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From: Patrick Palka <ppalka@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-3641] c++: requires-expr and access checking [PR107179] Date: Thu, 3 Nov 2022 19:36:00 +0000 (GMT) [thread overview] Message-ID: <20221103193600.78D1A3858D35@sourceware.org> (raw) https://gcc.gnu.org/g:40c34beef620ed13c4113c893ed4335ccc1b8f92 commit r13-3641-g40c34beef620ed13c4113c893ed4335ccc1b8f92 Author: Patrick Palka <ppalka@redhat.com> Date: Thu Nov 3 15:35:18 2022 -0400 c++: requires-expr and access checking [PR107179] Like during satisfaction, we also need to avoid deferring access checks during substitution of a requires-expr because the outcome of an access check can determine the value of the requires-expr. Otherwise (in deferred access checking contexts such as within a base-clause), the requires-expr may evaluate to the wrong result, and along the way a failed access check may leak out from it into a non-SFINAE context and cause a hard error (as in the below testcase). PR c++/107179 gcc/cp/ChangeLog: * constraint.cc (tsubst_requires_expr): Make sure we're not deferring access checks. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/concepts-requires31.C: New test. Diff: --- gcc/cp/constraint.cc | 3 +++ gcc/testsuite/g++.dg/cpp2a/concepts-requires31.C | 15 +++++++++++++++ 2 files changed, 18 insertions(+) diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc index 5e6a3bcf059..f6ef078171a 100644 --- a/gcc/cp/constraint.cc +++ b/gcc/cp/constraint.cc @@ -2252,6 +2252,9 @@ tsubst_requires_expr (tree t, tree args, sat_info info) { local_specialization_stack stack (lss_copy); + /* We need to check access during the substitution. */ + deferring_access_check_sentinel acs (dk_no_deferred); + /* A requires-expression is an unevaluated context. */ cp_unevaluated u; diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires31.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires31.C new file mode 100644 index 00000000000..cd26b9ca077 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires31.C @@ -0,0 +1,15 @@ +// PR c++/107179 +// { dg-do compile { target c++20 } } + +template<bool B> struct bool_constant { static constexpr bool value = B; }; + +template<typename T> + struct is_implicitly_default_constructible + : bool_constant<requires { T(); }> + { }; + +struct X { private: X(); }; +struct Y { }; + +static_assert( !is_implicitly_default_constructible<X>::value ); +static_assert( is_implicitly_default_constructible<Y>::value );
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