supplicant, t))
  87             return 1;
  88         }
  89     }
  90
  91   if (declp)
  92     {
  93       if (DECL_FUNCTION_MEMBER_P (supplicant))
  94         context = DECL_CONTEXT (supplicant);
  95       else
  96         context = NULL_TREE;
  97     }
  98   else
  99     {
 100       if (TYPE_CLASS_SCOPE_P (supplicant))
 101         /* Nested classes get the same access as their enclosing types, as
 102            per DR 45 (this is a change from the standard).  */
 103         context = TYPE_CONTEXT (supplicant);
 104       else
 105         /* Local classes have the same access as the enclosing function.  */
 106         context = decl_function_context (TYPE_MAIN_DECL (supplicant));
 107     }
 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 (0, "%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, decl,
 170                                    tf_warning_or_error);
 171
 172   maybe_add_class_template_decl_list (type, decl, /*friend_p=*/1);
 173
 174   DECL_FRIENDLIST (typedecl)
 175     = tree_cons (DECL_NAME (decl), build_tree_list (NULL_TREE, decl),
 176                  DECL_FRIENDLIST (typedecl));
 177   if (!uses_template_parms (type))
 178     DECL_BEFRIENDING_CLASSES (decl)
 179       = tree_cons (NULL_TREE, type,
 180                    DECL_BEFRIENDING_CLASSES (decl));
 181 }
 182
 183 /* Make FRIEND_TYPE a friend class to TYPE.  If FRIEND_TYPE has already
 184    been defined, we make all of its member functions friends of
 185    TYPE.  If not, we make it a pending friend, which can later be added
 186    when its definition is seen.  If a type is defined, then its TYPE_DECL's
 187    DECL_UNDEFINED_FRIENDS contains a (possibly empty) list of friend
 188    classes that are not defined.  If a type has not yet been defined,
 189    then the DECL_WAITING_FRIENDS contains a list of types
 190    waiting to make it their friend.  Note that these two can both
 191    be in use at the same time!
 192
 193    If COMPLAIN is true, warning about duplicate friend is issued.
 194    We want to have this diagnostics during parsing but not
 195    when a template is being instantiated.  */
 196
 197 void
 198 make_friend_class (tree type, tree friend_type, bool complain)
 199 {
 200   tree classes;
 201
 202   /* CLASS_TEMPLATE_DEPTH counts the number of template headers for
 203      the enclosing class.  FRIEND_DEPTH counts the number of template
 204      headers used for this friend declaration.  TEMPLATE_MEMBER_P,
 205      defined inside the `if' block for TYPENAME_TYPE case, is true if
 206      a template header in FRIEND_DEPTH is intended for DECLARATOR.
 207      For example, the code
 208
 209        template <class T> struct A {
 210          template <class U> struct B {
 211            template <class V> template <class W>
 212              friend class C<V>::D;
 213          };
 214        };
 215
 216      will eventually give the following results
 217
 218      1. CLASS_TEMPLATE_DEPTH equals 2 (for `T' and `U').
 219      2. FRIEND_DEPTH equals 2 (for `V' and `W').
 220      3. TEMPLATE_MEMBER_P is true (for `W').
 221
 222      The friend is a template friend iff FRIEND_DEPTH is nonzero.  */
 223
 224   int class_template_depth = template_class_depth (type);
 225   int friend_depth = processing_template_decl - class_template_depth;
 226
 227   if (! MAYBE_CLASS_TYPE_P (friend_type)
 228       && TREE_CODE (friend_type) != TEMPLATE_TEMPLATE_PARM)
 229     {
 230       /* N1791: If the type specifier in a friend declaration designates a
 231          (possibly cv-qualified) class type, that class is declared as a
 232          friend; otherwise, the friend declaration is ignored.
 233
 234          So don't complain in C++0x mode.  */
 235       if (cxx_dialect < cxx0x)
 236         pedwarn (input_location, complain ? 0 : OPT_Wpedantic,
 237                  "invalid type %qT declared %<friend%>", friend_type);
 238       return;
 239     }
 240
 241   friend_type = cv_unqualified (friend_type);
 242
 243   if (check_for_bare_parameter_packs (friend_type))
 244     return;
 245
 246   if (friend_depth)
 247     /* If the TYPE is a template then it makes sense for it to be
 248        friends with itself; this means that each instantiation is
 249        friends with all other instantiations.  */
 250     {
 251       if (CLASS_TYPE_P (friend_type)
 252           && CLASSTYPE_TEMPLATE_SPECIALIZATION (friend_type)
 253           && uses_template_parms (friend_type))
 254         {
 255           /* [temp.friend]
 256              Friend declarations shall not declare partial
 257              specializations.  */
 258           error ("partial specialization %qT declared %<friend%>",
 259                  friend_type);
 260           return;
 261         }
 262     }
 263   else if (same_type_p (type, friend_type))
 264     {
 265       if (complain)
 266         warning (0, "class %qT is implicitly friends with itself",
 267                  type);
 268       return;
 269     }
 270
 271   /* [temp.friend]
 272
 273      A friend of a class or class template can be a function or
 274      class template, a specialization of a function template or
 275      class template, or an ordinary (nontemplate) function or
 276      class.  */
 277   if (!friend_depth)
 278     ;/* ok */
 279   else if (TREE_CODE (friend_type) == TYPENAME_TYPE)
 280     {
 281       if (TREE_CODE (TYPENAME_TYPE_FULLNAME (friend_type))
 282           == TEMPLATE_ID_EXPR)
 283         {
 284           /* template <class U> friend class T::X<U>; */
 285           /* [temp.friend]
 286              Friend declarations shall not declare partial
 287              specializations.  */
 288           error ("partial specialization %qT declared %<friend%>",
 289                  friend_type);
 290           return;
 291         }
 292       else
 293         {
 294           /* We will figure this out later.  */
 295           bool template_member_p = false;
 296
 297           tree ctype = TYPE_CONTEXT (friend_type);
 298           tree name = TYPE_IDENTIFIER (friend_type);
 299           tree decl;
 300
 301           if (!uses_template_parms_level (ctype, class_template_depth
 302                                                  + friend_depth))
 303             template_member_p = true;
 304
 305           if (class_template_depth)
 306             {
 307               /* We rely on tsubst_friend_class to check the
 308                  validity of the declaration later.  */
 309               if (template_member_p)
 310                 friend_type
 311                   = make_unbound_class_template (ctype,
 312                                                  name,
 313                                                  current_template_parms,
 314                                                  tf_error);
 315               else
 316                 friend_type
 317                   = make_typename_type (ctype, name, class_type, tf_error);
 318             }
 319           else
 320             {
 321               decl = lookup_member (ctype, name, 0, true, tf_warning_or_error);
 322               if (!decl)
 323                 {
 324                   error ("%qT is not a member of %qT", name, ctype);
 325                   return;
 326                 }
 327               if (template_member_p && !DECL_CLASS_TEMPLATE_P (decl))
 328                 {
 329                   error ("%qT is not a member class template of %qT",
 330                          name, ctype);
 331                   error ("%q+D declared here", decl);
 332                   return;
 333                 }
 334               if (!template_member_p && (TREE_CODE (decl) != TYPE_DECL
 335                                          || !CLASS_TYPE_P (TREE_TYPE (decl))))
 336                 {
 337                   error ("%qT is not a nested class of %qT",
 338                          name, ctype);
 339                   error ("%q+D declared here", decl);
 340                   return;
 341                 }
 342
 343               friend_type = CLASSTYPE_TI_TEMPLATE (TREE_TYPE (decl));
 344             }
 345         }
 346     }
 347   else if (TREE_CODE (friend_type) == TEMPLATE_TYPE_PARM)
 348     {
 349       /* template <class T> friend class T; */
 350       error ("template parameter type %qT declared %<friend%>", friend_type);
 351       return;
 352     }
 353   else if (TREE_CODE (friend_type) == TEMPLATE_TEMPLATE_PARM)
 354     friend_type = TYPE_NAME (friend_type);
 355   else if (!CLASSTYPE_TEMPLATE_INFO (friend_type))
 356     {
 357       /* template <class T> friend class A; where A is not a template */
 358       error ("%q#T is not a template", friend_type);
 359       return;
 360     }
 361   else
 362     /* template <class T> friend class A; where A is a template */
 363     friend_type = CLASSTYPE_TI_TEMPLATE (friend_type);
 364
 365   if (friend_type == error_mark_node)
 366     return;
 367
 368   /* See if it is already a friend.  */
 369   for (classes = CLASSTYPE_FRIEND_CLASSES (type);
 370        classes;
 371        classes = TREE_CHAIN (classes))
 372     {
 373       tree probe = TREE_VALUE (classes);
 374
 375       if (TREE_CODE (friend_type) == TEMPLATE_DECL)
 376         {
 377           if (friend_type == probe)
 378             {
 379               if (complain)
 380                 warning (0, "%qD is already a friend of %qT", probe, type);
 381               break;
 382             }
 383         }
 384       else if (TREE_CODE (probe) != TEMPLATE_DECL)
 385         {
 386           if (same_type_p (probe, friend_type))
 387             {
 388               if (complain)
 389                 warning (0, "%qT is already a friend of %qT", probe, type);
 390               break;
 391             }
 392         }
 393     }
 394
 395   if (!classes)
 396     {
 397       maybe_add_class_template_decl_list (type, friend_type, /*friend_p=*/1);
 398
 399       CLASSTYPE_FRIEND_CLASSES (type)
 400         = tree_cons (NULL_TREE, friend_type, CLASSTYPE_FRIEND_CLASSES (type));
 401       if (TREE_CODE (friend_type) == TEMPLATE_DECL)
 402         friend_type = TREE_TYPE (friend_type);
 403       if (!uses_template_parms (type))
 404         CLASSTYPE_BEFRIENDING_CLASSES (friend_type)
 405           = tree_cons (NULL_TREE, type,
 406                        CLASSTYPE_BEFRIENDING_CLASSES (friend_type));
 407     }
 408 }
 409
 410 /* Record DECL (a FUNCTION_DECL) as a friend of the
 411    CURRENT_CLASS_TYPE.  If DECL is a member function, CTYPE is the
 412    class of which it is a member, as named in the friend declaration.
 413    DECLARATOR is the name of the friend.  FUNCDEF_FLAG is true if the
 414    friend declaration is a definition of the function.  FLAGS is as
 415    for grokclass fn.  */
 416
 417 tree
 418 do_friend (tree ctype, tree declarator, tree decl,
 419            tree attrlist, enum overload_flags flags,
 420            bool funcdef_flag)
 421 {
 422   gcc_assert (TREE_CODE (decl) == FUNCTION_DECL);
 423   gcc_assert (!ctype || MAYBE_CLASS_TYPE_P (ctype));
 424
 425   /* Every decl that gets here is a friend of something.  */
 426   DECL_FRIEND_P (decl) = 1;
 427
 428   /* Unfortunately, we have to handle attributes here.  Normally we would
 429      handle them in start_decl_1, but since this is a friend decl start_decl_1
 430      never gets to see it.  */
 431
 432   /* Set attributes here so if duplicate decl, will have proper attributes.  */
 433   cplus_decl_attributes (&decl, attrlist, 0);
 434
 435   if (TREE_CODE (declarator) == TEMPLATE_ID_EXPR)
 436     {
 437       declarator = TREE_OPERAND (declarator, 0);
 438       if (is_overloaded_fn (declarator))
 439         declarator = DECL_NAME (get_first_fn (declarator));
 440     }
 441
 442   if (ctype)
 443     {
 444       /* CLASS_TEMPLATE_DEPTH counts the number of template headers for
 445          the enclosing class.  FRIEND_DEPTH counts the number of template
 446          headers used for this friend declaration.  TEMPLATE_MEMBER_P is
 447          true if a template header in FRIEND_DEPTH is intended for
 448          DECLARATOR.  For example, the code
 449
 450            template <class T> struct A {
 451              template <class U> struct B {
 452                template <class V> template <class W>
 453                  friend void C<V>::f(W);
 454              };
 455            };
 456
 457          will eventually give the following results
 458
 459          1. CLASS_TEMPLATE_DEPTH equals 2 (for `T' and `U').
 460          2. FRIEND_DEPTH equals 2 (for `V' and `W').
 461          3. TEMPLATE_MEMBER_P is true (for `W').  */
 462
 463       int class_template_depth = template_class_depth (current_class_type);
 464       int friend_depth = processing_template_decl - class_template_depth;
 465       /* We will figure this out later.  */
 466       bool template_member_p = false;
 467
 468       tree cname = TYPE_NAME (ctype);
 469       if (TREE_CODE (cname) == TYPE_DECL)
 470         cname = DECL_NAME (cname);
 471
 472       /* A method friend.  */
 473       if (flags == NO_SPECIAL && declarator == cname)
 474         DECL_CONSTRUCTOR_P (decl) = 1;
 475
 476       grokclassfn (ctype, decl, flags);
 477
 478       if (friend_depth)
 479         {
 480           if (!uses_template_parms_level (ctype, class_template_depth
 481                                                  + friend_depth))
 482             template_member_p = true;
 483         }
 484
 485       /* A nested class may declare a member of an enclosing class
 486          to be a friend, so we do lookup here even if CTYPE is in
 487          the process of being defined.  */
 488       if (class_template_depth
 489           || COMPLETE_TYPE_P (ctype)
 490           || (CLASS_TYPE_P (ctype) && TYPE_BEING_DEFINED (ctype)))
 491         {
 492           if (DECL_TEMPLATE_INFO (decl))
 493             /* DECL is a template specialization.  No need to
 494                build a new TEMPLATE_DECL.  */
 495             ;
 496           else if (class_template_depth)
 497             /* We rely on tsubst_friend_function to check the
 498                validity of the declaration later.  */
 499             decl = push_template_decl_real (decl, /*is_friend=*/true);
 500           else
 501             decl = check_classfn (ctype, decl,
 502                                   template_member_p
 503                                   ? current_template_parms
 504                                   : NULL_TREE);
 505
 506           if (template_member_p && decl && TREE_CODE (decl) == FUNCTION_DECL)
 507             decl = DECL_TI_TEMPLATE (decl);
 508
 509           if (decl)
 510             add_friend (current_class_type, decl, /*complain=*/true);
 511         }
 512       else
 513         error ("member %qD declared as friend before type %qT defined",
 514                   decl, ctype);
 515     }
 516   /* A global friend.
 517      @@ or possibly a friend from a base class ?!?  */
 518   else if (TREE_CODE (decl) == FUNCTION_DECL)
 519     {
 520       int is_friend_template = PROCESSING_REAL_TEMPLATE_DECL_P ();
 521
 522       /* Friends must all go through the overload machinery,
 523          even though they may not technically be overloaded.
 524
 525          Note that because classes all wind up being top-level
 526          in their scope, their friend wind up in top-level scope as well.  */
 527       if (funcdef_flag)
 528         SET_DECL_FRIEND_CONTEXT (decl, current_class_type);
 529
 530       if (! DECL_USE_TEMPLATE (decl))
 531         {
 532           /* We must check whether the decl refers to template
 533              arguments before push_template_decl_real adds a
 534              reference to the containing template class.  */
 535           int warn = (warn_nontemplate_friend
 536                       && ! funcdef_flag && ! is_friend_template
 537                       && current_template_parms
 538                       && uses_template_parms (decl));
 539
 540           if (is_friend_template
 541               || template_class_depth (current_class_type) != 0)
 542             /* We can't call pushdecl for a template class, since in
 543                general, such a declaration depends on template
 544                parameters.  Instead, we call pushdecl when the class
 545                is instantiated.  */
 546             decl = push_template_decl_real (decl, /*is_friend=*/true);
 547           else if (current_function_decl)
 548             {
 549               /* This must be a local class.  11.5p11:
 550
 551                  If a friend declaration appears in a local class (9.8) and
 552                  the name specified is an unqualified name, a prior
 553                  declaration is looked up without considering scopes that
 554                  are outside the innermost enclosing non-class scope. For a
 555                  friend function declaration, if there is no prior
 556                  declaration, the program is ill-formed.  */
 557               tree t = lookup_name_innermost_nonclass_level (DECL_NAME (decl));
 558               if (t)
 559                 decl = pushdecl_maybe_friend (decl, /*is_friend=*/true);
 560               else
 561                 {
 562                   error ("friend declaration %qD in local class without "
 563                          "prior declaration", decl);
 564                   return error_mark_node;
 565                 }
 566             }
 567           else
 568             {
 569               /* We can't use pushdecl, as we might be in a template
 570                  class specialization, and pushdecl will insert an
 571                  unqualified friend decl into the template parameter
 572                  scope, rather than the namespace containing it.  */
 573               tree ns = decl_namespace_context (decl);
 574
 575               push_nested_namespace (ns);
 576               decl = pushdecl_namespace_level (decl, /*is_friend=*/true);
 577               pop_nested_namespace (ns);
 578             }
 579
 580           if (warn)
 581             {
 582               static int explained;
 583               bool warned;
 584
 585               warned = warning (OPT_Wnon_template_friend, "friend declaration "
 586                                 "%q#D declares a non-template function", decl);
 587               if (! explained && warned)
 588                 {
 589                   inform (input_location, "(if this is not what you intended, make sure "
 590                           "the function template has already been declared "
 591                           "and add <> after the function name here) ");
 592                   explained = 1;
 593                 }
 594             }
 595         }
 596
 597       if (decl == error_mark_node)
 598         return error_mark_node;
 599
 600       add_friend (current_class_type,
 601                   is_friend_template ? DECL_TI_TEMPLATE (decl) : decl,
 602                   /*complain=*/true);
 603       DECL_FRIEND_P (decl) = 1;
 604     }
 605
 606   return decl;
 607 }