1 /* Help friends in C++.
2 Copyright (C) 1997-2022 Free Software Foundation, Inc.
4 This file is part of GCC.
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)
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.
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/>. */
22 #include "coretypes.h"
25 /* Friend data structures are described in cp-tree.h. */
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). */
35 static GTY(()) tree global_friend
;
37 /* Set the GLOBAL_FRIEND for this compilation session. It might be
38 set multiple times, but always to the same scope. */
41 set_global_friend (tree scope
)
43 gcc_checking_assert (scope
!= NULL_TREE
);
44 gcc_assert (!global_friend
|| global_friend
== scope
);
45 global_friend
= scope
;
48 /* Return TRUE if SCOPE is the global friend. */
51 is_global_friend (tree scope
)
53 gcc_checking_assert (scope
!= NULL_TREE
);
55 if (global_friend
== scope
)
61 if (is_specialization_of_friend (global_friend
, scope
))
67 /* Returns nonzero if SUPPLICANT is a friend of TYPE. */
70 is_friend (tree type
, tree supplicant
)
76 if (supplicant
== NULL_TREE
|| type
== NULL_TREE
)
79 if (is_global_friend (supplicant
))
82 declp
= DECL_P (supplicant
);
85 /* It's a function decl. */
87 tree list
= DECL_FRIENDLIST (TYPE_MAIN_DECL (type
));
88 tree name
= DECL_NAME (supplicant
);
90 for (; list
; list
= TREE_CHAIN (list
))
92 if (name
== FRIEND_NAME (list
))
94 tree friends
= FRIEND_DECLS (list
);
95 for (; friends
; friends
= TREE_CHAIN (friends
))
97 tree this_friend
= TREE_VALUE (friends
);
99 if (this_friend
== NULL_TREE
)
102 if (supplicant
== this_friend
)
105 if (is_specialization_of_friend (supplicant
, this_friend
))
115 if (same_type_p (supplicant
, type
))
118 list
= CLASSTYPE_FRIEND_CLASSES (TREE_TYPE (TYPE_MAIN_DECL (type
)));
119 for (; list
; list
= TREE_CHAIN (list
))
121 tree t
= TREE_VALUE (list
);
123 if (TREE_CODE (t
) == TEMPLATE_DECL
?
124 is_specialization_of_friend (TYPE_MAIN_DECL (supplicant
), t
) :
125 same_type_p (supplicant
, t
))
132 if (DECL_FUNCTION_MEMBER_P (supplicant
))
133 context
= DECL_CONTEXT (supplicant
);
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
);
144 /* Local classes have the same access as the enclosing function. */
145 context
= decl_function_context (TYPE_MAIN_DECL (supplicant
));
148 /* A namespace is not friend to anybody. */
149 if (context
&& TREE_CODE (context
) == NAMESPACE_DECL
)
153 return is_friend (type
, context
);
158 /* Add a new friend to the friends of the aggregate type TYPE.
159 DECL is the FUNCTION_DECL of the friend being added.
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. */
166 add_friend (tree type
, tree decl
, bool complain
)
173 if (decl
== error_mark_node
)
176 typedecl
= TYPE_MAIN_DECL (type
);
177 list
= DECL_FRIENDLIST (typedecl
);
178 name
= DECL_NAME (decl
);
179 type
= TREE_TYPE (typedecl
);
183 if (name
== FRIEND_NAME (list
))
185 tree friends
= FRIEND_DECLS (list
);
186 for (; friends
; friends
= TREE_CHAIN (friends
))
188 if (decl
== TREE_VALUE (friends
))
191 warning (OPT_Wredundant_decls
,
192 "%qD is already a friend of class %qT",
198 TREE_VALUE (list
) = tree_cons (NULL_TREE
, decl
,
202 list
= TREE_CHAIN (list
);
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
);
210 maybe_add_class_template_decl_list (type
, decl
, /*friend_p=*/1);
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
));
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!
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. */
237 make_friend_class (tree type
, tree friend_type
, bool complain
)
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
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;
255 will eventually give the following results
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').
261 The friend is a template friend iff FRIEND_DEPTH is nonzero. */
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
;
271 /* Otherwise, we got here from instantiate_class_template. Determine
272 the friend depth by looking at the template parameters used within
274 gcc_checking_assert (class_template_depth
== 0);
275 while (uses_template_parms_level (friend_type
, friend_depth
+ 1))
279 if (! MAYBE_CLASS_TYPE_P (friend_type
)
280 && TREE_CODE (friend_type
) != TEMPLATE_TEMPLATE_PARM
)
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.
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
);
293 friend_type
= cv_unqualified (friend_type
);
295 if (check_for_bare_parameter_packs (friend_type
))
300 /* [temp.friend] Friend declarations shall not declare partial
302 if (CLASS_TYPE_P (friend_type
)
303 && CLASSTYPE_TEMPLATE_SPECIALIZATION (friend_type
)
304 && uses_template_parms (friend_type
))
306 error ("partial specialization %qT declared %<friend%>",
311 if (TYPE_TEMPLATE_INFO (friend_type
)
312 && !PRIMARY_TEMPLATE_P (TYPE_TI_TEMPLATE (friend_type
)))
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");
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
))
332 warning (0, "class %qT is implicitly friends with itself",
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
345 else if (TREE_CODE (friend_type
) == TYPENAME_TYPE
)
347 if (TREE_CODE (TYPENAME_TYPE_FULLNAME (friend_type
))
350 /* template <class U> friend class T::X<U>; */
352 Friend declarations shall not declare partial
354 error ("partial specialization %qT declared %<friend%>",
360 /* We will figure this out later. */
361 bool template_member_p
= false;
363 tree ctype
= TYPE_CONTEXT (friend_type
);
364 tree name
= TYPE_IDENTIFIER (friend_type
);
367 /* We need to distinguish a TYPENAME_TYPE for the non-template
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;
376 if (class_template_depth
)
378 /* We rely on tsubst_friend_class to check the
379 validity of the declaration later. */
380 if (template_member_p
)
382 = make_unbound_class_template (ctype
,
384 current_template_parms
,
388 = make_typename_type (ctype
, name
, class_type
, tf_error
);
392 decl
= lookup_member (ctype
, name
, 0, true, tf_warning_or_error
);
395 error ("%qT is not a member of %qT", name
, ctype
);
398 if (template_member_p
&& !DECL_CLASS_TEMPLATE_P (decl
))
400 auto_diagnostic_group d
;
401 error ("%qT is not a member class template of %qT",
403 inform (DECL_SOURCE_LOCATION (decl
),
404 "%qD declared here", decl
);
407 if (!template_member_p
&& (TREE_CODE (decl
) != TYPE_DECL
408 || !CLASS_TYPE_P (TREE_TYPE (decl
))))
410 auto_diagnostic_group d
;
411 error ("%qT is not a nested class of %qT",
413 inform (DECL_SOURCE_LOCATION (decl
),
414 "%qD declared here", decl
);
418 friend_type
= CLASSTYPE_TI_TEMPLATE (TREE_TYPE (decl
));
422 else if (TREE_CODE (friend_type
) == TEMPLATE_TYPE_PARM
)
424 /* template <class T> friend class T; */
425 error ("template parameter type %qT declared %<friend%>", friend_type
);
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
))
432 /* template <class T> friend class A; where A is not a template */
433 error ("%q#T is not a template", friend_type
);
437 /* template <class T> friend class A; where A is a template */
438 friend_type
= CLASSTYPE_TI_TEMPLATE (friend_type
);
440 if (friend_type
== error_mark_node
)
443 /* See if it is already a friend. */
444 for (classes
= CLASSTYPE_FRIEND_CLASSES (type
);
446 classes
= TREE_CHAIN (classes
))
448 tree probe
= TREE_VALUE (classes
);
450 if (TREE_CODE (friend_type
) == TEMPLATE_DECL
)
452 if (friend_type
== probe
)
455 warning (OPT_Wredundant_decls
,
456 "%qD is already a friend of %qT", probe
, type
);
460 else if (TREE_CODE (probe
) != TEMPLATE_DECL
)
462 if (same_type_p (probe
, friend_type
))
465 warning (OPT_Wredundant_decls
,
466 "%qT is already a friend of %qT", probe
, type
);
474 maybe_add_class_template_decl_list (type
, friend_type
, /*friend_p=*/1);
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
));
487 /* Record DECL (a FUNCTION_DECL) as a friend of the
488 CURRENT_CLASS_TYPE. If DECL is a member function, CTYPE is the
489 class of which it is a member, as named in the friend declaration.
490 DECLARATOR is the name of the friend. FUNCDEF_FLAG is true if the
491 friend declaration is a definition of the function. FLAGS is as
495 do_friend (tree ctype
, tree declarator
, tree decl
,
496 enum overload_flags flags
,
499 gcc_assert (TREE_CODE (decl
) == FUNCTION_DECL
);
500 gcc_assert (!ctype
|| MAYBE_CLASS_TYPE_P (ctype
));
502 /* Friend functions are unique, until proved otherwise. */
503 DECL_UNIQUE_FRIEND_P (decl
) = 1;
505 if (DECL_OVERRIDE_P (decl
) || DECL_FINAL_P (decl
))
506 error ("friend declaration %qD may not have virt-specifiers",
509 tree orig_declarator
= declarator
;
510 if (TREE_CODE (declarator
) == TEMPLATE_ID_EXPR
)
512 declarator
= TREE_OPERAND (declarator
, 0);
513 if (!identifier_p (declarator
))
514 declarator
= OVL_NAME (declarator
);
517 /* CLASS_TEMPLATE_DEPTH counts the number of template headers for
518 the enclosing class. FRIEND_DEPTH counts the number of template
519 headers used for this friend declaration. TEMPLATE_MEMBER_P is
520 true if a template header in FRIEND_DEPTH is intended for
521 DECLARATOR. For example, the code
523 template <class T> struct A {
524 template <class U> struct B {
525 template <class V> template <class W>
526 friend void C<V>::f(W);
530 will eventually give the following results
532 1. CLASS_TEMPLATE_DEPTH equals 2 (for `T' and `U').
533 2. FRIEND_DEPTH equals 2 (for `V' and `W').
534 3. CTYPE_DEPTH equals 1 (for `V').
535 4. TEMPLATE_MEMBER_P is true (for `W'). */
537 int class_template_depth
= template_class_depth (current_class_type
);
538 int friend_depth
= current_template_depth
- class_template_depth
;
539 int ctype_depth
= num_template_headers_for_class (ctype
);
540 bool template_member_p
= friend_depth
> ctype_depth
;
544 tree cname
= TYPE_NAME (ctype
);
545 if (TREE_CODE (cname
) == TYPE_DECL
)
546 cname
= DECL_NAME (cname
);
548 /* A method friend. */
549 if (flags
== NO_SPECIAL
&& declarator
== cname
)
550 DECL_CXX_CONSTRUCTOR_P (decl
) = 1;
552 grokclassfn (ctype
, decl
, flags
);
554 /* A nested class may declare a member of an enclosing class
555 to be a friend, so we do lookup here even if CTYPE is in
556 the process of being defined. */
557 if (class_template_depth
558 || COMPLETE_OR_OPEN_TYPE_P (ctype
))
560 if (DECL_TEMPLATE_INFO (decl
))
561 /* DECL is a template specialization. No need to
562 build a new TEMPLATE_DECL. */
564 else if (class_template_depth
)
565 /* We rely on tsubst_friend_function to check the
566 validity of the declaration later. */
567 decl
= push_template_decl (decl
, /*is_friend=*/true);
569 decl
= check_classfn (ctype
, decl
,
571 ? current_template_parms
574 if ((template_member_p
575 /* Always pull out the TEMPLATE_DECL if we have a friend
576 template in a class template so that it gets tsubsted
577 properly later on (59956). tsubst_friend_function knows
578 how to tell this apart from a member template. */
579 || (class_template_depth
&& friend_depth
))
580 && decl
&& TREE_CODE (decl
) == FUNCTION_DECL
)
581 decl
= DECL_TI_TEMPLATE (decl
);
584 error ("member %qD declared as friend before type %qT defined",
589 /* Namespace-scope friend function. */
592 SET_DECL_FRIEND_CONTEXT (decl
, current_class_type
);
594 if (! DECL_USE_TEMPLATE (decl
))
596 /* We must check whether the decl refers to template
597 arguments before push_template_decl adds a reference to
598 the containing template class. */
599 int warn
= (warn_nontemplate_friend
600 && ! funcdef_flag
&& ! friend_depth
601 && current_template_parms
602 && uses_template_parms (decl
));
604 if (friend_depth
|| class_template_depth
)
605 /* We can't call pushdecl for a template class, since in
606 general, such a declaration depends on template
607 parameters. Instead, we call pushdecl when the class
609 decl
= push_template_decl (decl
, /*is_friend=*/true);
610 else if (current_function_decl
)
611 /* pushdecl will check there's a local decl already. */
612 decl
= pushdecl (decl
, /*hiding=*/true);
615 /* We can't use pushdecl, as we might be in a template
616 class specialization, and pushdecl will insert an
617 unqualified friend decl into the template parameter
618 scope, rather than the namespace containing it. */
619 tree ns
= decl_namespace_context (decl
);
621 push_nested_namespace (ns
);
622 decl
= pushdecl_namespace_level (decl
, /*hiding=*/true);
623 pop_nested_namespace (ns
);
628 static int explained
;
631 auto_diagnostic_group d
;
632 warned
= warning (OPT_Wnon_template_friend
, "friend declaration "
633 "%q#D declares a non-template function", decl
);
634 if (! explained
&& warned
)
636 inform (input_location
, "(if this is not what you intended, "
637 "make sure the function template has already been "
638 "declared and add %<<>%> after the function name "
646 if (decl
== error_mark_node
)
647 return error_mark_node
;
649 if (!class_template_depth
&& DECL_IMPLICIT_INSTANTIATION (decl
))
650 /* "[if no non-template match is found,] each remaining function template
651 is replaced with the specialization chosen by deduction from the
652 friend declaration or discarded if deduction fails."
654 set_decl_namespace or check_classfn set DECL_IMPLICIT_INSTANTIATION to
655 indicate that we need a template match, so ask
656 check_explicit_specialization to find one. */
657 decl
= (check_explicit_specialization
658 (orig_declarator
, decl
, ctype_depth
,
659 2 * funcdef_flag
+ 4));
661 add_friend (current_class_type
,
662 (!ctype
&& friend_depth
) ? DECL_TI_TEMPLATE (decl
) : decl
,
668 #include "gt-cp-friend.h"