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* [gcc r12-9227] c++: requires-expr and access checking [PR107179]
@ 2023-03-07 2:18 Patrick Palka
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From: Patrick Palka @ 2023-03-07 2:18 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:668098c2e55c33f97e331c3160174bf12c3d88f7
commit r12-9227-g668098c2e55c33f97e331c3160174bf12c3d88f7
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.
(cherry picked from commit 40c34beef620ed13c4113c893ed4335ccc1b8f92)
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 ab238dbb4cb..4e074f8fdaf 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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