c++: requires-expr substitution and access checking [PR107179]
Commit Message
Like during satisfaction, we need to check access immediately during
substitution of a requires-expr since the outcome of an access check can
determine the value of the requires-expr. And otherwise, in contexts
where access checking is deferred (such as during substitution into a
base-clause), a failed access check may leak out from the requires-expr
into a non-SFINAE context and cause a hard error (as in the testcase
below).
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?
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.
---
gcc/cp/constraint.cc | 3 +++
gcc/testsuite/g++.dg/cpp2a/concepts-requires31.C | 13 +++++++++++++
2 files changed, 16 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires31.C
Comments
On 11/3/22 11:45, Patrick Palka wrote:
> Like during satisfaction, we need to check access immediately during
> substitution of a requires-expr since the outcome of an access check can
> determine the value of the requires-expr. And otherwise, in contexts
> where access checking is deferred (such as during substitution into a
> base-clause), a failed access check may leak out from the requires-expr
> into a non-SFINAE context and cause a hard error (as in the testcase
> below).
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?
OK.
> 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.
> ---
> gcc/cp/constraint.cc | 3 +++
> gcc/testsuite/g++.dg/cpp2a/concepts-requires31.C | 13 +++++++++++++
> 2 files changed, 16 insertions(+)
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires31.C
>
> 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..9b7e2a34889
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires31.C
> @@ -0,0 +1,13 @@
> +// 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(); };
> +
> +static_assert( !is_implicitly_default_constructible<X>::value );
@@ -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;
new file mode 100644
@@ -0,0 +1,13 @@
+// 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(); };
+
+static_assert( !is_implicitly_default_constructible<X>::value );