gcc/cp/friend.c

   1 /* Help friends in C++.
   2    Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
   3    2007, 2008  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 #include "output.h"
  29 #include "toplev.h"
  30
  31 /* Friend data structures are described in cp-tree.h.  */
  32
  33 /* Returns nonzero if SUPPLICANT is a friend of TYPE.  */
  34
  35 int
  36 is_friend (tree type, tree supplicant)
  37 {
  38   int declp;
  39   tree list;
  40   tree context;
  41
  42   if (supplicant == NULL_TREE || type == NULL_TREE)
  43     return 0;
  44
  45   declp = DECL_P (supplicant);
  46
  47   if (declp)
  48     /* It's a function decl.  */
  49     {
  50       tree list = DECL_FRIENDLIST (TYPE_MAIN_DECL (type));
  51       tree name = DECL_NAME (supplicant);
  52
  53       for (; list ; list = TREE_CHAIN (list))
  54         {
  55           if (name == FRIEND_NAME (list))
  56             {
  57               tree friends = FRIEND_DECLS (list);
  58               for (; friends ; friends = TREE_CHAIN (friends))
  59                 {
  60                   tree this_friend = TREE_VALUE (friends);
  61
  62                   if (this_friend == NULL_TREE)
  63                     continue;
  64
  65                   if (supplicant == this_friend)
  66                     return 1;
  67
  68                   if (is_specialization_of_friend (supplicant, this_friend))
  69                     return 1;
  70                 }
  71               break;
  72             }
  73         }
  74     }
  75   else
  76     /* It's a type.  */
  77     {
  78       if (same_type_p (supplicant, type))
  79         return 1;
  80
  81       list = CLASSTYPE_FRIEND_CLASSES (TREE_TYPE (TYPE_MAIN_DECL (type)));
  82       for (; list ; list = TREE_CHAIN (list))
  83         {
  84           tree t = TREE_VALUE (list);
  85
  86           if (TREE_CODE (t) == TEMPLATE_DECL ?
  87               is_specialization_of_friend (TYPE_MAIN_DECL (supplicant), t) :
  88               same_type_p (supplicant, t))
  89             return 1;
  90         }
  91     }
  92
  93   if (declp)
  94     {
  95       if (DECL_FUNCTION_MEMBER_P (supplicant))
  96         context = DECL_CONTEXT (supplicant);
  97       else
  98         context = NULL_TREE;
  99     }
 100   else
 101     {
 102       if (TYPE_CLASS_SCOPE_P (supplicant))
 103         /* Nested classes get the same access as their enclosing types, as
 104            per DR 45 (this is a change from the standard).  */
 105         context = TYPE_CONTEXT (supplicant);
 106       else
 107         /* Local classes have the same access as the enclosing function.  */
 108         context = decl_function_context (TYPE_MAIN_DECL (supplicant));
 109     }
 110
 111   /* A namespace is not friend to anybody.  */
 112   if (context && TREE_CODE (context) == NAMESPACE_DECL)
 113     context = NULL_TREE;
 114
 115   if (context)
 116     return is_friend (type, context);
 117
 118   return 0;
 119 }
 120
 121 /* Add a new friend to the friends of the aggregate type TYPE.
 122    DECL is the FUNCTION_DECL of the friend being added.
 123
 124    If COMPLAIN is true, warning about duplicate friend is issued.
 125    We want to have this diagnostics during parsing but not
 126    when a template is being instantiated.  */
 127
 128 void
 129 add_friend (tree type, tree decl, bool complain)
 130 {
 131   tree typedecl;
 132   tree list;
 133   tree name;
 134   tree ctx;
 135
 136   if (decl == error_mark_node)
 137     return;
 138
 139   typedecl = TYPE_MAIN_DECL (type);
 140   list = DECL_FRIENDLIST (typedecl);
 141   name = DECL_NAME (decl);
 142   type = TREE_TYPE (typedecl);
 143
 144   while (list)
 145     {
 146       if (name == FRIEND_NAME (list))
 147         {
 148           tree friends = FRIEND_DECLS (list);
 149           for (; friends ; friends = TREE_CHAIN (friends))
 150             {
 151               if (decl == TREE_VALUE (friends))
 152                 {
 153                   if (complain)
 154                     warning (0, "%qD is already a friend of class %qT",
 155                              decl, type);
 156                   return;
 157                 }
 158             }
 159
 160           maybe_add_class_template_decl_list (type, decl, /*friend_p=*/1);
 161
 162           TREE_VALUE (list) = tree_cons (NULL_TREE, decl,
 163                                          TREE_VALUE (list));
 164           return;
 165         }
 166       list = TREE_CHAIN (list);
 167     }
 168
 169   ctx = DECL_CONTEXT (decl);
 170   if (ctx && CLASS_TYPE_P (ctx) && !uses_template_parms (ctx))
 171     perform_or_defer_access_check (TYPE_BINFO (ctx), decl, decl);
 172
 173   maybe_add_class_template_decl_list (type, decl, /*friend_p=*/1);
 174
 175   DECL_FRIENDLIST (typedecl)
 176     = tree_cons (DECL_NAME (decl), build_tree_list (NULL_TREE, decl),
 177                  DECL_FRIENDLIST (typedecl));
 178   if (!uses_template_parms (type))
 179     DECL_BEFRIENDING_CLASSES (decl)
 180       = tree_cons (NULL_TREE, type,
 181                    DECL_BEFRIENDING_CLASSES (decl));
 182 }
 183
 184 /* Make FRIEND_TYPE a friend class to TYPE.  If FRIEND_TYPE has already
 185    been defined, we make all of its member functions friends of
 186    TYPE.  If not, we make it a pending friend, which can later be added
 187    when its definition is seen.  If a type is defined, then its TYPE_DECL's
 188    DECL_UNDEFINED_FRIENDS contains a (possibly empty) list of friend
 189    classes that are not defined.  If a type has not yet been defined,
 190    then the DECL_WAITING_FRIENDS contains a list of types
 191    waiting to make it their friend.  Note that these two can both
 192    be in use at the same time!
 193
 194    If COMPLAIN is true, warning about duplicate friend is issued.
 195    We want to have this diagnostics during parsing but not
 196    when a template is being instantiated.  */
 197
 198 void
 199 make_friend_class (tree type, tree friend_type, bool complain)
 200 {
 201   tree classes;
 202
 203   /* CLASS_TEMPLATE_DEPTH counts the number of template headers for
 204      the enclosing class.  FRIEND_DEPTH counts the number of template
 205      headers used for this friend declaration.  TEMPLATE_MEMBER_P,
 206      defined inside the `if' block for TYPENAME_TYPE case, is true if
 207      a template header in FRIEND_DEPTH is intended for DECLARATOR.
 208      For example, the code
 209
 210        template <class T> struct A {
 211          template <class U> struct B {
 212            template <class V> template <class W>
 213              friend class C<V>::D;
 214          };
 215        };
 216
 217      will eventually give the following results
 218
 219      1. CLASS_TEMPLATE_DEPTH equals 2 (for `T' and `U').
 220      2. FRIEND_DEPTH equals 2 (for `V' and `W').
 221      3. TEMPLATE_MEMBER_P is true (for `W').
 222
 223      The friend is a template friend iff FRIEND_DEPTH is nonzero.  */
 224
 225   int class_template_depth = template_class_depth (type);
 226   int friend_depth = processing_template_decl - class_template_depth;
 227
 228   if (! MAYBE_CLASS_TYPE_P (friend_type))
 229     {
 230       error ("invalid type %qT declared %<friend%>", friend_type);
 231       return;
 232     }
 233
 234   if (friend_depth)
 235     /* If the TYPE is a template then it makes sense for it to be
 236        friends with itself; this means that each instantiation is
 237        friends with all other instantiations.  */
 238     {
 239       if (CLASS_TYPE_P (friend_type)
 240           && CLASSTYPE_TEMPLATE_SPECIALIZATION (friend_type)
 241           && uses_template_parms (friend_type))
 242         {
 243           /* [temp.friend]
 244              Friend declarations shall not declare partial
 245              specializations.  */
 246           error ("partial specialization %qT declared %<friend%>",
 247                  friend_type);
 248           return;
 249         }
 250     }
 251   else if (same_type_p (type, friend_type))
 252     {
 253       if (complain)
 254         warning (0, "class %qT is implicitly friends with itself",
 255                  type);
 256       return;
 257     }
 258
 259   /* [temp.friend]
 260
 261      A friend of a class or class template can be a function or
 262      class template, a specialization of a function template or
 263      class template, or an ordinary (nontemplate) function or
 264      class.  */
 265   if (!friend_depth)
 266     ;/* ok */
 267   else if (TREE_CODE (friend_type) == TYPENAME_TYPE)
 268     {
 269       if (TREE_CODE (TYPENAME_TYPE_FULLNAME (friend_type))
 270           == TEMPLATE_ID_EXPR)
 271         {
 272           /* template <class U> friend class T::X<U>; */
 273           /* [temp.friend]
 274              Friend declarations shall not declare partial
 275              specializations.  */
 276           error ("partial specialization %qT declared %<friend%>",
 277                  friend_type);
 278           return;
 279         }
 280       else
 281         {
 282           /* We will figure this out later.  */
 283           bool template_member_p = false;
 284
 285           tree ctype = TYPE_CONTEXT (friend_type);
 286           tree name = TYPE_IDENTIFIER (friend_type);
 287           tree decl;
 288
 289           if (!uses_template_parms_level (ctype, class_template_depth
 290                                                  + friend_depth))
 291             template_member_p = true;
 292
 293           if (class_template_depth)
 294             {
 295               /* We rely on tsubst_friend_class to check the
 296                  validity of the declaration later.  */
 297               if (template_member_p)
 298                 friend_type
 299                   = make_unbound_class_template (ctype,
 300                                                  name,
 301                                                  current_template_parms,
 302                                                  tf_error);
 303               else
 304                 friend_type
 305                   = make_typename_type (ctype, name, class_type, tf_error);
 306             }
 307           else
 308             {
 309               decl = lookup_member (ctype, name, 0, true);
 310               if (!decl)
 311                 {
 312                   error ("%qT is not a member of %qT", name, ctype);
 313                   return;
 314                 }
 315               if (template_member_p && !DECL_CLASS_TEMPLATE_P (decl))
 316                 {
 317                   error ("%qT is not a member class template of %qT",
 318                          name, ctype);
 319                   error ("%q+D declared here", decl);
 320                   return;
 321                 }
 322               if (!template_member_p && (TREE_CODE (decl) != TYPE_DECL
 323                                          || !CLASS_TYPE_P (TREE_TYPE (decl))))
 324                 {
 325                   error ("%qT is not a nested class of %qT",
 326                          name, ctype);
 327                   error ("%q+D declared here", decl);
 328                   return;
 329                 }
 330
 331               friend_type = CLASSTYPE_TI_TEMPLATE (TREE_TYPE (decl));
 332             }
 333         }
 334     }
 335   else if (TREE_CODE (friend_type) == TEMPLATE_TYPE_PARM)
 336     {
 337       /* template <class T> friend class T; */
 338       error ("template parameter type %qT declared %<friend%>", friend_type);
 339       return;
 340     }
 341   else if (!CLASSTYPE_TEMPLATE_INFO (friend_type))
 342     {
 343       /* template <class T> friend class A; where A is not a template */
 344       error ("%q#T is not a template", friend_type);
 345       return;
 346     }
 347   else
 348     /* template <class T> friend class A; where A is a template */
 349     friend_type = CLASSTYPE_TI_TEMPLATE (friend_type);
 350
 351   if (friend_type == error_mark_node)
 352     return;
 353
 354   /* See if it is already a friend.  */
 355   for (classes = CLASSTYPE_FRIEND_CLASSES (type);
 356        classes;
 357        classes = TREE_CHAIN (classes))
 358     {
 359       tree probe = TREE_VALUE (classes);
 360
 361       if (TREE_CODE (friend_type) == TEMPLATE_DECL)
 362         {
 363           if (friend_type == probe)
 364             {
 365               if (complain)
 366                 warning (0, "%qD is already a friend of %qT", probe, type);
 367               break;
 368             }
 369         }
 370       else if (TREE_CODE (probe) != TEMPLATE_DECL)
 371         {
 372           if (same_type_p (probe, friend_type))
 373             {
 374               if (complain)
 375                 warning (0, "%qT is already a friend of %qT", probe, type);
 376               break;
 377             }
 378         }
 379     }
 380
 381   if (!classes)
 382     {
 383       maybe_add_class_template_decl_list (type, friend_type, /*friend_p=*/1);
 384
 385       CLASSTYPE_FRIEND_CLASSES (type)
 386         = tree_cons (NULL_TREE, friend_type, CLASSTYPE_FRIEND_CLASSES (type));
 387       if (TREE_CODE (friend_type) == TEMPLATE_DECL)
 388         friend_type = TREE_TYPE (friend_type);
 389       if (!uses_template_parms (type))
 390         CLASSTYPE_BEFRIENDING_CLASSES (friend_type)
 391           = tree_cons (NULL_TREE, type,
 392                        CLASSTYPE_BEFRIENDING_CLASSES (friend_type));
 393     }
 394 }
 395
 396 /* Record DECL (a FUNCTION_DECL) as a friend of the
 397    CURRENT_CLASS_TYPE.  If DECL is a member function, CTYPE is the
 398    class of which it is a member, as named in the friend declaration.
 399    DECLARATOR is the name of the friend.  FUNCDEF_FLAG is true if the
 400    friend declaration is a definition of the function.  FLAGS is as
 401    for grokclass fn.  */
 402
 403 tree
 404 do_friend (tree ctype, tree declarator, tree decl,
 405            tree attrlist, enum overload_flags flags,
 406            bool funcdef_flag)
 407 {
 408   gcc_assert (TREE_CODE (decl) == FUNCTION_DECL);
 409   gcc_assert (!ctype || MAYBE_CLASS_TYPE_P (ctype));
 410
 411   /* Every decl that gets here is a friend of something.  */
 412   DECL_FRIEND_P (decl) = 1;
 413
 414   /* Unfortunately, we have to handle attributes here.  Normally we would
 415      handle them in start_decl_1, but since this is a friend decl start_decl_1
 416      never gets to see it.  */
 417
 418   /* Set attributes here so if duplicate decl, will have proper attributes.  */
 419   cplus_decl_attributes (&decl, attrlist, 0);
 420
 421   if (TREE_CODE (declarator) == TEMPLATE_ID_EXPR)
 422     {
 423       declarator = TREE_OPERAND (declarator, 0);
 424       if (is_overloaded_fn (declarator))
 425         declarator = DECL_NAME (get_first_fn (declarator));
 426     }
 427
 428   if (ctype)
 429     {
 430       /* CLASS_TEMPLATE_DEPTH counts the number of template headers for
 431          the enclosing class.  FRIEND_DEPTH counts the number of template
 432          headers used for this friend declaration.  TEMPLATE_MEMBER_P is
 433          true if a template header in FRIEND_DEPTH is intended for
 434          DECLARATOR.  For example, the code
 435
 436            template <class T> struct A {
 437              template <class U> struct B {
 438                template <class V> template <class W>
 439                  friend void C<V>::f(W);
 440              };
 441            };
 442
 443          will eventually give the following results
 444
 445          1. CLASS_TEMPLATE_DEPTH equals 2 (for `T' and `U').
 446          2. FRIEND_DEPTH equals 2 (for `V' and `W').
 447          3. TEMPLATE_MEMBER_P is true (for `W').  */
 448
 449       int class_template_depth = template_class_depth (current_class_type);
 450       int friend_depth = processing_template_decl - class_template_depth;
 451       /* We will figure this out later.  */
 452       bool template_member_p = false;
 453
 454       tree cname = TYPE_NAME (ctype);
 455       if (TREE_CODE (cname) == TYPE_DECL)
 456         cname = DECL_NAME (cname);
 457
 458       /* A method friend.  */
 459       if (flags == NO_SPECIAL && declarator == cname)
 460         DECL_CONSTRUCTOR_P (decl) = 1;
 461
 462       grokclassfn (ctype, decl, flags);
 463
 464       if (friend_depth)
 465         {
 466           if (!uses_template_parms_level (ctype, class_template_depth
 467                                                  + friend_depth))
 468             template_member_p = true;
 469         }
 470
 471       /* A nested class may declare a member of an enclosing class
 472          to be a friend, so we do lookup here even if CTYPE is in
 473          the process of being defined.  */
 474       if (class_template_depth
 475           || COMPLETE_TYPE_P (ctype)
 476           || (CLASS_TYPE_P (ctype) && TYPE_BEING_DEFINED (ctype)))
 477         {
 478           if (DECL_TEMPLATE_INFO (decl))
 479             /* DECL is a template specialization.  No need to
 480                build a new TEMPLATE_DECL.  */
 481             ;
 482           else if (class_template_depth)
 483             /* We rely on tsubst_friend_function to check the
 484                validity of the declaration later.  */
 485             decl = push_template_decl_real (decl, /*is_friend=*/true);
 486           else
 487             decl = check_classfn (ctype, decl,
 488                                   template_member_p
 489                                   ? current_template_parms
 490                                   : NULL_TREE);
 491
 492           if (template_member_p && decl && TREE_CODE (decl) == FUNCTION_DECL)
 493             decl = DECL_TI_TEMPLATE (decl);
 494
 495           if (decl)
 496             add_friend (current_class_type, decl, /*complain=*/true);
 497         }
 498       else
 499         error ("member %qD declared as friend before type %qT defined",
 500                   decl, ctype);
 501     }
 502   /* A global friend.
 503      @@ or possibly a friend from a base class ?!?  */
 504   else if (TREE_CODE (decl) == FUNCTION_DECL)
 505     {
 506       int is_friend_template = PROCESSING_REAL_TEMPLATE_DECL_P ();
 507
 508       /* Friends must all go through the overload machinery,
 509          even though they may not technically be overloaded.
 510
 511          Note that because classes all wind up being top-level
 512          in their scope, their friend wind up in top-level scope as well.  */
 513       if (funcdef_flag)
 514         SET_DECL_FRIEND_CONTEXT (decl, current_class_type);
 515
 516       if (! DECL_USE_TEMPLATE (decl))
 517         {
 518           /* We must check whether the decl refers to template
 519              arguments before push_template_decl_real adds a
 520              reference to the containing template class.  */
 521           int warn = (warn_nontemplate_friend
 522                       && ! funcdef_flag && ! is_friend_template
 523                       && current_template_parms
 524                       && uses_template_parms (decl));
 525
 526           if (is_friend_template
 527               || template_class_depth (current_class_type) != 0)
 528             /* We can't call pushdecl for a template class, since in
 529                general, such a declaration depends on template
 530                parameters.  Instead, we call pushdecl when the class
 531                is instantiated.  */
 532             decl = push_template_decl_real (decl, /*is_friend=*/true);
 533           else if (current_function_decl)
 534             {
 535               /* This must be a local class.  11.5p11:
 536
 537                  If a friend declaration appears in a local class (9.8) and
 538                  the name specified is an unqualified name, a prior
 539                  declaration is looked up without considering scopes that
 540                  are outside the innermost enclosing non-class scope. For a
 541                  friend function declaration, if there is no prior
 542                  declaration, the program is ill-formed.  */
 543               tree t = lookup_name_innermost_nonclass_level (DECL_NAME (decl));
 544               if (t)
 545                 decl = pushdecl_maybe_friend (decl, /*is_friend=*/true);
 546               else
 547                 {
 548                   error ("friend declaration %qD in local class without "
 549                          "prior declaration", decl);
 550                   return error_mark_node;
 551                 }
 552             }
 553           else
 554             {
 555               /* We can't use pushdecl, as we might be in a template
 556                  class specialization, and pushdecl will insert an
 557                  unqualified friend decl into the template parameter
 558                  scope, rather than the namespace containing it.  */
 559               tree ns = decl_namespace_context (decl);
 560
 561               push_nested_namespace (ns);
 562               decl = pushdecl_namespace_level (decl, /*is_friend=*/true);
 563               pop_nested_namespace (ns);
 564             }
 565
 566           if (warn)
 567             {
 568               static int explained;
 569               bool warned;
 570
 571               warned = warning (OPT_Wnon_template_friend, "friend declaration "
 572                                 "%q#D declares a non-template function", decl);
 573               if (! explained && warned)
 574                 {
 575                   inform (input_location, "(if this is not what you intended, make sure "
 576                           "the function template has already been declared "
 577                           "and add <> after the function name here) ");
 578                   explained = 1;
 579                 }
 580             }
 581         }
 582
 583       if (decl == error_mark_node)
 584         return error_mark_node;
 585
 586       add_friend (current_class_type,
 587                   is_friend_template ? DECL_TI_TEMPLATE (decl) : decl,
 588                   /*complain=*/true);
 589       DECL_FRIEND_P (decl) = 1;
 590     }
 591
 592   return decl;
 593 }