[PR86823] retain deferred access checks from outside firewall

We used to preserve deferred access check along with resolved template
ids, but a tentative parsing firewall introduced additional layers of
deferred access checks, so that we don't preserve the checks we
want to any more.

This patch collapses the access check levels introduced by the
firewall with those we wanted to preserve to begin with, saves them,
pushes them one more layer up so that the firewall doesn't drop them,
and then pushes new empty levels so balance out with the upcoming
popping.

We may want to avoid the pop_to_parent and one push after the save, and
instead leave the firewall's scope before the final pop_to_parent.
However, this patch is what I regression-tested successfully with
check-g++ on x86_64-linux-gnu.  Regstrapping on i686- and
x86_64-linux-gnu now.  Ok to install?


for  gcc/cp/ChangeLog

	PR c++/86823
	* parser.c (cp_parser_template_id): Merge access checks from
	outside the tentative parsing firewall with those from inside,
	and save them all with the template id token.

for  gcc/testsuite/ChangeLog

	PR c++/86823
	* g++.dg/pr86823.C: New.
---
 gcc/cp/parser.c                |   12 ++++++++++++
 gcc/testsuite/g++.dg/pr86823.C |   15 +++++++++++++++
 2 files changed, 27 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/pr86823.C

On 11/16/18 9:16 PM, Alexandre Oliva wrote:
> We used to preserve deferred access check along with resolved template
> ids, but a tentative parsing firewall introduced additional layers of
> deferred access checks, so that we don't preserve the checks we
> want to any more.
> 
> This patch collapses the access check levels introduced by the
> firewall with those we wanted to preserve to begin with, saves them,
> pushes them one more layer up so that the firewall doesn't drop them,
> and then pushes new empty levels so balance out with the upcoming
> popping.
> 
> We may want to avoid the pop_to_parent and one push after the save, and
> instead leave the firewall's scope before the final pop_to_parent.
> However, this patch is what I regression-tested successfully with
> check-g++ on x86_64-linux-gnu.  Regstrapping on i686- and
> x86_64-linux-gnu now.  Ok to install?
> 
> 
> for  gcc/cp/ChangeLog
> 
> 	PR c++/86823
> 	* parser.c (cp_parser_template_id): Merge access checks from
> 	outside the tentative parsing firewall with those from inside,
> 	and save them all with the template id token.
> 
> for  gcc/testsuite/ChangeLog
> 
> 	PR c++/86823
> 	* g++.dg/pr86823.C: New.
> ---
>   gcc/cp/parser.c                |   12 ++++++++++++
>   gcc/testsuite/g++.dg/pr86823.C |   15 +++++++++++++++
>   2 files changed, 27 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/pr86823.C
> 
> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
> index db0f0338179e..6a08b09715a7 100644
> --- a/gcc/cp/parser.c
> +++ b/gcc/cp/parser.c
> @@ -16185,7 +16185,19 @@ cp_parser_template_id (cp_parser *parser,
>   	 so the memory will not be reclaimed during token replacing below.  */
>         token->u.tree_check_value = ggc_cleared_alloc<struct tree_check> ();
>         token->u.tree_check_value->value = template_id;
> +      /* Collapse the access check levels introduced by
> +	 tentative_firewall with the one we introduced ourselves.  */
> +      pop_to_parent_deferring_access_checks ();
> +      pop_to_parent_deferring_access_checks ();
>         token->u.tree_check_value->checks = get_deferred_access_checks ();
> +      /* Push the checks up one more level, so that the firewall
> +	 doesn't drop them on the floor when we return.  Then, push
> +	 empty levels back in place so that they are popped
> +	 properly.  */
> +      pop_to_parent_deferring_access_checks ();
> +      push_deferring_access_checks (dk_deferred);
> +      push_deferring_access_checks (dk_deferred);
> +      push_deferring_access_checks (dk_deferred);

Hmm, I'm uncomfortable with how this depends on the specific 
implementation of tentative_firewall.  What do you think of this 
alternate approach (untested other than with the testcase)?

Jason
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index ac19cb4b9bb..c7ec7dcf413 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -16182,16 +16182,18 @@ cp_parser_template_id (cp_parser *parser,
 				   is_declaration,
 				   tag_type,
 				   &is_identifier);
+
+  /* Push any access checks inside the firewall we're about to create.  */
+  vec<deferred_access_check, va_gc> *checks = get_deferred_access_checks ();
+  pop_deferring_access_checks ();
   if (templ == error_mark_node || is_identifier)
-    {
-      pop_deferring_access_checks ();
-      return templ;
-    }
+    return templ;
 
   /* Since we're going to preserve any side-effects from this parse, set up a
      firewall to protect our callers from cp_parser_commit_to_tentative_parse
      in the template arguments.  */
   tentative_firewall firewall (parser);
+  reopen_deferring_access_checks (checks);
 
   /* If we find the sequence `[:' after a template-name, it's probably
      a digraph-typo for `< ::'. Substitute the tokens and check if we can

On Dec  5, 2018, Jason Merrill <jason@redhat.com> wrote:

> Hmm, I'm uncomfortable with how this depends on the specific
> implementation of tentative_firewall.

*nod*

> What do you think of this alternate approach (untested other than with
> the testcase)?

If that won't drop any other deferred access checks that we might want
to keep when leaving the firewall by other paths, it looks much nicer
indeed!  I had been careful to only move access checks when I was
certain about the replacement, but even there I was concerned about
carrying stuff along with the preparsed token that didn't belong.

I'm giving your proposed patch a full round of testing along with other
patches.

On Dec  6, 2018, Alexandre Oliva <aoliva@redhat.com> wrote:

> I'm giving your proposed patch a full round of testing along with other
> patches.

[PR86823] retain deferred access checks from outside firewall

We used to preserve deferred access check along with resolved template
ids, but a tentative parsing firewall introduced additional layers of
deferred access checks, so that we don't preserve the checks we
want to any more.

This patch moves the deferred access checks from outside the firewall
into it.

Regstrapped on x86_64- and i686-linux-gnu.  Ok to install?


From: Jason Merrill <jason@redhat.com>
for  gcc/cp/ChangeLog

	PR c++/86823
	* parser.c (cp_parser_template_id): Rearrange deferred access
	checks into the firewall.

From: Alexandre Oliva <aoliva@redhat.com>
for  gcc/testsuite/ChangeLog

	PR c++/86823
	* g++.dg/pr86823.C: New.
---
 gcc/cp/parser.c                |   10 ++++++----
 gcc/testsuite/g++.dg/pr86823.C |   15 +++++++++++++++
 2 files changed, 21 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/pr86823.C

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index adfe09e494dc..0bf0e309a588 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -16182,16 +16182,18 @@ cp_parser_template_id (cp_parser *parser,
 				   is_declaration,
 				   tag_type,
 				   &is_identifier);
+
+  /* Push any access checks inside the firewall we're about to create.  */
+  vec<deferred_access_check, va_gc> *checks = get_deferred_access_checks ();
+  pop_deferring_access_checks ();
   if (templ == error_mark_node || is_identifier)
-    {
-      pop_deferring_access_checks ();
-      return templ;
-    }
+    return templ;
 
   /* Since we're going to preserve any side-effects from this parse, set up a
      firewall to protect our callers from cp_parser_commit_to_tentative_parse
      in the template arguments.  */
   tentative_firewall firewall (parser);
+  reopen_deferring_access_checks (checks);
 
   /* If we find the sequence `[:' after a template-name, it's probably
      a digraph-typo for `< ::'. Substitute the tokens and check if we can
diff --git a/gcc/testsuite/g++.dg/pr86823.C b/gcc/testsuite/g++.dg/pr86823.C
new file mode 100644
index 000000000000..18914b00aa8d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr86823.C
@@ -0,0 +1,15 @@
+// { dg-do compile }
+
+struct X {
+private:
+  template<typename T>
+  struct Y {
+    int data;
+  };
+public:
+  int value;
+};
+
+int main() {
+  typename X::Y<int> a; // { dg-error "private" }
+}

OK.
On Thu, Dec 13, 2018 at 8:35 PM Alexandre Oliva <aoliva@redhat.com> wrote:
>
> On Dec  6, 2018, Alexandre Oliva <aoliva@redhat.com> wrote:
>
> > I'm giving your proposed patch a full round of testing along with other
> > patches.
>
> [PR86823] retain deferred access checks from outside firewall
>
> We used to preserve deferred access check along with resolved template
> ids, but a tentative parsing firewall introduced additional layers of
> deferred access checks, so that we don't preserve the checks we
> want to any more.
>
> This patch moves the deferred access checks from outside the firewall
> into it.
>
> Regstrapped on x86_64- and i686-linux-gnu.  Ok to install?
>
>
> From: Jason Merrill <jason@redhat.com>
> for  gcc/cp/ChangeLog
>
>         PR c++/86823
>         * parser.c (cp_parser_template_id): Rearrange deferred access
>         checks into the firewall.
>
> From: Alexandre Oliva <aoliva@redhat.com>
> for  gcc/testsuite/ChangeLog
>
>         PR c++/86823
>         * g++.dg/pr86823.C: New.
> ---
>  gcc/cp/parser.c                |   10 ++++++----
>  gcc/testsuite/g++.dg/pr86823.C |   15 +++++++++++++++
>  2 files changed, 21 insertions(+), 4 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/pr86823.C
>
> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
> index adfe09e494dc..0bf0e309a588 100644
> --- a/gcc/cp/parser.c
> +++ b/gcc/cp/parser.c
> @@ -16182,16 +16182,18 @@ cp_parser_template_id (cp_parser *parser,
>                                    is_declaration,
>                                    tag_type,
>                                    &is_identifier);
> +
> +  /* Push any access checks inside the firewall we're about to create.  */
> +  vec<deferred_access_check, va_gc> *checks = get_deferred_access_checks ();
> +  pop_deferring_access_checks ();
>    if (templ == error_mark_node || is_identifier)
> -    {
> -      pop_deferring_access_checks ();
> -      return templ;
> -    }
> +    return templ;
>
>    /* Since we're going to preserve any side-effects from this parse, set up a
>       firewall to protect our callers from cp_parser_commit_to_tentative_parse
>       in the template arguments.  */
>    tentative_firewall firewall (parser);
> +  reopen_deferring_access_checks (checks);
>
>    /* If we find the sequence `[:' after a template-name, it's probably
>       a digraph-typo for `< ::'. Substitute the tokens and check if we can
> diff --git a/gcc/testsuite/g++.dg/pr86823.C b/gcc/testsuite/g++.dg/pr86823.C
> new file mode 100644
> index 000000000000..18914b00aa8d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/pr86823.C
> @@ -0,0 +1,15 @@
> +// { dg-do compile }
> +
> +struct X {
> +private:
> +  template<typename T>
> +  struct Y {
> +    int data;
> +  };
> +public:
> +  int value;
> +};
> +
> +int main() {
> +  typename X::Y<int> a; // { dg-error "private" }
> +}
>
>
> --
> Alexandre Oliva, freedom fighter   https://FSFLA.org/blogs/lxo
> Be the change, be Free!         FSF Latin America board member
> GNU Toolchain Engineer                Free Software Evangelist
> Hay que enGNUrecerse, pero sin perder la terGNUra jamás-GNUChe