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

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

[Patrick Palka]

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.
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.  We need to adjust
   cp_parser_make_typename_type since otherwise the diagnostic for
   typedef22.C regresses because cp_parser_invalid_type_name otherwise
   will emit "invalid combination of multiple type-specifiers" for what
   is an inaccessible qualified-id.

	PR c++/113908

gcc/cp/ChangeLog:

	* method.cc (implicitly_declare_fn): Clear current_template_parms
	alongside processing_template_decl.
	* parser.cc (cp_parser_make_typename_type): Temporarily defer
	access checks around the tf_none call to make_typename_type.
	* semantics.cc (enforce_access): Don't defer silent access
	checks from a template context.

gcc/testsuite/ChangeLog:

	* g++.dg/template/non-dependent31.C: New test.
---
 gcc/cp/method.cc                               |  8 +++++++-
 gcc/cp/parser.cc                               |  2 ++
 gcc/cp/semantics.cc                            |  1 +
 .../g++.dg/template/non-dependent31.C          | 18 ++++++++++++++++++
 4 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/template/non-dependent31.C

diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc
index 957496d3e18..17d42143299 100644
--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -3088,6 +3088,7 @@ implicitly_declare_fn (special_function_kind kind, tree type,
   tree this_parm;
   tree name;
   HOST_WIDE_INT saved_processing_template_decl;
+  tree saved_current_template_parms;
   bool deleted_p = false;
   bool constexpr_p = false;
   tree inherited_ctor = (kind == sfk_inheriting_constructor
@@ -3132,6 +3133,10 @@ implicitly_declare_fn (special_function_kind kind, tree type,
      when not in a template.  */
   saved_processing_template_decl = processing_template_decl;
   processing_template_decl = 0;
+  /* Also clear CURRENT_TEMPLATE_PARMS so enforce_access immediately checks
+     access even in a template context.  */
+  saved_current_template_parms = current_template_parms;
+  current_template_parms = NULL_TREE;
 
   type = TYPE_MAIN_VARIANT (type);
 
@@ -3341,8 +3346,9 @@ implicitly_declare_fn (special_function_kind kind, tree type,
         set_constraints (fn, new_ci);
       }
 
-  /* Restore PROCESSING_TEMPLATE_DECL.  */
+  /* Restore PROCESSING_TEMPLATE_DECL and CURRENT_TEMPLATE_PARMS.  */
   processing_template_decl = saved_processing_template_decl;
+  current_template_parms = saved_current_template_parms;
 
   if (inherited_ctor && TREE_CODE (inherited_ctor) == TEMPLATE_DECL)
     fn = add_inherited_template_parms (fn, inherited_ctor);
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index c4292c49ce2..29120995449 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -4350,8 +4350,10 @@ cp_parser_make_typename_type (cp_parser *parser, tree id,
   tree result;
   if (identifier_p (id))
     {
+      push_deferring_access_checks (dk_deferred);
       result = make_typename_type (parser->scope, id, typename_type,
 				   /*complain=*/tf_none);
+      pop_to_parent_deferring_access_checks ();
       if (result == error_mark_node)
 	cp_parser_diagnose_invalid_type_name (parser, id, id_location);
       return result;
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 3299e270446..0a18eaf9c2e 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -346,6 +346,7 @@ enforce_access (tree basetype_path, tree decl, tree diag_decl,
 
   tree cs = current_scope ();
   if (in_template_context
+      && (complain & tf_error)
       && (CLASS_TYPE_P (cs) || TREE_CODE (cs) == FUNCTION_DECL))
     if (tree template_info = get_template_info (cs))
       {
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&), "");
-- 
2.44.0.rc0.46.g2996f11c1d

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

[Jason Merrill]

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?

> 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.

Jason

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

[Patrick Palka]

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

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

[Jason Merrill]

On 2/14/24 08:46, Patrick Palka wrote:
> 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?

OK.

> -- >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; }();
> +};