gcc/cp/friend.c

   1 /* Help friends in C++.
   2    Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
   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, 51 Franklin Street, Fifth Floor,
  20 Boston, MA 02110-1301, 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       if (same_type_p (supplicant, type))
  82         return 1;
  83
  84       list = CLASSTYPE_FRIEND_CLASSES (TREE_TYPE (TYPE_MAIN_DECL (type)));
  85       for (; list ; list = TREE_CHAIN (list))
  86         {
  87           tree t = TREE_VALUE (list);
  88
  89           if (TREE_CODE (t) == TEMPLATE_DECL ?
  90               is_specialization_of_friend (TYPE_MAIN_DECL (supplicant), t) :
  91               same_type_p (supplicant, t))
  92             return 1;
  93         }
  94     }
  95
  96   if (declp)
  97     {
  98       if (DECL_FUNCTION_MEMBER_P (supplicant))
  99         context = DECL_CONTEXT (supplicant);
 100       else
 101         context = NULL_TREE;
 102     }
 103   else
 104     {
 105       if (TYPE_CLASS_SCOPE_P (supplicant))
 106         /* Nested classes get the same access as their enclosing types, as
 107            per DR 45 (this is a change from the standard).  */
 108         context = TYPE_CONTEXT (supplicant);
 109       else
 110         /* Local classes have the same access as the enclosing function.  */
 111         context = decl_function_context (TYPE_MAIN_DECL (supplicant));
 112     }
 113
 114   /* A namespace is not friend to anybody.  */
 115   if (context && TREE_CODE (context) == NAMESPACE_DECL)
 116     context = NULL_TREE;
 117
 118   if (context)
 119     return is_friend (type, context);
 120
 121   return 0;
 122 }
 123
 124 /* Add a new friend to the friends of the aggregate type TYPE.
 125    DECL is the FUNCTION_DECL of the friend being added.
 126
 127    If COMPLAIN is true, warning about duplicate friend is issued.
 128    We want to have this diagnostics during parsing but not
 129    when a template is being instantiated.  */
 130
 131 void
 132 add_friend (tree type, tree decl, bool complain)
 133 {
 134   tree typedecl;
 135   tree list;
 136   tree name;
 137   tree ctx;
 138
 139   if (decl == error_mark_node)
 140     return;
 141
 142   typedecl = TYPE_MAIN_DECL (type);
 143   list = DECL_FRIENDLIST (typedecl);
 144   name = DECL_NAME (decl);
 145   type = TREE_TYPE (typedecl);
 146
 147   while (list)
 148     {
 149       if (name == FRIEND_NAME (list))
 150         {
 151           tree friends = FRIEND_DECLS (list);
 152           for (; friends ; friends = TREE_CHAIN (friends))
 153             {
 154               if (decl == TREE_VALUE (friends))
 155                 {
 156                   if (complain)
 157                     warning (0, "%qD is already a friend of class %qT",
 158                              decl, type);
 159                   return;
 160                 }
 161             }
 162
 163           maybe_add_class_template_decl_list (type, decl, /*friend_p=*/1);
 164
 165           TREE_VALUE (list) = tree_cons (NULL_TREE, decl,
 166                                          TREE_VALUE (list));
 167           return;
 168         }
 169       list = TREE_CHAIN (list);
 170     }
 171
 172   ctx = DECL_CONTEXT (decl);
 173   if (ctx && CLASS_TYPE_P (ctx) && !uses_template_parms (ctx))
 174     perform_or_defer_access_check (TYPE_BINFO (ctx), decl);
 175
 176   maybe_add_class_template_decl_list (type, decl, /*friend_p=*/1);
 177
 178   DECL_FRIENDLIST (typedecl)
 179     = tree_cons (DECL_NAME (decl), build_tree_list (NULL_TREE, decl),
 180                  DECL_FRIENDLIST (typedecl));
 181   if (!uses_template_parms (type))
 182     DECL_BEFRIENDING_CLASSES (decl)
 183       = tree_cons (NULL_TREE, type,
 184                    DECL_BEFRIENDING_CLASSES (decl));
 185 }
 186
 187 /* Make FRIEND_TYPE a friend class to TYPE.  If FRIEND_TYPE has already
 188    been defined, we make all of its member functions friends of
 189    TYPE.  If not, we make it a pending friend, which can later be added
 190    when its definition is seen.  If a type is defined, then its TYPE_DECL's
 191    DECL_UNDEFINED_FRIENDS contains a (possibly empty) list of friend
 192    classes that are not defined.  If a type has not yet been defined,
 193    then the DECL_WAITING_FRIENDS contains a list of types
 194    waiting to make it their friend.  Note that these two can both
 195    be in use at the same time!
 196
 197    If COMPLAIN is true, warning about duplicate friend is issued.
 198    We want to have this diagnostics during parsing but not
 199    when a template is being instantiated.  */
 200
 201 void
 202 make_friend_class (tree type, tree friend_type, bool complain)
 203 {
 204   tree classes;
 205
 206   /* CLASS_TEMPLATE_DEPTH counts the number of template headers for
 207      the enclosing class.  FRIEND_DEPTH counts the number of template
 208      headers used for this friend declaration.  TEMPLATE_MEMBER_P,
 209      defined inside the `if' block for TYPENAME_TYPE case, is true if
 210      a template header in FRIEND_DEPTH is intended for DECLARATOR.
 211      For example, the code
 212
 213        template <class T> struct A {
 214          template <class U> struct B {
 215            template <class V> template <class W>
 216              friend class C<V>::D;
 217          };
 218        };
 219
 220      will eventually give the following results
 221
 222      1. CLASS_TEMPLATE_DEPTH equals 2 (for `T' and `U').
 223      2. FRIEND_DEPTH equals 2 (for `V' and `W').
 224      3. TEMPLATE_MEMBER_P is true (for `W').
 225
 226      The friend is a template friend iff FRIEND_DEPTH is nonzero.  */
 227
 228   int class_template_depth = template_class_depth (type);
 229   int friend_depth = processing_template_decl - class_template_depth;
 230
 231   if (! IS_AGGR_TYPE (friend_type))
 232     {
 233       error ("invalid type %qT declared %<friend%>", friend_type);
 234       return;
 235     }
 236
 237   if (friend_depth)
 238     /* If the TYPE is a template then it makes sense for it to be
 239        friends with itself; this means that each instantiation is
 240        friends with all other instantiations.  */
 241     {
 242       if (CLASS_TYPE_P (friend_type)
 243           && CLASSTYPE_TEMPLATE_SPECIALIZATION (friend_type)
 244           && uses_template_parms (friend_type))
 245         {
 246           /* [temp.friend]
 247              Friend declarations shall not declare partial
 248              specializations.  */
 249           error ("partial specialization %qT declared %<friend%>",
 250                  friend_type);
 251           return;
 252         }
 253     }
 254   else if (same_type_p (type, friend_type))
 255     {
 256       if (complain)
 257         pedwarn ("class %qT is implicitly friends with itself",
 258                  type);
 259       return;
 260     }
 261
 262   /* [temp.friend]
 263
 264      A friend of a class or class template can be a function or
 265      class template, a specialization of a function template or
 266      class template, or an ordinary (nontemplate) function or
 267      class.  */
 268   if (!friend_depth)
 269     ;/* ok */
 270   else if (TREE_CODE (friend_type) == TYPENAME_TYPE)
 271     {
 272       if (TREE_CODE (TYPENAME_TYPE_FULLNAME (friend_type))
 273           == TEMPLATE_ID_EXPR)
 274         {
 275           /* template <class U> friend class T::X<U>; */
 276           /* [temp.friend]
 277              Friend declarations shall not declare partial
 278              specializations.  */
 279           error ("partial specialization %qT declared %<friend%>",
 280                  friend_type);
 281           return;
 282         }
 283       else
 284         {
 285           /* We will figure this out later.  */
 286           bool template_member_p = false;
 287
 288           tree ctype = TYPE_CONTEXT (friend_type);
 289           tree name = TYPE_IDENTIFIER (friend_type);
 290           tree decl;
 291
 292           if (!uses_template_parms_level (ctype, class_template_depth
 293                                                  + friend_depth))
 294             template_member_p = true;
 295
 296           if (class_template_depth)
 297             {
 298               /* We rely on tsubst_friend_class to check the
 299                  validity of the declaration later.  */
 300               if (template_member_p)
 301                 friend_type
 302                   = make_unbound_class_template (ctype,
 303                                                  name,
 304                                                  current_template_parms,
 305                                                  tf_error);
 306               else
 307                 friend_type
 308                   = make_typename_type (ctype, name, class_type, tf_error);
 309             }
 310           else
 311             {
 312               decl = lookup_member (ctype, name, 0, true);
 313               if (!decl)
 314                 {
 315                   error ("%qT is not a member of %qT", name, ctype);
 316                   return;
 317                 }
 318               if (template_member_p && !DECL_CLASS_TEMPLATE_P (decl))
 319                 {
 320                   error ("%qT is not a member class template of %qT",
 321                          name, ctype);
 322                   error ("%q+D declared here", decl);
 323                   return;
 324                 }
 325               if (!template_member_p && (TREE_CODE (decl) != TYPE_DECL
 326                                          || !CLASS_TYPE_P (TREE_TYPE (decl))))
 327                 {
 328                   error ("%qT is not a nested class of %qT",
 329                          name, ctype);
 330                   error ("%q+D declared here", decl);
 331                   return;
 332                 }
 333
 334               friend_type = CLASSTYPE_TI_TEMPLATE (TREE_TYPE (decl));
 335             }
 336         }
 337     }
 338   else if (TREE_CODE (friend_type) == TEMPLATE_TYPE_PARM)
 339     {
 340       /* template <class T> friend class T; */
 341       error ("template parameter type %qT declared %<friend%>", friend_type);
 342       return;
 343     }
 344   else if (!CLASSTYPE_TEMPLATE_INFO (friend_type))
 345     {
 346       /* template <class T> friend class A; where A is not a template */
 347       error ("%q#T is not a template", friend_type);
 348       return;
 349     }
 350   else
 351     /* template <class T> friend class A; where A is a template */
 352     friend_type = CLASSTYPE_TI_TEMPLATE (friend_type);
 353
 354   if (friend_type == error_mark_node)
 355     return;
 356
 357   /* See if it is already a friend.  */
 358   for (classes = CLASSTYPE_FRIEND_CLASSES (type);
 359        classes;
 360        classes = TREE_CHAIN (classes))
 361     {
 362       tree probe = TREE_VALUE (classes);
 363
 364       if (TREE_CODE (friend_type) == TEMPLATE_DECL)
 365         {
 366           if (friend_type == probe)
 367             {
 368               if (complain)
 369                 warning (0, "%qD is already a friend of %qT", probe, type);
 370               break;
 371             }
 372         }
 373       else if (TREE_CODE (probe) != TEMPLATE_DECL)
 374         {
 375           if (same_type_p (probe, friend_type))
 376             {
 377               if (complain)
 378                 warning (0, "%qT is already a friend of %qT", probe, type);
 379               break;
 380             }
 381         }
 382     }
 383
 384   if (!classes)
 385     {
 386       maybe_add_class_template_decl_list (type, friend_type, /*friend_p=*/1);
 387
 388       CLASSTYPE_FRIEND_CLASSES (type)
 389         = tree_cons (NULL_TREE, friend_type, CLASSTYPE_FRIEND_CLASSES (type));
 390       if (TREE_CODE (friend_type) == TEMPLATE_DECL)
 391         friend_type = TREE_TYPE (friend_type);
 392       if (!uses_template_parms (type))
 393         CLASSTYPE_BEFRIENDING_CLASSES (friend_type)
 394           = tree_cons (NULL_TREE, type,
 395                        CLASSTYPE_BEFRIENDING_CLASSES (friend_type));
 396     }
 397 }
 398
 399 /* Record DECL (a FUNCTION_DECL) as a friend of the
 400    CURRENT_CLASS_TYPE.  If DECL is a member function, CTYPE is the
 401    class of which it is a member, as named in the friend declaration.
 402    DECLARATOR is the name of the friend.  FUNCDEF_FLAG is true if the
 403    friend declaration is a definition of the function.  FLAGS is as
 404    for grokclass fn.  */
 405
 406 tree
 407 do_friend (tree ctype, tree declarator, tree decl,
 408            tree attrlist, enum overload_flags flags,
 409            bool funcdef_flag)
 410 {
 411   gcc_assert (TREE_CODE (decl) == FUNCTION_DECL);
 412   gcc_assert (!ctype || IS_AGGR_TYPE (ctype));
 413
 414   /* Every decl that gets here is a friend of something.  */
 415   DECL_FRIEND_P (decl) = 1;
 416
 417   if (TREE_CODE (declarator) == TEMPLATE_ID_EXPR)
 418     {
 419       declarator = TREE_OPERAND (declarator, 0);
 420       if (is_overloaded_fn (declarator))
 421         declarator = DECL_NAME (get_first_fn (declarator));
 422     }
 423
 424   if (ctype)
 425     {
 426       /* CLASS_TEMPLATE_DEPTH counts the number of template headers for
 427          the enclosing class.  FRIEND_DEPTH counts the number of template
 428          headers used for this friend declaration.  TEMPLATE_MEMBER_P is
 429          true if a template header in FRIEND_DEPTH is intended for
 430          DECLARATOR.  For example, the code
 431
 432            template <class T> struct A {
 433              template <class U> struct B {
 434                template <class V> template <class W>
 435                  friend void C<V>::f(W);
 436              };
 437            };
 438
 439          will eventually give the following results
 440
 441          1. CLASS_TEMPLATE_DEPTH equals 2 (for `T' and `U').
 442          2. FRIEND_DEPTH equals 2 (for `V' and `W').
 443          3. TEMPLATE_MEMBER_P is true (for `W').  */
 444
 445       int class_template_depth = template_class_depth (current_class_type);
 446       int friend_depth = processing_template_decl - class_template_depth;
 447       /* We will figure this out later.  */
 448       bool template_member_p = false;
 449
 450       tree cname = TYPE_NAME (ctype);
 451       if (TREE_CODE (cname) == TYPE_DECL)
 452         cname = DECL_NAME (cname);
 453
 454       /* A method friend.  */
 455       if (flags == NO_SPECIAL && declarator == cname)
 456         DECL_CONSTRUCTOR_P (decl) = 1;
 457
 458       grokclassfn (ctype, decl, flags);
 459
 460       if (friend_depth)
 461         {
 462           if (!uses_template_parms_level (ctype, class_template_depth
 463                                                  + friend_depth))
 464             template_member_p = true;
 465         }
 466
 467       /* A nested class may declare a member of an enclosing class
 468          to be a friend, so we do lookup here even if CTYPE is in
 469          the process of being defined.  */
 470       if (class_template_depth
 471           || COMPLETE_TYPE_P (ctype)
 472           || TYPE_BEING_DEFINED (ctype))
 473         {
 474           if (DECL_TEMPLATE_INFO (decl))
 475             /* DECL is a template specialization.  No need to
 476                build a new TEMPLATE_DECL.  */
 477             ;
 478           else if (class_template_depth)
 479             /* We rely on tsubst_friend_function to check the
 480                validity of the declaration later.  */
 481             decl = push_template_decl_real (decl, /*is_friend=*/true);
 482           else
 483             decl = check_classfn (ctype, decl,
 484                                   template_member_p
 485                                   ? current_template_parms
 486                                   : NULL_TREE);
 487
 488           if (template_member_p && decl && TREE_CODE (decl) == FUNCTION_DECL)
 489             decl = DECL_TI_TEMPLATE (decl);
 490
 491           if (decl)
 492             add_friend (current_class_type, decl, /*complain=*/true);
 493         }
 494       else
 495         error ("member %qD declared as friend before type %qT defined",
 496                   decl, ctype);
 497     }
 498   /* A global friend.
 499      @@ or possibly a friend from a base class ?!?  */
 500   else if (TREE_CODE (decl) == FUNCTION_DECL)
 501     {
 502       int is_friend_template = PROCESSING_REAL_TEMPLATE_DECL_P ();
 503
 504       /* Friends must all go through the overload machinery,
 505          even though they may not technically be overloaded.
 506
 507          Note that because classes all wind up being top-level
 508          in their scope, their friend wind up in top-level scope as well.  */
 509       if (funcdef_flag)
 510         SET_DECL_FRIEND_CONTEXT (decl, current_class_type);
 511
 512       if (! DECL_USE_TEMPLATE (decl))
 513         {
 514           /* We must check whether the decl refers to template
 515              arguments before push_template_decl_real adds a
 516              reference to the containing template class.  */
 517           int warn = (warn_nontemplate_friend
 518                       && ! funcdef_flag && ! is_friend_template
 519                       && current_template_parms
 520                       && uses_template_parms (decl));
 521
 522           if (is_friend_template
 523               || template_class_depth (current_class_type) != 0)
 524             /* We can't call pushdecl for a template class, since in
 525                general, such a declaration depends on template
 526                parameters.  Instead, we call pushdecl when the class
 527                is instantiated.  */
 528             decl = push_template_decl_real (decl, /*is_friend=*/true);
 529           else if (current_function_decl)
 530             /* This must be a local class, so pushdecl will be ok, and
 531                insert an unqualified friend into the local scope
 532                (rather than the containing namespace scope, which the
 533                next choice will do).  */
 534             decl = pushdecl_maybe_friend (decl, /*is_friend=*/true);
 535           else
 536             {
 537               /* We can't use pushdecl, as we might be in a template
 538                  class specialization, and pushdecl will insert an
 539                  unqualified friend decl into the template parameter
 540                  scope, rather than the namespace containing it.  */
 541               tree ns = decl_namespace_context (decl);
 542
 543               push_nested_namespace (ns);
 544               decl = pushdecl_namespace_level (decl, /*is_friend=*/true);
 545               pop_nested_namespace (ns);
 546             }
 547
 548           if (warn)
 549             {
 550               static int explained;
 551               warning (0, "friend declaration %q#D declares a non-template "
 552                        "function", decl);
 553               if (! explained)
 554                 {
 555                   warning (0, "(if this is not what you intended, make sure "
 556                            "the function template has already been declared "
 557                            "and add <> after the function name here) "
 558                            "-Wno-non-template-friend disables this warning");
 559                   explained = 1;
 560                 }
 561             }
 562         }
 563
 564       if (decl == error_mark_node)
 565         return error_mark_node;
 566
 567       add_friend (current_class_type,
 568                   is_friend_template ? DECL_TI_TEMPLATE (decl) : decl,
 569                   /*complain=*/true);
 570       DECL_FRIEND_P (decl) = 1;
 571     }
 572
 573   /* Unfortunately, we have to handle attributes here.  Normally we would
 574      handle them in start_decl_1, but since this is a friend decl start_decl_1
 575      never gets to see it.  */
 576
 577   /* Set attributes here so if duplicate decl, will have proper attributes.  */
 578   cplus_decl_attributes (&decl, attrlist, 0);
 579
 580   return decl;
 581 }