The following program exits with code 1. test.cpp: struct a { using get = void; }; struct b : a { int get(int i) const; }; template <typename T> concept c = requires { typename T::get; }; int main() { return c<b>; } $ g++ test.cpp -std=c++20 $ ./a.out $ echo $? 1 Expected is exit code 0, because T::get is not a type for T=b. The code snippet is based on user "apple apple"'s comment on https://stackoverflow.com/questions/74509418/why-does-member-function-not-hide-type-alias-in-base-class-when-compiling-with-g. User "n. m." also notes that GCC happily compiles https://eel.is/c++draft/temp.res.general#example-4 which does not use concepts and should emit an error. $ g++ -v gcc version 11.1.0 (Ubuntu 11.1.0-1ubuntu1~20.04)
Confirmed, a compile time testcase: struct a { using get = void; }; struct b : a { int get(int i); }; template <typename T> concept c = requires { typename T::get; }; template <typename T> constexpr int f(T t) {return 0;} template <c T> constexpr int f(T t) { typename T::get t1; return 1; } static_assert(f(b{}) == 0);
accepts-invalid c++98 testcase (not a regression): struct a { typedef void get; }; struct b : a { int get(int i) const; }; template<class T> void f() { typedef typename T::get type; } template void f<b>();
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>: https://gcc.gnu.org/g:46711ff8e60d64b7e5550f4614c29d42b224f98b commit r13-6098-g46711ff8e60d64b7e5550f4614c29d42b224f98b Author: Patrick Palka <ppalka@redhat.com> Date: Thu Feb 16 11:12:19 2023 -0500 c++: TYPENAME_TYPE lookup ignoring non-types [PR107773] Currently when resolving a TYPENAME_TYPE for 'typename T::m' via make_typename_type, we consider only type bindings of 'm' and ignore non-type ones. But [temp.res.general]/3 says, in a note, "the usual qualified name lookup ([basic.lookup.qual]) applies even in the presence of 'typename'", and qualified name lookup doesn't discriminate between type and non-type bindings. So when resolving such a TYPENAME_TYPE we want the lookup to consider all bindings. An exception is when we have a TYPENAME_TYPE corresponding to the qualifying scope of the :: scope resolution operator, such as 'T::type' in 'T::type::m'. In that case, [basic.lookup.qual]/1 applies, and lookup for such a TYPENAME_TYPE must ignore non-type bindings. So in order to correctly handle all cases, make_typename_type needs an additional flag controlling whether to restrict the lookup. To that end this patch adds a new tsubst flag tf_qualifying_scope denoting whether we're substituting the LHS of the :: operator, which make_typename_type will look for to conditionally restrict the lookup to type bindings (by default we want to consider all bindings). So in contexts such as substituting into the scope of TYPENAME_TYPE, SCOPE_REF or USING_DECL we simply pass tf_qualifying_scope to the relevant tsubst / tsubst_copy call, and if that scope is a TYPENAME_TYPE then make_typename_type will restrict the lookup accordingly. This flag is intended to apply only to overall scope (TYPENAME_TYPE or not) so we must be careful to clear the flag to avoid propagating it when recursing into sub-trees of the scope. PR c++/107773 gcc/cp/ChangeLog: * cp-tree.h (enum tsubst_flags): New flag tf_qualifying_scope. * decl.cc (make_typename_type): Use lookup_member instead of lookup_field. If tf_qualifying_scope is set, pass want_type=true instead of =false to lookup_member. Generalize format specifier in diagnostic to handle both type and non-type bindings. * pt.cc (tsubst_aggr_type_1): Clear tf_qualifying_scope. Tidy the function. (tsubst_decl) <case USING_DECL>: Set tf_qualifying_scope when substituting USING_DECL_SCOPE. (tsubst): Clear tf_qualifying_scope right away and remember if it was set. Do the same for tf_tst_ok sooner. <case TYPENAME_TYPE>: Set tf_qualifying_scope when substituting TYPE_CONTEXT. Pass tf_qualifying_scope to make_typename_type if it was set. (tsubst_qualified_id): Set tf_qualifying_scope when substituting the scope. (tsubst_copy): Clear tf_qualifying_scope and remember if it was set. <case SCOPE_REF>: Set tf_qualifying_scope when substituting the scope. <case *_TYPE>: Pass tf_qualifying_scope to tsubst if it was set. * search.cc (lookup_member): Document default argument. gcc/testsuite/ChangeLog: * g++.dg/template/typename24.C: New test. * g++.dg/template/typename25.C: New test. * g++.dg/template/typename25a.C: New test. * g++.dg/template/typename26.C: New test.
Should be fixed for GCC 13, thanks for the bug report.
*** Bug 122192 has been marked as a duplicate of this bug. ***