1 /* Help friends in C++.
2 Copyright (C) 1997-2022 Free Software Foundation, Inc.
3
4 This file is part of GCC.
5
6 GCC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 3, or (at your option)
9 any later version.
10
11 GCC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
15
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
19
20 #include "config.h"
21 #include "system.h"
22 #include "coretypes.h"
23 #include "cp-tree.h"
24
25 /* Friend data structures are described in cp-tree.h. */
26
27
28 /* The GLOBAL_FRIEND scope (functions, classes, or templates) is
29 regarded as a friend of every class. This is only used by libcc1,
30 to enable GDB's code snippets to access private members without
31 disabling access control in general, which could cause different
32 template overload resolution results when accessibility matters
33 (e.g. tests for an accessible member). */
34
35 static GTY(()) tree global_friend;
36
37 /* Set the GLOBAL_FRIEND for this compilation session. It might be
38 set multiple times, but always to the same scope. */
39
40 void
set_global_friend(tree scope)41 set_global_friend (tree scope)
42 {
43 gcc_checking_assert (scope != NULL_TREE);
44 gcc_assert (!global_friend || global_friend == scope);
45 global_friend = scope;
46 }
47
48 /* Return TRUE if SCOPE is the global friend. */
49
50 bool
is_global_friend(tree scope)51 is_global_friend (tree scope)
52 {
53 gcc_checking_assert (scope != NULL_TREE);
54
55 if (global_friend == scope)
56 return true;
57
58 if (!global_friend)
59 return false;
60
61 if (is_specialization_of_friend (global_friend, scope))
62 return true;
63
64 return false;
65 }
66
67 /* Returns nonzero if SUPPLICANT is a friend of TYPE. */
68
69 int
is_friend(tree type,tree supplicant)70 is_friend (tree type, tree supplicant)
71 {
72 int declp;
73 tree list;
74 tree context;
75
76 if (supplicant == NULL_TREE || type == NULL_TREE)
77 return 0;
78
79 if (is_global_friend (supplicant))
80 return 1;
81
82 declp = DECL_P (supplicant);
83
84 if (declp)
85 /* It's a function decl. */
86 {
87 tree list = DECL_FRIENDLIST (TYPE_MAIN_DECL (type));
88 tree name = DECL_NAME (supplicant);
89
90 for (; list ; list = TREE_CHAIN (list))
91 {
92 if (name == FRIEND_NAME (list))
93 {
94 tree friends = FRIEND_DECLS (list);
95 for (; friends ; friends = TREE_CHAIN (friends))
96 {
97 tree this_friend = TREE_VALUE (friends);
98
99 if (this_friend == NULL_TREE)
100 continue;
101
102 if (supplicant == this_friend)
103 return 1;
104
105 if (is_specialization_of_friend (supplicant, this_friend))
106 return 1;
107 }
108 break;
109 }
110 }
111 }
112 else
113 /* It's a type. */
114 {
115 if (same_type_p (supplicant, type))
116 return 1;
117
118 list = CLASSTYPE_FRIEND_CLASSES (TREE_TYPE (TYPE_MAIN_DECL (type)));
119 for (; list ; list = TREE_CHAIN (list))
120 {
121 tree t = TREE_VALUE (list);
122
123 if (TREE_CODE (t) == TEMPLATE_DECL ?
124 is_specialization_of_friend (TYPE_MAIN_DECL (supplicant), t) :
125 same_type_p (supplicant, t))
126 return 1;
127 }
128 }
129
130 if (declp)
131 {
132 if (DECL_FUNCTION_MEMBER_P (supplicant))
133 context = DECL_CONTEXT (supplicant);
134 else
135 context = NULL_TREE;
136 }
137 else
138 {
139 if (TYPE_CLASS_SCOPE_P (supplicant))
140 /* Nested classes get the same access as their enclosing types, as
141 per DR 45 (this is a change from the standard). */
142 context = TYPE_CONTEXT (supplicant);
143 else
144 /* Local classes have the same access as the enclosing function. */
145 context = decl_function_context (TYPE_MAIN_DECL (supplicant));
146 }
147
148 /* A namespace is not friend to anybody. */
149 if (context && TREE_CODE (context) == NAMESPACE_DECL)
150 context = NULL_TREE;
151
152 if (context)
153 return is_friend (type, context);
154
155 return 0;
156 }
157
158 /* Add a new friend to the friends of the aggregate type TYPE.
159 DECL is the FUNCTION_DECL of the friend being added.
160
161 If COMPLAIN is true, warning about duplicate friend is issued.
162 We want to have this diagnostics during parsing but not
163 when a template is being instantiated. */
164
165 void
add_friend(tree type,tree decl,bool complain)166 add_friend (tree type, tree decl, bool complain)
167 {
168 tree typedecl;
169 tree list;
170 tree name;
171 tree ctx;
172
173 if (decl == error_mark_node)
174 return;
175
176 typedecl = TYPE_MAIN_DECL (type);
177 list = DECL_FRIENDLIST (typedecl);
178 name = DECL_NAME (decl);
179 type = TREE_TYPE (typedecl);
180
181 while (list)
182 {
183 if (name == FRIEND_NAME (list))
184 {
185 tree friends = FRIEND_DECLS (list);
186 for (; friends ; friends = TREE_CHAIN (friends))
187 {
188 if (decl == TREE_VALUE (friends))
189 {
190 if (complain)
191 warning (OPT_Wredundant_decls,
192 "%qD is already a friend of class %qT",
193 decl, type);
194 return;
195 }
196 }
197
198 TREE_VALUE (list) = tree_cons (NULL_TREE, decl,
199 TREE_VALUE (list));
200 break;
201 }
202 list = TREE_CHAIN (list);
203 }
204
205 ctx = DECL_CONTEXT (decl);
206 if (ctx && CLASS_TYPE_P (ctx) && !uses_template_parms (ctx))
207 perform_or_defer_access_check (TYPE_BINFO (ctx), decl, decl,
208 tf_warning_or_error);
209
210 maybe_add_class_template_decl_list (type, decl, /*friend_p=*/1);
211
212 if (!list)
213 DECL_FRIENDLIST (typedecl)
214 = tree_cons (DECL_NAME (decl), build_tree_list (NULL_TREE, decl),
215 DECL_FRIENDLIST (typedecl));
216 if (!uses_template_parms (type))
217 DECL_BEFRIENDING_CLASSES (decl)
218 = tree_cons (NULL_TREE, type,
219 DECL_BEFRIENDING_CLASSES (decl));
220 }
221
222 /* Make FRIEND_TYPE a friend class to TYPE. If FRIEND_TYPE has already
223 been defined, we make all of its member functions friends of
224 TYPE. If not, we make it a pending friend, which can later be added
225 when its definition is seen. If a type is defined, then its TYPE_DECL's
226 DECL_UNDEFINED_FRIENDS contains a (possibly empty) list of friend
227 classes that are not defined. If a type has not yet been defined,
228 then the DECL_WAITING_FRIENDS contains a list of types
229 waiting to make it their friend. Note that these two can both
230 be in use at the same time!
231
232 If COMPLAIN is true, warning about duplicate friend is issued.
233 We want to have this diagnostics during parsing but not
234 when a template is being instantiated. */
235
236 void
make_friend_class(tree type,tree friend_type,bool complain)237 make_friend_class (tree type, tree friend_type, bool complain)
238 {
239 tree classes;
240
241 /* CLASS_TEMPLATE_DEPTH counts the number of template headers for
242 the enclosing class. FRIEND_DEPTH counts the number of template
243 headers used for this friend declaration. TEMPLATE_MEMBER_P,
244 defined inside the `if' block for TYPENAME_TYPE case, is true if
245 a template header in FRIEND_DEPTH is intended for DECLARATOR.
246 For example, the code
247
248 template <class T> struct A {
249 template <class U> struct B {
250 template <class V> template <class W>
251 friend class C<V>::D;
252 };
253 };
254
255 will eventually give the following results
256
257 1. CLASS_TEMPLATE_DEPTH equals 2 (for `T' and `U').
258 2. FRIEND_DEPTH equals 2 (for `V' and `W').
259 3. TEMPLATE_MEMBER_P is true (for `W').
260
261 The friend is a template friend iff FRIEND_DEPTH is nonzero. */
262
263 int class_template_depth = template_class_depth (type);
264 int friend_depth = 0;
265 if (current_template_depth)
266 /* When processing a friend declaration at parse time, just compare the
267 current depth to that of the class template. */
268 friend_depth = current_template_depth - class_template_depth;
269 else
270 {
271 /* Otherwise, we got here from instantiate_class_template. Determine
272 the friend depth by looking at the template parameters used within
273 FRIEND_TYPE. */
274 gcc_checking_assert (class_template_depth == 0);
275 while (uses_template_parms_level (friend_type, friend_depth + 1))
276 ++friend_depth;
277 }
278
279 if (! MAYBE_CLASS_TYPE_P (friend_type)
280 && TREE_CODE (friend_type) != TEMPLATE_TEMPLATE_PARM)
281 {
282 /* N1791: If the type specifier in a friend declaration designates a
283 (possibly cv-qualified) class type, that class is declared as a
284 friend; otherwise, the friend declaration is ignored.
285
286 So don't complain in C++11 mode. */
287 if (cxx_dialect < cxx11)
288 pedwarn (input_location, complain ? 0 : OPT_Wpedantic,
289 "invalid type %qT declared %<friend%>", friend_type);
290 return;
291 }
292
293 friend_type = cv_unqualified (friend_type);
294
295 if (check_for_bare_parameter_packs (friend_type))
296 return;
297
298 if (friend_depth)
299 {
300 /* [temp.friend] Friend declarations shall not declare partial
301 specializations. */
302 if (CLASS_TYPE_P (friend_type)
303 && CLASSTYPE_TEMPLATE_SPECIALIZATION (friend_type)
304 && uses_template_parms (friend_type))
305 {
306 error ("partial specialization %qT declared %<friend%>",
307 friend_type);
308 return;
309 }
310
311 if (TYPE_TEMPLATE_INFO (friend_type)
312 && !PRIMARY_TEMPLATE_P (TYPE_TI_TEMPLATE (friend_type)))
313 {
314 auto_diagnostic_group d;
315 error ("%qT is not a template", friend_type);
316 inform (location_of (friend_type), "previous declaration here");
317 if (TYPE_CLASS_SCOPE_P (friend_type)
318 && CLASSTYPE_TEMPLATE_INFO (TYPE_CONTEXT (friend_type))
319 && currently_open_class (TYPE_CONTEXT (friend_type)))
320 inform (input_location, "perhaps you need explicit template "
321 "arguments in your nested-name-specifier");
322 return;
323 }
324 }
325
326 /* It makes sense for a template class to be friends with itself,
327 that means the instantiations can be friendly. Other cases are
328 not so meaningful. */
329 if (!friend_depth && same_type_p (type, friend_type))
330 {
331 if (complain)
332 warning (0, "class %qT is implicitly friends with itself",
333 type);
334 return;
335 }
336
337 /* [temp.friend]
338
339 A friend of a class or class template can be a function or
340 class template, a specialization of a function template or
341 class template, or an ordinary (nontemplate) function or
342 class. */
343 if (!friend_depth)
344 ;/* ok */
345 else if (TREE_CODE (friend_type) == TYPENAME_TYPE)
346 {
347 if (TREE_CODE (TYPENAME_TYPE_FULLNAME (friend_type))
348 == TEMPLATE_ID_EXPR)
349 {
350 /* template <class U> friend class T::X<U>; */
351 /* [temp.friend]
352 Friend declarations shall not declare partial
353 specializations. */
354 error ("partial specialization %qT declared %<friend%>",
355 friend_type);
356 return;
357 }
358 else
359 {
360 /* We will figure this out later. */
361 bool template_member_p = false;
362
363 tree ctype = TYPE_CONTEXT (friend_type);
364 tree name = TYPE_IDENTIFIER (friend_type);
365 tree decl;
366
367 /* We need to distinguish a TYPENAME_TYPE for the non-template
368 class B in
369 template<class T> friend class A<T>::B;
370 vs for the class template B in
371 template<class T> template<class U> friend class A<T>::B; */
372 if (current_template_depth
373 && !uses_template_parms_level (ctype, current_template_depth))
374 template_member_p = true;
375
376 if (class_template_depth)
377 {
378 /* We rely on tsubst_friend_class to check the
379 validity of the declaration later. */
380 if (template_member_p)
381 friend_type
382 = make_unbound_class_template (ctype,
383 name,
384 current_template_parms,
385 tf_error);
386 else
387 friend_type
388 = make_typename_type (ctype, name, class_type, tf_error);
389 }
390 else
391 {
392 decl = lookup_member (ctype, name, 0, true, tf_warning_or_error);
393 if (!decl)
394 {
395 error ("%qT is not a member of %qT", name, ctype);
396 return;
397 }
398 if (template_member_p && !DECL_CLASS_TEMPLATE_P (decl))
399 {
400 auto_diagnostic_group d;
401 error ("%qT is not a member class template of %qT",
402 name, ctype);
403 inform (DECL_SOURCE_LOCATION (decl),
404 "%qD declared here", decl);
405 return;
406 }
407 if (!template_member_p && (TREE_CODE (decl) != TYPE_DECL
408 || !CLASS_TYPE_P (TREE_TYPE (decl))))
409 {
410 auto_diagnostic_group d;
411 error ("%qT is not a nested class of %qT",
412 name, ctype);
413 inform (DECL_SOURCE_LOCATION (decl),
414 "%qD declared here", decl);
415 return;
416 }
417
418 friend_type = CLASSTYPE_TI_TEMPLATE (TREE_TYPE (decl));
419 }
420 }
421 }
422 else if (TREE_CODE (friend_type) == TEMPLATE_TYPE_PARM)
423 {
424 /* template <class T> friend class T; */
425 error ("template parameter type %qT declared %<friend%>", friend_type);
426 return;
427 }
428 else if (TREE_CODE (friend_type) == TEMPLATE_TEMPLATE_PARM)
429 friend_type = TYPE_NAME (friend_type);
430 else if (!CLASSTYPE_TEMPLATE_INFO (friend_type))
431 {
432 /* template <class T> friend class A; where A is not a template */
433 error ("%q#T is not a template", friend_type);
434 return;
435 }
436 else
437 /* template <class T> friend class A; where A is a template */
438 friend_type = CLASSTYPE_TI_TEMPLATE (friend_type);
439
440 if (friend_type == error_mark_node)
441 return;
442
443 /* See if it is already a friend. */
444 for (classes = CLASSTYPE_FRIEND_CLASSES (type);
445 classes;
446 classes = TREE_CHAIN (classes))
447 {
448 tree probe = TREE_VALUE (classes);
449
450 if (TREE_CODE (friend_type) == TEMPLATE_DECL)
451 {
452 if (friend_type == probe)
453 {
454 if (complain)
455 warning (OPT_Wredundant_decls,
456 "%qD is already a friend of %qT", probe, type);
457 break;
458 }
459 }
460 else if (TREE_CODE (probe) != TEMPLATE_DECL)
461 {
462 if (same_type_p (probe, friend_type))
463 {
464 if (complain)
465 warning (OPT_Wredundant_decls,
466 "%qT is already a friend of %qT", probe, type);
467 break;
468 }
469 }
470 }
471
472 if (!classes)
473 {
474 maybe_add_class_template_decl_list (type, friend_type, /*friend_p=*/1);
475
476 CLASSTYPE_FRIEND_CLASSES (type)
477 = tree_cons (NULL_TREE, friend_type, CLASSTYPE_FRIEND_CLASSES (type));
478 if (TREE_CODE (friend_type) == TEMPLATE_DECL)
479 friend_type = TREE_TYPE (friend_type);
480 if (!uses_template_parms (type))
481 CLASSTYPE_BEFRIENDING_CLASSES (friend_type)
482 = tree_cons (NULL_TREE, type,
483 CLASSTYPE_BEFRIENDING_CLASSES (friend_type));
484 }
485 }
486
487 /* Record DECL (a FUNCTION_DECL) as a friend of the
488 CURRENT_CLASS_TYPE. If DECL is a member function, SCOPE is the
489 class of which it is a member, as named in the friend declaration.
490 If the friend declaration was explicitly namespace-qualified, SCOPE
491 is that namespace.
492 DECLARATOR is the name of the friend. FUNCDEF_FLAG is true if the
493 friend declaration is a definition of the function. FLAGS is as
494 for grokclass fn. */
495
496 tree
do_friend(tree scope,tree declarator,tree decl,enum overload_flags flags,bool funcdef_flag)497 do_friend (tree scope, tree declarator, tree decl,
498 enum overload_flags flags,
499 bool funcdef_flag)
500 {
501 gcc_assert (TREE_CODE (decl) == FUNCTION_DECL);
502
503 tree ctype = NULL_TREE;
504 tree in_namespace = NULL_TREE;
505 if (!scope)
506 ;
507 else if (MAYBE_CLASS_TYPE_P (scope))
508 ctype = scope;
509 else
510 {
511 gcc_checking_assert (TREE_CODE (scope) == NAMESPACE_DECL);
512 in_namespace = scope;
513 }
514
515 /* Friend functions are unique, until proved otherwise. */
516 DECL_UNIQUE_FRIEND_P (decl) = 1;
517
518 if (DECL_OVERRIDE_P (decl) || DECL_FINAL_P (decl))
519 error ("friend declaration %qD may not have virt-specifiers",
520 decl);
521
522 if (TREE_CODE (declarator) == TEMPLATE_ID_EXPR)
523 {
524 declarator = TREE_OPERAND (declarator, 0);
525 if (!identifier_p (declarator))
526 declarator = OVL_NAME (declarator);
527 }
528
529 if (ctype)
530 {
531 /* CLASS_TEMPLATE_DEPTH counts the number of template headers for
532 the enclosing class. FRIEND_DEPTH counts the number of template
533 headers used for this friend declaration. TEMPLATE_MEMBER_P is
534 true if a template header in FRIEND_DEPTH is intended for
535 DECLARATOR. For example, the code
536
537 template <class T> struct A {
538 template <class U> struct B {
539 template <class V> template <class W>
540 friend void C<V>::f(W);
541 };
542 };
543
544 will eventually give the following results
545
546 1. CLASS_TEMPLATE_DEPTH equals 2 (for `T' and `U').
547 2. FRIEND_DEPTH equals 2 (for `V' and `W').
548 3. TEMPLATE_MEMBER_P is true (for `W'). */
549
550 int class_template_depth = template_class_depth (current_class_type);
551 int friend_depth = current_template_depth - class_template_depth;
552 /* We will figure this out later. */
553 bool template_member_p = false;
554
555 tree cname = TYPE_NAME (ctype);
556 if (TREE_CODE (cname) == TYPE_DECL)
557 cname = DECL_NAME (cname);
558
559 /* A method friend. */
560 if (flags == NO_SPECIAL && declarator == cname)
561 DECL_CXX_CONSTRUCTOR_P (decl) = 1;
562
563 grokclassfn (ctype, decl, flags);
564
565 if (friend_depth)
566 {
567 if (!uses_template_parms_level (ctype, class_template_depth
568 + friend_depth))
569 template_member_p = true;
570 }
571
572 /* A nested class may declare a member of an enclosing class
573 to be a friend, so we do lookup here even if CTYPE is in
574 the process of being defined. */
575 if (class_template_depth
576 || COMPLETE_OR_OPEN_TYPE_P (ctype))
577 {
578 if (DECL_TEMPLATE_INFO (decl))
579 /* DECL is a template specialization. No need to
580 build a new TEMPLATE_DECL. */
581 ;
582 else if (class_template_depth)
583 /* We rely on tsubst_friend_function to check the
584 validity of the declaration later. */
585 decl = push_template_decl (decl, /*is_friend=*/true);
586 else
587 decl = check_classfn (ctype, decl,
588 template_member_p
589 ? current_template_parms
590 : NULL_TREE);
591
592 if ((template_member_p
593 /* Always pull out the TEMPLATE_DECL if we have a friend
594 template in a class template so that it gets tsubsted
595 properly later on (59956). tsubst_friend_function knows
596 how to tell this apart from a member template. */
597 || (class_template_depth && friend_depth))
598 && decl && TREE_CODE (decl) == FUNCTION_DECL)
599 decl = DECL_TI_TEMPLATE (decl);
600
601 if (decl)
602 add_friend (current_class_type, decl, /*complain=*/true);
603 }
604 else
605 error ("member %qD declared as friend before type %qT defined",
606 decl, ctype);
607 }
608 else
609 {
610 /* Namespace-scope friend function. */
611 int is_friend_template = PROCESSING_REAL_TEMPLATE_DECL_P ();
612
613 if (funcdef_flag)
614 SET_DECL_FRIEND_CONTEXT (decl, current_class_type);
615
616 if (! DECL_USE_TEMPLATE (decl))
617 {
618 /* We must check whether the decl refers to template
619 arguments before push_template_decl adds a reference to
620 the containing template class. */
621 int warn = (warn_nontemplate_friend
622 && ! funcdef_flag && ! is_friend_template
623 && current_template_parms
624 && uses_template_parms (decl));
625
626 if (is_friend_template
627 || template_class_depth (current_class_type) != 0)
628 /* We can't call pushdecl for a template class, since in
629 general, such a declaration depends on template
630 parameters. Instead, we call pushdecl when the class
631 is instantiated. */
632 decl = push_template_decl (decl, /*is_friend=*/true);
633 else if (current_function_decl && !in_namespace)
634 /* pushdecl will check there's a local decl already. */
635 decl = pushdecl (decl, /*hiding=*/true);
636 else
637 {
638 /* We can't use pushdecl, as we might be in a template
639 class specialization, and pushdecl will insert an
640 unqualified friend decl into the template parameter
641 scope, rather than the namespace containing it. */
642 tree ns = decl_namespace_context (decl);
643
644 push_nested_namespace (ns);
645 decl = pushdecl_namespace_level (decl, /*hiding=*/true);
646 pop_nested_namespace (ns);
647 }
648
649 if (warn)
650 {
651 static int explained;
652 bool warned;
653
654 auto_diagnostic_group d;
655 warned = warning (OPT_Wnon_template_friend, "friend declaration "
656 "%q#D declares a non-template function", decl);
657 if (! explained && warned)
658 {
659 inform (input_location, "(if this is not what you intended, "
660 "make sure the function template has already been "
661 "declared and add %<<>%> after the function name "
662 "here)");
663 explained = 1;
664 }
665 }
666 }
667
668 if (decl == error_mark_node)
669 return error_mark_node;
670
671 add_friend (current_class_type,
672 is_friend_template ? DECL_TI_TEMPLATE (decl) : decl,
673 /*complain=*/true);
674 }
675
676 return decl;
677 }
678
679 #include "gt-cp-friend.h"
680