Re: [PATCH] c++: implicitly_declare_fn and access checks [PR113908]

[Patrick Palka <ppalka@redhat.com>]

On Tue, 13 Feb 2024, Jason Merrill wrote:

> On 2/13/24 11:49, Patrick Palka wrote:
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, are one of
> > both of these fixes OK for trunk?
> > 
> > -- >8 --
> > 
> > Here during ahead of time checking of the non-dependent new-expr we
> > synthesize B's copy constructor, which should be defined as deleted
> > due to A's inaccessible copy constructor.  But enforce_access incorrectly
> > decides to defer the (silent) access check for A::A(const A&) during
> > synthesization since current_template_parms is still set (before r14-557
> > it checked processing_template_decl which got cleared from
> > implicitly_declare_fn), which leads to the access check leaking out to
> > the template context that needed the synthesization.
> > 
> > This patch narrowly fixes this regression in two sufficient ways:
> > 
> > 1. Clear current_template_parms alongside processing_template_decl
> >     in implicitly_declare_fn so that it's more independent of context.
> 
> Hmm, perhaps it or synthesized_method_walk should use maybe_push_to_top_level?

That works nicely, and also fixes the other regression PR113332.  There
the lambda context triggering synthesization of a default ctor was
causing maybe_dummy_object to misbehave during overload resolution of
one of its member's default ctors, and now synthesization is context
independent.

> 
> > 2. Don't defer a silent access check when in a template context,
> >     since such deferred checks will be replayed noisily at instantiation
> >     time which may not be what the caller intended.
> 
> True, but returning a possibly incorrect 'false' is probably also not what the
> caller intended.  It would be better to see that we never call enforce_access
> with tf_none in a template.  If that's not feasible, I think we should still
> conservatively return true.

Makes sense, I can experiment with that enforce_access access change as
a follow-up.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?

-- >8 --

Subject: [PATCH] c++: synthesized_method_walk context independence [PR113908]

	PR c++/113908
	PR c++/113332

gcc/cp/ChangeLog:

	* method.cc (synthesized_method_walk): Use maybe_push_to_top_level.

gcc/testsuite/ChangeLog:

	* g++.dg/template/non-dependent31.C: New test.
	* g++.dg/template/non-dependent32.C: New test.
---
 gcc/cp/method.cc                              |  2 ++
 .../g++.dg/template/non-dependent31.C         | 18 +++++++++++++++++
 .../g++.dg/template/non-dependent32.C         | 20 +++++++++++++++++++
 3 files changed, 40 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/template/non-dependent31.C
 create mode 100644 gcc/testsuite/g++.dg/template/non-dependent32.C

diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc
index 957496d3e18..98c10e6a8b5 100644
--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -2760,6 +2760,7 @@ synthesized_method_walk (tree ctype, special_function_kind sfk, bool const_p,
 	return;
     }
 
+  bool push_to_top = maybe_push_to_top_level (TYPE_NAME (ctype));
   ++cp_unevaluated_operand;
   ++c_inhibit_evaluation_warnings;
   push_deferring_access_checks (dk_no_deferred);
@@ -2857,6 +2858,7 @@ synthesized_method_walk (tree ctype, special_function_kind sfk, bool const_p,
   pop_deferring_access_checks ();
   --cp_unevaluated_operand;
   --c_inhibit_evaluation_warnings;
+  maybe_pop_from_top_level (push_to_top);
 }
 
 /* DECL is a defaulted function whose exception specification is now
diff --git a/gcc/testsuite/g++.dg/template/non-dependent31.C b/gcc/testsuite/g++.dg/template/non-dependent31.C
new file mode 100644
index 00000000000..3fa68f40fe1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent31.C
@@ -0,0 +1,18 @@
+// PR c++/113908
+// { dg-do compile { target c++11 } }
+
+struct A {
+  A();
+private:
+  A(const A&);
+};
+
+struct B {
+  A a;
+
+  template<class T>
+  static void f() { new B(); }
+};
+
+template void B::f<int>();
+static_assert(!__is_constructible(B, const B&), "");
diff --git a/gcc/testsuite/g++.dg/template/non-dependent32.C b/gcc/testsuite/g++.dg/template/non-dependent32.C
new file mode 100644
index 00000000000..246654c5b50
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent32.C
@@ -0,0 +1,20 @@
+// PR c++/113332
+// { dg-do compile { target c++11 } }
+
+struct tuple {
+  template<class _Tp>
+  static constexpr bool __is_implicitly_default_constructible() { return true; }
+
+  template<class _Tp = void,
+           bool = __is_implicitly_default_constructible<_Tp>()>
+  tuple();
+};
+
+struct DBusStruct {
+private:
+  tuple data_;
+};
+
+struct IBusService {
+  int m = [] { DBusStruct{}; return 42; }();
+};
-- 
2.44.0.rc0.46.g2996f11c1d